From 16c8dcb45ba39df5b7f1c48faddc75ed914ff358 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 12:59:22 +0000 Subject: [PATCH 01/43] Moving changes in zsa-zips to zsa1 (#10) Co-authored-by: daniben31 Co-authored-by: Deirdre Connolly Co-authored-by: Daira-Emma Hopwood Co-authored-by: Jonathan S. Rouach Co-authored-by: str4d Co-authored-by: Paul --- zip-0226.rst | 355 +++++++++++++++++++- zip-0227-asset-identifier-relation.png | Bin 0 -> 44943 bytes zip-0227-asset-identifier-relation.svg | 293 ++++++++++++++++ zip-0227-key-components-zsa.png | Bin 0 -> 61722 bytes zip-0227-key-components-zsa.svg | 270 +++++++++++++++ zip-0227.rst | 443 ++++++++++++++++++++++++- 6 files changed, 1357 insertions(+), 4 deletions(-) create mode 100644 zip-0227-asset-identifier-relation.png create mode 100644 zip-0227-asset-identifier-relation.svg create mode 100644 zip-0227-key-components-zsa.png create mode 100644 zip-0227-key-components-zsa.svg diff --git a/zip-0226.rst b/zip-0226.rst index 98fdb79a6..7d7bccc1f 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -9,7 +9,358 @@ Credits: Daniel Benarroch Aurelien Nicolas Deirdre Connolly - Status: Reserved + Teor + Status: Draft Category: Consensus + Created: 2022-05-01 + License: MIT Discussions-To: - Pull-Request: + Pull-Request: + + +Terminology +=========== + +The key word "MUST" in this document is to be interpreted as described in RFC 2119 [#RFC2119]_. + +The term "network upgrade" in this document is to be interpreted as described in ZIP 200 [#zip-0200]_. + +The term "Orchard" in this document is to be interpreted as described in ZIP 224 [#zip-0224]_. + +We define the following additional terms: + +- Asset: A type of note that can be transferred on the Zcash block chain, identified by the :math:`\mathsf{AssetId}` parameter. + + - ZEC is the default (and currently the only defined) Asset for the Zcash mainnet. + - TAZ is the default (and currently the only defined) Asset for the Zcash testnet. + - We use the term "Custom Asset" to refer to any Asset other than ZEC and TAZ. + +- Native Asset: a Custom Asset with issuance defined on the Zcash block chain. +- Wrapped Asset: a Custom Asset with native issuance defined outside the Zcash block chain. +- Split Input: an Action input identifying a Custom Asset note, used to ensure that the output note of that Action is of a validly issued :math:`\mathsf{AssetId}` when there is no corresponding real input note to spend. The Action does not spend the note identified by the Split Input. +- Split Action: an Action that contains a Split Input. + +Abstract +======== + +ZIP 226 and ZIP 227 propose in conjunction the Zcash Shielded Assets (ZSA) protocol — a set +of protocol features that enable the creation, transfer, and burn of Custom Assets on the Zcash chain. + +Creation of such Assets is defined in ZIP 227 [#zip-0227]_. Transfer and burn of such Assets is defined +in ZIP 226 [#zip-0226]_. The ZSA protocol is proposed to be instantiated by a modification to the +Orchard protocol, as specified in these ZIPs. + +Motivation +========== + +None of the currently deployed Zcash transfer protocols support Custom Assets. Enabling +multi-asset support on the Zcash chain will open the door for a host of applications, and +enhance the ecosystem with application developers and Asset custody institutions for +issuance and bridging purposes. + +Overview +======== +In order to be able to represent different Assets, we need to define a data field that uniquely represents the Asset in question, which we call the Asset Identifier :math:`\mathsf{AssetId}`. +This Asset Identifier maps to an Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` that is stored in Orchard-based ZSA notes. +These terms are formally defined in ZIP 227 [#zip-0227]_. + +The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-binding]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is specially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. + +As was initially proposed by Jack Grigg and Daira Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}`, of the *net value* in an Orchard Action. + +Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point :math:`\mathcal{V}^\mathsf{Orchard}` in the value commitment [#protocol-concretevaluecommit]_. This ensures (1) that the input and output notes are of the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`, and (2) that only actions with the same Asset Base will balance out in the Orchard binding signature. + +In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the output note of that split Action is the output of a valid :math:`\mathsf{ZSAValueBase^{Orchard}}` computation defined in ZIP 227 [#zip-0227]_. + +Finally, in this ZIP we also describe the *burn* mechanism, which is a direct extension of the transfer mechanism. The burn process uses a similar mechanism to what is used in Orchard to unshield ZEC, by using the :math:`\mathsf{valueBalance}` of the Asset in question. Burning Assets is useful for many purposes, including bridging of Wrapped Assets and removing supply of Assets. + +Specification +============= + +Most of the protocol is kept the same as the Orchard protocol released with NU5, except for the following. + +Asset Identifiers +----------------- + +For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}` , the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. + +This :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` will be the base point of the value commitment for the specific Custom Asset. Note that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. + +In future network and protocol upgrades, the same Asset description string can be carried on, with potentially a mapping into a different shielded protocol. In that case, the turnstile should know how to transform the Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base from one shielded protocol to another. + +Note Structure & Commitment +--------------------------- + +Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. +:math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P*}`. + +A ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}}})`, +where + +- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P*}` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. + +Specifically, we define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: + +.. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor} \times \mathbb{B}^{[l_{\mathbb{P}}]} \times \mathbb{B}^{[l_{\mathbb{P}}]} \times \{0 .. 2^{l_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P*} \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Output} + +where :math:`\mathbb{P}, l_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and :math:`\mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor}, \mathsf{Orchard}.\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. +This note commitment scheme is instantiated using the Sinsemilla Commitment [#protocol-concretesinsemillacommit]_ as follows: + +.. math:: \begin{align} + \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} + :=\begin{cases} + \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi)}, &\text{... if } \mathsf{AssetBase}^{\mathsf{Orchard}} = \mathcal{V}^{\mathsf{Orchard}} \\ + \mathsf{cm}_{\mathsf{ZSA}} &\text{... otherwise} + \end{cases} + \end{align} + +where (note that :math:`\mathsf{repr}_{\mathbb{P}}` is as defined for the Pallas curve [#protocol-pallasandvesta]_, :math:`l^{\mathsf{Orchard}}_{\mathsf{base}}` is as defined in §5.3 [#protocol-constants]_, and :math:`\mathsf{I2LEBSP}` is as defined in §5.1 [#protocol-endian]_ of the Zcash protocol specification): + +.. math:: \begin{align} + \mathsf{cm}_{\mathsf{ZSA}} &:= \mathsf{SinsemillaCommit}_{\mathsf{rcm}}( \texttt{"z.cash:ZSA-NoteCommit"}, \\ + &\mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{l^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{l^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})) + \end{align} + +The nullifier is generated in the same manner as in the Orchard protocol [#protocol-commitmentsandnullifiers]_. + +The ZSA note plaintext also includes the Asset Base in addition to the components in the Orchard note plaintext [#protocol-notept]_. +It consists of + +.. math:: (\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[l_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{l_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]}) + +Rationale for Note Commitment +''''''''''''''''''''''''''''' + +In the ZSA protocol, the instance of the note commitment scheme, :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}`, differs from the Orchard note commitment :math:`\mathsf{NoteCommit^{Orchard}_{rcm}}` in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. +In the case where the Asset is the ZEC Asset, the commitment is computed identically to the Orchard note commitment, without making use of the ZEC Asset Base as an input. +As we will see, the nested structure of the Sinsemilla-based commitment [#protocol-concretesinsemillacommit]_ allows us to add the Asset Base as a final recursive step, and hence keep a single instance of the Sinsemilla hash function in the circuit for the note commitment verification. + +The note commitment output is still indistinguishable from the original Orchard ZEC note commitments, by definition of the Sinsemilla hash function [#protocol-concretesinsemillahash]_. ZSA note commitments will therefore be added to the same Orchard Note Commitment Tree. In essence, we have: + +.. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} \in \mathsf{NoteCommit^{Orchard}.Output} + + + + +Value Commitment +---------------- + +In the case of the ZSA protocol, the value of different Asset Identifiers in a given transaction will be committed using a **different value base point**. The value commitment becomes: + +.. math:: \mathsf{cv^{net}:=ValueCommit^{OrchardZSA}_{rcv}(v^{net}_{AssetId}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}:= \mathsf{[v^{net}_{AssetId}]}\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}} + [\mathsf{rcv}]\mathcal{R}^{\mathsf{Orchard}} + +where :math:`\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId} - v^{new}_{AssetId}}` such that :math:`\mathsf{v^{old}_{AssetId}}` and :math:`\mathsf{v^{new}_{AssetId}}` are the values of the old and new notes of Asset Identifier :math:`\mathsf{AssetId}` respectively, + +.. _`value base`: + +:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}` is defined in ZIP 227 [#zip-0227]_, and + +:math:`\mathcal{R}^{\mathsf{Orchard}}:=\mathsf{GroupHash^{\mathbb{P}}}\texttt{("z.cash:Orchard-cv", "r")}`, as in the Orchard protocol. + +We define :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{ZEC}} :=\mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. + +Rationale for Value Commitment +'''''''''''''''''''''''''''''' + +The Orchard Protocol uses a Homomorphic Pedersen Commitment [#protocol-concretevaluecommit]_ to perform the value commitment, with fixed base points :math:`\mathcal{V}^{\mathsf{Orchard}}` and :math:`\mathcal{R}^{\mathsf{Orchard}}` as the values represent the amount of ZEC being transferred. + +The use of different value base points for different Assets enables the final balance of the transaction to be securely computed, such that each Asset Identifier is balanced independently, which is required as different Assets are not meant to be mutually fungible. + + +Value Balance Verification +-------------------------- + +In order to verify the balance of the different Assets, the verifier MUST perform exactly the same process as for the Orchard protocol [#protocol-binding]_. + +For a total of :math:`n` Actions in a transfer, the prover MUST still sign the `SIGHASH` of the transaction using the binding signature key +:math:`\mathsf{bsk} = \sum_{\mathsf{ \forall i\in \{1,...,n\}}} \mathsf{rcv_{i}}`. + +Then the verifier MUST compute + +.. math:: \mathsf{bvk = (\sum cv_i^{net})} - \mathsf{ ValueCommit_0^{Orchard}(v^{balanceOrchard})} = \sum \mathsf{rcv_{i}^{net}}\mathcal{R}^{\mathsf{Orchard}} + +and use it to verify the `bindingSignature` on the `SIGHASH` message. + +Rationale for Value Balance Verification +'''''''''''''''''''''''''''''''''''''''' + +The main reason why no changes to the Orchard process are needed is that no Custom Assets can be unshielded, so all Custom Assets are contained within the shielded pool. This means that the net balance of the input and output values is zero, with only one Asset of value balance published, that of ZEC, :math:`\mathsf{v^{balanceOrchard}}`. No net amount of any other Asset will be revealed, and the number of Assets in the transaction is also hidden. The only exception to this is in the case that an Asset is *burnt*, as we will see below in the `burn mechanism`_. + +As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values only sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. + + +Split Notes +----------- + +One of the key functionalities in a UTXO-based protocol is the fact that input notes are usually split in two (or more) output notes, as in most cases, not all the value in a single note is sent to a single output. This requires a 1-to-many (Orchard) transaction. However, because each Action represents an input and an output, the resulting transaction must have multiple inputs. In order to cope with this today, the Actions that have not been assigned input notes are instead given *dummy spend notes* [#protocol-dummynotes]_, which we call split Actions and split notes respectively. Basically, the input note is “faked” inside of the proof in order to hide which Action contains the *real* spend note. + +This, however, brings some issues when it comes to adding multiple Asset Identifiers, as the output note of the split Actions *cannot* contain *any* Asset Base, but it must be enforced to be an actual output of a GroupHash computation (in fact we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). If not, then the prover could essentially input a multiple (or linear combination) of an existing Asset Base, with the goal to attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds. + +In order to prevent this, we make some modifications to the circuit. Specifically we remove the dummy note functionality for Custom Assets and we enforce that *every* input note to an ZSA Action must be proven to exist in the set of note commitments in the note commitment tree. We then enforce this real note to be “unspendable” in the sense that its value +will be zeroed in split Actions and the nullifier will be randomized, making the note not spendable in the specific Action. Then, the proof itself ensures that the output note is of the same Asset Base as the input note. In the circuit, the split note functionality will be activated by a boolean private input to the proof. + +This creates a chain of induction that ensures that the value base points of all output notes of a transfer are actual outputs of a GroupHash, as they originate in the Issuance protocol which is publicly verified. If this were not done then it would be possible to violate balance, for example by using a value base point derived from those of other Assets. + +Note that we do not care about whether the note identified by a Split Input is owned by the sender, or whether it was nullified before. + +Wallets and other clients have a choice to make to ensure the Asset Base is preserved for the output note of a Split Action: + +1. The Split Input note could be another note containing the same Asset Base that is being spent by this transaction (but not by this Split Input). +2. The Split Input note could be a different unspent note containing the same Asset Base (note that the note will not actually be spent). +3. The Split Input note could be an already spent note containing the same Asset Base (note that by zeroing the value in the circuit, we prevent double spending). + +The specific circuit changes are presented below. + +Circuit Statement +----------------- + +The advantage of the design described above, with respect to the circuit statement, is that every *ZSA Action statement* is kept closely similar to the Orchard Action statement [#protocol-actionstatement]_, except for a few additions that ensure the security of the Asset Identifier system. + +**Asset Identifier Equality:** the following constraints must be added to ensure that +the input and output note are of the same :math:`\mathsf{AssetId}`: + +- The Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`, for the note is witnessed once, as an auxiliary input. +- In the Old note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. +- In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. + +**Correct Value Commitment:** the following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base, as represented in the notes: + +- The fixed-base multiplication constraints between the value and the value base point of the value commitment, :math:`\mathsf{cv}`, is replaced with a variable-base multiplication between the two. +- The witness to the value base point, as defined in the `value base`_ equation is the auxiliary input :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`. + +**Enforce Secure Identifier for Split Actions:** the following constraints must be added to prevent senders from changing the Asset Base for the output note in a Split Action: + +- The Value Commitment Integrity should be changed + - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(v’ - v^new, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}` +- Add a boolean ``split`` variable as an auxiliary witness. This variable is to be activated ``split = 1`` if the Action in question is a split and ``split = 0`` if the Action is actually spending an input note: + - If ``split = 1`` then set :math:`\mathsf{v}' = 0` otherwise :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. +- The Merkle Path Validity should check the existence of the note commitment as usual (and not like with dummy notes): + - Check that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^old}` to the anchor :math:`\mathsf{rt^Orchard}`. +- The Nullifier Integrity will be changed to prevent the identification of notes + - Replace the :math:`\psi_{old}` value with a generic :math:`\psi'` as :math:`\mathsf{nf_old = DeriveNullifier_nk}(\rho^\mathsf{old}, \psi', \mathsf{cm^old})` + - if :math:`\mathtt{split} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled randomly.) + +**Enabling Backwards Compatibility with ZEC Notes:** the following constraints must be added to enable backwards compatibility with Orchard ZEC notes. + +The old note commitment is computed using a “rolling-aggregate” Sinsemilla commitment. This means that the commitment is computed by adding new chunks or windows to the accumulated value. This method will be used in order to maintain a single commitment instance for the old note commitment, that will be used both for Orchard ZEC notes and for ZSA notes. The original Orchard ZEC notes will be conserved and not actually be converted into ZSA notes, as we will always need to compute them. +However, new notes will always be ZSA notes with an Asset Base. + +The input note in the old note commitment integrity check must either include an Asset Base (ZSA note) or not (ZEC-Orchard note). If the note is an old note, from before the upgrade, the commitment is computed in the original Orchard fashion. If the note is a new ZSA note, there are two cases: + +- If the Asset Base auxiliary input present but set to :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` = :math:`\mathcal{V}^\mathsf{Orchard}` + - NoteCommitment has a “compatibility” path that computes the note commitment as in plain Orchard (i.e.: without including the Asset Base) + - This path also uses the original domain separator for ZEC note commitment +- Else, + - The note commitment adds the identfier, :math:`\mathsf{AssetId}`, as a final “chunk” of the Sinsemilla commitment + - The note commitment uses a different domain separator for ZSA note commitment + + +Backward Compatibility +---------------------- + +In order to have a "clean" backwards compatibility with the ZEC notes, we have designed the circuit to support both ZEC and ZSA notes. As we specify above, there are three main reasons we can do this: +- The input notes with an Asset Base denote the Custom Assets, generating a note commitment that includes the Asset Identifier; whereas the notes without an Asset Base denote the ZEC notes from before the protocol upgrade, and generate a note commitment that does not include the Asset Base, in order to maintain the referencability to the Merkle tree +- The value commitment is abstracted to allow for the value base-point as a variable private input to the proof +- The ZEC-based Actions will still include dummy input notes, whereas the ZSA-based Actions will include split input notes. + + +Burn Mechanism +============== +The burn mechanism may be needed for off-boarding the Wrapped Assets from the chain, or enabling advanced tokenomics on Assets. It is part of the Issuance/Burn protocol, but given that it can be seen as an extension of the Transfer protocol, we add it here for readability. + +In essence, the burn mechanism is a transparent / revealing extension to the transfer protocol that enables a specific amount of any Asset identifier to be sent into “oblivion”. Our burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. + +First, contrary to the strict transfer transaction, we allow the sender to include a :math:`\mathsf{valueBalance_{AssetId}}` variable for every Asset Identifier that is being burnt. As we will show in the transaction structure, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset. +We require that for every :math:`\mathsf{valueBalance_{AssetId}}` provided as above by the sender, :math:`\mathsf{valueBalance_{AssetId}} \neq 0`. This is enforced via a consensus rule. + +For every custom Asset that is burnt, we add to the `assetBurn` vector the tuple :math:`(\mathsf{valueBalance_{AssetId}, AssetId})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. + + +:math:`\mathsf{assetBurn = \{ (v^{AssetId}, AssetId)}\ |\ \forall\ \mathsf{AssetId}\ \textit{s.t.}\ \mathsf{v^{AssetId}} \neq 0 \}` + +The value balances for each Asset Identifier in `assetBurn` represents the amount of that Asset that is being burnt. In the case of ZEC, the value balance represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). + +Finally, the validator needs to verify the Balance and Binding Signature by adding the value balances for all Assets, as committed using their respective :math:`\mathsf{AssetId}` as the value base point of the Pedersen Commitment. This is done as follows + +:math:`\mathsf{bvk = (\sum cv_i^{net})} - \mathsf{ ValueCommit_0^{Orchard}(v^{balanceOrchard})} - \sum_{\forall \mathsf{AssetId}\textit{ s.t. }\mathsf{v^{AssetId}\neq 0}} \mathsf{ValueCommit_0^{OrchardZSA}(v^{AssetId}, AssetId) } = \sum \mathsf{rcv_{i,j}^{net}}\mathcal{R}^{\mathsf{Orchard}}` + +In the case that the balance of all the Action values related to a specific Asset will be zero, there will be no value added to the vector. This way, neither the number of Assets nor their Asset Identifiers will be revealed, except in the case that an Asset is burnt. + +**Note:** Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets. + +ZSA Transaction Structure +========================= + +The transaction format is similar to the version 5 transaction format described in the Zcash specification [#protocol-transactionstructure]_, with the following additions to the Orchard bundle: + ++-----------------+-------------+-----------------------------------+-------------------------+ +| Bytes | Name | Data Type | Description | ++=================+=============+===================================+=========================+ +| varies | nAssetBurn | compactSize | number of Assets burnt | ++-----------------+-------------+-----------------------------------+-------------------------+ +| 40*nAssetBurn | vAssetBurn | bytes[40][nAssetBurn] | 32 bytes Asset type_t, | +| | | | 8 bytes of valueBalance | ++-----------------+-------------+-----------------------------------+-------------------------+ + +In terms of the Action size, the ZSA action size differs from the Orchard action size by 32 bytes (due to the addition of the :math:`\mathsf{AssetId}`). This implies that the size goes from 820 bytes in the Orchard action to 852 bytes in the ZSA Action. + +Other Considerations +==================== + +Transaction Fees +---------------- + +The fee mechanism for the upgrades proposed in this ZIP will follow the mechanism described in ZIP 317 for the ZSA protocol upgrade [#zip-0317b]_. + +Security and Privacy +-------------------- + +- Even if the Orchard protocol and ZSA protocol do not share the same anonymity pool (nodes can keep track of the notes that where published with different transaction structures), the migration from one to the other is done automatically and seamlessly. The Orchard bundle will be replaced by the ZSA bundle and all ZEC notes will be fully spendable with the new transaction structure. +- When including new Assets we would like to maintain the amount and identifiers of Assets private, which is achieved with the design. +- We prevent the "roadblock" attack on the Asset Identifier by ensuring the output notes receive an Asset Base that exists on the global state. +- Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are the use of a petname system or a list of well-known Assets. + + - One proposal for a petname system for the zcashd wallet is the use of an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. + +Deployment +----------- +The Zcash Shielded Assets protocol should be deployed by replacing the Orchard protocol in a subsequent Network Upgrade. The design of this protocol ensures that there is no need to use any turnstile mechanism, being that Orchard-based ZEC notes can be used directly within the ZSA Actions. + +Test Vectors +============ + +- LINK TBD + +Reference Implementation +======================== + +- LINK TBD +- LINK TBD + +References +========== + +.. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels `_ +.. [#zip-0200] `ZIP 200: Network Upgrade Mechanism `_ +.. [#zip-0224] `ZIP 224: Orchard `_ +.. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ +.. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ +.. [#protocol-notes] `Zcash Protocol Specification, Version 2022.3.8. Section 3.2: Notes `_ +.. [#protocol-notept] `Zcash Protocol Specification, Version 2022.3.8. Section 5.5: Encodings of Note Plaintexts and Memo Fields `_ +.. [#protocol-actions] `Zcash Protocol Specification, Version 2022.3.8. Section 3.7: Action Transfers and their Descriptions `_ +.. [#protocol-abstractcommit] `Zcash Protocol Specification, Version 2022.3.8. Section 4.1.8: Commitment `_ +.. [#protocol-binding] `Zcash Protocol Specification, Version 2022.3.8. Section 4.14: Balance and Binding Signature (Orchard) `_ +.. [#protocol-commitmentsandnullifiers] `Zcash Protocol Specification, Version 2022.3.8. Section 4.16: Note Commitments and Nullifiers `_ +.. [#protocol-endian] `Zcash Protocol Specification, Version 2022.3.8. Section 5.1: Integers, Bit Sequences, and Endianness `_ +.. [#protocol-constants] `Zcash Protocol Specification, Version 2022.3.8. Section 5.3: Constants `_ +.. [#protocol-pallasandvesta] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.9.6: Pallas and Vesta `_ +.. [#pasta-evidence] `Pallas/Vesta supporting evidence `_ +.. [#protocol-concretesinsemillahash] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.1.9: Sinsemilla hash function `_ +.. [#protocol-concretesinsemillacommit] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.8.4: Sinsemilla commitments `_ +.. [#protocol-concretevaluecommit] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.8.3: Homomorphic Pedersen commitments (Sapling and Orchard) `_ +.. [#protocol-dummynotes] `Zcash Protocol Specification, Version 2022.3.8. Section 4.8.3: Dummy Notes (Orchard) `_ +.. [#protocol-actionstatement] `Zcash Protocol Specification, Version 2022.3.8. Section 4.17.4: Action Statement (Orchard) `_ +.. [#protocol-transactionstructure] `Zcash Protocol Specification, Version 2022.3.8. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5) `_ +.. [#initial-zsa-issue] `User-Defined Assets and Wrapped Assets `_ +.. [#generalized-value-commitments] `Comment on Generalized Value Commitments `_ +.. 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a/zip-0227.rst b/zip-0227.rst index ed5d8d322..4f48a9853 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -9,7 +9,446 @@ Credits: Daniel Benarroch Aurelien Nicolas Deirdre Connolly - Status: Reserved + Teor + Status: Draft Category: Consensus + Created: 2022-05-01 + License: MIT Discussions-To: - Pull-Request: + Pull-Request: + + +Terminology +=========== + +The key word "MUST" in this document is to be interpreted as described in RFC 2119 [#RFC2119]_. + +The term "network upgrade" in this document is to be interpreted as described in ZIP 200 [#zip-0200]_. + +The term "Orchard" in this document is to be interpreted as described in ZIP 224 [#zip-0224]_. + +The terms "Asset", "custom Asset", and "Wrapped Asset" in this document are to be interpreted as described in ZIP 226 [#zip-0226]_. + +We define the following additional terms: + +- Issuance Action: an instance of a single issuance of a Zcash Shielded Asset. It defines the issuance of a single Asset Identifier. +- Issuance Bundle: the bundle in the transaction that contains all the issuance actions of that transaction. + +Abstract +======== + +ZIP 226 [#zip-0226]_ and ZIP 227 [#zip-0227]_ propose in conjunction the Zcash Shielded Assets (ZSA) protocol, which is an extension of the Orchard protocol that enables the creation, transfer and burn of custom Assets on the Zcash chain. The creation of such Assets is defined in ZIP 227 [#zip-0227]_. The transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. This ZIP must only be implemented in conjuction with ZIP 226 [#zip-0226]_, as the issuance mechanism is only valid for the ZSA transfer protocol, because it produces notes that can only be transferred under ZSA. + +Motivation +========== + +This ZIP is a supporting ZIP for ZIP 226 [#zip-0226]_, which lays out its motivations, but requires an issuance mechanism to be defined (which is substantial enough to stand on its own) in order to function. + +This ZIP enables only *transparent* issuance, since as a first step, transparency will allow for proper testing of the applications that will be most used in the Zcash ecosystem, and will enable the supply of Assets to be tracked. + +The issuance mechanism described in this ZIP is broad enough for issuers to either create Assets on Zcash (i.e. Assets that originate on the Zcash block chain), as well as for institutions to create bridges from other chains and import "wrapped" Assets. This enables what we hope will be a useful set of applications. + + +Use Cases +========= + +The design presented in this ZIP enables issuance of shielded Assets in various modes: + +- The issuer may or may not know the receivers of the issued Asset in advance. +- The Asset can be of non-fungible type, where each Asset type can be made part of a single “series”. +- The supply of the Asset can be limited in advance or not. +- The Asset can be a wrapped version of an Asset issued by another chain (as long as there is a bridge that supports transfer of that Asset between chains). + +See the `Concrete Applications`_ section for more details. + +Requirements +============ + +- Any user of the Zcash block chain can issue custom Assets on chain. +- The issuance mechanism should enable public tracking of the supply of the Assets on the Zcash block chain. +- At the time of issuance, the issuer should be able to allocate all the Assets to the corresponding owners by creating the corresponding (shielded) output notes to the respective addresses. This allows for allocation to be totally private even though the issuance mechanism is itself transparent. +- Issuing or changing the attributes of a specific Asset should require cryptographic authorization. +- The Asset identification should be unique (among all shielded pools) and different issuer public keys should not be able to generate the same Asset Identifier. +- An issuer should be able to issue different Assets in the same transaction. In other words, in a single "issuance bundle", the issuer should be able publish many "issuance actions", potentially creating multiple Custom Assets. +- Every "issuance action" should contain a ``finalize`` boolean that defines whether the specific Custom Asset can have further tokens issued or not. + + +Specification +============= + +As explained, the issuance protocol allows for a single issuance action to be sent to many receivers, by generating as many output notes as distinct recipients. Furthermore, every bundle can contain many issuance actions. + +Issuance Keys and Issuance Authorization Signature Scheme +--------------------------------------------------------- + +The ZSA Protocol adds the following three keys to the key components [#protocol-addressesandkeys]_: + +1. The issuance master key, denoted as :math:`\mathsf{sk}_{\mathsf{iss}}`, as the name suggests, is the master key that is used to derive the other two keys. + +2. The issuance authorizing key is the key that is used to sign the issuance transaction, and is denoted as :math:`\mathsf{isk}`. This key is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. + +3. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all block chain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. + +Issuance Authorization Signature Scheme +``````````````````````````````````````` + +We define the issuance authorization signature scheme :math:`\mathsf{IssueAuthSig}` similar to :math:`\mathsf{SpendAuthSig}^{\mathsf{Orchard}}`, the Orchard spend authorization signature scheme [#protocol-concretespendauthsig]_. +Specifically, we instantiate :math:`\mathsf{IssueAuthSig}` as :math:`\mathsf{RedPallas}` without key re-randomization using generator :math:`\mathcal{P}_{\mathbb{G}} = \mathcal{G}^{\mathsf{Issuance}} := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:ZSA"}, \texttt{"Issuance"})` where :math:`\mathsf{GroupHash}^\mathbb{P}` is defined as in the Zcash protocol specification [#protocol-concretegrouphashpallasandvesta]_. + +Issuance Key Derivation +``````````````````````` + +The issuance master key is generated by choosing a bit sequence uniformly at random from :math:`\mathbb{B}^{\mathbb{Y}[32]}`, like the Orchard spending key [#protocol-orchardkeycomponents]_. +In :math:`\mathsf{zcashd}`, this key is derived in a manner similar to the generation of the Orchard master key in ZIP 32 [#zip-0032-orchard-master]_, as detailed below: + +- Details TBD + +The issuance authorizing key and issuance validating key are derived from the issuance master key in an analogous manner to the derivation of the Orchard spend authorizing key and Orchard spend validating key from the Orchard spending key [#protocol-orchardkeycomponents]_, as described below. + +- The issuance authorizing key is derived from the issuance master key, :math:`\mathsf{sk}_{\mathsf{iss}}`, as a private signature key: + +.. math:: \mathsf{isk} := \mathsf{ToScalar}^{\mathsf{Orchard}}(︀ \mathsf{sk}_{\mathsf{iss}} ) + +- The issuance validating key is derived from the issuance authorizing key, :math:`\mathsf{isk}`, as a public verification key: + +.. math:: \mathsf{ik} := \mathsf{IssueAuthSig}.\mathsf{DerivePublic}(\mathsf{isk}) + +This allows the issuer to use the same wallet it usually uses to transfer Assets, while keeping a disconnect from the other keys. Specifically, this method is aligned with the requirements and motivation of ZIP 32 [#zip-0032]_. It provides further anonymity and the ability to delegate issuance of an Asset (or in the future, generate a multi-signature protocol) while the rest of the keys remain in the wallet safe. + +The derivation of these keys are shown in the following diagram: + +.. figure:: zip-0227-key-components-zsa.png + :width: 450px + :align: center + :figclass: align-center + + Diagram of Issuance Key Components for the ZSA Protocol + + +Asset Identifier +---------------- + +For every new Asset, there must be a new and unique Asset Identifier. We define this to be a globally unique pair :math:`(\mathsf{ik}, \mathsf{asset\_desc})`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. + +A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-based ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. +From the Asset Digest, we derive a specific Asset Base within each such shielded protocol (for example :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}` for the Orchard-based ZSA protocol), using the applicable hash-to-curve algorithm. This Asset Base is included in shielded notes. + +Let + +- :math:`\mathsf{asset\_desc}` be the asset description, a UTF-8 encoded string of up to 512 bytes, which includes any information pertaining to the issuance. +- :math:`\mathsf{ik}` be the issuance validating key of the issuer, a public key used to verify the signature on the issuance transaction's SIGHASH. + +Define :math:`\mathsf{AssetDigest_{\mathsf{AssetId}}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))`, +where + +- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}(\mathsf{ik}, \mathsf{asset\_desc}) := \mathsf{0x00} || \mathsf{repr}_{\mathbb{P}}(\mathsf{ik}) || \mathsf{asset\_desc}\!`. + +Define :math:`\mathsf{AssetBase^{Protocol}_{\mathsf{AssetId}}} := \mathsf{ZSAValueBase^{Protocol}}(\mathsf{AssetDigest}_{\mathsf{AssetId}})`, +where + +In the case of Orchard, we define :math:`\mathsf{ZSAValueBase^{Orchard}}(\mathsf{asset\_digest}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{asset\_digest})` +where :math:`\mathsf{GroupHash}^\mathbb{P}` is defined as in [#protocol-concretegrouphashpallasandvesta]_. + +The relations between the Asset Identifier, Asset Digest, and Asset Base are shown in the following diagram: + +.. figure:: zip-0227-asset-identifier-relation.png + :width: 600px + :align: center + :figclass: align-center + + Diagram relating the Asset Identifier, Asset Digest, and Asset Base in the ZSA Protocol + + +Global Issuance State +--------------------- + +Issuance requires the following additions to the global state defined at block boundaries: + +- :math:`\mathsf{previously\_finalized}`, a set of :math:`\mathsf{AssetId}` that have been finalized (i.e.: the ``finalize`` flag has been set to ``1`` in some issuance transaction preceding the block boundary). + +Issuance Action Description +--------------------------- + +An issuance action, `IssueAction`, is the instance of issuing a specific custom Asset, and contains the following fields: + +- :math:`\mathsf{assetDescSize}`: the size of the Asset description, a number between :math:`0` and :math:`512`, stored in two bytes. +- :math:`\mathsf{asset\_desc}`: the Asset description, a UTF-8 encoded string of up to 512 bytes +- `notes`: an array containing the unencrypted output notes of the recipients of the Asset, of type `Note` +- ``finalize``: a boolean that defines whether the issuance of that specific custom Asset is finalized or not + +An asset's :math:`\mathsf{AssetId}` is added to the :math:`\mathsf{previously\_finalized}` set after a block that contains any issuance transaction for that asset with ``finalize = 1``. It then cannot be removed from this set. For Assets with :math:`\mathsf{AssetId} \in \mathsf{previously\_finalized}`, no further tokens can be issued, so as seen below, the validators will reject the transaction. For Assets with :math:`\mathsf{AssetId} \not\in \mathsf{previously\_finalized}`, new issuance actions can be issued in future transactions. These must use the same Asset description, :math:`\mathsf{asset\_desc}`, and can either maintain ``finalize = 0`` or change it to ``finalize = 1``, denoting that this custom Asset cannot be issued after the containing block. + +================= =============================== ========================== =========================================================================================== +Size Name Data Type Description +================= =============================== ========================== =========================================================================================== +2 bytes :math:`\mathsf{assetDescSize}` byte The length of the :math:`\mathsf{asset\_desc}` string in bytes +Varies :math:`\mathsf{asset\_desc}` byte UTF-8 encoded string, of size :math:`\mathsf{assetDescSize}` bytes +Varies nNotes compactSize The number of notes in the issuance action +noteSize * nNotes vNotes Note[nNotes] A sequence of note descriptions within the issuance action +1 byte ``flagsIssuance`` byte An 8-bit value with the ``finalize`` boolean value as the LSB, and the other bits set to 0. +================= =============================== ========================== =========================================================================================== + +We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the `NoteCommitmentTree` as a shielded note. This prevents future usage of the note from being linked to the issuance transaction, as the nullifier key is not known to the validators and chain observers. + +Issuance Bundle +--------------- + +An issuance bundle, `IssueBundle`, is the aggregate of all the issuance-related information. Specifically, contains all the issuance actions and the issuer signature on the transaction SIGHASH that validates the issuance itself. It contains the following fields: + +- :math:`\mathsf{ik}`: the issuance validating key, that allows the validators to verify that the :math:`\mathsf{AssetId}` is properly associated with the issuer. +- `actions`: an array of issuance actions, of type `IssueAction`. +- `issueAuthSig`: the signature of the transaction SIGHASH, signed by the issuance authorizing key, :math:`\mathsf{isk}`, that validates the issuance . + +The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-transactionstructure]_. + +======= ==================== ========================== ========================================================================= +Bytes Name Data Type Description +======= ==================== ========================== ========================================================================= +Varies nIssueActions compactSize The number of issuance actions in the bundle +Varies vIssueActions IssueAction[nIssueActions] A sequence of issuance actions descriptions +32 :math:`\mathsf{ik}` byte[32] The issuance validating key of the issuer, used to validate the signature +64 issueAuthSig byte[64] The signature of the transaction SIGHASH, signed by the issuer +======= ==================== ========================== ========================================================================= + +Issuance Protocol +----------------- +The issuer program performs the following operations + +For all actions `IssueAction`: + +- encode :math:`\mathsf{asset\_desc}` as a UTF-8 byte string of size up to 512. +- compute :math:`\mathsf{AssetDigest}` from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as decribed in the `Asset Identifier`_ section. +- compute :math:`\mathsf{AssetBase^{Protocol}}` from :math:`\mathsf{AssetDigest}` as decribed in the `Asset Identifier`_ section. +- set the ``finalize`` boolean as desired (if more more issuance actions are to be created for this Asset Identifier, set ``finalize = 0``, otherwise set ``finalize = 1``) +- For each recipient :math:`i`: + + - generate a ZSA output note that includes the Asset Base. For an Orchard-based ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d},i}, \mathsf{v}_i, \rho_i, \psi_i, \mathsf{AssetBase^{Orchard}}, \mathsf{rcm}_i)\!`. + +- encode the `IssueAction` into the vector `vIssueActions` of the bundle + +For the `IssueBundle`: + +- encode the `vIssueActions` vector +- encode the :math:`\mathsf{ik}` as 32 byte-string +- sign the `SIGHASH` of the transaction with the issuance authorizing key, :math:`\mathsf{isk}`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. + + +NOTE that the commitment is not included in the `IssuanceAction` itself. As explained below, it is later computed by the validators and added to the `NoteCommitmentTree`. + + +Consensus Rule Changes +---------------------- + +For the IssueBundle: + +- Verify the RedPallas-based issuance authorization signature on `SIGHASH`, `issueAuthSig`, is verified by invoking `issueAuthSig.VerifySig(ik, SIGHASH)` + +For each `IssueAction` in `IssueBundle`: + +- check that :math:`0 < \mathsf{assetDescSize} <= 512`. +- check that :math:`\mathsf{asset\_desc}` is a string of length :math:`\mathsf{assetDescSize}` bytes. +- retrieve :math:`\mathsf{AssetBase}` from the first note in the sequence and check that :math:`\mathsf{AssetBase}` is derived from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as described in the `Asset Identifier`_ section. +- check that the :math:`\mathsf{AssetId}` does not exist in the ``previously_finalized`` set in the global state. +- check that every note in the `IssueAction` contains the same :math:`\mathsf{AssetBase}` and is properly constructed as :math:`note = (\mathsf{g_d, pk_d, v, \rho, \psi, AssetBase})`. + +If all of the above checks pass, do the following: + +- For each note, compute the note commitment as :math:`\mathsf{cm} = \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, AssetBase)}` as defined in the Note Structure and Commitment section of ZIP 226 [#zip-0226-notestructure]_ and +- add :math:`\mathsf{cm}` to the Merkle tree of note commitments, `NoteCommitmentTree`. +- If ``finalize = 1``, add :math:`\mathsf{AssetId}` to the ``previously_finalized`` set immediately after the block in which this transaction occurs. + + +Rationale +========= +The following is a list of rationale for different decisions made in the proposal: + +- The issuance key structure is independent of the original key tree, but derived in an analogous manner (via ZIP 32). This is in order to keep the issuance details and the Asset Identifiers consistent across multiple shielded pools. +- The design decision is not to have a chosen name to describe the Custom Asset, but to delegate it to an off-chain mapping, as this would imply a land-grab “war”. +- The :math:`\mathsf{asset\_desc}` is a general byte string in order to allow for a wide range of information type to be included that may be associated with the Assets. Some are: + + - links for storage such as for NFTs. + - metadata for Assets, encoded in any format. + - bridging information for Wrapped Assets (chain of origin, issuer name, etc) + - information to be committed by the issuer, though not enforceable by the protocol. + +- We require a check whether the ``finalize`` flag only has been set in a previous block rather than a previous transaction in the same block. In other words, we only update the ``previously_finalized`` set at the block boundary. This is in keeping with the current property which allows for a miner to reorder transactions in a block without changing the meaning, which we aim to preserve. + +Concrete Applications +--------------------- + +**Asset Features** + +- By using the ``finalize`` boolean and the burning mechanism defined in [#zip-0226]_, issuers can control the supply production of any Asset associated to their issuer keys. For example, + + - by setting ``finalize = 1`` from the first issuance action for that Asset Identifier, the issuer is in essence creating a one-time issuance transaction. This is useful when the max supply is capped from the beginning and the distribution is known in advance. All tokens are issued at once and distributed as needed. + +- Issuers can also stop the existing supply production of any Asset associated to their issuer keys. This could be done by + + - issuing a last set of tokens of that specific :math:`\mathsf{AssetId}`, for which ``finalize = 1``, or by + - issuing a transaction with a single note in the issuance action pertaining to that :math:`\mathsf{AssetId}`, where the note will contain a ``value = 0``. This can be used for application-specific purposes (NFT collections) or for security purposes to revoke the Asset issuance (see Security and Privacy Considerations). + - Note in the above cases, that the setting of the ``finalize`` flag will take effect at the block boundary, that is, after all the transactions in the block. + +- The issuance and burn mechanisms can be used in conjunction to determine the supply of Assets on the Zcash ecosystem. This allows for the bridging of Assets defined on other chains. + +- Furthermore, NFT issuance is enabled by issuing in a single bundle several issuance actions, where each :math:`\mathsf{AssetId}` corresponds to ``value = 1`` at the fundamental unit level. Issuers and users should make sure that ``finalize = 1`` for each of the actions in this scenario. + + + +TxId Digest +=========== + +As in ZIP 244 [#zip-0244]_, the digests are all personalized BLAKE2b-256 hashes, and in cases where no elements are available for hashing, a personalized hash of the empty byte array is used. + +A new issuance transaction digest algorithm is defined that constructs the identifier for an issuance transaction. Each branch of the tree of hashes will correspond to a specific subset of issuance transaction data. The overall structure of the hash is as follows; each name referenced here will be described in detail below:: + + issuance_txid_digest + ├── issue_actions_digest + └── issuanceValidatingKey + +In the specification below, nodes of the tree are presented in depth-first order. + +issuance_txid_digest +-------------------- +A BLAKE2b-256 hash of the following values :: + + T.1: issue_actions_digest (32-byte hash output) + T.2: issuanceValidatingKey (32 bytes) + +The personalization field of this hash is set to:: + + "ZTxIdSAIssueHash" + +In case the transaction has no issuance components, ''issue_actions_digest'' is:: + + BLAKE2b-256("ZTxIdSAIssueHash", []) + +T.1: issue_actions_digest +````````````````````````` +A BLAKE2b-256 hash of Issue Action information for all Issuance Actions belonging to the transaction. For each Action, the following elements are included in the hash:: + + T.1a: notes_digest (32-byte hash output) + T.1b: assetDescription (field encoding bytes) + T.1c: flagsIssuance (1 byte) + +The personalization field of this hash is set to:: + + "ZTxIdIssActHash" + +T.1a: notes_digest +'''''''''''''''''' +A BLAKE2b-256 hash of Note information for all Notes belonging to the Issuance Action. For each Note, the following elements are included in the hash:: + + T.1a.1: recipient (field encoding bytes) + T.1a.2: value (field encoding bytes) + T.1a.3: asset (field encoding bytes) + T.1a.4: rho (field encoding bytes) + T.1a.5: rseed (field encoding bytes) + +The personalization field of this hash is set to:: + + "ZTxIdIANoteHash" + +T.1a.1: recipient +................. +This is the raw encoding of an Orchard shielded payment address as defined in the protocol specification [#protocol-orchardpaymentaddrencoding]_. + +T.1a.2: value +............. +Note value encoded as little-endian 8-byte representation of u64 raw value. + +T.1a.3: asset +............. +Asset Base encoded as 32-byte representation of Pallas point. + +T.1a.4: rho +........... +Nullifier encoded as 32-byte representation of Pallas point. + +T.1a.5: rseed +............. +The ZIP 212 32-byte seed randomness for a note. + +T.1b: assetDescription +'''''''''''''''''''''' +UTF-8 encoding of the Asset description string. + +T.1c: flagsIssuance +''''''''''''''''''' +An 8-bit value representing a set of flags. Ordered from LSB to MSB: + +- ``finalize`` +- The remaining bits are set to `0`. + + +T.2: issuanceValidatingKey +`````````````````````````` +A byte encoding of issuance validating key for the bundle as defined in the `Issuance Key Derivation`_ section. + + +Security and Privacy Considerations +=================================== + +**Issuer Key or AssetId Compromise** + +The design of this protocol does not allow for a rotation of the issuer validating key, that would allow for replacing the key of a specific Asset (see Future Work). In case of compromise, the following actions are recommended: + +- If an issuer validating key is compromised, the ``finalize`` boolean for all the Assets issued with that key should be set to `1` and the issuer should change to a new issuance authorizing key, and issue new Assets, each with a new :math:`\mathsf{AssetId}`. + +**Bridging Assets** +For bridging purposes, the secure method of off-boarding Assets is to burn an Asset with the burning mechanism in ZIP 226 [#zip-0226]_. Users should be aware of issuers that demand the Assets be sent to a specific address on the Zcash chain to be redeemed elsewhere, as this may not reflect the real reserve value of the specific Wrapped Asset. + +Other Considerations +==================== + +Implementing Zcash Nodes +------------------------ + +Although not enforced in the global state, it is RECOMMENDED that Zcash full validators keep track of the total supply of Assets as a mutable mapping `issuanceSupplyInfoMap` from :math:`\mathsf{AssetId}` to :math:`\mathsf{issuanceSupplyInfoMap := (totalSupply, finalize)}` in order to properly keep track of the total supply for different Asset Identifiers. This is useful for wallets and other applications that need to keep track of the total supply of Assets. + +Fee Structures +-------------- + +The fee mechanism described in this ZIP will follow the mechanism described in ZIP 317b [#zip-0317b]_. + +Future Work +----------- + +In future versions of this ZIP, the protocol may also include a "key rotation" mechanism. This would allow an issuer to change the underlying :math:`\mathsf{ik}` of a given Asset, in case the original one was compromised, without having to change the Asset Identifier altogether. + +Test Vectors +============ + +- LINK TBD + +Reference Implementation +======================== + +- LINK TBD +- LINK TBD + +Deployment +========== + +This ZIP is proposed to activate with Network Upgrade 6. + +References +========== + +.. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels `_ +.. [#zip-0200] `ZIP 200: Network Upgrade Mechanism `_ +.. [#zip-0224] `ZIP 224: Orchard `_ +.. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ +.. [#zip-0226-notestructure] `ZIP 226: Transfer and Burn of Zcash Shielded Assets - Note Structure & Commitment `_ +.. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ +.. [#zip-0244] `ZIP 244: Transaction Identifier Non-Malleability `_ +.. [#zip-0317b] `ZIP 317b: ZSA Extension Proportional Fee Mechanism `_ +.. [#zip-0032] `ZIP 32: Shielded Hierarchical Deterministic Wallets `_ +.. [#zip-0032-orchard-master] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard master key generation `_ +.. [#zip-0316] `ZIP 316: Unified Addresses and Unified Viewing Keys `_ +.. [#protocol-addressesandkeys] `Zcash Protocol Specification, Version 2022.3.8. Section 3.1: Payment Addresses and Keys `_ +.. [#protocol-concretegrouphashpallasandvesta] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.9.8: Group Hash into Pallas and Vesta `_ +.. [#protocol-orchardkeycomponents] `Zcash Protocol Specification, Version 2022.3.8. Section 4.2.3: Orchard Key Components `_ +.. [#protocol-spendauthsig] `Zcash Protocol Specification, Version 2022.3.8. Section 4.15: Spend Authorization Signature (Sapling and Orchard) `_ +.. [#protocol-concretespendauthsig] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.7.1: Spend Authorization Signature (Sapling and Orchard) `_ +.. [#protocol-orchardpaymentaddrencoding] `Zcash Protocol Specification, Version 2022.3.8. Section 5.6.4.2: Orchard Raw Payment Addresses `_ +.. [#protocol-transactionstructure] `Zcash Protocol Specification, Version 2022.3.8. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5) `_ From 5a1222bc2d19354d5270f8b0996aaebf3e05207c Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Mon, 17 Apr 2023 13:45:18 +0530 Subject: [PATCH 02/43] ZIP 226: editorial change to terminology. Co-authored-by: Daira-Emma Hopwood --- zip-0226.rst | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/zip-0226.rst b/zip-0226.rst index 7d7bccc1f..3ff87fb0c 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -25,7 +25,8 @@ The key word "MUST" in this document is to be interpreted as described in RFC 21 The term "network upgrade" in this document is to be interpreted as described in ZIP 200 [#zip-0200]_. -The term "Orchard" in this document is to be interpreted as described in ZIP 224 [#zip-0224]_. +The terms "Orchard" and "Action" in this document are to be interpreted as described in +ZIP 224 [#zip-0224]_. We define the following additional terms: From 325c6e4d92efedfd235e890872cf0d5968a9fc51 Mon Sep 17 00:00:00 2001 From: Vivek Arte <46618816+vivek-arte@users.noreply.github.com> Date: Mon, 17 Apr 2023 15:01:59 +0530 Subject: [PATCH 03/43] Suggestions from ZIP review: improvements to mathematical notation, and typographical edits. Co-authored-by: Daira-Emma Hopwood Co-authored-by: Deirdre Connolly --- zip-0226.rst | 27 ++++++++++++++------------- 1 file changed, 14 insertions(+), 13 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 3ff87fb0c..091a91eb1 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -49,7 +49,8 @@ of protocol features that enable the creation, transfer, and burn of Custom Asse Creation of such Assets is defined in ZIP 227 [#zip-0227]_. Transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. The ZSA protocol is proposed to be instantiated by a modification to the -Orchard protocol, as specified in these ZIPs. +Orchard protocol, as specified in these ZIPs (although it has been designed with adaption +to possible future shielded protocols in mind). Motivation ========== @@ -65,13 +66,13 @@ In order to be able to represent different Assets, we need to define a data fiel This Asset Identifier maps to an Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` that is stored in Orchard-based ZSA notes. These terms are formally defined in ZIP 227 [#zip-0227]_. -The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-binding]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is specially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. +The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-binding]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. As was initially proposed by Jack Grigg and Daira Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}`, of the *net value* in an Orchard Action. -Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point :math:`\mathcal{V}^\mathsf{Orchard}` in the value commitment [#protocol-concretevaluecommit]_. This ensures (1) that the input and output notes are of the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`, and (2) that only actions with the same Asset Base will balance out in the Orchard binding signature. +Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point :math:`\mathcal{V}^\mathsf{Orchard}` in the value commitment [#protocol-concretevaluecommit]_. This ensures (1) that the input and output notes are of the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature. -In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the output note of that split Action is the output of a valid :math:`\mathsf{ZSAValueBase^{Orchard}}` computation defined in ZIP 227 [#zip-0227]_. +In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the output note of that Split Action is the output of a valid :math:`\mathsf{ZSAValueBase^{Orchard}}` computation defined in ZIP 227 [#zip-0227]_. Finally, in this ZIP we also describe the *burn* mechanism, which is a direct extension of the transfer mechanism. The burn process uses a similar mechanism to what is used in Orchard to unshield ZEC, by using the :math:`\mathsf{valueBalance}` of the Asset in question. Burning Assets is useful for many purposes, including bridging of Wrapped Assets and removing supply of Assets. @@ -83,35 +84,35 @@ Most of the protocol is kept the same as the Orchard protocol released with NU5, Asset Identifiers ----------------- -For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}` , the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. +For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. This :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` will be the base point of the value commitment for the specific Custom Asset. Note that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. -In future network and protocol upgrades, the same Asset description string can be carried on, with potentially a mapping into a different shielded protocol. In that case, the turnstile should know how to transform the Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base from one shielded protocol to another. +In future network and protocol upgrades, the same Asset description string can be carried on, potentially mapping into a different shielded protocol. In that case, the turnstile should know how to transform the Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base from one shielded protocol to another. Note Structure & Commitment --------------------------- Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. -:math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P*}`. +:math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}*`. A ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}}})`, where -- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P*}` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. +- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. Specifically, we define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: -.. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor} \times \mathbb{B}^{[l_{\mathbb{P}}]} \times \mathbb{B}^{[l_{\mathbb{P}}]} \times \{0 .. 2^{l_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P*} \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Output} +.. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \{0 .. 2^{\ell_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P}* \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Output} -where :math:`\mathbb{P}, l_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and :math:`\mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor}, \mathsf{Orchard}.\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. +where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and :math:`\mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor}, \mathsf{Orchard}.\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. This note commitment scheme is instantiated using the Sinsemilla Commitment [#protocol-concretesinsemillacommit]_ as follows: .. math:: \begin{align} \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} :=\begin{cases} - \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi)}, &\text{... if } \mathsf{AssetBase}^{\mathsf{Orchard}} = \mathcal{V}^{\mathsf{Orchard}} \\ - \mathsf{cm}_{\mathsf{ZSA}} &\text{... otherwise} + \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase}^{\mathsf{Orchard}} = \mathcal{V}^{\mathsf{Orchard}} \\ + \mathsf{cm^{OrchardZSA}} &\text{otherwise} \end{cases} \end{align} @@ -119,7 +120,7 @@ where (note that :math:`\mathsf{repr}_{\mathbb{P}}` is as defined for the Pallas .. math:: \begin{align} \mathsf{cm}_{\mathsf{ZSA}} &:= \mathsf{SinsemillaCommit}_{\mathsf{rcm}}( \texttt{"z.cash:ZSA-NoteCommit"}, \\ - &\mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{l^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{l^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})) + &\mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})) \end{align} The nullifier is generated in the same manner as in the Orchard protocol [#protocol-commitmentsandnullifiers]_. From 59e305e1d43d9e6cdd9c7f90e8ab59ca3c282bb4 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 13:00:45 +0000 Subject: [PATCH 04/43] Changes to issuance key derivation details (#8) This covers the changes made to derive the issuance key independently of the Orchard key structure, using the techniques from [ZIP 32](https://zips.z.cash/zip-0032). --- zip-0227.rst | 81 +++++++++++++++++++++++++++++++++------------------- 1 file changed, 51 insertions(+), 30 deletions(-) diff --git a/zip-0227.rst b/zip-0227.rst index 4f48a9853..b086ffbbb 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -73,13 +73,8 @@ Requirements - Every "issuance action" should contain a ``finalize`` boolean that defines whether the specific Custom Asset can have further tokens issued or not. -Specification -============= - -As explained, the issuance protocol allows for a single issuance action to be sent to many receivers, by generating as many output notes as distinct recipients. Furthermore, every bundle can contain many issuance actions. - -Issuance Keys and Issuance Authorization Signature Scheme ---------------------------------------------------------- +Specification: Issuance Keys and Issuance Authorization Signature Scheme +======================================================================== The ZSA Protocol adds the following three keys to the key components [#protocol-addressesandkeys]_: @@ -89,19 +84,48 @@ The ZSA Protocol adds the following three keys to the key components [#protocol- 3. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all block chain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. +The relations between these keys are shown in the following diagram: + +.. figure:: zip-0227-key-components-zsa.png + :width: 450px + :align: center + :figclass: align-center + + Diagram of Issuance Key Components for the ZSA Protocol + + Issuance Authorization Signature Scheme -``````````````````````````````````````` +--------------------------------------- We define the issuance authorization signature scheme :math:`\mathsf{IssueAuthSig}` similar to :math:`\mathsf{SpendAuthSig}^{\mathsf{Orchard}}`, the Orchard spend authorization signature scheme [#protocol-concretespendauthsig]_. Specifically, we instantiate :math:`\mathsf{IssueAuthSig}` as :math:`\mathsf{RedPallas}` without key re-randomization using generator :math:`\mathcal{P}_{\mathbb{G}} = \mathcal{G}^{\mathsf{Issuance}} := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:ZSA"}, \texttt{"Issuance"})` where :math:`\mathsf{GroupHash}^\mathbb{P}` is defined as in the Zcash protocol specification [#protocol-concretegrouphashpallasandvesta]_. Issuance Key Derivation -``````````````````````` +----------------------- The issuance master key is generated by choosing a bit sequence uniformly at random from :math:`\mathbb{B}^{\mathbb{Y}[32]}`, like the Orchard spending key [#protocol-orchardkeycomponents]_. -In :math:`\mathsf{zcashd}`, this key is derived in a manner similar to the generation of the Orchard master key in ZIP 32 [#zip-0032-orchard-master]_, as detailed below: -- Details TBD +Issuance master key derivation for hierarchical deterministic wallets +````````````````````````````````````````````````````````````````````` + +The issuance master key is derived using the Orchard master key derivation procedure defined in ZIP 32 [#zip-0032-orchard-master]_. We reuse the functions defined there in what follows in this section. + +Let :math:`S` be a seed byte sequence of a chosen length, which MUST be at least 32 and at most 252 bytes. +We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssuance"}, S)`. + +As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance master key. +We reuse the :math:`\mathsf{CDKsk}` function for Orchard child key derivation from ZIP 32. + +We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance master key path as :math:`m_\mathsf{Issuance} / purpose / coin\_type' / account'`. We fix the path levels as follows: + +- :math:`purpose`: a constant set to :math:`227'` (or :math:`\texttt{0x800000e3}`) following the BIP 43 recommendation. +- :math:`coin\_type`: Defined as in ZIP 32 [#zip-0032-key-path-levels]_. +- :math:`account`: fixed to index :math:`0`. + +Given the *extended issuance master key* :math:`(\mathsf{sk}, \mathsf{c})`, we set the issuance master key to be :math:`\mathsf{sk_{iss}} := \mathsf{sk}`. + +Derivation of issuance authorizing key and issuance validating key +`````````````````````````````````````````````````````````````````` The issuance authorizing key and issuance validating key are derived from the issuance master key in an analogous manner to the derivation of the Orchard spend authorizing key and Orchard spend validating key from the Orchard spending key [#protocol-orchardkeycomponents]_, as described below. @@ -115,18 +139,8 @@ The issuance authorizing key and issuance validating key are derived from the is This allows the issuer to use the same wallet it usually uses to transfer Assets, while keeping a disconnect from the other keys. Specifically, this method is aligned with the requirements and motivation of ZIP 32 [#zip-0032]_. It provides further anonymity and the ability to delegate issuance of an Asset (or in the future, generate a multi-signature protocol) while the rest of the keys remain in the wallet safe. -The derivation of these keys are shown in the following diagram: - -.. figure:: zip-0227-key-components-zsa.png - :width: 450px - :align: center - :figclass: align-center - - Diagram of Issuance Key Components for the ZSA Protocol - - -Asset Identifier ----------------- +Specification: Asset Identifier +=============================== For every new Asset, there must be a new and unique Asset Identifier. We define this to be a globally unique pair :math:`(\mathsf{ik}, \mathsf{asset\_desc})`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. @@ -159,13 +173,17 @@ The relations between the Asset Identifier, Asset Digest, and Asset Base are sho Diagram relating the Asset Identifier, Asset Digest, and Asset Base in the ZSA Protocol -Global Issuance State ---------------------- +Specification: Global Issuance State +==================================== Issuance requires the following additions to the global state defined at block boundaries: - :math:`\mathsf{previously\_finalized}`, a set of :math:`\mathsf{AssetId}` that have been finalized (i.e.: the ``finalize`` flag has been set to ``1`` in some issuance transaction preceding the block boundary). + +Specification: Issuance Action, Issuance Bundle and Issuance Protocol +================================================================================= + Issuance Action Description --------------------------- @@ -217,8 +235,8 @@ The issuer program performs the following operations For all actions `IssueAction`: - encode :math:`\mathsf{asset\_desc}` as a UTF-8 byte string of size up to 512. -- compute :math:`\mathsf{AssetDigest}` from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as decribed in the `Asset Identifier`_ section. -- compute :math:`\mathsf{AssetBase^{Protocol}}` from :math:`\mathsf{AssetDigest}` as decribed in the `Asset Identifier`_ section. +- compute :math:`\mathsf{AssetDigest}` from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as decribed in the `Specification: Asset Identifier`_ section. +- compute :math:`\mathsf{AssetBase^{Protocol}}` from :math:`\mathsf{AssetDigest}` as decribed in the `Specification: Asset Identifier`_ section. - set the ``finalize`` boolean as desired (if more more issuance actions are to be created for this Asset Identifier, set ``finalize = 0``, otherwise set ``finalize = 1``) - For each recipient :math:`i`: @@ -236,8 +254,8 @@ For the `IssueBundle`: NOTE that the commitment is not included in the `IssuanceAction` itself. As explained below, it is later computed by the validators and added to the `NoteCommitmentTree`. -Consensus Rule Changes ----------------------- +Specification: Consensus Rule Changes +===================================== For the IssueBundle: @@ -247,7 +265,7 @@ For each `IssueAction` in `IssueBundle`: - check that :math:`0 < \mathsf{assetDescSize} <= 512`. - check that :math:`\mathsf{asset\_desc}` is a string of length :math:`\mathsf{assetDescSize}` bytes. -- retrieve :math:`\mathsf{AssetBase}` from the first note in the sequence and check that :math:`\mathsf{AssetBase}` is derived from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as described in the `Asset Identifier`_ section. +- retrieve :math:`\mathsf{AssetBase}` from the first note in the sequence and check that :math:`\mathsf{AssetBase}` is derived from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as described in the `Specification: Asset Identifier`_ section. - check that the :math:`\mathsf{AssetId}` does not exist in the ``previously_finalized`` set in the global state. - check that every note in the `IssueAction` contains the same :math:`\mathsf{AssetBase}` and is properly constructed as :math:`note = (\mathsf{g_d, pk_d, v, \rho, \psi, AssetBase})`. @@ -444,6 +462,9 @@ References .. [#zip-0317b] `ZIP 317b: ZSA Extension Proportional Fee Mechanism `_ .. [#zip-0032] `ZIP 32: Shielded Hierarchical Deterministic Wallets `_ .. [#zip-0032-orchard-master] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard master key generation `_ +.. [#zip-0032-orchard-child-key-derivation] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard child key derivation `_ +.. [#zip-0032-key-path-levels] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Key path levels `_ +.. [#zip-0032-orchard-key-path] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard key path `_ .. [#zip-0316] `ZIP 316: Unified Addresses and Unified Viewing Keys `_ .. [#protocol-addressesandkeys] `Zcash Protocol Specification, Version 2022.3.8. Section 3.1: Payment Addresses and Keys `_ .. [#protocol-concretegrouphashpallasandvesta] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.9.8: Group Hash into Pallas and Vesta `_ From 948d5dd2b1a90e8e5d234ac0b9d14164eb2785d3 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 13:02:22 +0000 Subject: [PATCH 05/43] Rearrangements and minor changes to the Security and Privacy Considerations (#13) Minor changes to the Security and Privacy Considerations to make it more in line with the format specified in ZIP 0. --- zip-0226.rst | 23 ++++++++++++----------- zip-0227.rst | 11 +++++++---- 2 files changed, 19 insertions(+), 15 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 091a91eb1..058d902ae 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -306,16 +306,8 @@ The transaction format is similar to the version 5 transaction format described In terms of the Action size, the ZSA action size differs from the Orchard action size by 32 bytes (due to the addition of the :math:`\mathsf{AssetId}`). This implies that the size goes from 820 bytes in the Orchard action to 852 bytes in the ZSA Action. -Other Considerations -==================== - -Transaction Fees ----------------- - -The fee mechanism for the upgrades proposed in this ZIP will follow the mechanism described in ZIP 317 for the ZSA protocol upgrade [#zip-0317b]_. - -Security and Privacy --------------------- +Security and Privacy Considerations +=================================== - Even if the Orchard protocol and ZSA protocol do not share the same anonymity pool (nodes can keep track of the notes that where published with different transaction structures), the migration from one to the other is done automatically and seamlessly. The Orchard bundle will be replaced by the ZSA bundle and all ZEC notes will be fully spendable with the new transaction structure. - When including new Assets we would like to maintain the amount and identifiers of Assets private, which is achieved with the design. @@ -324,8 +316,17 @@ Security and Privacy - One proposal for a petname system for the zcashd wallet is the use of an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. +Other Considerations +==================== + +Transaction Fees +---------------- + +The fee mechanism for the upgrades proposed in this ZIP will follow the mechanism described in ZIP 317 for the ZSA protocol upgrade [#zip-0317b]_. + Deployment ------------ +========== + The Zcash Shielded Assets protocol should be deployed by replacing the Orchard protocol in a subsequent Network Upgrade. The design of this protocol ensures that there is no need to use any turnstile mechanism, being that Orchard-based ZEC notes can be used directly within the ZSA Actions. Test Vectors diff --git a/zip-0227.rst b/zip-0227.rst index b086ffbbb..a34d0cafb 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -406,13 +406,16 @@ A byte encoding of issuance validating key for the bundle as defined in the `Iss Security and Privacy Considerations =================================== -**Issuer Key or AssetId Compromise** +Issuance Key Compromise +----------------------- + +The design of this protocol does not currently allow for a rotation of the issuance validating key that would allow for replacing the key of a specific Asset (see `Future Work`_). In case of compromise, the following actions are recommended: -The design of this protocol does not allow for a rotation of the issuer validating key, that would allow for replacing the key of a specific Asset (see Future Work). In case of compromise, the following actions are recommended: +- If an issuance validating key is compromised, the ``finalize`` boolean for all the Assets issued with that key should be set to :math:`1` and the issuer should change to a new issuance authorizing key, and issue new Assets, each with a new :math:`\mathsf{AssetId}`. -- If an issuer validating key is compromised, the ``finalize`` boolean for all the Assets issued with that key should be set to `1` and the issuer should change to a new issuance authorizing key, and issue new Assets, each with a new :math:`\mathsf{AssetId}`. +Bridging Assets +--------------- -**Bridging Assets** For bridging purposes, the secure method of off-boarding Assets is to burn an Asset with the burning mechanism in ZIP 226 [#zip-0226]_. Users should be aware of issuers that demand the Assets be sent to a specific address on the Zcash chain to be redeemed elsewhere, as this may not reflect the real reserve value of the specific Wrapped Asset. Other Considerations From 01298df551c2afca11c55ebd7542f81f7836d71a Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 13:06:00 +0000 Subject: [PATCH 06/43] Rearranging ZIP structure (#14) This rearranges and rewrites various sections of the ZIP to make it more in line with the suggestions in ZIP 0. It also updates the Split Notes, Circuit Statement and Burn Mechanism sections with more information. --- zip-0226.rst | 178 ++++++++++++++++++++++++++++++--------------------- zip-0227.rst | 22 ++++--- 2 files changed, 116 insertions(+), 84 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 058d902ae..d156261fb 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -15,7 +15,7 @@ Created: 2022-05-01 License: MIT Discussions-To: - Pull-Request: + Pull-Request: Terminology @@ -38,13 +38,13 @@ We define the following additional terms: - Native Asset: a Custom Asset with issuance defined on the Zcash block chain. - Wrapped Asset: a Custom Asset with native issuance defined outside the Zcash block chain. -- Split Input: an Action input identifying a Custom Asset note, used to ensure that the output note of that Action is of a validly issued :math:`\mathsf{AssetId}` when there is no corresponding real input note to spend. The Action does not spend the note identified by the Split Input. +- Split Input: an Action input used to ensure that the output note of that Action is of a validly issued :math:`\mathsf{AssetBase}` when there is no corresponding real input note, in situations where the number of outputs are larger than the number of inputs. See formal definition in `Split Notes`_. - Split Action: an Action that contains a Split Input. Abstract ======== -ZIP 226 and ZIP 227 propose in conjunction the Zcash Shielded Assets (ZSA) protocol — a set +ZIP 226 and ZIP 227 propose in conjunction the Zcash Shielded Assets (ZSA) protocol — a set of protocol features that enable the creation, transfer, and burn of Custom Assets on the Zcash chain. Creation of such Assets is defined in ZIP 227 [#zip-0227]_. Transfer and burn of such Assets is defined @@ -88,7 +88,10 @@ For every new Asset, there must be a new and unique Asset Identifier. Every Asse This :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` will be the base point of the value commitment for the specific Custom Asset. Note that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. -In future network and protocol upgrades, the same Asset description string can be carried on, potentially mapping into a different shielded protocol. In that case, the turnstile should know how to transform the Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base from one shielded protocol to another. +Rationale for Asset Identifiers +''''''''''''''''''''''''''''''' + +In future network and protocol upgrades, the same Asset description string can be carried on, potentially mapping into a different shielded pool. In that case, nodes should know how to transform the Asset Identifier, the Asset Digest, and the Asset Base from one shielded pool to another, while ensuring there are no balance violations [#zip-0209]_. Note Structure & Commitment --------------------------- @@ -116,19 +119,21 @@ This note commitment scheme is instantiated using the Sinsemilla Commitment [#pr \end{cases} \end{align} -where (note that :math:`\mathsf{repr}_{\mathbb{P}}` is as defined for the Pallas curve [#protocol-pallasandvesta]_, :math:`l^{\mathsf{Orchard}}_{\mathsf{base}}` is as defined in §5.3 [#protocol-constants]_, and :math:`\mathsf{I2LEBSP}` is as defined in §5.1 [#protocol-endian]_ of the Zcash protocol specification): +where: .. math:: \begin{align} \mathsf{cm}_{\mathsf{ZSA}} &:= \mathsf{SinsemillaCommit}_{\mathsf{rcm}}( \texttt{"z.cash:ZSA-NoteCommit"}, \\ &\mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})) \end{align} +Note that :math:`\mathsf{repr}_{\mathbb{P}}` is as defined for the Pallas curve [#protocol-pallasandvesta]_, :math:`\ell^{\mathsf{Orchard}}_{\mathsf{base}}` is as defined in §5.3 [#protocol-constants]_, and :math:`\mathsf{I2LEBSP}` is as defined in §5.1 [#protocol-endian]_ of the Zcash protocol specification. + The nullifier is generated in the same manner as in the Orchard protocol [#protocol-commitmentsandnullifiers]_. The ZSA note plaintext also includes the Asset Base in addition to the components in the Orchard note plaintext [#protocol-notept]_. It consists of -.. math:: (\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[l_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{l_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]}) +.. math:: (\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[\ell_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{\ell_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]}) Rationale for Note Commitment ''''''''''''''''''''''''''''' @@ -141,8 +146,7 @@ The note commitment output is still indistinguishable from the original Orchard .. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} \in \mathsf{NoteCommit^{Orchard}.Output} - - +This definition can be viewed as a hypernym of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes. Value Commitment ---------------- @@ -153,7 +157,7 @@ In the case of the ZSA protocol, the value of different Asset Identifiers in a g where :math:`\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId} - v^{new}_{AssetId}}` such that :math:`\mathsf{v^{old}_{AssetId}}` and :math:`\mathsf{v^{new}_{AssetId}}` are the values of the old and new notes of Asset Identifier :math:`\mathsf{AssetId}` respectively, -.. _`value base`: +.. _`asset base`: :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}` is defined in ZIP 227 [#zip-0227]_, and @@ -194,128 +198,145 @@ As in the Orchard protocol, the binding signature verification key, :math:`\math Split Notes ----------- -One of the key functionalities in a UTXO-based protocol is the fact that input notes are usually split in two (or more) output notes, as in most cases, not all the value in a single note is sent to a single output. This requires a 1-to-many (Orchard) transaction. However, because each Action represents an input and an output, the resulting transaction must have multiple inputs. In order to cope with this today, the Actions that have not been assigned input notes are instead given *dummy spend notes* [#protocol-dummynotes]_, which we call split Actions and split notes respectively. Basically, the input note is “faked” inside of the proof in order to hide which Action contains the *real* spend note. - -This, however, brings some issues when it comes to adding multiple Asset Identifiers, as the output note of the split Actions *cannot* contain *any* Asset Base, but it must be enforced to be an actual output of a GroupHash computation (in fact we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). If not, then the prover could essentially input a multiple (or linear combination) of an existing Asset Base, with the goal to attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds. +A Split Input is a copy of a previously issued input note (that is, a note that has previously been included in the Merkle tree), with the following changes: -In order to prevent this, we make some modifications to the circuit. Specifically we remove the dummy note functionality for Custom Assets and we enforce that *every* input note to an ZSA Action must be proven to exist in the set of note commitments in the note commitment tree. We then enforce this real note to be “unspendable” in the sense that its value -will be zeroed in split Actions and the nullifier will be randomized, making the note not spendable in the specific Action. Then, the proof itself ensures that the output note is of the same Asset Base as the input note. In the circuit, the split note functionality will be activated by a boolean private input to the proof. +- A ``split_flag`` boolean is set to 1. +- The value of the note is replaced with the value 0 during the computation of the value commitment. -This creates a chain of induction that ensures that the value base points of all output notes of a transfer are actual outputs of a GroupHash, as they originate in the Issuance protocol which is publicly verified. If this were not done then it would be possible to violate balance, for example by using a value base point derived from those of other Assets. +Input notes are sometimes split in two (or more) output notes, as in most cases, not all the value in a single note is sent to a single output. -Note that we do not care about whether the note identified by a Split Input is owned by the sender, or whether it was nullified before. +When the number of input notes of a particular Asset Base is smaller than the required number of output notes for the same Asset Base, the sender creates Split Inputs of the same Asset Base as padding for the input-less Actions. Note that we do not care about whether the previously issued note copied to create a Split Input is owned by the sender, or whether it was nullified before. -Wallets and other clients have a choice to make to ensure the Asset Base is preserved for the output note of a Split Action: +Wallets and other clients have to choose from the following to ensure the Asset Base is preserved for the output note of a Split Action: 1. The Split Input note could be another note containing the same Asset Base that is being spent by this transaction (but not by this Split Input). 2. The Split Input note could be a different unspent note containing the same Asset Base (note that the note will not actually be spent). 3. The Split Input note could be an already spent note containing the same Asset Base (note that by zeroing the value in the circuit, we prevent double spending). -The specific circuit changes are presented below. +Rationale for Split Notes +''''''''''''''''''''''''' + +In the Orchard protocol, since each Action represents an input and an output, the transaction that wants to send one input to multiple outputs must have multiple inputs. The Orchard protocol gives *dummy spend notes* [#protocol-dummynotes]_ to the Actions that have not been assigned input notes. + +The Orchard technique requires modification for the ZSA protocol with multiple Asset Identifiers, as the output note of the split Actions *cannot* contain *any* Asset Base. We must enforce it to be an actual output of a GroupHash computation (in fact, we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). Without this enforcement the prover could input a multiple (or linear combination) of an existing Asset Base, and thereby attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds. + +Therefore, for Custom Assets we enforce that *every* input note to an ZSA Action must be proven to exist in the set of note commitments in the note commitment tree. We then enforce this real note to be “unspendable” in the sense that its value will be zeroed in split Actions and the nullifier will be randomized, making the note not spendable in the specific Action. Then, the proof itself ensures that the output note is of the same Asset Base as the input note. In the circuit, the split note functionality will be activated by a boolean private input to the proof (aka the ``split_flag`` boolean). +This ensures that the value base points of all output notes of a transfer are actual outputs of a GroupHash, as they originate in the Issuance protocol which is publicly verified. + +Note that the Orchard dummy note functionality remains in use for ZEC notes, and the Split Input technique is used in order to support Custom Assets. + Circuit Statement ----------------- -The advantage of the design described above, with respect to the circuit statement, is that every *ZSA Action statement* is kept closely similar to the Orchard Action statement [#protocol-actionstatement]_, except for a few additions that ensure the security of the Asset Identifier system. +Every *ZSA Action statement* is closely similar to the Orchard Action statement [#protocol-actionstatement]_, except for a few additions that ensure the security of the Asset Identifier system. We detail these changes below. + +Asset Base Equality +''''''''''''''''''''''''' -**Asset Identifier Equality:** the following constraints must be added to ensure that -the input and output note are of the same :math:`\mathsf{AssetId}`: +The following constraints must be added to ensure that the input and output note are of the same :math:`\mathsf{AssetBase}`: - The Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`, for the note is witnessed once, as an auxiliary input. - In the Old note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. - In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. -**Correct Value Commitment:** the following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base, as represented in the notes: +Value Commitment Correctness +'''''''''''''''''''''''''''' + +The following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base, as represented in the notes: - The fixed-base multiplication constraints between the value and the value base point of the value commitment, :math:`\mathsf{cv}`, is replaced with a variable-base multiplication between the two. -- The witness to the value base point, as defined in the `value base`_ equation is the auxiliary input :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`. +- The witness to the value base point (as defined in the `asset base`_ equation) is the auxiliary input :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`. -**Enforce Secure Identifier for Split Actions:** the following constraints must be added to prevent senders from changing the Asset Base for the output note in a Split Action: +Asset Identifier Consistency for Split Actions +'''''''''''''''''''''''''''''''''''''''''''''' + +The following constraints must be added to prevent senders from changing the Asset Base for the output note in a Split Action: - The Value Commitment Integrity should be changed - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(v’ - v^new, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}` -- Add a boolean ``split`` variable as an auxiliary witness. This variable is to be activated ``split = 1`` if the Action in question is a split and ``split = 0`` if the Action is actually spending an input note: - - If ``split = 1`` then set :math:`\mathsf{v}' = 0` otherwise :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. +- Add a boolean ``split_flag`` variable as an auxiliary witness. This variable is to be activated ``split_flag = 1`` if the Action in question has a Split Input and ``split_flag = 0`` if the Action is actually spending an input note: + - If ``split_flag = 1`` then set :math:`\mathsf{v}' = 0` otherwise :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. - The Merkle Path Validity should check the existence of the note commitment as usual (and not like with dummy notes): - - Check that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^old}` to the anchor :math:`\mathsf{rt^Orchard}`. + - Check that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}`. - The Nullifier Integrity will be changed to prevent the identification of notes - - Replace the :math:`\psi_{old}` value with a generic :math:`\psi'` as :math:`\mathsf{nf_old = DeriveNullifier_nk}(\rho^\mathsf{old}, \psi', \mathsf{cm^old})` - - if :math:`\mathtt{split} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled randomly.) + - Replace the :math:`\psi_{old}` value with a generic :math:`\psi'` as :math:`\mathsf{nf_{old}} = \mathsf{DeriveNullifier_{nk}}(\rho^\mathsf{old}, \psi', \mathsf{cm^{old}})` + - if :math:`\mathtt{split\_flag} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled randomly.) -**Enabling Backwards Compatibility with ZEC Notes:** the following constraints must be added to enable backwards compatibility with Orchard ZEC notes. +Backwards Compatibility with ZEC Notes +'''''''''''''''''''''''''''''''''''''' -The old note commitment is computed using a “rolling-aggregate” Sinsemilla commitment. This means that the commitment is computed by adding new chunks or windows to the accumulated value. This method will be used in order to maintain a single commitment instance for the old note commitment, that will be used both for Orchard ZEC notes and for ZSA notes. The original Orchard ZEC notes will be conserved and not actually be converted into ZSA notes, as we will always need to compute them. -However, new notes will always be ZSA notes with an Asset Base. +The input note in the old note commitment integrity check must either include an Asset Base (ZSA note) or not (pre-ZSA Orchard note). If the note is a pre-ZSA Orchard note, the note commitment is computed in the original Orchard fashion [#protocol-abstractcommit]_. If the note is a ZSA note, the note commitment is computed as defined in the `Note Structure & Commitment`_ section. -The input note in the old note commitment integrity check must either include an Asset Base (ZSA note) or not (ZEC-Orchard note). If the note is an old note, from before the upgrade, the commitment is computed in the original Orchard fashion. If the note is a new ZSA note, there are two cases: +Burn Mechanism +============== -- If the Asset Base auxiliary input present but set to :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` = :math:`\mathcal{V}^\mathsf{Orchard}` - - NoteCommitment has a “compatibility” path that computes the note commitment as in plain Orchard (i.e.: without including the Asset Base) - - This path also uses the original domain separator for ZEC note commitment -- Else, - - The note commitment adds the identfier, :math:`\mathsf{AssetId}`, as a final “chunk” of the Sinsemilla commitment - - The note commitment uses a different domain separator for ZSA note commitment +The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. +The sender includes a :math:`\mathsf{v^{AssetBase}}` variable for every Asset Identifier that is being burnt. As we will show in the `ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset. -Backward Compatibility ----------------------- +For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` vector the tuple :math:`(\mathsf{AssetBase},\mathsf{v^{AssetBase}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. -In order to have a "clean" backwards compatibility with the ZEC notes, we have designed the circuit to support both ZEC and ZSA notes. As we specify above, there are three main reasons we can do this: -- The input notes with an Asset Base denote the Custom Assets, generating a note commitment that includes the Asset Identifier; whereas the notes without an Asset Base denote the ZEC notes from before the protocol upgrade, and generate a note commitment that does not include the Asset Base, in order to maintain the referencability to the Merkle tree -- The value commitment is abstracted to allow for the value base-point as a variable private input to the proof -- The ZEC-based Actions will still include dummy input notes, whereas the ZSA-based Actions will include split input notes. +.. math:: \mathsf{assetBurn} = \{ (\mathsf{AssetBase},\mathsf{v^{AssetBase}})\ |\ \forall\ \mathsf{AssetBase}\ \textit{s.t.}\ \mathsf{v^{AssetBase}} \neq 0 \} +The value balances for each Asset Identifier in :math:`\mathsf{assetBurn}` represents the amount of that Asset that is being burnt. In the case of ZEC, the value balance represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). -Burn Mechanism -============== -The burn mechanism may be needed for off-boarding the Wrapped Assets from the chain, or enabling advanced tokenomics on Assets. It is part of the Issuance/Burn protocol, but given that it can be seen as an extension of the Transfer protocol, we add it here for readability. +The validator needs to verify the Balance and Binding Signature by adding the value balances for all Assets, as committed using their respective :math:`\mathsf{AssetBase}` as the value base point of the Pedersen Commitment. This is done as follows -In essence, the burn mechanism is a transparent / revealing extension to the transfer protocol that enables a specific amount of any Asset identifier to be sent into “oblivion”. Our burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. +.. math:: \mathsf{bvk = (\sum cv_i^{net})} - \mathsf{ ValueCommit_0^{Orchard}(v^{balanceOrchard})} - \sum_{\mathsf{assetBurn}} \mathsf{ValueCommit_0^{OrchardZSA}(AssetBase, v^{AssetBase}) } = \sum \mathsf{rcv_{i,j}^{net}}\mathcal{R}^{\mathsf{Orchard}} -First, contrary to the strict transfer transaction, we allow the sender to include a :math:`\mathsf{valueBalance_{AssetId}}` variable for every Asset Identifier that is being burnt. As we will show in the transaction structure, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset. -We require that for every :math:`\mathsf{valueBalance_{AssetId}}` provided as above by the sender, :math:`\mathsf{valueBalance_{AssetId}} \neq 0`. This is enforced via a consensus rule. +In the case that the balance of all the Action values related to a specific Asset will be zero, there will be no value added to the vector. This way, neither the number of Assets nor their Asset Identifiers will be revealed, except in the case that an Asset is burnt. -For every custom Asset that is burnt, we add to the `assetBurn` vector the tuple :math:`(\mathsf{valueBalance_{AssetId}, AssetId})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. +Burn Mechanism Consensus Rules +------------------------------ +1. We require that :math:`\forall (\mathsf{AssetBase},\mathsf{v^{AssetBase}}) \in \mathsf{assetBurn}\ ,\ \mathsf{AssetBase} \neq \mathcal{V}^{\mathsf{Orchard}}`. That is, Native Assets are not allowed to be burnt. +2. We require that for every :math:`\forall (\mathsf{AssetBase},\mathsf{v^{AssetBase}}) \in \mathsf{assetBurn}\ ,\ \mathsf{v^{AssetBase}} \neq 0`. +3. We require that there be no duplication of Custom Assets in the :math:`\mathsf{assetBurn}` set. That is, every :math:`\mathsf{AssetBase}` has at most one entry in :math:`\mathsf{assetBurn}`. -:math:`\mathsf{assetBurn = \{ (v^{AssetId}, AssetId)}\ |\ \forall\ \mathsf{AssetId}\ \textit{s.t.}\ \mathsf{v^{AssetId}} \neq 0 \}` +**Note:** Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets. -The value balances for each Asset Identifier in `assetBurn` represents the amount of that Asset that is being burnt. In the case of ZEC, the value balance represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). -Finally, the validator needs to verify the Balance and Binding Signature by adding the value balances for all Assets, as committed using their respective :math:`\mathsf{AssetId}` as the value base point of the Pedersen Commitment. This is done as follows +ZSA Transaction Structure +========================= -:math:`\mathsf{bvk = (\sum cv_i^{net})} - \mathsf{ ValueCommit_0^{Orchard}(v^{balanceOrchard})} - \sum_{\forall \mathsf{AssetId}\textit{ s.t. }\mathsf{v^{AssetId}\neq 0}} \mathsf{ValueCommit_0^{OrchardZSA}(v^{AssetId}, AssetId) } = \sum \mathsf{rcv_{i,j}^{net}}\mathcal{R}^{\mathsf{Orchard}}` +The transaction format is similar to the version 5 transaction format described in the Zcash specification [#protocol-transactionstructure]_, with the following additions to the Orchard bundle: -In the case that the balance of all the Action values related to a specific Asset will be zero, there will be no value added to the vector. This way, neither the number of Assets nor their Asset Identifiers will be revealed, except in the case that an Asset is burnt. ++---------------+------------+-------------------------+-----------------------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++===============+============+=========================+===================================================================================+ +| varies | nAssetBurn | compactSize | The number of Assets burnt. | ++---------------+------------+-------------------------+-----------------------------------------------------------------------------------+ +| 40*nAssetBurn | vAssetBurn | AssetBurn[nAssetBurn] | A sequence of Asset Burn descriptions, encoded per `ZSA Asset Burn Description`_. | ++---------------+------------+-------------------------+-----------------------------------------------------------------------------------+ -**Note:** Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets. +In terms of the Action size, the ZSA action size differs from the Orchard action size by 32 bytes (due to the addition of the :math:`\mathsf{AssetBase}`). This implies that the size goes from 820 bytes in the Orchard action to 852 bytes in the ZSA Action. -ZSA Transaction Structure -========================= +ZSA Asset Burn Description +-------------------------- -The transaction format is similar to the version 5 transaction format described in the Zcash specification [#protocol-transactionstructure]_, with the following additions to the Orchard bundle: +A ZSA Asset Burn description is encoded in a transaction as an of a AssetBurn type: -+-----------------+-------------+-----------------------------------+-------------------------+ -| Bytes | Name | Data Type | Description | -+=================+=============+===================================+=========================+ -| varies | nAssetBurn | compactSize | number of Assets burnt | -+-----------------+-------------+-----------------------------------+-------------------------+ -| 40*nAssetBurn | vAssetBurn | bytes[40][nAssetBurn] | 32 bytes Asset type_t, | -| | | | 8 bytes of valueBalance | -+-----------------+-------------+-----------------------------------+-------------------------+ ++-------+-----------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=======+===========+=============================+===========================================================================================================================+ +| 32 | AssetBase | byte[32] | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. | ++-------+-----------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ +| 8 | valueBurn | :math:`\{1 .. 2^{64} - 1\}` | The amount of the AssetType being burnt. | ++-------+-----------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ -In terms of the Action size, the ZSA action size differs from the Orchard action size by 32 bytes (due to the addition of the :math:`\mathsf{AssetId}`). This implies that the size goes from 820 bytes in the Orchard action to 852 bytes in the ZSA Action. Security and Privacy Considerations =================================== -- Even if the Orchard protocol and ZSA protocol do not share the same anonymity pool (nodes can keep track of the notes that where published with different transaction structures), the migration from one to the other is done automatically and seamlessly. The Orchard bundle will be replaced by the ZSA bundle and all ZEC notes will be fully spendable with the new transaction structure. +- The notes generated via the ZSA protocol are different from those generated via the Orchard protocol. As with any protocol upgrade, it will be possible to distinguish between notes generated by each protocol. However, all ZEC notes will be fully spendable with the ZSA protocol transaction structure due to the built-in backward compatibility. - When including new Assets we would like to maintain the amount and identifiers of Assets private, which is achieved with the design. - We prevent the "roadblock" attack on the Asset Identifier by ensuring the output notes receive an Asset Base that exists on the global state. - Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are the use of a petname system or a list of well-known Assets. - One proposal for a petname system for the zcashd wallet is the use of an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. + Other Considerations ==================== @@ -324,10 +345,18 @@ Transaction Fees The fee mechanism for the upgrades proposed in this ZIP will follow the mechanism described in ZIP 317 for the ZSA protocol upgrade [#zip-0317b]_. -Deployment -========== +Backward Compatibility +---------------------- + +In order to have backward compatibility with the ZEC notes, we have designed the circuit to support both ZEC and ZSA notes. As we specify above, there are three main reasons we can do this: +- Note commitments for ZEC notes will remain the same, while note commitments for Custom Assets will be computed taking into account the :math:`AssetBase` value as well. +- The existing Orchard shielded pool will continue to be used for the new ZSA notes post the upgrade. +- The value commitment is abstracted to allow for the value base-point as a variable private input to the proof. +- The ZEC-based Actions will still include dummy input notes, whereas the ZSA-based Actions will include both dummy and split input notes. -The Zcash Shielded Assets protocol should be deployed by replacing the Orchard protocol in a subsequent Network Upgrade. The design of this protocol ensures that there is no need to use any turnstile mechanism, being that Orchard-based ZEC notes can be used directly within the ZSA Actions. +Deployment +----------- +The Zcash Shielded Assets protocol will be deployed in a subsequent Network Upgrade. Test Vectors ============ @@ -345,6 +374,7 @@ References .. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels `_ .. [#zip-0200] `ZIP 200: Network Upgrade Mechanism `_ +.. [#zip-0209] `ZIP 209: Prohibit Negative Shielded Chain Value Pool Balances `_ .. [#zip-0224] `ZIP 224: Orchard `_ .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ diff --git a/zip-0227.rst b/zip-0227.rst index a34d0cafb..9766daf6e 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -15,7 +15,7 @@ Created: 2022-05-01 License: MIT Discussions-To: - Pull-Request: + Pull-Request: Terminology @@ -66,7 +66,6 @@ Requirements - Any user of the Zcash block chain can issue custom Assets on chain. - The issuance mechanism should enable public tracking of the supply of the Assets on the Zcash block chain. -- At the time of issuance, the issuer should be able to allocate all the Assets to the corresponding owners by creating the corresponding (shielded) output notes to the respective addresses. This allows for allocation to be totally private even though the issuance mechanism is itself transparent. - Issuing or changing the attributes of a specific Asset should require cryptographic authorization. - The Asset identification should be unique (among all shielded pools) and different issuer public keys should not be able to generate the same Asset Identifier. - An issuer should be able to issue different Assets in the same transaction. In other words, in a single "issuance bundle", the issuer should be able publish many "issuance actions", potentially creating multiple Custom Assets. @@ -111,7 +110,7 @@ Issuance master key derivation for hierarchical deterministic wallets The issuance master key is derived using the Orchard master key derivation procedure defined in ZIP 32 [#zip-0032-orchard-master]_. We reuse the functions defined there in what follows in this section. Let :math:`S` be a seed byte sequence of a chosen length, which MUST be at least 32 and at most 252 bytes. -We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssuance"}, S)`. +We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssue_V1"}, S)`. As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance master key. We reuse the :math:`\mathsf{CDKsk}` function for Orchard child key derivation from ZIP 32. @@ -149,7 +148,7 @@ From the Asset Digest, we derive a specific Asset Base within each such shielded Let -- :math:`\mathsf{asset\_desc}` be the asset description, a UTF-8 encoded string of up to 512 bytes, which includes any information pertaining to the issuance. +- :math:`\mathsf{asset\_desc}` be the asset description, which includes any information pertaining to the issuance, and is a byte sequence of up to 512 bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later. - :math:`\mathsf{ik}` be the issuance validating key of the issuer, a public key used to verify the signature on the issuance transaction's SIGHASH. Define :math:`\mathsf{AssetDigest_{\mathsf{AssetId}}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))`, @@ -190,7 +189,7 @@ Issuance Action Description An issuance action, `IssueAction`, is the instance of issuing a specific custom Asset, and contains the following fields: - :math:`\mathsf{assetDescSize}`: the size of the Asset description, a number between :math:`0` and :math:`512`, stored in two bytes. -- :math:`\mathsf{asset\_desc}`: the Asset description, a UTF-8 encoded string of up to 512 bytes +- :math:`\mathsf{asset\_desc}`: the Asset description, a byte string of up to 512 bytes as defined in the `Specification: Asset Identifier`_ section. - `notes`: an array containing the unencrypted output notes of the recipients of the Asset, of type `Note` - ``finalize``: a boolean that defines whether the issuance of that specific custom Asset is finalized or not @@ -219,14 +218,14 @@ An issuance bundle, `IssueBundle`, is the aggregate of all the issuance-related The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-transactionstructure]_. -======= ==================== ========================== ========================================================================= +======= ==================== ========================== ========================================================================================================================== Bytes Name Data Type Description -======= ==================== ========================== ========================================================================= +======= ==================== ========================== ========================================================================================================================== Varies nIssueActions compactSize The number of issuance actions in the bundle Varies vIssueActions IssueAction[nIssueActions] A sequence of issuance actions descriptions 32 :math:`\mathsf{ik}` byte[32] The issuance validating key of the issuer, used to validate the signature -64 issueAuthSig byte[64] The signature of the transaction SIGHASH, signed by the issuer -======= ==================== ========================== ========================================================================= +64 issueAuthSig byte[64] The signature of the transaction SIGHASH, signed by the issuer, validated as in `Issuance Authorization Signature Scheme`_ +======= ==================== ========================== ========================================================================================================================== Issuance Protocol ----------------- @@ -274,6 +273,8 @@ If all of the above checks pass, do the following: - For each note, compute the note commitment as :math:`\mathsf{cm} = \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, AssetBase)}` as defined in the Note Structure and Commitment section of ZIP 226 [#zip-0226-notestructure]_ and - add :math:`\mathsf{cm}` to the Merkle tree of note commitments, `NoteCommitmentTree`. - If ``finalize = 1``, add :math:`\mathsf{AssetId}` to the ``previously_finalized`` set immediately after the block in which this transaction occurs. +- (Replay Protection) If issue bundle is present, the fees MUST be greater than zero. + Rationale @@ -290,6 +291,7 @@ The following is a list of rationale for different decisions made in the proposa - information to be committed by the issuer, though not enforceable by the protocol. - We require a check whether the ``finalize`` flag only has been set in a previous block rather than a previous transaction in the same block. In other words, we only update the ``previously_finalized`` set at the block boundary. This is in keeping with the current property which allows for a miner to reorder transactions in a block without changing the meaning, which we aim to preserve. +- We require non-zero fees in the presence of an issue bundle, in order to preclude the possibility of a transaction containing only an issue bundle. If a transaction includes only an issue bundle, the ``SIGHASH`` would be computed solely based on the issue bundle. A duplicate bundle would have the same ``SIGHASH``, potentially allowing for a replay attack. Concrete Applications --------------------- @@ -388,7 +390,7 @@ The ZIP 212 32-byte seed randomness for a note. T.1b: assetDescription '''''''''''''''''''''' -UTF-8 encoding of the Asset description string. +The Asset description byte string. T.1c: flagsIssuance ''''''''''''''''''' From 14c9f4d8cb9554c610dfa2ec70f1b799389198f1 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 13:06:36 +0000 Subject: [PATCH 07/43] Corrections and addition of reference links (#16) This adds in the reference links to the test vectors and reference implementations corresponding to the ZSA Protocol. Some corrections to the notation for better consistency and some updates to the formulae for syncing with the implementation are also included here. --- zip-0226.rst | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index d156261fb..509d8c07d 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -102,7 +102,7 @@ Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. A ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}}})`, where -- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. +- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. Specifically, we define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: @@ -115,25 +115,26 @@ This note commitment scheme is instantiated using the Sinsemilla Commitment [#pr \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} :=\begin{cases} \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase}^{\mathsf{Orchard}} = \mathcal{V}^{\mathsf{Orchard}} \\ - \mathsf{cm^{OrchardZSA}} &\text{otherwise} + \mathsf{cm}_{\mathsf{ZSA}} &\text{otherwise} \end{cases} \end{align} where: - + .. math:: \begin{align} - \mathsf{cm}_{\mathsf{ZSA}} &:= \mathsf{SinsemillaCommit}_{\mathsf{rcm}}( \texttt{"z.cash:ZSA-NoteCommit"}, \\ - &\mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})) + \mathsf{cm}_{\mathsf{ZSA}} :=&\ \mathsf{SinsemillaHashToPoint}( \texttt{"z.cash:ZSA-NoteCommit-M"}, \\ + &\ \ \ \mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})) \\ + &\ + [\mathsf{rcm}] \mathsf{GroupHash}^{\mathbb{P}}(\texttt{"z.cash:Orchard-NoteCommit-r"},\texttt{""}) \end{align} -Note that :math:`\mathsf{repr}_{\mathbb{P}}` is as defined for the Pallas curve [#protocol-pallasandvesta]_, :math:`\ell^{\mathsf{Orchard}}_{\mathsf{base}}` is as defined in §5.3 [#protocol-constants]_, and :math:`\mathsf{I2LEBSP}` is as defined in §5.1 [#protocol-endian]_ of the Zcash protocol specification. +Note that :math:`\mathsf{repr}_{\mathbb{P}}` and :math:`\mathsf{GroupHash}^{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, :math:`\ell^{\mathsf{Orchard}}_{\mathsf{base}}` is as defined in §5.3 [#protocol-constants]_, and :math:`\mathsf{I2LEBSP}` is as defined in §5.1 [#protocol-endian]_ of the Zcash protocol specification. The nullifier is generated in the same manner as in the Orchard protocol [#protocol-commitmentsandnullifiers]_. The ZSA note plaintext also includes the Asset Base in addition to the components in the Orchard note plaintext [#protocol-notept]_. It consists of -.. math:: (\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[\ell_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{\ell_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]}) +.. math:: (\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[\ell_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{\ell_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]}) Rationale for Note Commitment ''''''''''''''''''''''''''''' @@ -331,7 +332,7 @@ Security and Privacy Considerations - The notes generated via the ZSA protocol are different from those generated via the Orchard protocol. As with any protocol upgrade, it will be possible to distinguish between notes generated by each protocol. However, all ZEC notes will be fully spendable with the ZSA protocol transaction structure due to the built-in backward compatibility. - When including new Assets we would like to maintain the amount and identifiers of Assets private, which is achieved with the design. -- We prevent the "roadblock" attack on the Asset Identifier by ensuring the output notes receive an Asset Base that exists on the global state. +- We prevent a potential malleability attack on the Asset Identifier by ensuring the output notes receive an Asset Base that exists on the global state. - Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are the use of a petname system or a list of well-known Assets. - One proposal for a petname system for the zcashd wallet is the use of an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. @@ -361,13 +362,15 @@ The Zcash Shielded Assets protocol will be deployed in a subsequent Network Upgr Test Vectors ============ -- LINK TBD +- https://github.com/QED-it/zcash-test-vectors Reference Implementation ======================== -- LINK TBD -- LINK TBD +- https://github.com/QED-it/zcash (in `zcashd`) +- https://github.com/QED-it/orchard (in `orchard`) +- https://github.com/QED-it/librustzcash (in `librustzcash`) +- https://github.com/QED-it/halo2 (in `halo2`) References ========== From 9dcb234117db678eab8aae6efbd60fe0f16d5103 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Tue, 16 May 2023 16:38:43 +0530 Subject: [PATCH 08/43] Suggestions from ZIP review: editorial changes. Co-authored-by: Daira-Emma Hopwood --- zip-0226.rst | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 509d8c07d..bef01b51a 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -147,7 +147,7 @@ The note commitment output is still indistinguishable from the original Orchard .. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} \in \mathsf{NoteCommit^{Orchard}.Output} -This definition can be viewed as a hypernym of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes. +This definition can be viewed as a generalization of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes. Value Commitment ---------------- @@ -262,7 +262,7 @@ The following constraints must be added to prevent senders from changing the Ass - Check that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}`. - The Nullifier Integrity will be changed to prevent the identification of notes - Replace the :math:`\psi_{old}` value with a generic :math:`\psi'` as :math:`\mathsf{nf_{old}} = \mathsf{DeriveNullifier_{nk}}(\rho^\mathsf{old}, \psi', \mathsf{cm^{old}})` - - if :math:`\mathtt{split\_flag} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled randomly.) + - if :math:`\mathtt{split\_flag} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}`.) Backwards Compatibility with ZEC Notes '''''''''''''''''''''''''''''''''''''' @@ -291,7 +291,7 @@ In the case that the balance of all the Action values related to a specific Asse Burn Mechanism Consensus Rules ------------------------------ -1. We require that :math:`\forall (\mathsf{AssetBase},\mathsf{v^{AssetBase}}) \in \mathsf{assetBurn}\ ,\ \mathsf{AssetBase} \neq \mathcal{V}^{\mathsf{Orchard}}`. That is, Native Assets are not allowed to be burnt. +1. We require that :math:`\forall (\mathsf{AssetBase},\mathsf{v^{AssetBase}}) \in \mathsf{assetBurn}\ ,\ \mathsf{AssetBase} \neq \mathcal{V}^{\mathsf{Orchard}}`. That is, ZEC or TAZ is not allowed to be burnt. 2. We require that for every :math:`\forall (\mathsf{AssetBase},\mathsf{v^{AssetBase}}) \in \mathsf{assetBurn}\ ,\ \mathsf{v^{AssetBase}} \neq 0`. 3. We require that there be no duplication of Custom Assets in the :math:`\mathsf{assetBurn}` set. That is, every :math:`\mathsf{AssetBase}` has at most one entry in :math:`\mathsf{assetBurn}`. From e6503116ae65fd73675adf211f7a75073378a77f Mon Sep 17 00:00:00 2001 From: Antoine Rondelet Date: Sun, 21 May 2023 16:18:50 +0100 Subject: [PATCH 09/43] Added link to nested README for build deps (#17) Link to the nested README in `protocol/README` to install all the dependencies needed to build ZIPs and the specs. --- README.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/README.rst b/README.rst index e5ff03941..6d9e6b8d3 100644 --- a/README.rst +++ b/README.rst @@ -37,7 +37,7 @@ Use ``make`` to check that you are using correct `reStructuredText `__ or `Markdown `__ syntax, and double-check the generated ``draft-*.html`` file before filing a Pull Request. - +See `here `__ for the project dependencies. NU5 ZIPs -------- From 9c82f321266409ff999dd9ca0dee03f57d9419e6 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 13:07:00 +0000 Subject: [PATCH 10/43] Handling additional suggestions from PR#649 and PR#628 (#19) Making updates based on pending reviews from [PR#649](https://github.com/zcash/zips/pull/649) and [PR#628](https://github.com/zcash/zips/pull/628). --- zip-0226.rst | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index bef01b51a..eea334b10 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -102,7 +102,7 @@ Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. A ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}}})`, where -- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. +- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid non-bottom group element that is not the identity. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. Specifically, we define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: @@ -233,7 +233,7 @@ Circuit Statement Every *ZSA Action statement* is closely similar to the Orchard Action statement [#protocol-actionstatement]_, except for a few additions that ensure the security of the Asset Identifier system. We detail these changes below. Asset Base Equality -''''''''''''''''''''''''' +''''''''''''''''''' The following constraints must be added to ensure that the input and output note are of the same :math:`\mathsf{AssetBase}`: @@ -244,7 +244,7 @@ The following constraints must be added to ensure that the input and output note Value Commitment Correctness '''''''''''''''''''''''''''' -The following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base, as represented in the notes: +The following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base: - The fixed-base multiplication constraints between the value and the value base point of the value commitment, :math:`\mathsf{cv}`, is replaced with a variable-base multiplication between the two. - The witness to the value base point (as defined in the `asset base`_ equation) is the auxiliary input :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`. @@ -252,12 +252,13 @@ The following constraints must be added to ensure that the value commitment is c Asset Identifier Consistency for Split Actions '''''''''''''''''''''''''''''''''''''''''''''' -The following constraints must be added to prevent senders from changing the Asset Base for the output note in a Split Action: +Senders must not be able to change the Asset Base for the output note in a Split Action. We do this via the following constraints: -- The Value Commitment Integrity should be changed +- The Value Commitment Integrity should be changed: - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(v’ - v^new, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}` - Add a boolean ``split_flag`` variable as an auxiliary witness. This variable is to be activated ``split_flag = 1`` if the Action in question has a Split Input and ``split_flag = 0`` if the Action is actually spending an input note: - - If ``split_flag = 1`` then set :math:`\mathsf{v}' = 0` otherwise :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. + - If :math:`\texttt{split_flag} = 1` then constrain :math:`\mathsf{v}' = 0` otherwise constrain :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. + - If :math:`\texttt{split_flag} = 1` then constrain :math:`\mathsf{v^{old}} \neq 0`. - The Merkle Path Validity should check the existence of the note commitment as usual (and not like with dummy notes): - Check that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}`. - The Nullifier Integrity will be changed to prevent the identification of notes From 32b7f1e54b775dfc437fb7600aafef65661c4628 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 13:07:33 +0000 Subject: [PATCH 11/43] Updates to `txid_digest` (#15) This details the changes to the transaction digest algorithm for the ZSA protocol. - A new branch is added for hashing the information in a transaction related to issuance. - Some branches are added and modified in the orchard_digest subtree to account for the additional Asset Base value that needs to be hashed. --- zip-0226.rst | 109 +++++++++++++++++++++++++++++++++--- zip-0227.rst | 155 ++++++++++++++++++++++++++++++++++++++------------- 2 files changed, 216 insertions(+), 48 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index eea334b10..ac2d2942a 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -89,7 +89,7 @@ For every new Asset, there must be a new and unique Asset Identifier. Every Asse This :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` will be the base point of the value commitment for the specific Custom Asset. Note that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. Rationale for Asset Identifiers -''''''''''''''''''''''''''''''' +``````````````````````````````` In future network and protocol upgrades, the same Asset description string can be carried on, potentially mapping into a different shielded pool. In that case, nodes should know how to transform the Asset Identifier, the Asset Digest, and the Asset Base from one shielded pool to another, while ensuring there are no balance violations [#zip-0209]_. @@ -137,7 +137,7 @@ It consists of .. math:: (\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[\ell_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{\ell_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]}) Rationale for Note Commitment -''''''''''''''''''''''''''''' +````````````````````````````` In the ZSA protocol, the instance of the note commitment scheme, :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}`, differs from the Orchard note commitment :math:`\mathsf{NoteCommit^{Orchard}_{rcm}}` in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. In the case where the Asset is the ZEC Asset, the commitment is computed identically to the Orchard note commitment, without making use of the ZEC Asset Base as an input. @@ -167,7 +167,7 @@ where :math:`\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId} - v^{new}_{A We define :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{ZEC}} :=\mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. Rationale for Value Commitment -'''''''''''''''''''''''''''''' +`````````````````````````````` The Orchard Protocol uses a Homomorphic Pedersen Commitment [#protocol-concretevaluecommit]_ to perform the value commitment, with fixed base points :math:`\mathcal{V}^{\mathsf{Orchard}}` and :math:`\mathcal{R}^{\mathsf{Orchard}}` as the values represent the amount of ZEC being transferred. @@ -189,7 +189,7 @@ Then the verifier MUST compute and use it to verify the `bindingSignature` on the `SIGHASH` message. Rationale for Value Balance Verification -'''''''''''''''''''''''''''''''''''''''' +```````````````````````````````````````` The main reason why no changes to the Orchard process are needed is that no Custom Assets can be unshielded, so all Custom Assets are contained within the shielded pool. This means that the net balance of the input and output values is zero, with only one Asset of value balance published, that of ZEC, :math:`\mathsf{v^{balanceOrchard}}`. No net amount of any other Asset will be revealed, and the number of Assets in the transaction is also hidden. The only exception to this is in the case that an Asset is *burnt*, as we will see below in the `burn mechanism`_. @@ -215,7 +215,7 @@ Wallets and other clients have to choose from the following to ensure the Asset 3. The Split Input note could be an already spent note containing the same Asset Base (note that by zeroing the value in the circuit, we prevent double spending). Rationale for Split Notes -''''''''''''''''''''''''' +````````````````````````` In the Orchard protocol, since each Action represents an input and an output, the transaction that wants to send one input to multiple outputs must have multiple inputs. The Orchard protocol gives *dummy spend notes* [#protocol-dummynotes]_ to the Actions that have not been assigned input notes. @@ -233,7 +233,7 @@ Circuit Statement Every *ZSA Action statement* is closely similar to the Orchard Action statement [#protocol-actionstatement]_, except for a few additions that ensure the security of the Asset Identifier system. We detail these changes below. Asset Base Equality -''''''''''''''''''' +``````````````````` The following constraints must be added to ensure that the input and output note are of the same :math:`\mathsf{AssetBase}`: @@ -242,7 +242,7 @@ The following constraints must be added to ensure that the input and output note - In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. Value Commitment Correctness -'''''''''''''''''''''''''''' +```````````````````````````` The following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base: @@ -250,7 +250,7 @@ The following constraints must be added to ensure that the value commitment is c - The witness to the value base point (as defined in the `asset base`_ equation) is the auxiliary input :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`. Asset Identifier Consistency for Split Actions -'''''''''''''''''''''''''''''''''''''''''''''' +`````````````````````````````````````````````` Senders must not be able to change the Asset Base for the output note in a Split Action. We do this via the following constraints: @@ -266,7 +266,7 @@ Senders must not be able to change the Asset Base for the output note in a Split - if :math:`\mathtt{split\_flag} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}`.) Backwards Compatibility with ZEC Notes -'''''''''''''''''''''''''''''''''''''' +`````````````````````````````````````` The input note in the old note commitment integrity check must either include an Asset Base (ZSA note) or not (pre-ZSA Orchard note). If the note is a pre-ZSA Orchard note, the note commitment is computed in the original Orchard fashion [#protocol-abstractcommit]_. If the note is a ZSA note, the note commitment is computed as defined in the `Note Structure & Commitment`_ section. @@ -327,6 +327,92 @@ A ZSA Asset Burn description is encoded in a transaction as an of a AssetBurn ty | 8 | valueBurn | :math:`\{1 .. 2^{64} - 1\}` | The amount of the AssetType being burnt. | +-------+-----------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ +TxId Digest +=========== + +The transaction digest algorithm defined in ZIP 244 [#zip-0244]_ is modified by the ZSA protocol to add a new branch for issuance information, along with modifications within the ``orchard_digest`` to account for the inclusion of the Asset Base. +The details of these changes are described in this section, and highlighted using the ``[UPDATED FOR ZSA]`` or ``[ADDED FOR ZSA]`` text label. We omit the details of the sections that do not change for the ZSA protocol. + +txid_digest +----------- +A BLAKE2b-256 hash of the following values :: + + T.1: header_digest (32-byte hash output) + T.2: transparent_digest (32-byte hash output) + T.3: sapling_digest (32-byte hash output) + T.4: orchard_digest (32-byte hash output) [UPDATED FOR ZSA] + T.5: issuance_digest (32-byte hash output) [ADDED FOR ZSA] + +The personalization field remains the same as in ZIP 244 [#zip-0244]_. + +T.4: orchard_digest +``````````````````` +When Orchard Actions are present in the transaction, this digest is a BLAKE2b-256 hash of the following values :: + + T.4a: orchard_actions_compact_digest (32-byte hash output) [UPDATED FOR ZSA] + T.4b: orchard_actions_memos_digest (32-byte hash output) [UPDATED FOR ZSA] + T.4c: orchard_actions_noncompact_digest (32-byte hash output) [UPDATED FOR ZSA] + T.4d: flagsOrchard (1 byte) + T.4e: valueBalanceOrchard (64-bit signed little-endian) + T.4f: anchorOrchard (32 bytes) + +T.4a: orchard_actions_compact_digest +'''''''''''''''''''''''''''''''''''' + +A BLAKE2b-256 hash of the subset of Orchard Action information intended to be included in +an updated version of the ZIP-307 [#zip-0307]_ ``CompactBlock`` format for all Orchard +Actions belonging to the transaction. For each Action, the following elements are included +in the hash:: + + T.4a.i : nullifier (field encoding bytes) + T.4a.ii : cmx (field encoding bytes) + T.4a.iii: ephemeralKey (field encoding bytes) + T.4a.iv : encCiphertext[..84] (First 84 bytes of field encoding) [UPDATED FOR ZSA] + +The personalization field of this hash is the same as in ZIP 244:: + + "ZTxIdOrcActCHash" + + +T.4b: orchard_actions_memos_digest +'''''''''''''''''''''''''''''''''' + +A BLAKE2b-256 hash of the subset of Orchard shielded memo field data for all Orchard +Actions belonging to the transaction. For each Action, the following elements are included +in the hash:: + + T.4b.i: encCiphertext[84..596] (contents of the encrypted memo field) [UPDATED FOR ZSA] + +The personalization field of this hash remains identical to ZIP 244:: + + "ZTxIdOrcActMHash" + + +T.4c: orchard_actions_noncompact_digest +''''''''''''''''''''''''''''''''''''''' + +A BLAKE2b-256 hash of the remaining subset of Orchard Action information **not** intended +for inclusion in an updated version of the the ZIP 307 [#zip-0307]_ ``CompactBlock`` +format, for all Orchard Actions belonging to the transaction. For each Action, +the following elements are included in the hash:: + + T.4d.i : cv (field encoding bytes) + T.4d.ii : rk (field encoding bytes) + T.4d.iii: encCiphertext[596..] (post-memo suffix of field encoding) [UPDATED FOR ZSA] + T.4d.iv : outCiphertext (field encoding bytes) + +The personalization field of this hash is defined identically to ZIP 244:: + + "ZTxIdOrcActNHash" + +T.5: issuance_digest +```````````````````` +The details of the computation of this value are in ZIP 227 [#zip-0227-txiddigest]_. + +Signature Digest and Authorizing Data Commitment +================================================ + +The details of the changes to these algorithms are in ZIP 227 [#zip-0227-sigdigest]_ [#zip-0227-authcommitment]_. Security and Privacy Considerations =================================== @@ -382,6 +468,11 @@ References .. [#zip-0224] `ZIP 224: Orchard `_ .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ +.. [#zip-0227-txiddigest] `ZIP 227: Issuance of Zcash Shielded Assets: TxId Digest - Issuance `_ +.. [#zip-0227-sigdigest] `ZIP 227: Issuance of Zcash Shielded Assets: Signature Digest `_ +.. [#zip-0227-authcommitment] `ZIP 227: Issuance of Zcash Shielded Assets: Authorizing Data Commitment `_ +.. [#zip-0244] `ZIP 244: Transaction Identifier Non-Malleability `_ +.. [#zip-0307] `ZIP 307: Light Client Protocol for Payment Detection `_ .. [#protocol-notes] `Zcash Protocol Specification, Version 2022.3.8. Section 3.2: Notes `_ .. [#protocol-notept] `Zcash Protocol Specification, Version 2022.3.8. Section 5.5: Encodings of Note Plaintexts and Memo Fields `_ .. [#protocol-actions] `Zcash Protocol Specification, Version 2022.3.8. Section 3.7: Action Transfers and their Descriptions `_ diff --git a/zip-0227.rst b/zip-0227.rst index 9766daf6e..1d7ab7502 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -314,25 +314,30 @@ Concrete Applications -TxId Digest -=========== +TxId Digest - Issuance +====================== +This section details the construction of the subtree of hashes in the transaction digest that corresponds to issuance transaction data. +Details of the overall changes to the transaction digest due to the ZSA protocol can be found in ZIP 226 [#zip-0226-txiddigest]_. As in ZIP 244 [#zip-0244]_, the digests are all personalized BLAKE2b-256 hashes, and in cases where no elements are available for hashing, a personalized hash of the empty byte array is used. -A new issuance transaction digest algorithm is defined that constructs the identifier for an issuance transaction. Each branch of the tree of hashes will correspond to a specific subset of issuance transaction data. The overall structure of the hash is as follows; each name referenced here will be described in detail below:: +A new issuance transaction digest algorithm is defined that constructs the subtree of the transaction digest tree of hashes for the issuance portion of a transaction. Each branch of the subtree will correspond to a specific subset of issuance transaction data. The overall structure of the hash is as follows; each name referenced here will be described in detail below:: - issuance_txid_digest - ├── issue_actions_digest - └── issuanceValidatingKey + issuance_digest + ├── issue_actions_digest + │   ├── issue_notes_digest + │   ├── assetDescription + │   └── flagsIssuance + └── issuanceValidatingKey In the specification below, nodes of the tree are presented in depth-first order. -issuance_txid_digest +T.5: issuance_digest -------------------- A BLAKE2b-256 hash of the following values :: - T.1: issue_actions_digest (32-byte hash output) - T.2: issuanceValidatingKey (32 bytes) + T.5a: issue_actions_digest (32-byte hash output) + T.5b: issuanceValidatingKey (32 bytes) The personalization field of this hash is set to:: @@ -342,68 +347,137 @@ In case the transaction has no issuance components, ''issue_actions_digest'' is: BLAKE2b-256("ZTxIdSAIssueHash", []) -T.1: issue_actions_digest -````````````````````````` +T.5a: issue_actions_digest +`````````````````````````` A BLAKE2b-256 hash of Issue Action information for all Issuance Actions belonging to the transaction. For each Action, the following elements are included in the hash:: - T.1a: notes_digest (32-byte hash output) - T.1b: assetDescription (field encoding bytes) - T.1c: flagsIssuance (1 byte) + T.5a.i : notes_digest (32-byte hash output) + T.5a.ii : assetDescription (field encoding bytes) + T.5a.iii: flagsIssuance (1 byte) The personalization field of this hash is set to:: "ZTxIdIssActHash" -T.1a: notes_digest -'''''''''''''''''' +T.5a.i: issue_notes_digest +'''''''''''''''''''''''''' A BLAKE2b-256 hash of Note information for all Notes belonging to the Issuance Action. For each Note, the following elements are included in the hash:: - T.1a.1: recipient (field encoding bytes) - T.1a.2: value (field encoding bytes) - T.1a.3: asset (field encoding bytes) - T.1a.4: rho (field encoding bytes) - T.1a.5: rseed (field encoding bytes) + T.5a.i.1: recipient (field encoding bytes) + T.5a.i.2: value (field encoding bytes) + T.5a.i.3: assetBase (field encoding bytes) + T.5a.i.4: rho (field encoding bytes) + T.5a.i.5: rseed (field encoding bytes) The personalization field of this hash is set to:: "ZTxIdIANoteHash" -T.1a.1: recipient -................. +T.5a.i.1: recipient +................... This is the raw encoding of an Orchard shielded payment address as defined in the protocol specification [#protocol-orchardpaymentaddrencoding]_. -T.1a.2: value -............. +T.5a.i.2: value +............... Note value encoded as little-endian 8-byte representation of u64 raw value. -T.1a.3: asset -............. -Asset Base encoded as 32-byte representation of Pallas point. +T.5a.i.3: assetBase +................... +Asset Base encoded as the 32-byte representation of a point on the Pallas curve. -T.1a.4: rho -........... -Nullifier encoded as 32-byte representation of Pallas point. - -T.1a.5: rseed +T.5a.i.4: rho ............. +Nullifier encoded as 32-byte representation of a point on the Pallas curve. + +T.5a.i.5: rseed +............... The ZIP 212 32-byte seed randomness for a note. -T.1b: assetDescription -'''''''''''''''''''''' +T.5a.ii: assetDescription +''''''''''''''''''''''''' The Asset description byte string. -T.1c: flagsIssuance -''''''''''''''''''' +T.5a.iii: flagsIssuance +''''''''''''''''''''''' An 8-bit value representing a set of flags. Ordered from LSB to MSB: - ``finalize`` - The remaining bits are set to `0`. -T.2: issuanceValidatingKey -`````````````````````````` +T.5b: issuanceValidatingKey +``````````````````````````` A byte encoding of issuance validating key for the bundle as defined in the `Issuance Key Derivation`_ section. +Signature Digest +================ + +The per-input transaction digest algorithm to generate the signature digest in ZIP 244 [#zip-0244-sigdigest]_ is modified so that a signature digest is produced for each transparent input, each Sapling input, each Orchard action, and additionally for each Issuance Action. +For Issuance Actions, this algorithm has the exact same output as the transaction digest algorithm, thus the txid may be signed directly. + +The overall structure of the hash is as follows. We highlight the changes for the ZSA protocol via the ``[ADDED FOR ZSA]`` text label, and we omit the descriptions of the sections that do not change for the ZSA protocol:: + + signature_digest + ├── header_digest + ├── transparent_sig_digest + ├── sapling_digest + ├── orchard_digest + └── issuance_digest [ADDED FOR ZSA] + +signature_digest +---------------- +A BLAKE2b-256 hash of the following values :: + + S.1: header_digest (32-byte hash output) + S.2: transparent_sig_digest (32-byte hash output) + S.3: sapling_digest (32-byte hash output) + S.4: orchard_digest (32-byte hash output) + S.5: issuance_digest (32-byte hash output) [ADDED FOR ZSA] + +The personalization field remains the same as in ZIP 244 [#zip-0244]_. + +S.5: issuance_digest +```````````````````` +Identical to that specified for the transaction identifier. + +Authorizing Data Commitment +=========================== + +The transaction digest algorithm defined in ZIP 244 [#zip-0244-authcommitment]_ which commits to the authorizing data of a transaction is modified by the ZSA protocol to have the following structure. +We highlight the changes for the ZSA protocol via the ``[ADDED FOR ZSA]`` text label, and we omit the descriptions of the sections that do not change for the ZSA protocol:: + + auth_digest + ├── transparent_scripts_digest + ├── sapling_auth_digest + ├── orchard_auth_digest + └── issuance_auth_digest [ADDED FOR ZSA] + +The pair (Transaction Identifier, Auth Commitment) constitutes a commitment to all the data of a serialized transaction that may be included in a block. + +auth_digest +----------- +A BLAKE2b-256 hash of the following values :: + + A.1: transparent_scripts_digest (32-byte hash output) + A.2: sapling_auth_digest (32-byte hash output) + A.3: orchard_auth_digest (32-byte hash output) + A.4: issuance_auth_digest (32-byte hash output) [ADDED FOR ZSA] + +The personalization field of this hash remains the same as in ZIP 244. + +A.4: issuance_auth_digest +````````````````````````` +In the case that Issuance Actions are present, this is a BLAKE2b-256 hash of the field encoding of the ``issueAuthSig`` field of the transaction:: + + A.4a: issueAuthSig (field encoding bytes) + +The personalization field of this hash is set to:: + + "ZTxAuthZSAOrHash" + +In the case that the transaction has no Orchard Actions, ``issuance_auth_digest`` is :: + + BLAKE2b-256("ZTxAuthZSAOrHash", []) Security and Privacy Considerations =================================== @@ -462,8 +536,11 @@ References .. [#zip-0224] `ZIP 224: Orchard `_ .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0226-notestructure] `ZIP 226: Transfer and Burn of Zcash Shielded Assets - Note Structure & Commitment `_ +.. [#zip-0226-txiddigest] `ZIP 226: Transfer and Burn of Zcash Shielded Assets - TxId Digest `_ .. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ .. [#zip-0244] `ZIP 244: Transaction Identifier Non-Malleability `_ +.. [#zip-0244-sigdigest] `ZIP 244: Transaction Identifier Non-Malleability: Signature Digest `_ +.. [#zip-0244-authcommitment] `ZIP 244: Transaction Identifier Non-Malleability: Authorizing Data Commitment `_ .. [#zip-0317b] `ZIP 317b: ZSA Extension Proportional Fee Mechanism `_ .. [#zip-0032] `ZIP 32: Shielded Hierarchical Deterministic Wallets `_ .. [#zip-0032-orchard-master] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard master key generation `_ From 2630ffb40b0c1ac8527b2dd9789536b1cf3b1592 Mon Sep 17 00:00:00 2001 From: Antoine Rondelet Date: Wed, 7 Feb 2024 13:08:03 +0000 Subject: [PATCH 12/43] First round of modifications on ZIP227 (#20) Improved style and content of ZIP 227. Co-authored-by: Vivek Arte --- zip-0227.rst | 88 +++++++++++++++++++++++++++++----------------------- 1 file changed, 50 insertions(+), 38 deletions(-) diff --git a/zip-0227.rst b/zip-0227.rst index 1d7ab7502..02be01f04 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -25,29 +25,35 @@ The key word "MUST" in this document is to be interpreted as described in RFC 21 The term "network upgrade" in this document is to be interpreted as described in ZIP 200 [#zip-0200]_. -The term "Orchard" in this document is to be interpreted as described in ZIP 224 [#zip-0224]_. - -The terms "Asset", "custom Asset", and "Wrapped Asset" in this document are to be interpreted as described in ZIP 226 [#zip-0226]_. +The terms "Orchard" and "Action" in this document are to be interpreted as described in +ZIP 224 [#zip-0224]_. We define the following additional terms: +- Asset: A type of note that can be transferred on the Zcash blockchain. Each Asset is identified by an Asset Identifier `Specification: Asset Identifier`_. + + - ZEC is the default (and currently the only defined) Asset for the Zcash mainnet. + - TAZ is the default (and currently the only defined) Asset for the Zcash testnet. + - We use the term "Custom Asset" to refer to any Asset other than ZEC and TAZ. + +- Native Asset: a Custom Asset with issuance defined on the Zcash blockchain. +- Wrapped Asset: a Custom Asset with native issuance defined outside the Zcash blockchain. - Issuance Action: an instance of a single issuance of a Zcash Shielded Asset. It defines the issuance of a single Asset Identifier. - Issuance Bundle: the bundle in the transaction that contains all the issuance actions of that transaction. Abstract ======== -ZIP 226 [#zip-0226]_ and ZIP 227 [#zip-0227]_ propose in conjunction the Zcash Shielded Assets (ZSA) protocol, which is an extension of the Orchard protocol that enables the creation, transfer and burn of custom Assets on the Zcash chain. The creation of such Assets is defined in ZIP 227 [#zip-0227]_. The transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. This ZIP must only be implemented in conjuction with ZIP 226 [#zip-0226]_, as the issuance mechanism is only valid for the ZSA transfer protocol, because it produces notes that can only be transferred under ZSA. +This ZIP (ZIP 227) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunction with ZIP 226 [#zip-0226]_. This protocol is an extension of the Orchard protocol that enables the creation, transfer and burn of custom Assets on the Zcash chain. The creation of such Assets is defined in this ZIP (ZIP 227), while the transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. This ZIP must only be implemented in conjuction with ZIP 226 [#zip-0226]_. The proposed issuance mechanism is only valid for the ZSA transfer protocol, because it produces notes that can only be transferred under ZSA. Motivation ========== -This ZIP is a supporting ZIP for ZIP 226 [#zip-0226]_, which lays out its motivations, but requires an issuance mechanism to be defined (which is substantial enough to stand on its own) in order to function. - -This ZIP enables only *transparent* issuance, since as a first step, transparency will allow for proper testing of the applications that will be most used in the Zcash ecosystem, and will enable the supply of Assets to be tracked. +This ZIP introduces the issuance mechanism for custom Assets on the Zcash chain. While originally part of a same ZSA ZIP (ZIP 226 [#zip-0226]_) the issuance mechanism turned out to be substantial enough to stand on its own and justify the creation of this supporting ZIP for ZIP 226 [#zip-0226]_. -The issuance mechanism described in this ZIP is broad enough for issuers to either create Assets on Zcash (i.e. Assets that originate on the Zcash block chain), as well as for institutions to create bridges from other chains and import "wrapped" Assets. This enables what we hope will be a useful set of applications. +This ZIP only enables *transparent* issuance. As a first step, transparency will allow for proper testing of the applications that will be most used in the Zcash ecosystem, and will enable the supply of Assets to be tracked. +The issuance mechanism described in this ZIP is broad enough for issuers to either create Assets on Zcash (i.e. Assets that originate on the Zcash blockchain), as well as for institutions to create bridges from other chains and import Wrapped Assets. This enables what we hope will be a useful set of applications. Use Cases ========= @@ -64,8 +70,8 @@ See the `Concrete Applications`_ section for more details. Requirements ============ -- Any user of the Zcash block chain can issue custom Assets on chain. -- The issuance mechanism should enable public tracking of the supply of the Assets on the Zcash block chain. +- Any user of the Zcash blockchain can issue custom Assets on chain. +- The issuance mechanism should enable public tracking of the supply of the Assets on the Zcash blockchain. - Issuing or changing the attributes of a specific Asset should require cryptographic authorization. - The Asset identification should be unique (among all shielded pools) and different issuer public keys should not be able to generate the same Asset Identifier. - An issuer should be able to issue different Assets in the same transaction. In other words, in a single "issuance bundle", the issuer should be able publish many "issuance actions", potentially creating multiple Custom Assets. @@ -81,7 +87,7 @@ The ZSA Protocol adds the following three keys to the key components [#protocol- 2. The issuance authorizing key is the key that is used to sign the issuance transaction, and is denoted as :math:`\mathsf{isk}`. This key is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. -3. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all block chain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. +3. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all blockchain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. The relations between these keys are shown in the following diagram: @@ -115,9 +121,9 @@ We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \math As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance master key. We reuse the :math:`\mathsf{CDKsk}` function for Orchard child key derivation from ZIP 32. -We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance master key path as :math:`m_\mathsf{Issuance} / purpose / coin\_type' / account'`. We fix the path levels as follows: +We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance master key path as :math:`m_\mathsf{Issuance} / purpose' / coin\_type' / account'`. We fix the path levels as follows: -- :math:`purpose`: a constant set to :math:`227'` (or :math:`\texttt{0x800000e3}`) following the BIP 43 recommendation. +- :math:`purpose`: a constant set to :math:`227` (i.e. :math:`\texttt{0xe3}). :math:`purpose'` is thus :math:`227'` (or :math:`\texttt{0x800000e3}`) following the BIP 43 recommendation. - :math:`coin\_type`: Defined as in ZIP 32 [#zip-0032-key-path-levels]_. - :math:`account`: fixed to index :math:`0`. @@ -141,7 +147,7 @@ This allows the issuer to use the same wallet it usually uses to transfer Assets Specification: Asset Identifier =============================== -For every new Asset, there must be a new and unique Asset Identifier. We define this to be a globally unique pair :math:`(\mathsf{ik}, \mathsf{asset\_desc})`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. +For every new Asset, there must be a new and unique Asset Identifier, denoted :math:`\mathsf{AssetId}`. We define this to be a globally unique pair :math:`\mathsf{AssetId} := (\mathsf{ik}, \mathsf{asset\_desc})`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-based ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. From the Asset Digest, we derive a specific Asset Base within each such shielded protocol (for example :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}` for the Orchard-based ZSA protocol), using the applicable hash-to-curve algorithm. This Asset Base is included in shielded notes. @@ -154,12 +160,12 @@ Let Define :math:`\mathsf{AssetDigest_{\mathsf{AssetId}}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))`, where -- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}(\mathsf{ik}, \mathsf{asset\_desc}) := \mathsf{0x00} || \mathsf{repr}_{\mathbb{P}}(\mathsf{ik}) || \mathsf{asset\_desc}\!`. +- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathsf{ik}, \mathsf{asset\_desc})) := \mathsf{0x00} || \mathsf{repr}_{\mathbb{P}}(\mathsf{ik}) || \mathsf{asset\_desc}\!`. Define :math:`\mathsf{AssetBase^{Protocol}_{\mathsf{AssetId}}} := \mathsf{ZSAValueBase^{Protocol}}(\mathsf{AssetDigest}_{\mathsf{AssetId}})`, where -In the case of Orchard, we define :math:`\mathsf{ZSAValueBase^{Orchard}}(\mathsf{asset\_digest}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{asset\_digest})` +In the case of Orchard, we define :math:`\mathsf{ZSAValueBase^{Orchard}}(\mathsf{AssetDigest}_{\mathsf{AssetId}}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{AssetDigest}_{\mathsf{AssetId}})` where :math:`\mathsf{GroupHash}^\mathbb{P}` is defined as in [#protocol-concretegrouphashpallasandvesta]_. The relations between the Asset Identifier, Asset Digest, and Asset Base are shown in the following diagram: @@ -172,6 +178,8 @@ The relations between the Asset Identifier, Asset Digest, and Asset Base are sho Diagram relating the Asset Identifier, Asset Digest, and Asset Base in the ZSA Protocol +**Note:** To keep notations light and concise, we may omit :math:`\mathsf{AssetId}` (resp. :math:`\mathsf{Protocol}`) in the subscript (resp. superscript) when the Asset Identifier (resp. Protocol) is clear from the context. + Specification: Global Issuance State ==================================== @@ -190,20 +198,22 @@ An issuance action, `IssueAction`, is the instance of issuing a specific custom - :math:`\mathsf{assetDescSize}`: the size of the Asset description, a number between :math:`0` and :math:`512`, stored in two bytes. - :math:`\mathsf{asset\_desc}`: the Asset description, a byte string of up to 512 bytes as defined in the `Specification: Asset Identifier`_ section. -- `notes`: an array containing the unencrypted output notes of the recipients of the Asset, of type `Note` +- `notes`: an array of `Note` containing the unencrypted output notes of the recipients of the Asset. - ``finalize``: a boolean that defines whether the issuance of that specific custom Asset is finalized or not An asset's :math:`\mathsf{AssetId}` is added to the :math:`\mathsf{previously\_finalized}` set after a block that contains any issuance transaction for that asset with ``finalize = 1``. It then cannot be removed from this set. For Assets with :math:`\mathsf{AssetId} \in \mathsf{previously\_finalized}`, no further tokens can be issued, so as seen below, the validators will reject the transaction. For Assets with :math:`\mathsf{AssetId} \not\in \mathsf{previously\_finalized}`, new issuance actions can be issued in future transactions. These must use the same Asset description, :math:`\mathsf{asset\_desc}`, and can either maintain ``finalize = 0`` or change it to ``finalize = 1``, denoting that this custom Asset cannot be issued after the containing block. -================= =============================== ========================== =========================================================================================== -Size Name Data Type Description -================= =============================== ========================== =========================================================================================== -2 bytes :math:`\mathsf{assetDescSize}` byte The length of the :math:`\mathsf{asset\_desc}` string in bytes -Varies :math:`\mathsf{asset\_desc}` byte UTF-8 encoded string, of size :math:`\mathsf{assetDescSize}` bytes -Varies nNotes compactSize The number of notes in the issuance action -noteSize * nNotes vNotes Note[nNotes] A sequence of note descriptions within the issuance action -1 byte ``flagsIssuance`` byte An 8-bit value with the ``finalize`` boolean value as the LSB, and the other bits set to 0. -================= =============================== ========================== =========================================================================================== +==================== ===================== ======================= =========================================================================================== +Bytes Name Data Type Description +==================== ===================== ======================= =========================================================================================== +2 assetDescSize byte The length of the asset\_desc string in bytes +Varies asset\_desc byte UTF-8 encoded string, of size assetDescSize bytes +Varies nNotes compactSize The number of notes in the issuance action +noteSize * nNotes vNotes Note[nNotes] A sequence of note descriptions within the issuance action +1 flagsIssuance byte An 8-bit value with the ``finalize`` boolean value as the LSB, and the other bits set to 0. (See: `T.5a.iii: flagsIssuance`_) +==================== ===================== ======================= =========================================================================================== + +, where noteSize is the size, in bytes, of a Note. We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the `NoteCommitmentTree` as a shielded note. This prevents future usage of the note from being linked to the issuance transaction, as the nullifier key is not known to the validators and chain observers. @@ -218,14 +228,16 @@ An issuance bundle, `IssueBundle`, is the aggregate of all the issuance-related The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-transactionstructure]_. -======= ==================== ========================== ========================================================================================================================== -Bytes Name Data Type Description -======= ==================== ========================== ========================================================================================================================== -Varies nIssueActions compactSize The number of issuance actions in the bundle -Varies vIssueActions IssueAction[nIssueActions] A sequence of issuance actions descriptions -32 :math:`\mathsf{ik}` byte[32] The issuance validating key of the issuer, used to validate the signature -64 issueAuthSig byte[64] The signature of the transaction SIGHASH, signed by the issuer, validated as in `Issuance Authorization Signature Scheme`_ -======= ==================== ========================== ========================================================================================================================== +================================= ===================== ========================== =============================================================================== +Bytes Name Data Type Description +================================= ===================== ========================== =============================================================================== +Varies nIssueActions compactSize The number of issuance actions in the bundle +IssueActionSize * nIssueActions vIssueActions IssueAction[nIssueActions] A sequence of issuance actions descriptions +32 ik byte[32] The issuance validating key of the issuer, used to validate the signature +64 issueAuthSig byte[64] The signature of the transaction SIGHASH, signed by the issuer, validated as in `Issuance Authorization Signature Scheme`_ +================================= ===================== ========================== =============================================================================== + +, where IssueActionSize is the size, in bytes, of an IssueAction description. Issuance Protocol ----------------- @@ -236,7 +248,7 @@ For all actions `IssueAction`: - encode :math:`\mathsf{asset\_desc}` as a UTF-8 byte string of size up to 512. - compute :math:`\mathsf{AssetDigest}` from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as decribed in the `Specification: Asset Identifier`_ section. - compute :math:`\mathsf{AssetBase^{Protocol}}` from :math:`\mathsf{AssetDigest}` as decribed in the `Specification: Asset Identifier`_ section. -- set the ``finalize`` boolean as desired (if more more issuance actions are to be created for this Asset Identifier, set ``finalize = 0``, otherwise set ``finalize = 1``) +- set the ``finalize`` boolean as desired (if more issuance actions are to be created for this Asset Identifier, set ``finalize = 0``, otherwise set ``finalize = 1``) - For each recipient :math:`i`: - generate a ZSA output note that includes the Asset Base. For an Orchard-based ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d},i}, \mathsf{v}_i, \rho_i, \psi_i, \mathsf{AssetBase^{Orchard}}, \mathsf{rcm}_i)\!`. @@ -250,7 +262,7 @@ For the `IssueBundle`: - sign the `SIGHASH` of the transaction with the issuance authorizing key, :math:`\mathsf{isk}`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. -NOTE that the commitment is not included in the `IssuanceAction` itself. As explained below, it is later computed by the validators and added to the `NoteCommitmentTree`. +**Note:** that the commitment is not included in the `IssuanceAction` itself. As explained below, it is computed later by the validators and added to the `NoteCommitmentTree`. Specification: Consensus Rule Changes @@ -264,6 +276,7 @@ For each `IssueAction` in `IssueBundle`: - check that :math:`0 < \mathsf{assetDescSize} <= 512`. - check that :math:`\mathsf{asset\_desc}` is a string of length :math:`\mathsf{assetDescSize}` bytes. + - retrieve :math:`\mathsf{AssetBase}` from the first note in the sequence and check that :math:`\mathsf{AssetBase}` is derived from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as described in the `Specification: Asset Identifier`_ section. - check that the :math:`\mathsf{AssetId}` does not exist in the ``previously_finalized`` set in the global state. - check that every note in the `IssueAction` contains the same :math:`\mathsf{AssetBase}` and is properly constructed as :math:`note = (\mathsf{g_d, pk_d, v, \rho, \psi, AssetBase})`. @@ -379,7 +392,7 @@ This is the raw encoding of an Orchard shielded payment address as defined in th T.5a.i.2: value ............... -Note value encoded as little-endian 8-byte representation of u64 raw value. +Note value encoded as little-endian 8-byte representation of 64-bit unsigned integer (e.g. u64 in Rust) raw value. T.5a.i.3: assetBase ................... @@ -537,7 +550,6 @@ References .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0226-notestructure] `ZIP 226: Transfer and Burn of Zcash Shielded Assets - Note Structure & Commitment `_ .. [#zip-0226-txiddigest] `ZIP 226: Transfer and Burn of Zcash Shielded Assets - TxId Digest `_ -.. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ .. [#zip-0244] `ZIP 244: Transaction Identifier Non-Malleability `_ .. [#zip-0244-sigdigest] `ZIP 244: Transaction Identifier Non-Malleability: Signature Digest `_ .. [#zip-0244-authcommitment] `ZIP 244: Transaction Identifier Non-Malleability: Authorizing Data Commitment `_ From 3d26c5a4e030760fe619ac1f81d3b62a23388d02 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 13:08:30 +0000 Subject: [PATCH 13/43] Adding ZSA Orchard Action Description encoding details (#21) This adds details of the changes to the Orchard Action encodings and the changes to the transaction format that occur due to the ZSA Protocol. It also improves the formatting of existing tables for Asset Burn. --- zip-0226.rst | 99 ++++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 80 insertions(+), 19 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index ac2d2942a..6f4dae51b 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -302,30 +302,90 @@ Burn Mechanism Consensus Rules ZSA Transaction Structure ========================= -The transaction format is similar to the version 5 transaction format described in the Zcash specification [#protocol-transactionstructure]_, with the following additions to the Orchard bundle: +The transaction format closely follows the version 5 transaction format described in the Zcash specification [#protocol-transactionstructure]_. +The Common Transaction Fields, Transparent Transaction Fields, and Sapling Transaction Fields remain the same as in the version 5 transaction format. +We make some modifications to the Orchard Transaction Fields and the Orchard Action Descriptions, which we detail in the first and second tables below respectively. +We also add ZSA Burn Fields to the transaction format, which we detail in the first table below. +For brevity, we omit the descriptions from the table below unless they differ from the descriptions in §7.1 of the Zcash specification [#protocol-transactionstructure]_. + + ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=============================+==========================+===========================================+=====================================================================+ +| **Orchard Transaction Fields** | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``varies`` |``nActionsOrchard`` |``compactSize`` | | +| | | | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``852 * nActionsOrchard`` |``vActionsOrchard`` |``ZSAOrchardAction[nActionsOrchard]`` |A sequence of ZSA Orchard Action descriptions, encoded per | +| | | |the `ZSA Orchard Action Description Encoding`_. **[UPDATED FOR ZSA]**| ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``1`` |``flagsOrchard`` |``byte`` | | +| | | | | +| | | | | +| | | | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``8`` |``valueBalanceOrchard`` |``int64`` | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``32`` |``anchorOrchard`` |``byte[32]`` | | +| | | | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``varies`` |``sizeProofsOrchard`` |``compactSize`` | | +| | | | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``sizeProofsOrchard`` |``proofsOrchard`` |``byte[sizeProofsOrchard]`` | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``64 * nActionsOrchard`` |``vSpendAuthSigsOrchard`` |``byte[64 * nActionsOrchard]`` | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``64`` |``bindingSigOrchard`` |``byte[64]`` | | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +| **ZSA Burn Fields** | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +| ``varies`` | ``nAssetBurn`` | ``compactSize`` | The number of Assets burnt. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +| ``40 * nAssetBurn`` | ``vAssetBurn`` | ``AssetBurn[nAssetBurn]`` | A sequence of Asset Burn descriptions, | +| | | | encoded per `ZSA Asset Burn Description`_. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ + +ZSA Orchard Action Description Encoding +--------------------------------------- + +The ZSA Orchard Action size differs from the Orchard Action size by 32 bytes. +This means that the size goes from 820 bytes in the Orchard Action to 852 bytes in the ZSA Orchard Action. +We omit the descriptions from the table below since they are identical to the descriptions in §7.5 of the Zcash specification [#protocol-actionencodingandconsensus]_. +A ZSA Orchard Action description is encoded in a transaction as an instance of an ``ZSAOrchardAction`` type: + ++-------+-------------------+---------------+----------------------+ +| Bytes | Name | Data Type | | ++=======+===================+===============+======================+ +| 32 | ``cv`` | ``byte[32]`` | | ++-------+-------------------+---------------+----------------------+ +| 32 | ``nullifier`` | ``byte[32]`` | | ++-------+-------------------+---------------+----------------------+ +| 32 | ``rk`` | ``byte[32]`` | | ++-------+-------------------+---------------+----------------------+ +| 32 | ``cmx`` | ``byte[32]`` | | ++-------+-------------------+---------------+----------------------+ +| 32 | ``ephemeralKey`` | ``byte[32]`` | | ++-------+-------------------+---------------+----------------------+ +| 612 | ``encCiphertext`` | ``byte[612]`` |**[UPDATED FOR ZSA]** | ++-------+-------------------+---------------+----------------------+ +| 80 | ``outCiphertext`` | ``byte[32]`` | | ++-------+-------------------+---------------+----------------------+ -+---------------+------------+-------------------------+-----------------------------------------------------------------------------------+ -| Bytes | Name | Data Type | Description | -+===============+============+=========================+===================================================================================+ -| varies | nAssetBurn | compactSize | The number of Assets burnt. | -+---------------+------------+-------------------------+-----------------------------------------------------------------------------------+ -| 40*nAssetBurn | vAssetBurn | AssetBurn[nAssetBurn] | A sequence of Asset Burn descriptions, encoded per `ZSA Asset Burn Description`_. | -+---------------+------------+-------------------------+-----------------------------------------------------------------------------------+ - -In terms of the Action size, the ZSA action size differs from the Orchard action size by 32 bytes (due to the addition of the :math:`\mathsf{AssetBase}`). This implies that the size goes from 820 bytes in the Orchard action to 852 bytes in the ZSA Action. ZSA Asset Burn Description -------------------------- -A ZSA Asset Burn description is encoded in a transaction as an of a AssetBurn type: +A ZSA Asset Burn description is encoded in a transaction as an instance of an ``AssetBurn`` type: -+-------+-----------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ -| Bytes | Name | Data Type | Description | -+=======+===========+=============================+===========================================================================================================================+ -| 32 | AssetBase | byte[32] | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. | -+-------+-----------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ -| 8 | valueBurn | :math:`\{1 .. 2^{64} - 1\}` | The amount of the AssetType being burnt. | -+-------+-----------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ ++-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=======+===============+=============================+===========================================================================================================================+ +| 32 | ``AssetBase`` | ``byte[32]`` | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. | ++-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ +| 8 | ``valueBurn`` | :math:`\{1 .. 2^{64} - 1\}` | The amount being burnt. | ++-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ TxId Digest =========== @@ -488,7 +548,8 @@ References .. [#protocol-concretevaluecommit] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.8.3: Homomorphic Pedersen commitments (Sapling and Orchard) `_ .. [#protocol-dummynotes] `Zcash Protocol Specification, Version 2022.3.8. Section 4.8.3: Dummy Notes (Orchard) `_ .. [#protocol-actionstatement] `Zcash Protocol Specification, Version 2022.3.8. Section 4.17.4: Action Statement (Orchard) `_ -.. [#protocol-transactionstructure] `Zcash Protocol Specification, Version 2022.3.8. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5) `_ +.. [#protocol-transactionstructure] `Zcash Protocol Specification, Version 2022.3.8. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5) `_ +.. [#protocol-actionencodingandconsensus] `Zcash Protocol Specification, Version 2022.3.8. Section 7.5: Action Description Encoding and Consensus `_ .. [#initial-zsa-issue] `User-Defined Assets and Wrapped Assets `_ .. [#generalized-value-commitments] `Comment on Generalized Value Commitments `_ .. [#zip-0317b] `ZIP 317: Proportional Transfer Fee Mechanism - Pull Request #667 for ZSA Protocol ZIPs `_ From b76813c01895a69541f6cc2eb9f0d18f0dce2621 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:48:15 +0000 Subject: [PATCH 14/43] Updates to issue bundle hash personalizations (#22) A few of the issue bundle hash personalizations were 15 characters long instead of the required 16. This is being fixed here. --- zip-0227.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/zip-0227.rst b/zip-0227.rst index 02be01f04..e5ccc4813 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -370,7 +370,7 @@ A BLAKE2b-256 hash of Issue Action information for all Issuance Actions belongin The personalization field of this hash is set to:: - "ZTxIdIssActHash" + "ZTxIdIssActHash_" (1 underscore character) T.5a.i: issue_notes_digest '''''''''''''''''''''''''' @@ -384,7 +384,7 @@ A BLAKE2b-256 hash of Note information for all Notes belonging to the Issuance A The personalization field of this hash is set to:: - "ZTxIdIANoteHash" + "ZTxIdIANoteHash_" (1 underscore character) T.5a.i.1: recipient ................... From 709874d76bc73fa7e9b9f9c1314c1c5f2cb1b6b7 Mon Sep 17 00:00:00 2001 From: Antoine Rondelet Date: Wed, 7 Feb 2024 14:49:49 +0000 Subject: [PATCH 15/43] Fixed math boundary around purpose (#23) As per the title, this is a tiny fix to adjust the boundary of the math environment which wasn't properly closed and thus rendered poorly on the html. --- zip-0227.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/zip-0227.rst b/zip-0227.rst index e5ccc4813..602d4dc08 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -123,7 +123,7 @@ We reuse the :math:`\mathsf{CDKsk}` function for Orchard child key derivation fr We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance master key path as :math:`m_\mathsf{Issuance} / purpose' / coin\_type' / account'`. We fix the path levels as follows: -- :math:`purpose`: a constant set to :math:`227` (i.e. :math:`\texttt{0xe3}). :math:`purpose'` is thus :math:`227'` (or :math:`\texttt{0x800000e3}`) following the BIP 43 recommendation. +- :math:`purpose`: a constant set to :math:`227` (i.e. :math:`\texttt{0xe3}`). :math:`purpose'` is thus :math:`227'` (or :math:`\texttt{0x800000e3}`) following the BIP 43 recommendation. - :math:`coin\_type`: Defined as in ZIP 32 [#zip-0032-key-path-levels]_. - :math:`account`: fixed to index :math:`0`. From f8936acdae5ae918b7eb142ac8f6a4e859e02f89 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:50:50 +0000 Subject: [PATCH 16/43] Updates to naming conventions and table format (#28) This makes the naming conventions for variables more consistent, largely with a view to using double backticks for terms that appear in the transaction format and datatype description tables. These tables have also been reformatted to be consistent with other ZIPs in their rst form. The `previously_finalized` set is renamed to `finalized_assets`, and this set now stores `AssetDigest` values rather than `AssetId` values for more compactness in the global state. --- zip-0226.rst | 4 +- zip-0227.rst | 158 ++++++++++++++++++++++++++++----------------------- 2 files changed, 88 insertions(+), 74 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 6f4dae51b..14666b980 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -84,7 +84,7 @@ Most of the protocol is kept the same as the Orchard protocol released with NU5, Asset Identifiers ----------------- -For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. +For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, ``assetDesc``, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. This :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` will be the base point of the value commitment for the specific Custom Asset. Note that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. @@ -322,8 +322,6 @@ For brevity, we omit the descriptions from the table below unless they differ fr +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ |``1`` |``flagsOrchard`` |``byte`` | | | | | | | -| | | | | -| | | | | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ |``8`` |``valueBalanceOrchard`` |``int64`` | | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ diff --git a/zip-0227.rst b/zip-0227.rst index 602d4dc08..6419fb661 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -85,9 +85,9 @@ The ZSA Protocol adds the following three keys to the key components [#protocol- 1. The issuance master key, denoted as :math:`\mathsf{sk}_{\mathsf{iss}}`, as the name suggests, is the master key that is used to derive the other two keys. -2. The issuance authorizing key is the key that is used to sign the issuance transaction, and is denoted as :math:`\mathsf{isk}`. This key is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. +2. The issuance authorizing key is the key that is used to sign the issuance transaction, and is denoted as ``isk``. This key is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. -3. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all blockchain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. +3. The issuance validating key, denoted as ``ik``, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all blockchain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. The relations between these keys are shown in the following diagram: @@ -136,31 +136,31 @@ The issuance authorizing key and issuance validating key are derived from the is - The issuance authorizing key is derived from the issuance master key, :math:`\mathsf{sk}_{\mathsf{iss}}`, as a private signature key: -.. math:: \mathsf{isk} := \mathsf{ToScalar}^{\mathsf{Orchard}}(︀ \mathsf{sk}_{\mathsf{iss}} ) +.. math:: \mathtt{isk} := \mathsf{ToScalar}^{\mathsf{Orchard}}(︀ \mathsf{sk}_{\mathsf{iss}} ) -- The issuance validating key is derived from the issuance authorizing key, :math:`\mathsf{isk}`, as a public verification key: +- The issuance validating key is derived from the issuance authorizing key, :math:`\mathtt{isk}`, as a public verification key: -.. math:: \mathsf{ik} := \mathsf{IssueAuthSig}.\mathsf{DerivePublic}(\mathsf{isk}) +.. math:: \mathtt{ik} := \mathsf{IssueAuthSig}.\mathsf{DerivePublic}(\mathtt{isk}) This allows the issuer to use the same wallet it usually uses to transfer Assets, while keeping a disconnect from the other keys. Specifically, this method is aligned with the requirements and motivation of ZIP 32 [#zip-0032]_. It provides further anonymity and the ability to delegate issuance of an Asset (or in the future, generate a multi-signature protocol) while the rest of the keys remain in the wallet safe. Specification: Asset Identifier =============================== -For every new Asset, there must be a new and unique Asset Identifier, denoted :math:`\mathsf{AssetId}`. We define this to be a globally unique pair :math:`\mathsf{AssetId} := (\mathsf{ik}, \mathsf{asset\_desc})`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. +For every new Asset, there must be a new and unique Asset Identifier, denoted :math:`\mathsf{AssetId}`. We define this to be a globally unique pair :math:`\mathsf{AssetId} := (\mathtt{ik}, \mathtt{assetDesc})`, where ``ik`` is the issuance key and ``assetDesc`` is a byte string. A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-based ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. From the Asset Digest, we derive a specific Asset Base within each such shielded protocol (for example :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}` for the Orchard-based ZSA protocol), using the applicable hash-to-curve algorithm. This Asset Base is included in shielded notes. Let -- :math:`\mathsf{asset\_desc}` be the asset description, which includes any information pertaining to the issuance, and is a byte sequence of up to 512 bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later. -- :math:`\mathsf{ik}` be the issuance validating key of the issuer, a public key used to verify the signature on the issuance transaction's SIGHASH. +- ``assetDesc`` be the asset description, which includes any information pertaining to the issuance, and is a byte sequence of up to 512 bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later. +- ``ik`` be the issuance validating key of the issuer, a public key used to verify the signature on the issuance transaction's SIGHASH. Define :math:`\mathsf{AssetDigest_{\mathsf{AssetId}}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))`, where -- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathsf{ik}, \mathsf{asset\_desc})) := \mathsf{0x00} || \mathsf{repr}_{\mathbb{P}}(\mathsf{ik}) || \mathsf{asset\_desc}\!`. +- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathtt{ik}, \mathtt{assetDesc})) := \mathsf{0x00} || \mathsf{repr}_{\mathbb{P}}(\mathtt{ik}) || \mathtt{assetDesc}\!`. Define :math:`\mathsf{AssetBase^{Protocol}_{\mathsf{AssetId}}} := \mathsf{ZSAValueBase^{Protocol}}(\mathsf{AssetDigest}_{\mathsf{AssetId}})`, where @@ -185,107 +185,123 @@ Specification: Global Issuance State Issuance requires the following additions to the global state defined at block boundaries: -- :math:`\mathsf{previously\_finalized}`, a set of :math:`\mathsf{AssetId}` that have been finalized (i.e.: the ``finalize`` flag has been set to ``1`` in some issuance transaction preceding the block boundary). +- ``finalized_assets``, a set of :math:`\mathsf{AssetDigest}` that have been finalized (i.e.: the ``finalize`` flag has been set to ``1`` in some issuance transaction preceding the block boundary). Specification: Issuance Action, Issuance Bundle and Issuance Protocol -================================================================================= +===================================================================== Issuance Action Description --------------------------- -An issuance action, `IssueAction`, is the instance of issuing a specific custom Asset, and contains the following fields: - -- :math:`\mathsf{assetDescSize}`: the size of the Asset description, a number between :math:`0` and :math:`512`, stored in two bytes. -- :math:`\mathsf{asset\_desc}`: the Asset description, a byte string of up to 512 bytes as defined in the `Specification: Asset Identifier`_ section. -- `notes`: an array of `Note` containing the unencrypted output notes of the recipients of the Asset. -- ``finalize``: a boolean that defines whether the issuance of that specific custom Asset is finalized or not - -An asset's :math:`\mathsf{AssetId}` is added to the :math:`\mathsf{previously\_finalized}` set after a block that contains any issuance transaction for that asset with ``finalize = 1``. It then cannot be removed from this set. For Assets with :math:`\mathsf{AssetId} \in \mathsf{previously\_finalized}`, no further tokens can be issued, so as seen below, the validators will reject the transaction. For Assets with :math:`\mathsf{AssetId} \not\in \mathsf{previously\_finalized}`, new issuance actions can be issued in future transactions. These must use the same Asset description, :math:`\mathsf{asset\_desc}`, and can either maintain ``finalize = 0`` or change it to ``finalize = 1``, denoting that this custom Asset cannot be issued after the containing block. - -==================== ===================== ======================= =========================================================================================== -Bytes Name Data Type Description -==================== ===================== ======================= =========================================================================================== -2 assetDescSize byte The length of the asset\_desc string in bytes -Varies asset\_desc byte UTF-8 encoded string, of size assetDescSize bytes -Varies nNotes compactSize The number of notes in the issuance action -noteSize * nNotes vNotes Note[nNotes] A sequence of note descriptions within the issuance action -1 flagsIssuance byte An 8-bit value with the ``finalize`` boolean value as the LSB, and the other bits set to 0. (See: `T.5a.iii: flagsIssuance`_) -==================== ===================== ======================= =========================================================================================== - -, where noteSize is the size, in bytes, of a Note. - -We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the `NoteCommitmentTree` as a shielded note. This prevents future usage of the note from being linked to the issuance transaction, as the nullifier key is not known to the validators and chain observers. +An issuance action, ``IssueAction``, is the instance of issuing a specific custom Asset, and contains the following fields: + +- ``assetDescSize``: the size of the Asset description, a number between :math:`0` and :math:`512`, stored in two bytes. +- ``assetDesc``: the Asset description, a byte string of up to 512 bytes as defined in the `Specification: Asset Identifier`_ section. +- ``vNotes``: an array of ``Note`` containing the unencrypted output notes of the recipients of the Asset. +- ``flagsIssuance``: a byte that stores the ``finalize`` boolean that defines whether the issuance of that specific Custom Asset is finalized or not + +An asset's :math:`\mathsf{AssetDigest}` is added to the ``finalized_assets`` set after a block that contains any issuance transaction for that asset with ``finalize = 1``. It then cannot be removed from this set. +For Assets with :math:`\mathsf{AssetDigest} \in \mathtt{finalized\_assets}`, no further tokens can be issued, so as seen below, the validators will reject the transaction. +For Assets with :math:`\mathsf{AssetDigest} \not\in \mathtt{finalized\_assets}`, new issuance actions can be issued in future transactions. +These must use the same Asset description, ``assetDesc``, and can either maintain ``finalize = 0`` or change it to ``finalize = 1``, denoting that this Custom Asset cannot be issued after the containing block. + ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=============================+==========================+===========================================+=====================================================================+ +|``2`` |``assetDescSize`` |``byte`` |The length of the ``assetDesc`` string in bytes. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``assetDescSize`` |``assetDesc`` |``byte[assetDescSize]`` |A byte sequence of length ``assetDescSize`` bytes which SHOULD be a | +| | | |well-formed UTF-8 code unit sequence according to Unicode 15.0.0 | +| | | |or later. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``varies`` |``nNotes`` |``compactSize`` |The number of notes in the issuance action. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``noteSize * nNotes`` |``vNotes`` |``Note[nNotes]`` |A sequence of note descriptions within the issuance action, | +| | | |where ``noteSize`` is the size, in bytes, of a Note. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``1`` |``flagsIssuance`` |``byte`` |An 8-bit value representing a set of flags. Ordered from LSB to MSB: | +| | | | * ``finalize`` | +| | | | * The remaining bits are set to ``0``. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ + +We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the note commitment tree as a shielded note. +This prevents future usage of the note from being linked to the issuance transaction, as the nullifier key is not known to the validators and chain observers. Issuance Bundle --------------- -An issuance bundle, `IssueBundle`, is the aggregate of all the issuance-related information. Specifically, contains all the issuance actions and the issuer signature on the transaction SIGHASH that validates the issuance itself. It contains the following fields: +An issuance bundle, ``IssueBundle``, is the aggregate of all the issuance-related information. +Specifically, contains all the issuance actions and the issuer signature on the transaction SIGHASH that validates the issuance itself. +It contains the following fields: -- :math:`\mathsf{ik}`: the issuance validating key, that allows the validators to verify that the :math:`\mathsf{AssetId}` is properly associated with the issuer. -- `actions`: an array of issuance actions, of type `IssueAction`. -- `issueAuthSig`: the signature of the transaction SIGHASH, signed by the issuance authorizing key, :math:`\mathsf{isk}`, that validates the issuance . +- ``ik``: the issuance validating key, that allows the validators to verify that the :math:`\mathsf{AssetId}` is properly associated with the issuer. +- ``vIssueActions``: an array of issuance actions, of type `IssueAction`. +- ``issueAuthSig``: the signature of the transaction SIGHASH, signed by the issuance authorizing key, :math:`\mathtt{isk}`, that validates the issuance . The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-transactionstructure]_. -================================= ===================== ========================== =============================================================================== -Bytes Name Data Type Description -================================= ===================== ========================== =============================================================================== -Varies nIssueActions compactSize The number of issuance actions in the bundle -IssueActionSize * nIssueActions vIssueActions IssueAction[nIssueActions] A sequence of issuance actions descriptions -32 ik byte[32] The issuance validating key of the issuer, used to validate the signature -64 issueAuthSig byte[64] The signature of the transaction SIGHASH, signed by the issuer, validated as in `Issuance Authorization Signature Scheme`_ -================================= ===================== ========================== =============================================================================== - -, where IssueActionSize is the size, in bytes, of an IssueAction description. ++------------------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++====================================+==========================+===========================================+===========================================================================+ +|``varies`` |``nIssueActions`` |``compactSize`` |The number of issuance actions in the bundle. | ++------------------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------------+ +|``IssueActionSize * nIssueActions`` |``vIssueActions`` |``IssueAction[nIssueActions]`` |A sequence of issuance action descriptions, where IssueActionSize is | +| | | |the size, in bytes, of an IssueAction description. | ++------------------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------------+ +|``32`` |``ik`` |``byte[32]`` |The issuance validating key of the issuer, used to validate the signature. | ++------------------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------------+ +|``64`` |``issueAuthSig`` |``byte[64]`` |The signature of the transaction SIGHASH, signed by the issuer, | +| | | |validated as in `Issuance Authorization Signature Scheme`_. | ++------------------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------------+ Issuance Protocol ----------------- The issuer program performs the following operations -For all actions `IssueAction`: +For all actions ``IssueAction``: -- encode :math:`\mathsf{asset\_desc}` as a UTF-8 byte string of size up to 512. -- compute :math:`\mathsf{AssetDigest}` from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as decribed in the `Specification: Asset Identifier`_ section. +- encode ``assetDesc`` as a UTF-8 byte string of size up to 512. +- compute :math:`\mathsf{AssetDigest}` from the issuance validating key ``ik`` and ``assetDesc`` as decribed in the `Specification: Asset Identifier`_ section. - compute :math:`\mathsf{AssetBase^{Protocol}}` from :math:`\mathsf{AssetDigest}` as decribed in the `Specification: Asset Identifier`_ section. -- set the ``finalize`` boolean as desired (if more issuance actions are to be created for this Asset Identifier, set ``finalize = 0``, otherwise set ``finalize = 1``) +- set the ``finalize`` boolean as desired (if more issuance actions are to be created for this Asset Identifier, set ``finalize = 0``, otherwise set ``finalize = 1``). - For each recipient :math:`i`: - - generate a ZSA output note that includes the Asset Base. For an Orchard-based ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d},i}, \mathsf{v}_i, \rho_i, \psi_i, \mathsf{AssetBase^{Orchard}}, \mathsf{rcm}_i)\!`. + - generate a ZSA output note that includes the Asset Base. For an Orchard-based ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d}_i}, \mathsf{v}_i, \rho_i, \mathsf{rseed}_i, \mathsf{AssetBase^{Orchard}}, \mathsf{rcm}_i)\!`. -- encode the `IssueAction` into the vector `vIssueActions` of the bundle +- encode the ``IssueAction`` into the vector ``vIssueActions`` of the bundle. -For the `IssueBundle`: +For the ``IssueBundle``: -- encode the `vIssueActions` vector -- encode the :math:`\mathsf{ik}` as 32 byte-string -- sign the `SIGHASH` of the transaction with the issuance authorizing key, :math:`\mathsf{isk}`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. +- encode the ``vIssueActions`` vector. +- encode the ``ik`` as 32 byte-string. +- sign the ``SIGHASH`` of the transaction with the issuance authorizing key, :math:`\mathtt{isk}`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. -**Note:** that the commitment is not included in the `IssuanceAction` itself. As explained below, it is computed later by the validators and added to the `NoteCommitmentTree`. +**Note:** that the commitment is not included in the ``IssuanceAction`` itself. As explained below, it is computed later by the validators and added to the note commitment tree. Specification: Consensus Rule Changes ===================================== -For the IssueBundle: +For the ``IssueBundle``: -- Verify the RedPallas-based issuance authorization signature on `SIGHASH`, `issueAuthSig`, is verified by invoking `issueAuthSig.VerifySig(ik, SIGHASH)` +- Verify the RedPallas-based issuance authorization signature on ``SIGHASH``, ``issueAuthSig``, is verified by invoking :math:`\mathsf{issueAuthSig.VerifySig}(\mathtt{ik}, \mathtt{SIGHASH})`. -For each `IssueAction` in `IssueBundle`: +For each ``IssueAction`` in ``IssueBundle``: -- check that :math:`0 < \mathsf{assetDescSize} <= 512`. -- check that :math:`\mathsf{asset\_desc}` is a string of length :math:`\mathsf{assetDescSize}` bytes. +- check that :math:`0 < \mathtt{assetDescSize} <= 512`. +- check that :math:`\mathtt{assetDesc}` is a string of length :math:`\mathtt{assetDescSize}` bytes. -- retrieve :math:`\mathsf{AssetBase}` from the first note in the sequence and check that :math:`\mathsf{AssetBase}` is derived from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as described in the `Specification: Asset Identifier`_ section. -- check that the :math:`\mathsf{AssetId}` does not exist in the ``previously_finalized`` set in the global state. -- check that every note in the `IssueAction` contains the same :math:`\mathsf{AssetBase}` and is properly constructed as :math:`note = (\mathsf{g_d, pk_d, v, \rho, \psi, AssetBase})`. +- retrieve :math:`\mathsf{AssetBase}` from the first note in the sequence and check that :math:`\mathsf{AssetBase}` is derived from the issuance validating key ``ik`` and ``assetDesc`` as described in the `Specification: Asset Identifier`_ section. +- check that the :math:`\mathsf{AssetDigest}` does not exist in the ``finalized_assets`` set in the global state. +- check that every note in the ``IssueAction`` contains the same :math:`\mathsf{AssetBase}` and is properly constructed as :math:`\mathsf{note} = (\mathsf{g_d, pk_d, v, \rho, rseed, AssetBase})`. If all of the above checks pass, do the following: - For each note, compute the note commitment as :math:`\mathsf{cm} = \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, AssetBase)}` as defined in the Note Structure and Commitment section of ZIP 226 [#zip-0226-notestructure]_ and -- add :math:`\mathsf{cm}` to the Merkle tree of note commitments, `NoteCommitmentTree`. -- If ``finalize = 1``, add :math:`\mathsf{AssetId}` to the ``previously_finalized`` set immediately after the block in which this transaction occurs. +- Add :math:`\mathsf{cm}` to the Merkle tree of note commitments. +- If ``finalize = 1``, add :math:`\mathsf{AssetDigest}` to the ``finalized_assets`` set immediately after the block in which this transaction occurs. - (Replay Protection) If issue bundle is present, the fees MUST be greater than zero. @@ -296,14 +312,14 @@ The following is a list of rationale for different decisions made in the proposa - The issuance key structure is independent of the original key tree, but derived in an analogous manner (via ZIP 32). This is in order to keep the issuance details and the Asset Identifiers consistent across multiple shielded pools. - The design decision is not to have a chosen name to describe the Custom Asset, but to delegate it to an off-chain mapping, as this would imply a land-grab “war”. -- The :math:`\mathsf{asset\_desc}` is a general byte string in order to allow for a wide range of information type to be included that may be associated with the Assets. Some are: +- The ``assetDesc`` is a general byte string in order to allow for a wide range of information type to be included that may be associated with the Assets. Some are: - links for storage such as for NFTs. - metadata for Assets, encoded in any format. - bridging information for Wrapped Assets (chain of origin, issuer name, etc) - information to be committed by the issuer, though not enforceable by the protocol. -- We require a check whether the ``finalize`` flag only has been set in a previous block rather than a previous transaction in the same block. In other words, we only update the ``previously_finalized`` set at the block boundary. This is in keeping with the current property which allows for a miner to reorder transactions in a block without changing the meaning, which we aim to preserve. +- We require a check whether the ``finalize`` flag only has been set in a previous block rather than a previous transaction in the same block. In other words, we only update the ``finalized_assets`` set at the block boundary. This is in keeping with the current property which allows for a miner to reorder transactions in a block without changing the meaning, which we aim to preserve. - We require non-zero fees in the presence of an issue bundle, in order to preclude the possibility of a transaction containing only an issue bundle. If a transaction includes only an issue bundle, the ``SIGHASH`` would be computed solely based on the issue bundle. A duplicate bundle would have the same ``SIGHASH``, potentially allowing for a replay attack. Concrete Applications @@ -523,7 +539,7 @@ The fee mechanism described in this ZIP will follow the mechanism described in Z Future Work ----------- -In future versions of this ZIP, the protocol may also include a "key rotation" mechanism. This would allow an issuer to change the underlying :math:`\mathsf{ik}` of a given Asset, in case the original one was compromised, without having to change the Asset Identifier altogether. +In future versions of this ZIP, the protocol may also include a "key rotation" mechanism. This would allow an issuer to change the underlying ``ik`` of a given Asset, in case the original one was compromised, without having to change the Asset Identifier altogether. Test Vectors ============ From cd55e625c33fa4a977dac3d5a1d1c5492ac8094f Mon Sep 17 00:00:00 2001 From: Antoine Rondelet Date: Wed, 7 Feb 2024 14:51:23 +0000 Subject: [PATCH 17/43] Removed redundant terminology in ZIP226, building on ZIP227 (#26) Removed redundant terminology in ZIP226, building on ZIP227, fixed abstract and used consistent terminology to stick to issuance instead of creation of assets. Co-authored-by: Vivek Arte <46618816+vivek-arte@users.noreply.github.com> --- zip-0226.rst | 31 +++++++++---------------------- 1 file changed, 9 insertions(+), 22 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 14666b980..ea753b025 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -25,40 +25,26 @@ The key word "MUST" in this document is to be interpreted as described in RFC 21 The term "network upgrade" in this document is to be interpreted as described in ZIP 200 [#zip-0200]_. -The terms "Orchard" and "Action" in this document are to be interpreted as described in -ZIP 224 [#zip-0224]_. +The terms "Orchard" and "Action" in this document are to be interpreted as described in ZIP 224 [#zip-0224]_. -We define the following additional terms: - -- Asset: A type of note that can be transferred on the Zcash block chain, identified by the :math:`\mathsf{AssetId}` parameter. +The terms "Asset", "Custom Asset" and "Wrapped Asset" in this document are to be interpreted as described in ZIP 227 [#zip-0227]_. - - ZEC is the default (and currently the only defined) Asset for the Zcash mainnet. - - TAZ is the default (and currently the only defined) Asset for the Zcash testnet. - - We use the term "Custom Asset" to refer to any Asset other than ZEC and TAZ. +We define the following additional terms: -- Native Asset: a Custom Asset with issuance defined on the Zcash block chain. -- Wrapped Asset: a Custom Asset with native issuance defined outside the Zcash block chain. -- Split Input: an Action input used to ensure that the output note of that Action is of a validly issued :math:`\mathsf{AssetBase}` when there is no corresponding real input note, in situations where the number of outputs are larger than the number of inputs. See formal definition in `Split Notes`_. +- Split Input: an Action input used to ensure that the output note of that Action is of a validly issued :math:`\mathsf{AssetBase}` (see [#zip-0227-assetidentifier]_) when there is no corresponding real input note, in situations where the number of outputs are larger than the number of inputs. See formal definition in `Split Notes`_. - Split Action: an Action that contains a Split Input. Abstract ======== -ZIP 226 and ZIP 227 propose in conjunction the Zcash Shielded Assets (ZSA) protocol — a set -of protocol features that enable the creation, transfer, and burn of Custom Assets on the Zcash chain. - -Creation of such Assets is defined in ZIP 227 [#zip-0227]_. Transfer and burn of such Assets is defined -in ZIP 226 [#zip-0226]_. The ZSA protocol is proposed to be instantiated by a modification to the -Orchard protocol, as specified in these ZIPs (although it has been designed with adaption -to possible future shielded protocols in mind). +This ZIP (ZIP 226) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunction with ZIP 227 [#zip-0227]_. The ZSA protocol is an extension of the Orchard protocol that enables the issuance, transfer and burn of custom Assets on the Zcash chain. The issuance of such Assets is defined in ZIP 227 [#zip-0227]_, while the transfer and burn of such Assets is defined in this ZIP (ZIP 226). +While the proposed ZSA protocol is a modification to the Orchard protocol, it has been designed with adaptation to possible future shielded protocols in mind. Motivation ========== -None of the currently deployed Zcash transfer protocols support Custom Assets. Enabling -multi-asset support on the Zcash chain will open the door for a host of applications, and -enhance the ecosystem with application developers and Asset custody institutions for -issuance and bridging purposes. +None of the currently deployed Zcash transfer protocols support Custom Assets. Enabling multi-asset support on the Zcash chain will open the door for a host of applications, and enhance the ecosystem with application developers and Asset custody institutions for issuance and bridging purposes. +This ZIP builds on the issuance mechanism introduced in ZIP 227 [#zip-0227]_. Overview ======== @@ -526,6 +512,7 @@ References .. [#zip-0224] `ZIP 224: Orchard `_ .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ +.. [#zip-0227-assetidentifier] `ZIP 227: Issuance of Zcash Shielded Assets: Specification: Asset Identifier `_ .. [#zip-0227-txiddigest] `ZIP 227: Issuance of Zcash Shielded Assets: TxId Digest - Issuance `_ .. [#zip-0227-sigdigest] `ZIP 227: Issuance of Zcash Shielded Assets: Signature Digest `_ .. [#zip-0227-authcommitment] `ZIP 227: Issuance of Zcash Shielded Assets: Authorizing Data Commitment `_ From 4ec6bf65056678fa90310c1885ca15ce1cab819d Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:51:48 +0000 Subject: [PATCH 18/43] Changing issue digest hash personalization values to match with implementation (#29) This makes the changes in ZIP 227 based on [this comment](https://github.com/QED-it/orchard/pull/66#discussion_r1227395737). --- zip-0227.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/zip-0227.rst b/zip-0227.rst index 6419fb661..0f8b3278c 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -386,7 +386,7 @@ A BLAKE2b-256 hash of Issue Action information for all Issuance Actions belongin The personalization field of this hash is set to:: - "ZTxIdIssActHash_" (1 underscore character) + "ZTxIdIssuActHash" T.5a.i: issue_notes_digest '''''''''''''''''''''''''' @@ -400,7 +400,7 @@ A BLAKE2b-256 hash of Note information for all Notes belonging to the Issuance A The personalization field of this hash is set to:: - "ZTxIdIANoteHash_" (1 underscore character) + "ZTxIdIAcNoteHash" T.5a.i.1: recipient ................... From a7f5ffa0e9234a59d9c9434cdb886e125e5c5e12 Mon Sep 17 00:00:00 2001 From: Antoine Rondelet Date: Wed, 7 Feb 2024 14:52:08 +0000 Subject: [PATCH 19/43] Added missing indices over sums (#27) This PR adds missing indices over sums. It also fixes and makes improvements to the burn mechanism description. Co-authored-by: Vivek Arte <46618816+vivek-arte@users.noreply.github.com> --- zip-0226.rst | 40 ++++++++++++++++++++++++++++++++-------- 1 file changed, 32 insertions(+), 8 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index ea753b025..9f53beee5 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -150,7 +150,7 @@ where :math:`\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId} - v^{new}_{A :math:`\mathcal{R}^{\mathsf{Orchard}}:=\mathsf{GroupHash^{\mathbb{P}}}\texttt{("z.cash:Orchard-cv", "r")}`, as in the Orchard protocol. -We define :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{ZEC}} :=\mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. +We define :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{ZEC}} :=\mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. As such :math:`\mathsf{ValueCommit^{Orchard}_{rcv}(v)}` as defined in [#zip-0224]_ is used as :math:`\mathsf{ValueCommit^{OrchardZSA}_{rcv}(v, \mathcal{V}^{\mathsf{Orchard}})}` here. Rationale for Value Commitment `````````````````````````````` @@ -163,21 +163,29 @@ The use of different value base points for different Assets enables the final ba Value Balance Verification -------------------------- -In order to verify the balance of the different Assets, the verifier MUST perform exactly the same process as for the Orchard protocol [#protocol-binding]_. +In order to verify the balance of the different Assets, the verifier MUST perform exactly the same process as for the Orchard protocol [#protocol-binding]_. For a total of :math:`n` Actions in a transfer, the prover MUST still sign the `SIGHASH` of the transaction using the binding signature key -:math:`\mathsf{bsk} = \sum_{\mathsf{ \forall i\in \{1,...,n\}}} \mathsf{rcv_{i}}`. +:math:`\mathsf{bsk} = \sum_{i=1}^{n} \mathsf{rcv}_{i}`. Then the verifier MUST compute -.. math:: \mathsf{bvk = (\sum cv_i^{net})} - \mathsf{ ValueCommit_0^{Orchard}(v^{balanceOrchard})} = \sum \mathsf{rcv_{i}^{net}}\mathcal{R}^{\mathsf{Orchard}} +.. math:: \mathsf{bvk} =(\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}(v^{balanceOrchard}, \mathcal{V}^{\mathsf{Orchard}})} -and use it to verify the `bindingSignature` on the `SIGHASH` message. +After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the `bindingSignature` on the `SIGHASH` message. Rationale for Value Balance Verification ```````````````````````````````````````` -The main reason why no changes to the Orchard process are needed is that no Custom Assets can be unshielded, so all Custom Assets are contained within the shielded pool. This means that the net balance of the input and output values is zero, with only one Asset of value balance published, that of ZEC, :math:`\mathsf{v^{balanceOrchard}}`. No net amount of any other Asset will be revealed, and the number of Assets in the transaction is also hidden. The only exception to this is in the case that an Asset is *burnt*, as we will see below in the `burn mechanism`_. +We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of verbosity and clarity) between Actions related to ZEC and Actions related to Custom Assets. We assume :math:`m` Actions related to ZEC and :math:`n-m` actions related to Custom Assets, where :math:`m \in [0,n]`. Furthermore, we assume for simplicity that given a tuple of :math:`n` Actions in a transfer, the :math:`m` Actions related to ZEC are first (in practice Actions could be in whatever order). + +The value balance verification is equivalent to: + +.. math:: \mathsf{bvk} = (\sum_{i=1}^{m} \mathsf{cv^{net}}_{i}) + (\sum_{j=m+1}^{n} \mathsf{cv^{net}}_j) - \mathsf{ValueCommit_0^{OrchardZSA}(v^{balanceOrchard}, \mathcal{V}^{Orchard})} + +This equation contains the balance check of the Orchard protocol [#protocol-binding]_. With ZSA, transfer Actions for Custom Assets MUST also be balanced across asset bases. As such, for a correctly constructed transaction, we MUST get :math:`\mathsf{(\sum_{j=m+1}^{n} v_j^{net}) = 0}`, and thus be left with :math:`\mathsf{\sum_{j=m+1}^{n} rcv_{j}^{net}}\mathcal{R}^{\mathsf{Orchard}}` in the expression. If :math:`m=n` (resp. :math:`m=0`), i.e. all Actions relate to ZEC (resp. Custom Assets), then :math:`m+1>n` (resp. :math:`1>m`), and thus the sum :math:`\sum_{j=m+1}^{n}` (resp. :math:`\sum_{i=1}^{m}`) returns the identity element of the group. + +So, the main reason why no changes to the Orchard process are needed is that no Custom Assets can be unshielded, so all Custom Assets are contained within the shielded pool. This means that the net balance of the input and output values is zero, with only one Asset of value balance published, that of ZEC, :math:`\mathsf{v^{balanceOrchard}}`. No net amount of any other Asset will be revealed, and the number of Assets in the transaction is also hidden. The only exception to this is in the case that an Asset is *burnt*, as we will see below in the `burn mechanism`_. As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values only sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. @@ -267,11 +275,17 @@ For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` v .. math:: \mathsf{assetBurn} = \{ (\mathsf{AssetBase},\mathsf{v^{AssetBase}})\ |\ \forall\ \mathsf{AssetBase}\ \textit{s.t.}\ \mathsf{v^{AssetBase}} \neq 0 \} +We denote by :math:`L` the cardinality of the :math:`\mathsf{assetBurn}` set. + The value balances for each Asset Identifier in :math:`\mathsf{assetBurn}` represents the amount of that Asset that is being burnt. In the case of ZEC, the value balance represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). -The validator needs to verify the Balance and Binding Signature by adding the value balances for all Assets, as committed using their respective :math:`\mathsf{AssetBase}` as the value base point of the Pedersen Commitment. This is done as follows +The validator needs to verify the Balance and Binding Signature by adding the value balances for all Assets, as committed using their respective :math:`\mathsf{AssetBase}` as the value base point of the Pedersen Commitment. + +This is done as follows: -.. math:: \mathsf{bvk = (\sum cv_i^{net})} - \mathsf{ ValueCommit_0^{Orchard}(v^{balanceOrchard})} - \sum_{\mathsf{assetBurn}} \mathsf{ValueCommit_0^{OrchardZSA}(AssetBase, v^{AssetBase}) } = \sum \mathsf{rcv_{i,j}^{net}}\mathcal{R}^{\mathsf{Orchard}} +.. math:: \mathsf{bvk} = (\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{v^{balanceOrchard}}, \mathcal{V}^{\mathsf{Orchard}}) - \sum_{k=1}^{L} \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{v}_{k}, \mathsf{AssetBase}_{k}) + +After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the `bindingSignature` on the `SIGHASH` message. In the case that the balance of all the Action values related to a specific Asset will be zero, there will be no value added to the vector. This way, neither the number of Assets nor their Asset Identifiers will be revealed, except in the case that an Asset is burnt. @@ -284,6 +298,16 @@ Burn Mechanism Consensus Rules **Note:** Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets. +Rationale for Burn Mechanism +```````````````````````````` + +As for the value balance verification, we assume :math:`n` Actions, :math:`m` of which are related to ZEC and the remaining :math:`n-m` Actions related to Custom Assets. + +The burn mechanism verification is equivalent to: + +.. math:: \mathsf{bvk} = ((\sum_{i=1}^{m} \mathsf{cv^{net}}_{i}) + (\sum_{j=m+1}^{n} \mathsf{cv^{net}}_{j})) - ([\mathsf{v^{balanceOrchard}}]\mathcal{V}^{\mathsf{Orchard}} + [0]\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{k=1}^{L} [\mathsf{v}_{k}]\mathsf{AssetBase}_{k} + [0]\mathcal{R}^{\mathsf{Orchard}}) + +The relationship between :math:`\mathsf{bvk}` and :math:`\mathsf{bsk}` will hold only if the sum of the net values of the Actions equals the sum of :math:`\mathsf{v^{balanceOrchard}}` and the :math:`\mathsf{v_k}` values, across base points (i.e. Asset Base). ZSA Transaction Structure ========================= From d92ccecb480f16832e3daea0596187ba1e41110b Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:52:32 +0000 Subject: [PATCH 20/43] Consistency changes for notation and updates to issuance key derivation (#30) This PR improves the naming of variables to make them consistent with the broader ZIPs conventions. It also makes changes to the issuance key derivation and the terms used for the various keys. --- zip-0226.rst | 29 ++++---- zip-0227-key-components-zsa.png | Bin 61722 -> 61500 bytes zip-0227-key-components-zsa.svg | 28 +++----- zip-0227.rst | 123 +++++++++++++++----------------- 4 files changed, 83 insertions(+), 97 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 9f53beee5..cd33e7309 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -70,7 +70,7 @@ Most of the protocol is kept the same as the Orchard protocol released with NU5, Asset Identifiers ----------------- -For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, ``assetDesc``, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. +For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. This :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` will be the base point of the value commitment for the specific Custom Asset. Note that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. @@ -109,7 +109,7 @@ where: .. math:: \begin{align} \mathsf{cm}_{\mathsf{ZSA}} :=&\ \mathsf{SinsemillaHashToPoint}( \texttt{"z.cash:ZSA-NoteCommit-M"}, \\ - &\ \ \ \mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})) \\ + &\ \ \ \mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{asset\_base}) \\ &\ + [\mathsf{rcm}] \mathsf{GroupHash}^{\mathbb{P}}(\texttt{"z.cash:Orchard-NoteCommit-r"},\texttt{""}) \end{align} @@ -165,14 +165,14 @@ Value Balance Verification In order to verify the balance of the different Assets, the verifier MUST perform exactly the same process as for the Orchard protocol [#protocol-binding]_. -For a total of :math:`n` Actions in a transfer, the prover MUST still sign the `SIGHASH` of the transaction using the binding signature key +For a total of :math:`n` Actions in a transfer, the prover MUST still sign the SIGHASH transaction hash using the binding signature key :math:`\mathsf{bsk} = \sum_{i=1}^{n} \mathsf{rcv}_{i}`. -Then the verifier MUST compute +The verifier MUST compute .. math:: \mathsf{bvk} =(\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}(v^{balanceOrchard}, \mathcal{V}^{\mathsf{Orchard}})} -After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the `bindingSignature` on the `SIGHASH` message. +After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the binding signature on the SIGHASH transaction hash. Rationale for Value Balance Verification ```````````````````````````````````````` @@ -195,7 +195,7 @@ Split Notes A Split Input is a copy of a previously issued input note (that is, a note that has previously been included in the Merkle tree), with the following changes: -- A ``split_flag`` boolean is set to 1. +- A :math:`\mathsf{split\_flag}` boolean is set to 1. - The value of the note is replaced with the value 0 during the computation of the value commitment. Input notes are sometimes split in two (or more) output notes, as in most cases, not all the value in a single note is sent to a single output. @@ -215,7 +215,7 @@ In the Orchard protocol, since each Action represents an input and an output, th The Orchard technique requires modification for the ZSA protocol with multiple Asset Identifiers, as the output note of the split Actions *cannot* contain *any* Asset Base. We must enforce it to be an actual output of a GroupHash computation (in fact, we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). Without this enforcement the prover could input a multiple (or linear combination) of an existing Asset Base, and thereby attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds. -Therefore, for Custom Assets we enforce that *every* input note to an ZSA Action must be proven to exist in the set of note commitments in the note commitment tree. We then enforce this real note to be “unspendable” in the sense that its value will be zeroed in split Actions and the nullifier will be randomized, making the note not spendable in the specific Action. Then, the proof itself ensures that the output note is of the same Asset Base as the input note. In the circuit, the split note functionality will be activated by a boolean private input to the proof (aka the ``split_flag`` boolean). +Therefore, for Custom Assets we enforce that *every* input note to an ZSA Action must be proven to exist in the set of note commitments in the note commitment tree. We then enforce this real note to be “unspendable” in the sense that its value will be zeroed in split Actions and the nullifier will be randomized, making the note not spendable in the specific Action. Then, the proof itself ensures that the output note is of the same Asset Base as the input note. In the circuit, the split note functionality will be activated by a boolean private input to the proof (aka the :math:`\mathsf{split\_flag}` boolean). This ensures that the value base points of all output notes of a transfer are actual outputs of a GroupHash, as they originate in the Issuance protocol which is publicly verified. Note that the Orchard dummy note functionality remains in use for ZEC notes, and the Split Input technique is used in order to support Custom Assets. @@ -250,14 +250,14 @@ Senders must not be able to change the Asset Base for the output note in a Split - The Value Commitment Integrity should be changed: - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(v’ - v^new, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}` -- Add a boolean ``split_flag`` variable as an auxiliary witness. This variable is to be activated ``split_flag = 1`` if the Action in question has a Split Input and ``split_flag = 0`` if the Action is actually spending an input note: - - If :math:`\texttt{split_flag} = 1` then constrain :math:`\mathsf{v}' = 0` otherwise constrain :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. - - If :math:`\texttt{split_flag} = 1` then constrain :math:`\mathsf{v^{old}} \neq 0`. +- Add a boolean :math:`\mathsf{split\_flag}` variable as an auxiliary witness. This variable is to be activated :math:`\mathsf{split\_flag} = 1` if the Action in question has a Split Input and :math:`\mathsf{split\_flag} = 0` if the Action is actually spending an input note: + - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{v}' = 0` otherwise constrain :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. + - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{v^{old}} \neq 0`. - The Merkle Path Validity should check the existence of the note commitment as usual (and not like with dummy notes): - Check that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}`. - The Nullifier Integrity will be changed to prevent the identification of notes - Replace the :math:`\psi_{old}` value with a generic :math:`\psi'` as :math:`\mathsf{nf_{old}} = \mathsf{DeriveNullifier_{nk}}(\rho^\mathsf{old}, \psi', \mathsf{cm^{old}})` - - if :math:`\mathtt{split\_flag} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}`.) + - if :math:`\mathsf{split\_flag} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}`.) Backwards Compatibility with ZEC Notes `````````````````````````````````````` @@ -285,7 +285,7 @@ This is done as follows: .. math:: \mathsf{bvk} = (\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{v^{balanceOrchard}}, \mathcal{V}^{\mathsf{Orchard}}) - \sum_{k=1}^{L} \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{v}_{k}, \mathsf{AssetBase}_{k}) -After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the `bindingSignature` on the `SIGHASH` message. +After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the binding signature on the SIGHASH transaction hash. In the case that the balance of all the Action values related to a specific Asset will be zero, there will be no value added to the vector. This way, neither the number of Assets nor their Asset Identifiers will be revealed, except in the case that an Asset is burnt. @@ -307,7 +307,7 @@ The burn mechanism verification is equivalent to: .. math:: \mathsf{bvk} = ((\sum_{i=1}^{m} \mathsf{cv^{net}}_{i}) + (\sum_{j=m+1}^{n} \mathsf{cv^{net}}_{j})) - ([\mathsf{v^{balanceOrchard}}]\mathcal{V}^{\mathsf{Orchard}} + [0]\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{k=1}^{L} [\mathsf{v}_{k}]\mathsf{AssetBase}_{k} + [0]\mathcal{R}^{\mathsf{Orchard}}) -The relationship between :math:`\mathsf{bvk}` and :math:`\mathsf{bsk}` will hold only if the sum of the net values of the Actions equals the sum of :math:`\mathsf{v^{balanceOrchard}}` and the :math:`\mathsf{v_k}` values, across base points (i.e. Asset Base). +The relationship between :math:`\mathsf{bvk}` and :math:`\mathsf{bsk}` will hold only if the sum of the net values of the Actions equals the sum of :math:`\mathsf{v^{balanceOrchard}}` and the :math:`\mathsf{v}_k` values, across base points (i.e. Asset Base). ZSA Transaction Structure ========================= @@ -505,7 +505,8 @@ Backward Compatibility ---------------------- In order to have backward compatibility with the ZEC notes, we have designed the circuit to support both ZEC and ZSA notes. As we specify above, there are three main reasons we can do this: -- Note commitments for ZEC notes will remain the same, while note commitments for Custom Assets will be computed taking into account the :math:`AssetBase` value as well. + +- Note commitments for ZEC notes will remain the same, while note commitments for Custom Assets will be computed taking into account the :math:`\mathsf{AssetBase}` value as well. - The existing Orchard shielded pool will continue to be used for the new ZSA notes post the upgrade. - The value commitment is abstracted to allow for the value base-point as a variable private input to the proof. - The ZEC-based Actions will still include dummy input notes, whereas the ZSA-based Actions will include both dummy and split input notes. diff --git a/zip-0227-key-components-zsa.png b/zip-0227-key-components-zsa.png index aa9fa5d21d48885d21a987130a4504a92b74614e..4b6b017635100b27a61f3bfe2123f84a3f1544f1 100644 GIT binary patch delta 23936 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b/zip-0227-key-components-zsa.svg index 217acc635..a7d9d866a 100644 --- a/zip-0227-key-components-zsa.svg +++ b/zip-0227-key-components-zsa.svg @@ -7,7 +7,7 @@ id="svg2" version="1.1" inkscape:version="1.2.2 (b0a84865, 2022-12-01)" - sodipodi:docname="key_components_zsa.svg" + sodipodi:docname="zip-0227-key-components-zsa.svg" inkscape:export-filename="key_components_zsa.png" inkscape:export-xdpi="179.99957" inkscape:export-ydpi="179.99957" @@ -33,8 +33,8 @@ showgrid="false" inkscape:window-width="1158" inkscape:window-height="916" - inkscape:window-x="177" - inkscape:window-y="38" + inkscape:window-x="381" + inkscape:window-y="81" inkscape:window-maximized="0" inkscape:showpageshadow="2" inkscape:pagecheckerboard="0" @@ -179,25 +179,15 @@ id="rect2985-9-7-8" style="fill:#fdb341;fill-opacity:1;stroke:#000000;stroke-width:1.06667;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1" />skissidkIssuance master keyIssuance derivation key`_ .. [#protocol-addressesandkeys] `Zcash Protocol Specification, Version 2022.3.8. Section 3.1: Payment Addresses and Keys `_ .. [#protocol-concretegrouphashpallasandvesta] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.9.8: Group Hash into Pallas and Vesta `_ +.. [#protocol-abstractprfs] `Zcash Protocol Specification, Version 2022.3.8. Section 4.1.2: Pseudo Random Functions `_ .. [#protocol-orchardkeycomponents] `Zcash Protocol Specification, Version 2022.3.8. Section 4.2.3: Orchard Key Components `_ .. [#protocol-spendauthsig] `Zcash Protocol Specification, Version 2022.3.8. Section 4.15: Spend Authorization Signature (Sapling and Orchard) `_ .. [#protocol-concretespendauthsig] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.7.1: Spend Authorization Signature (Sapling and Orchard) `_ From e5f03d9bceb2b4ddbdcf4b0153e3879f3d93e537 Mon Sep 17 00:00:00 2001 From: Constance Beguier Date: Wed, 7 Feb 2024 14:54:35 +0000 Subject: [PATCH 21/43] Update with circuit changes (#31) - Add the new nullifier equation for split notes - Add a link to Orchard circuit document - Add is_native_asset auxiliary witness - Remove constraint (split_flag=1) => (v_old != 0) - Add constraint (split_flag=1) => (is_native_asset=0) --- zip-0226.rst | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index cd33e7309..1e06c9b10 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -127,7 +127,7 @@ Rationale for Note Commitment In the ZSA protocol, the instance of the note commitment scheme, :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}`, differs from the Orchard note commitment :math:`\mathsf{NoteCommit^{Orchard}_{rcm}}` in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. In the case where the Asset is the ZEC Asset, the commitment is computed identically to the Orchard note commitment, without making use of the ZEC Asset Base as an input. -As we will see, the nested structure of the Sinsemilla-based commitment [#protocol-concretesinsemillacommit]_ allows us to add the Asset Base as a final recursive step, and hence keep a single instance of the Sinsemilla hash function in the circuit for the note commitment verification. +As we will see, the nested structure of the Sinsemilla-based commitment [#protocol-concretesinsemillacommit]_ allows us to add the Asset Base as a final recursive step. The note commitment output is still indistinguishable from the original Orchard ZEC note commitments, by definition of the Sinsemilla hash function [#protocol-concretesinsemillahash]_. ZSA note commitments will therefore be added to the same Orchard Note Commitment Tree. In essence, we have: @@ -208,6 +208,12 @@ Wallets and other clients have to choose from the following to ensure the Asset 2. The Split Input note could be a different unspent note containing the same Asset Base (note that the note will not actually be spent). 3. The Split Input note could be an already spent note containing the same Asset Base (note that by zeroing the value in the circuit, we prevent double spending). +For Split Notes, the nullifier is generated as follows + +.. math:: \mathsf{nf_{old}} = \mathsf{Extract}_{\mathbb{P}} ([(\mathsf{PRF^{nfOrchard}_{nk}} (\rho^{\mathsf{old}}) + \psi') \bmod q_{\mathbb{P}}] \mathcal{K}^\mathsf{Orchard} + \mathsf{cm^{old}} + \mathcal{L}^\mathsf{Orchard}) + +where :math:`\psi'` is sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}`, :math:`\mathcal{K}^{\mathsf{Orchard}}` is the Orchard Nullifier Base as defined in [#protocol-commitmentsandnullifiers]_, and :math:`\mathcal{L}^{\mathsf{Orchard}} := \mathsf{GroupHash^{\mathbb{P}}}\texttt{("z.cash:Orchard", "L")}`. + Rationale for Split Notes ````````````````````````` @@ -226,6 +232,8 @@ Circuit Statement Every *ZSA Action statement* is closely similar to the Orchard Action statement [#protocol-actionstatement]_, except for a few additions that ensure the security of the Asset Identifier system. We detail these changes below. +All modifications in the Circuit are detailed in [#circuit-modifications]_. + Asset Base Equality ``````````````````` @@ -235,6 +243,8 @@ The following constraints must be added to ensure that the input and output note - In the Old note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. - In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. +To make the evaluation of the note commitment easier, we add a boolean :math:`\mathsf{is\_native\_asset}` as an auxiliary witness. We also add some constraints to verify that this variable is activated (i.e. :math:`\mathsf{is\_native\_asset} = 1`) if the Asset Base is equal to :math:`\mathcal{V}^\mathsf{Orchard}` and this variable is not activated (i.e. :math:`\mathsf{is\_native\_asset} = 0`) if the Asset Base is not equal to :math:`\mathcal{V}^\mathsf{Orchard}`. + Value Commitment Correctness ```````````````````````````` @@ -252,12 +262,11 @@ Senders must not be able to change the Asset Base for the output note in a Split - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(v’ - v^new, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}` - Add a boolean :math:`\mathsf{split\_flag}` variable as an auxiliary witness. This variable is to be activated :math:`\mathsf{split\_flag} = 1` if the Action in question has a Split Input and :math:`\mathsf{split\_flag} = 0` if the Action is actually spending an input note: - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{v}' = 0` otherwise constrain :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. - - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{v^{old}} \neq 0`. + - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{is\_native\_asset} = 0` because split notes are only available for Custom Assets. - The Merkle Path Validity should check the existence of the note commitment as usual (and not like with dummy notes): - - Check that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}`. -- The Nullifier Integrity will be changed to prevent the identification of notes - - Replace the :math:`\psi_{old}` value with a generic :math:`\psi'` as :math:`\mathsf{nf_{old}} = \mathsf{DeriveNullifier_{nk}}(\rho^\mathsf{old}, \psi', \mathsf{cm^{old}})` - - if :math:`\mathsf{split\_flag} = 0` then constrain :math:`\psi' = \psi^{old}`. (Otherwise :math:`\psi'` should be sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}`.) + - Check for all notes except dummy notes that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}`. + - The new constraint is :math:`\underbrace{(\mathsf{v^{old}} = 0 \land \mathsf{is\_native\_asset} = 1)}_\text{It is a dummy note} \lor \underbrace{(\mathsf{Valid\,Merkle\,Path})}_\text{The Merkle Path is valid}`. +- The Nullifier Integrity will be changed to prevent the identification of notes as defined in the `Split Notes`_ section. Backwards Compatibility with ZEC Notes `````````````````````````````````````` @@ -509,7 +518,7 @@ In order to have backward compatibility with the ZEC notes, we have designed the - Note commitments for ZEC notes will remain the same, while note commitments for Custom Assets will be computed taking into account the :math:`\mathsf{AssetBase}` value as well. - The existing Orchard shielded pool will continue to be used for the new ZSA notes post the upgrade. - The value commitment is abstracted to allow for the value base-point as a variable private input to the proof. -- The ZEC-based Actions will still include dummy input notes, whereas the ZSA-based Actions will include both dummy and split input notes. +- The ZEC-based Actions will still include dummy input notes, whereas the ZSA-based Actions will include split input notes and will not include dummy input notes. Deployment ----------- @@ -563,3 +572,4 @@ References .. [#initial-zsa-issue] `User-Defined Assets and Wrapped Assets `_ .. [#generalized-value-commitments] `Comment on Generalized Value Commitments `_ .. [#zip-0317b] `ZIP 317: Proportional Transfer Fee Mechanism - Pull Request #667 for ZSA Protocol ZIPs `_ +.. [#circuit-modifications] `Modifications to the Orchard circuit for the ZSA Protocol `_ From 3651df5ffc17efca3dd86d25b70dc898596cfb3b Mon Sep 17 00:00:00 2001 From: Vivek Arte <46618816+vivek-arte@users.noreply.github.com> Date: Tue, 15 Aug 2023 01:17:07 +0530 Subject: [PATCH 22/43] Suggestions from ZIP review: clarifications and typographical edits. Co-authored-by: Deirdre Connolly --- zip-0226.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 1e06c9b10..a15d413db 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -177,7 +177,7 @@ After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the bin Rationale for Value Balance Verification ```````````````````````````````````````` -We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of verbosity and clarity) between Actions related to ZEC and Actions related to Custom Assets. We assume :math:`m` Actions related to ZEC and :math:`n-m` actions related to Custom Assets, where :math:`m \in [0,n]`. Furthermore, we assume for simplicity that given a tuple of :math:`n` Actions in a transfer, the :math:`m` Actions related to ZEC are first (in practice Actions could be in whatever order). +We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of clarity) between Actions related to ZEC and Actions related to Custom Assets. We assume :math:`m` Actions related to ZEC and :math:`n-m` Actions related to Custom Assets, where :math:`m \in [0,n]`. Furthermore, we assume for simplicity that given a tuple of :math:`n` Actions in a transfer, the :math:`m` Actions related to ZEC are first (in practice Actions could be in whatever order). The value balance verification is equivalent to: @@ -185,7 +185,7 @@ The value balance verification is equivalent to: This equation contains the balance check of the Orchard protocol [#protocol-binding]_. With ZSA, transfer Actions for Custom Assets MUST also be balanced across asset bases. As such, for a correctly constructed transaction, we MUST get :math:`\mathsf{(\sum_{j=m+1}^{n} v_j^{net}) = 0}`, and thus be left with :math:`\mathsf{\sum_{j=m+1}^{n} rcv_{j}^{net}}\mathcal{R}^{\mathsf{Orchard}}` in the expression. If :math:`m=n` (resp. :math:`m=0`), i.e. all Actions relate to ZEC (resp. Custom Assets), then :math:`m+1>n` (resp. :math:`1>m`), and thus the sum :math:`\sum_{j=m+1}^{n}` (resp. :math:`\sum_{i=1}^{m}`) returns the identity element of the group. -So, the main reason why no changes to the Orchard process are needed is that no Custom Assets can be unshielded, so all Custom Assets are contained within the shielded pool. This means that the net balance of the input and output values is zero, with only one Asset of value balance published, that of ZEC, :math:`\mathsf{v^{balanceOrchard}}`. No net amount of any other Asset will be revealed, and the number of Assets in the transaction is also hidden. The only exception to this is in the case that an Asset is *burnt*, as we will see below in the `burn mechanism`_. +Thus, the main reason why no changes to the Orchard process are needed is that no Custom Assets can be unshielded within a regular transaction (as opposed to a *burn*, covered below in the `burn mechanism`_). All Custom Assets are contained within the shielded pool. This means that the net balance of the input and output values is zero, with only one value balance published, which corresponds to the ZEC value balance :math:`\mathsf{v^{balanceOrchard}}`. No net amount of any other Asset will be revealed, and the number of Assets in the transaction is also hidden. As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values only sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. From 33b23d074fe1c45ac9ca5441781cd4a08ab7fe0e Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:55:50 +0000 Subject: [PATCH 23/43] Guidelines to wallets regarding representing Assets to clients (#32) This adds to the specification to provide wallets instructions on displaying Asset information to users in an unambiguous way. This addresses [this comment](https://github.com/zcash/zips/pull/680#discussion_r1147019628). --- zip-0226.rst | 4 ---- zip-0227.rst | 10 ++++++++++ 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index a15d413db..9f115256b 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -497,10 +497,6 @@ Security and Privacy Considerations - The notes generated via the ZSA protocol are different from those generated via the Orchard protocol. As with any protocol upgrade, it will be possible to distinguish between notes generated by each protocol. However, all ZEC notes will be fully spendable with the ZSA protocol transaction structure due to the built-in backward compatibility. - When including new Assets we would like to maintain the amount and identifiers of Assets private, which is achieved with the design. - We prevent a potential malleability attack on the Asset Identifier by ensuring the output notes receive an Asset Base that exists on the global state. -- Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are the use of a petname system or a list of well-known Assets. - - - One proposal for a petname system for the zcashd wallet is the use of an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. - Other Considerations ==================== diff --git a/zip-0227.rst b/zip-0227.rst index 7d2601a1c..9b730dae6 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -180,6 +180,11 @@ The relations between the Asset Identifier, Asset Digest, and Asset Base are sho **Note:** To keep notations light and concise, we may omit :math:`\mathsf{AssetId}` (resp. :math:`\mathsf{Protocol}`) in the subscript (resp. superscript) when the Asset Identifier (resp. Protocol) is clear from the context. +Wallets MUST NOT display just the :math:`\mathsf{asset\_desc}` string to their users as the name of the Asset. Some possible alternatives include: + +- Wallets could allow clients to provide an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers via a petname system. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. +- The Asset Digest could be used as a more compact bytestring to uniquely determine an Asset, and wallets could support clients scanning QR codes to load Asset information into their wallets. + Specification: Global Issuance State ==================================== @@ -509,6 +514,11 @@ In the case that the transaction has no Orchard Actions, ``issuance_auth_digest` Security and Privacy Considerations =================================== +Displaying Asset Identifier information to users +------------------------------------------------ + +Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are provided in the `Specification: Asset Identifier`_ section. + Issuance Key Compromise ----------------------- From c70e0fd92bb347c8c0306d781ead724d948d789b Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:56:12 +0000 Subject: [PATCH 24/43] Adding explicit assumption for canonical encodings for the Asset Base. (#33) This addresses [this comment](https://github.com/zcash/zips/pull/680#discussion_r1268669667). --- zip-0226.rst | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/zip-0226.rst b/zip-0226.rst index 9f115256b..14cd653d5 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -90,7 +90,9 @@ where - :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid non-bottom group element that is not the identity. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. -Specifically, we define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: +Note that the above assumes a canonical encoding, which is true for the Pallas group, but may not hold for future shielded protocols. + +We define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: .. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \{0 .. 2^{\ell_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P}* \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Output} From 28832be8f00e63ee8b35d66f422cdd852de9fe57 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:56:38 +0000 Subject: [PATCH 25/43] Burn Mechanism Rearrangement (#35) This rearranges the positioning of the burn mechanism in order to remove duplication of material between the burn mechanism section and the value balance verification section. There is also some simplification of the naming convention for the Asset Base variable. --- zip-0226.rst | 131 +++++++++++-------------- zip-0227-asset-identifier-relation.png | Bin 44943 -> 38462 bytes zip-0227-asset-identifier-relation.svg | 17 ++-- zip-0227.rst | 17 ++-- 4 files changed, 75 insertions(+), 90 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 14cd653d5..2e4fd5417 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -49,16 +49,16 @@ This ZIP builds on the issuance mechanism introduced in ZIP 227 [#zip-0227]_. Overview ======== In order to be able to represent different Assets, we need to define a data field that uniquely represents the Asset in question, which we call the Asset Identifier :math:`\mathsf{AssetId}`. -This Asset Identifier maps to an Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` that is stored in Orchard-based ZSA notes. +This Asset Identifier maps to an Asset Base :math:`\mathsf{AssetBase}` that is stored in Orchard-based ZSA notes. These terms are formally defined in ZIP 227 [#zip-0227]_. The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-binding]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. As was initially proposed by Jack Grigg and Daira Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}`, of the *net value* in an Orchard Action. -Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point :math:`\mathcal{V}^\mathsf{Orchard}` in the value commitment [#protocol-concretevaluecommit]_. This ensures (1) that the input and output notes are of the same :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature. +Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same Asset Base is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point in the value commitment [#protocol-concretevaluecommit]_. This ensures (1) that the input and output notes are of the same Asset Base, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature. -In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the output note of that Split Action is the output of a valid :math:`\mathsf{ZSAValueBase^{Orchard}}` computation defined in ZIP 227 [#zip-0227]_. +In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}` of the output note of that Split Action is the output of a valid :math:`\mathsf{ZSAValueBase}` computation defined in ZIP 227 [#zip-0227]_. Finally, in this ZIP we also describe the *burn* mechanism, which is a direct extension of the transfer mechanism. The burn process uses a similar mechanism to what is used in Orchard to unshield ZEC, by using the :math:`\mathsf{valueBalance}` of the Asset in question. Burning Assets is useful for many purposes, including bridging of Wrapped Assets and removing supply of Assets. @@ -70,9 +70,9 @@ Most of the protocol is kept the same as the Orchard protocol released with NU5, Asset Identifiers ----------------- -For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` for the Orchard-based ZSA protocol) are derived as defined in ZIP 227 [#zip-0227]_. +For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}`) are derived as defined in ZIP 227 [#zip-0227]_. -This :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` will be the base point of the value commitment for the specific Custom Asset. Note that the :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}` of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. +This Asset Base will be the base point of the value commitment for the specific Custom Asset. Note that the Asset Base of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. Rationale for Asset Identifiers ``````````````````````````````` @@ -85,10 +85,10 @@ Note Structure & Commitment Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. :math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}*`. -A ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}}})`, +An Orchard ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}})`, where -- :math:`\mathsf{AssetBase}^{\mathsf{Orchard}} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid non-bottom group element that is not the identity. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase}^{\mathsf{Orchard}})`. +- :math:`\mathsf{AssetBase} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid non-bottom group element that is not the identity. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase})`. Note that the above assumes a canonical encoding, which is true for the Pallas group, but may not hold for future shielded protocols. @@ -100,9 +100,9 @@ where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for t This note commitment scheme is instantiated using the Sinsemilla Commitment [#protocol-concretesinsemillacommit]_ as follows: .. math:: \begin{align} - \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} + \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase})} :=\begin{cases} - \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase}^{\mathsf{Orchard}} = \mathcal{V}^{\mathsf{Orchard}} \\ + \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ \mathsf{cm}_{\mathsf{ZSA}} &\text{otherwise} \end{cases} \end{align} @@ -133,26 +133,26 @@ As we will see, the nested structure of the Sinsemilla-based commitment [#protoc The note commitment output is still indistinguishable from the original Orchard ZEC note commitments, by definition of the Sinsemilla hash function [#protocol-concretesinsemillahash]_. ZSA note commitments will therefore be added to the same Orchard Note Commitment Tree. In essence, we have: -.. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, \mathsf{AssetBase}^{\mathsf{Orchard}})} \in \mathsf{NoteCommit^{Orchard}.Output} +.. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, \mathsf{AssetBase})} \in \mathsf{NoteCommit^{Orchard}.Output} This definition can be viewed as a generalization of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes. Value Commitment ---------------- -In the case of the ZSA protocol, the value of different Asset Identifiers in a given transaction will be committed using a **different value base point**. The value commitment becomes: +In the case of the Orchard-based ZSA protocol, the value of different Asset Identifiers in a given transaction will be committed using a **different value base point**. The value commitment becomes: -.. math:: \mathsf{cv^{net}:=ValueCommit^{OrchardZSA}_{rcv}(v^{net}_{AssetId}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}:= \mathsf{[v^{net}_{AssetId}]}\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}} + [\mathsf{rcv}]\mathcal{R}^{\mathsf{Orchard}} +.. math:: \mathsf{cv^{net}:=ValueCommit^{OrchardZSA}_{rcv}(\mathsf{AssetBase}_{\mathsf{AssetId}}, v^{net}_{AssetId})}:= \mathsf{[v^{net}_{AssetId}]}\mathsf{AssetBase}_{\mathsf{AssetId}} + [\mathsf{rcv}]\mathcal{R}^{\mathsf{Orchard}} where :math:`\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId} - v^{new}_{AssetId}}` such that :math:`\mathsf{v^{old}_{AssetId}}` and :math:`\mathsf{v^{new}_{AssetId}}` are the values of the old and new notes of Asset Identifier :math:`\mathsf{AssetId}` respectively, .. _`asset base`: -:math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}` is defined in ZIP 227 [#zip-0227]_, and +:math:`\mathsf{AssetBase}_{\mathsf{AssetId}}` is defined in ZIP 227 [#zip-0227]_, and :math:`\mathcal{R}^{\mathsf{Orchard}}:=\mathsf{GroupHash^{\mathbb{P}}}\texttt{("z.cash:Orchard-cv", "r")}`, as in the Orchard protocol. -We define :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{ZEC}} :=\mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. As such :math:`\mathsf{ValueCommit^{Orchard}_{rcv}(v)}` as defined in [#zip-0224]_ is used as :math:`\mathsf{ValueCommit^{OrchardZSA}_{rcv}(v, \mathcal{V}^{\mathsf{Orchard}})}` here. +For ZEC, we define :math:`\mathsf{AssetBase}_{\mathsf{AssetId}} :=\mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. As such :math:`\mathsf{ValueCommit^{Orchard}_{rcv}(v)}` as defined in [#zip-0224]_ is used as :math:`\mathsf{ValueCommit^{OrchardZSA}_{rcv}(\mathcal{V}^{\mathsf{Orchard}}, v)}` here. Rationale for Value Commitment `````````````````````````````` @@ -161,35 +161,63 @@ The Orchard Protocol uses a Homomorphic Pedersen Commitment [#protocol-concretev The use of different value base points for different Assets enables the final balance of the transaction to be securely computed, such that each Asset Identifier is balanced independently, which is required as different Assets are not meant to be mutually fungible. +Burn Mechanism +-------------- + +The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. + +The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). + +For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` vector the tuple :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. + +.. math:: \mathsf{assetBurn} = \{ (\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})\ |\ \forall\ \mathsf{AssetBase}_{\mathsf{AssetId}}\ \textit{s.t.}\ \mathsf{v_{AssetId}} \neq 0 \} + +We denote by :math:`L` the cardinality of the :math:`\mathsf{assetBurn}` set. + +Additional Consensus Rules +`````````````````````````` + +1. We require that for every :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}}) \in \mathsf{assetBurn}\ ,\ \mathsf{AssetBase}_{\mathsf{AssetId}} \neq \mathcal{V}^{\mathsf{Orchard}}`. That is, ZEC or TAZ is not allowed to be burnt. +2. We require that for every :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}}) \in \mathsf{assetBurn}\ ,\ \mathsf{v_{AssetId}} \neq 0`. +3. We require that there be no duplication of Custom Assets in the :math:`\mathsf{assetBurn}` set. That is, every :math:`\mathsf{AssetBase}_{\mathsf{AssetId}}` has at most one entry in :math:`\mathsf{assetBurn}`. + +**Note:** Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets. Value Balance Verification -------------------------- -In order to verify the balance of the different Assets, the verifier MUST perform exactly the same process as for the Orchard protocol [#protocol-binding]_. +In order to verify the balance of the different Assets, the verifier MUST perform a similar process as for the Orchard protocol [#protocol-binding]_, with the addition of the burn information. For a total of :math:`n` Actions in a transfer, the prover MUST still sign the SIGHASH transaction hash using the binding signature key :math:`\mathsf{bsk} = \sum_{i=1}^{n} \mathsf{rcv}_{i}`. -The verifier MUST compute +The verifier MUST compute the value balance verification equation: -.. math:: \mathsf{bvk} =(\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}(v^{balanceOrchard}, \mathcal{V}^{\mathsf{Orchard}})} +.. math:: \mathsf{bvk} =(\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}(\mathcal{V}^{\mathsf{Orchard}}, v^{balanceOrchard})} - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{AssetBase}, \mathsf{v}) After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the binding signature on the SIGHASH transaction hash. + Rationale for Value Balance Verification ```````````````````````````````````````` -We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of clarity) between Actions related to ZEC and Actions related to Custom Assets. We assume :math:`m` Actions related to ZEC and :math:`n-m` Actions related to Custom Assets, where :math:`m \in [0,n]`. Furthermore, we assume for simplicity that given a tuple of :math:`n` Actions in a transfer, the :math:`m` Actions related to ZEC are first (in practice Actions could be in whatever order). +We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of clarity) between Actions related to ZEC and Actions related to Custom Assets. +We denote by :math:`S_{\mathsf{ZEC}} \subseteq [1,n]` the set of indices of Actions that are related to ZEC, and by :math:`S_{\mathsf{CA}} = [1,n] \setminus S_{\mathsf{ZEC}}` the set of indices of Actions that are related to Custom Assets. -The value balance verification is equivalent to: +The right hand side of the value balance verification equation can be expanded to: -.. math:: \mathsf{bvk} = (\sum_{i=1}^{m} \mathsf{cv^{net}}_{i}) + (\sum_{j=m+1}^{n} \mathsf{cv^{net}}_j) - \mathsf{ValueCommit_0^{OrchardZSA}(v^{balanceOrchard}, \mathcal{V}^{Orchard})} +.. math:: ((\sum_{i \in S_{\mathsf{ZEC}}} \mathsf{cv^{net}}_{i}) + (\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv^{net}}_{j})) - ([\mathsf{v^{balanceOrchard}}]\mathcal{V}^{\mathsf{Orchard}} + [0]\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\mathsf{AssetBase} + [0]\mathcal{R}^{\mathsf{Orchard}}) -This equation contains the balance check of the Orchard protocol [#protocol-binding]_. With ZSA, transfer Actions for Custom Assets MUST also be balanced across asset bases. As such, for a correctly constructed transaction, we MUST get :math:`\mathsf{(\sum_{j=m+1}^{n} v_j^{net}) = 0}`, and thus be left with :math:`\mathsf{\sum_{j=m+1}^{n} rcv_{j}^{net}}\mathcal{R}^{\mathsf{Orchard}}` in the expression. If :math:`m=n` (resp. :math:`m=0`), i.e. all Actions relate to ZEC (resp. Custom Assets), then :math:`m+1>n` (resp. :math:`1>m`), and thus the sum :math:`\sum_{j=m+1}^{n}` (resp. :math:`\sum_{i=1}^{m}`) returns the identity element of the group. +This equation contains the balance check of the Orchard protocol [#protocol-binding]_. +With ZSA, transfer Actions for Custom Assets must also be balanced across Asset Bases. +All Custom Assets are contained within the shielded pool, and cannot be unshielded via a regular transfer. +Custom Assets can be burnt, the mechanism for which reveals the amount and identifier of the Asset being burnt, within the :math:`\mathsf{assetBurn}` set. +As such, for a correctly constructed transaction, we will get :math:`\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv}_j^{\mathsf{net}} - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\mathsf{AssetBase} = \mathsf{\sum_{j \in S_{\mathsf{CA}}} rcv_{j}^{net}}\mathcal{R}^{\mathsf{Orchard}}`. -Thus, the main reason why no changes to the Orchard process are needed is that no Custom Assets can be unshielded within a regular transaction (as opposed to a *burn*, covered below in the `burn mechanism`_). All Custom Assets are contained within the shielded pool. This means that the net balance of the input and output values is zero, with only one value balance published, which corresponds to the ZEC value balance :math:`\mathsf{v^{balanceOrchard}}`. No net amount of any other Asset will be revealed, and the number of Assets in the transaction is also hidden. +When the Asset is not being burnt, the net balance of the input and output values is zero, and there will be no addition to the :math:`\mathsf{assetBurn}` vector. +Therefore, the relationship between :math:`\mathsf{bvk}` and :math:`\mathsf{bsk}` will hold if and only if, per Custom Asset, the sum of the net values of the relevant Actions equals the corresponding :math:`\mathsf{v}_k` value (or equals :math:`0` if that Asset is not in the :math:`\mathsf{assetBurn}` set), and for ZEC, the sum of the net values of the relevant Actions equals the :math:`\mathsf{v^{balanceOrchard}}` value. -As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values only sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. +As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values must sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. Split Notes @@ -241,9 +269,9 @@ Asset Base Equality The following constraints must be added to ensure that the input and output note are of the same :math:`\mathsf{AssetBase}`: -- The Asset Base, :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`, for the note is witnessed once, as an auxiliary input. -- In the Old note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. -- In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new}, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}`. +- The Asset Base, :math:`\mathsf{AssetBase}_{\mathsf{AssetId}}`, for the note is witnessed once, as an auxiliary input. +- In the Old note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old}, \mathsf{AssetBase}_{\mathsf{AssetId}})}`. +- In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new}, \mathsf{AssetBase}_{\mathsf{AssetId}})}`. To make the evaluation of the note commitment easier, we add a boolean :math:`\mathsf{is\_native\_asset}` as an auxiliary witness. We also add some constraints to verify that this variable is activated (i.e. :math:`\mathsf{is\_native\_asset} = 1`) if the Asset Base is equal to :math:`\mathcal{V}^\mathsf{Orchard}` and this variable is not activated (i.e. :math:`\mathsf{is\_native\_asset} = 0`) if the Asset Base is not equal to :math:`\mathcal{V}^\mathsf{Orchard}`. @@ -253,7 +281,7 @@ Value Commitment Correctness The following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base: - The fixed-base multiplication constraints between the value and the value base point of the value commitment, :math:`\mathsf{cv}`, is replaced with a variable-base multiplication between the two. -- The witness to the value base point (as defined in the `asset base`_ equation) is the auxiliary input :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}}`. +- The witness to the value base point (as defined in the `asset base`_ equation) is the auxiliary input :math:`\mathsf{AssetBase}_{\mathsf{AssetId}}`. Asset Identifier Consistency for Split Actions `````````````````````````````````````````````` @@ -261,7 +289,7 @@ Asset Identifier Consistency for Split Actions Senders must not be able to change the Asset Base for the output note in a Split Action. We do this via the following constraints: - The Value Commitment Integrity should be changed: - - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(v’ - v^new, \mathsf{AssetBase}^{\mathsf{Orchard}}_{\mathsf{AssetId}})}` + - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(\mathsf{AssetBase}_{\mathsf{AssetId}}, v’ - v^new)}` - Add a boolean :math:`\mathsf{split\_flag}` variable as an auxiliary witness. This variable is to be activated :math:`\mathsf{split\_flag} = 1` if the Action in question has a Split Input and :math:`\mathsf{split\_flag} = 0` if the Action is actually spending an input note: - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{v}' = 0` otherwise constrain :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{is\_native\_asset} = 0` because split notes are only available for Custom Assets. @@ -275,51 +303,6 @@ Backwards Compatibility with ZEC Notes The input note in the old note commitment integrity check must either include an Asset Base (ZSA note) or not (pre-ZSA Orchard note). If the note is a pre-ZSA Orchard note, the note commitment is computed in the original Orchard fashion [#protocol-abstractcommit]_. If the note is a ZSA note, the note commitment is computed as defined in the `Note Structure & Commitment`_ section. -Burn Mechanism -============== - -The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. - -The sender includes a :math:`\mathsf{v^{AssetBase}}` variable for every Asset Identifier that is being burnt. As we will show in the `ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset. - -For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` vector the tuple :math:`(\mathsf{AssetBase},\mathsf{v^{AssetBase}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. - -.. math:: \mathsf{assetBurn} = \{ (\mathsf{AssetBase},\mathsf{v^{AssetBase}})\ |\ \forall\ \mathsf{AssetBase}\ \textit{s.t.}\ \mathsf{v^{AssetBase}} \neq 0 \} - -We denote by :math:`L` the cardinality of the :math:`\mathsf{assetBurn}` set. - -The value balances for each Asset Identifier in :math:`\mathsf{assetBurn}` represents the amount of that Asset that is being burnt. In the case of ZEC, the value balance represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). - -The validator needs to verify the Balance and Binding Signature by adding the value balances for all Assets, as committed using their respective :math:`\mathsf{AssetBase}` as the value base point of the Pedersen Commitment. - -This is done as follows: - -.. math:: \mathsf{bvk} = (\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{v^{balanceOrchard}}, \mathcal{V}^{\mathsf{Orchard}}) - \sum_{k=1}^{L} \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{v}_{k}, \mathsf{AssetBase}_{k}) - -After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the binding signature on the SIGHASH transaction hash. - -In the case that the balance of all the Action values related to a specific Asset will be zero, there will be no value added to the vector. This way, neither the number of Assets nor their Asset Identifiers will be revealed, except in the case that an Asset is burnt. - -Burn Mechanism Consensus Rules ------------------------------- - -1. We require that :math:`\forall (\mathsf{AssetBase},\mathsf{v^{AssetBase}}) \in \mathsf{assetBurn}\ ,\ \mathsf{AssetBase} \neq \mathcal{V}^{\mathsf{Orchard}}`. That is, ZEC or TAZ is not allowed to be burnt. -2. We require that for every :math:`\forall (\mathsf{AssetBase},\mathsf{v^{AssetBase}}) \in \mathsf{assetBurn}\ ,\ \mathsf{v^{AssetBase}} \neq 0`. -3. We require that there be no duplication of Custom Assets in the :math:`\mathsf{assetBurn}` set. That is, every :math:`\mathsf{AssetBase}` has at most one entry in :math:`\mathsf{assetBurn}`. - -**Note:** Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets. - -Rationale for Burn Mechanism -```````````````````````````` - -As for the value balance verification, we assume :math:`n` Actions, :math:`m` of which are related to ZEC and the remaining :math:`n-m` Actions related to Custom Assets. - -The burn mechanism verification is equivalent to: - -.. math:: \mathsf{bvk} = ((\sum_{i=1}^{m} \mathsf{cv^{net}}_{i}) + (\sum_{j=m+1}^{n} \mathsf{cv^{net}}_{j})) - ([\mathsf{v^{balanceOrchard}}]\mathcal{V}^{\mathsf{Orchard}} + [0]\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{k=1}^{L} [\mathsf{v}_{k}]\mathsf{AssetBase}_{k} + [0]\mathcal{R}^{\mathsf{Orchard}}) - -The relationship between :math:`\mathsf{bvk}` and :math:`\mathsf{bsk}` will hold only if the sum of the net values of the Actions equals the sum of :math:`\mathsf{v^{balanceOrchard}}` and the :math:`\mathsf{v}_k` values, across base points (i.e. Asset Base). - ZSA Transaction Structure ========================= @@ -401,7 +384,7 @@ A ZSA Asset Burn description is encoded in a transaction as an instance of an `` +-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ | Bytes | Name | Data Type | Description | +=======+===============+=============================+===========================================================================================================================+ -| 32 | ``AssetBase`` | ``byte[32]`` | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. | +| 32 | ``AssetBase`` | ``byte[32]`` | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}`. | +-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ | 8 | ``valueBurn`` | :math:`\{1 .. 2^{64} - 1\}` | The amount being burnt. | +-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ diff --git a/zip-0227-asset-identifier-relation.png b/zip-0227-asset-identifier-relation.png index d073f7aa80a0ddecd60084dc28a7502c111470b5..064e519600ba816498c8813043db229e9db4af0b 100644 GIT binary patch literal 38462 zcmXtfbzIcV8!hn?k}4vlARyf#AgM?$4bt7+-5^MZbcevw-Q6MG-QC@Nhu^*T55>Z7##&41qKENT~tIs76t}U5&T;p84>(FGF%l1e!Q|0QMQGFAt-+N z0~?}ldjnp?vlCRZle09ibJVuchjDatq&K!Owbj+O(xr^`@enqpouzfzbwY5-h@z*GmUn>*A*>u z44u&pRyUi$rV&hxcJ^#t8#;m$Q)k@1zdgC-a5T6gj9E-cusyDWjI*K;K%?PT&?iLi zPhm~q$zU8?u_;rl={h?;;|0KFc;kM0UyJ4omow%eX_DwLZtw<$SO9|(dH};9+cNI% 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--git a/zip-0227-asset-identifier-relation.svg b/zip-0227-asset-identifier-relation.svg index de18d9914..670ed1784 100644 --- a/zip-0227-asset-identifier-relation.svg +++ b/zip-0227-asset-identifier-relation.svg @@ -26,15 +26,15 @@ inkscape:pageopacity="0.0" inkscape:pageshadow="2" inkscape:zoom="0.80392436" - inkscape:cx="147.40193" - inkscape:cy="90.804563" + inkscape:cx="261.84055" + inkscape:cy="53.487619" inkscape:document-units="px" - inkscape:current-layer="layer1" + inkscape:current-layer="g481" showgrid="false" inkscape:window-width="1158" inkscape:window-height="916" - inkscape:window-x="2102" - inkscape:window-y="136" + inkscape:window-x="1893" + inkscape:window-y="81" inkscape:window-maximized="0" inkscape:showpageshadow="2" inkscape:pagecheckerboard="0" @@ -177,7 +177,10 @@ inkscape:groupmode="layer" inkscape:label="Layer 1" transform="translate(256.28448,-836.58665)">Protocol`_ .. [#zip-0244-sigdigest] `ZIP 244: Transaction Identifier Non-Malleability: Signature Digest `_ .. [#zip-0244-authcommitment] `ZIP 244: Transaction Identifier Non-Malleability: Authorizing Data Commitment `_ -.. [#zip-0317b] `ZIP 317b: ZSA Extension Proportional Fee Mechanism `_ +.. [#zip-0317b] `ZIP 317: Proportional Transfer Fee Mechanism `_ .. [#zip-0032] `ZIP 32: Shielded Hierarchical Deterministic Wallets `_ .. [#zip-0032-orchard-master] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard master key generation `_ .. [#zip-0032-orchard-child-key-derivation] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard child key derivation `_ From 8753f711ba871269222754591696908f379eb2a0 Mon Sep 17 00:00:00 2001 From: Constance Beguier Date: Wed, 7 Feb 2024 14:56:55 +0000 Subject: [PATCH 26/43] Add enable_zsa flag (#37) This PR adds enable_zsa flag into ZIP 226. --- zip-0226.rst | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/zip-0226.rst b/zip-0226.rst index 2e4fd5417..880094172 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -60,6 +60,8 @@ Because in a single transaction all value commitments are balanced, there must b In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}` of the output note of that Split Action is the output of a valid :math:`\mathsf{ZSAValueBase}` computation defined in ZIP 227 [#zip-0227]_. +We include the ability to pause the ZSA functionality, via a :math:`\mathsf{enableZSA}` boolean flag. When this flag is set to false, it is not possible to perform transactions involving Custom Assets (the circuit will fail). + Finally, in this ZIP we also describe the *burn* mechanism, which is a direct extension of the transfer mechanism. The burn process uses a similar mechanism to what is used in Orchard to unshield ZEC, by using the :math:`\mathsf{valueBalance}` of the Asset in question. Burning Assets is useful for many purposes, including bridging of Wrapped Assets and removing supply of Assets. Specification @@ -275,6 +277,13 @@ The following constraints must be added to ensure that the input and output note To make the evaluation of the note commitment easier, we add a boolean :math:`\mathsf{is\_native\_asset}` as an auxiliary witness. We also add some constraints to verify that this variable is activated (i.e. :math:`\mathsf{is\_native\_asset} = 1`) if the Asset Base is equal to :math:`\mathcal{V}^\mathsf{Orchard}` and this variable is not activated (i.e. :math:`\mathsf{is\_native\_asset} = 0`) if the Asset Base is not equal to :math:`\mathcal{V}^\mathsf{Orchard}`. +The :math:`\mathsf{enableZSA}` Flag +````````````````````````````````````` + +The following constraints must be added to disable transactions involving Custom Assets when the :math:`\mathsf{enableZSA}` flag is set to false: + +- if :math:`\mathsf{enableZSA}` is not activated (i.e. :math:`\mathsf{enableZSA} = 0`), then constrain :math:`\mathsf{is\_native\_asset} = 1`, since the :math:`\mathsf{AsssetBase}` must be equal to the native asset. + Value Commitment Correctness ```````````````````````````` From 57aaf2948b58b212fc6da5a535d2b608d6a8e8e4 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 14:57:27 +0000 Subject: [PATCH 27/43] Renaming `idk` to `imk` throughout ZIP 227 (#41) This is a consistent renaming of the issuance derivation key to call it the issuance master key. --- zip-0227.rst | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/zip-0227.rst b/zip-0227.rst index caaa919f7..02932de5e 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -83,7 +83,7 @@ Specification: Issuance Keys and Issuance Authorization Signature Scheme The ZSA Protocol adds the following three keys to the key components [#protocol-addressesandkeys]_: -1. The issuance derivation key, denoted as :math:`\mathsf{idk}`, as the name suggests, is the key that is used to derive the other two keys. +1. The issuance master key, denoted as :math:`\mathsf{imk}`, is the key that is used to derive the other two keys. 2. The issuance authorizing key is the key that is used to sign the issuance transaction, and is denoted as :math:`\mathsf{isk}`. This key is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. @@ -108,35 +108,35 @@ Specifically, we instantiate :math:`\mathsf{IssueAuthSig}` as :math:`\mathsf{Red Issuance Key Derivation ----------------------- -The issuance derivation key is generated by choosing a bit sequence uniformly at random from :math:`\mathbb{B}^{\mathbb{Y}[32]}`, like the Orchard spending key [#protocol-orchardkeycomponents]_. +The issuance master key is generated by choosing a bit sequence uniformly at random from :math:`\mathbb{B}^{\mathbb{Y}[32]}`, like the Orchard spending key [#protocol-orchardkeycomponents]_. -Issuance derivation key generation for hierarchical deterministic wallets -````````````````````````````````````````````````````````````````````````` +Issuance master key generation for hierarchical deterministic wallets +````````````````````````````````````````````````````````````````````` -The issuance derivation key is generated using the Orchard master key derivation procedure defined in ZIP 32 [#zip-0032-orchard-master]_. We reuse the functions defined there in what follows in this section. +The issuance master key is generated using the Orchard master key derivation procedure defined in ZIP 32 [#zip-0032-orchard-master]_. We reuse the functions defined there in what follows in this section. Let :math:`S` be a seed byte sequence of a chosen length, which MUST be at least 32 and at most 252 bytes. We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssue_V1"}, S)`. -As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance derivation key. +As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance master key. We reuse the :math:`\mathsf{CDKsk}` function for Orchard child key derivation from ZIP 32. -We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance derivation key path as :math:`m_\mathsf{Issuance} / purpose' / coin\_type' / account'`. We fix the path levels as follows: +We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance master key path as :math:`m_\mathsf{Issuance} / purpose' / coin\_type' / account'`. We fix the path levels as follows: - :math:`purpose`: a constant set to :math:`227` (i.e. :math:`\texttt{0xe3}`). :math:`purpose'` is thus :math:`227'` (or :math:`\texttt{0x800000e3}`) following the BIP 43 recommendation. - :math:`coin\_type`: Defined as in ZIP 32 [#zip-0032-key-path-levels]_. - :math:`account`: fixed to index :math:`0`. -From the generated :math:`(\mathsf{sk}, \mathsf{c})`, we set the issuance derivation key to be :math:`\mathsf{idk} := \mathsf{sk}`. +From the generated :math:`(\mathsf{sk}, \mathsf{c})`, we set the issuance master key to be :math:`\mathsf{imk} := \mathsf{sk}`. Derivation of issuance authorizing key and issuance validating key `````````````````````````````````````````````````````````````````` -The issuance authorizing key and issuance validating key are derived from the issuance derivation key in an analogous manner to the derivation of the Orchard spend authorizing key and Orchard spend validating key from the Orchard spending key [#protocol-orchardkeycomponents]_, as described below. +The issuance authorizing key and issuance validating key are derived from the issuance master key in an analogous manner to the derivation of the Orchard spend authorizing key and Orchard spend validating key from the Orchard spending key [#protocol-orchardkeycomponents]_, as described below. -- The issuance authorizing key is derived from the issuance derivation key, :math:`\mathsf{idk}`, as a private signature key. The function :math:`\mathsf{PRF^{expand}_{idk}}` is as defined in the Zcash protocol specification [#protocol-abstractprfs]_: +- The issuance authorizing key is derived from the issuance master key, :math:`\mathsf{imk}`, as a private signature key. The function :math:`\mathsf{PRF^{expand}_{imk}}` is as defined in the Zcash protocol specification [#protocol-abstractprfs]_: -.. math:: \mathsf{isk} := \mathsf{ToScalar}^{\mathsf{Orchard}}(︀ \mathsf{PRF^{expand}_{idk}}([\mathtt{0x0a}]) ) +.. math:: \mathsf{isk} := \mathsf{ToScalar}^{\mathsf{Orchard}}(︀ \mathsf{PRF^{expand}_{imk}}([\mathtt{0x0a}]) ) - The issuance validating key is derived from the issuance authorizing key, :math:`\mathsf{isk}`, as a public verification key: From 9b1a0c24e584869fdc9cf20effc4f947b213cb1d Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 15:02:21 +0000 Subject: [PATCH 28/43] Move the updated transaction structure from ZIP 226 to ZIP 230 (#42) This removes the transaction structure fields from ZIP 226 in favour of adding them to ZIP 230, for the v6 Transaction Format. Co-authored-by: Deirdre Connolly Co-authored-by: Daira-Emma Hopwood Co-authored-by: str4d Co-authored-by: Paul Co-authored-by: Antoine Rondelet Co-authored-by: Constance Beguier --- zip-0226.rst | 89 +------------- zip-0230.rst | 339 ++++++++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 343 insertions(+), 85 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 880094172..144ded774 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -168,7 +168,7 @@ Burn Mechanism The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. -The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). +The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `Orchard-ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` vector the tuple :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. @@ -312,91 +312,11 @@ Backwards Compatibility with ZEC Notes The input note in the old note commitment integrity check must either include an Asset Base (ZSA note) or not (pre-ZSA Orchard note). If the note is a pre-ZSA Orchard note, the note commitment is computed in the original Orchard fashion [#protocol-abstractcommit]_. If the note is a ZSA note, the note commitment is computed as defined in the `Note Structure & Commitment`_ section. -ZSA Transaction Structure -========================= - -The transaction format closely follows the version 5 transaction format described in the Zcash specification [#protocol-transactionstructure]_. -The Common Transaction Fields, Transparent Transaction Fields, and Sapling Transaction Fields remain the same as in the version 5 transaction format. -We make some modifications to the Orchard Transaction Fields and the Orchard Action Descriptions, which we detail in the first and second tables below respectively. -We also add ZSA Burn Fields to the transaction format, which we detail in the first table below. -For brevity, we omit the descriptions from the table below unless they differ from the descriptions in §7.1 of the Zcash specification [#protocol-transactionstructure]_. - - -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -| Bytes | Name | Data Type | Description | -+=============================+==========================+===========================================+=====================================================================+ -| **Orchard Transaction Fields** | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``varies`` |``nActionsOrchard`` |``compactSize`` | | -| | | | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``852 * nActionsOrchard`` |``vActionsOrchard`` |``ZSAOrchardAction[nActionsOrchard]`` |A sequence of ZSA Orchard Action descriptions, encoded per | -| | | |the `ZSA Orchard Action Description Encoding`_. **[UPDATED FOR ZSA]**| -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``1`` |``flagsOrchard`` |``byte`` | | -| | | | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``8`` |``valueBalanceOrchard`` |``int64`` | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``32`` |``anchorOrchard`` |``byte[32]`` | | -| | | | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``varies`` |``sizeProofsOrchard`` |``compactSize`` | | -| | | | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``sizeProofsOrchard`` |``proofsOrchard`` |``byte[sizeProofsOrchard]`` | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``64 * nActionsOrchard`` |``vSpendAuthSigsOrchard`` |``byte[64 * nActionsOrchard]`` | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -|``64`` |``bindingSigOrchard`` |``byte[64]`` | | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -| **ZSA Burn Fields** | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -| ``varies`` | ``nAssetBurn`` | ``compactSize`` | The number of Assets burnt. | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -| ``40 * nAssetBurn`` | ``vAssetBurn`` | ``AssetBurn[nAssetBurn]`` | A sequence of Asset Burn descriptions, | -| | | | encoded per `ZSA Asset Burn Description`_. | -+-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ - -ZSA Orchard Action Description Encoding ---------------------------------------- - -The ZSA Orchard Action size differs from the Orchard Action size by 32 bytes. -This means that the size goes from 820 bytes in the Orchard Action to 852 bytes in the ZSA Orchard Action. -We omit the descriptions from the table below since they are identical to the descriptions in §7.5 of the Zcash specification [#protocol-actionencodingandconsensus]_. -A ZSA Orchard Action description is encoded in a transaction as an instance of an ``ZSAOrchardAction`` type: - -+-------+-------------------+---------------+----------------------+ -| Bytes | Name | Data Type | | -+=======+===================+===============+======================+ -| 32 | ``cv`` | ``byte[32]`` | | -+-------+-------------------+---------------+----------------------+ -| 32 | ``nullifier`` | ``byte[32]`` | | -+-------+-------------------+---------------+----------------------+ -| 32 | ``rk`` | ``byte[32]`` | | -+-------+-------------------+---------------+----------------------+ -| 32 | ``cmx`` | ``byte[32]`` | | -+-------+-------------------+---------------+----------------------+ -| 32 | ``ephemeralKey`` | ``byte[32]`` | | -+-------+-------------------+---------------+----------------------+ -| 612 | ``encCiphertext`` | ``byte[612]`` |**[UPDATED FOR ZSA]** | -+-------+-------------------+---------------+----------------------+ -| 80 | ``outCiphertext`` | ``byte[32]`` | | -+-------+-------------------+---------------+----------------------+ - - -ZSA Asset Burn Description --------------------------- +Orchard-ZSA Transaction Structure +================================= -A ZSA Asset Burn description is encoded in a transaction as an instance of an ``AssetBurn`` type: +The transaction format for v6 transactions is described in ZIP 230 [#zip-0230]_. -+-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ -| Bytes | Name | Data Type | Description | -+=======+===============+=============================+===========================================================================================================================+ -| 32 | ``AssetBase`` | ``byte[32]`` | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}`. | -+-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ -| 8 | ``valueBurn`` | :math:`\{1 .. 2^{64} - 1\}` | The amount being burnt. | -+-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ TxId Digest =========== @@ -536,6 +456,7 @@ References .. [#zip-0224] `ZIP 224: Orchard `_ .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ +.. [#zip-0230] `ZIP 230: Version 6 Transaction Format `_ .. [#zip-0227-assetidentifier] `ZIP 227: Issuance of Zcash Shielded Assets: Specification: Asset Identifier `_ .. [#zip-0227-txiddigest] `ZIP 227: Issuance of Zcash Shielded Assets: TxId Digest - Issuance `_ .. [#zip-0227-sigdigest] `ZIP 227: Issuance of Zcash Shielded Assets: Signature Digest `_ diff --git a/zip-0230.rst b/zip-0230.rst index 068267498..2ca7456db 100644 --- a/zip-0230.rst +++ b/zip-0230.rst @@ -6,9 +6,346 @@ Jack Grigg Sean Bowe Kris Nuttycombe + Pablo Kogan + Vivek Arte Original-Authors: Greg Pfeil Deirdre Connolly Credits: Ying Tong Lai - Status: Reserved + Status: Draft Category: Consensus + Created: 2023-04-18 + License: MIT Discussions-To: + + +Terminology +=========== + +The key words "MUST" and "MAY" in this document are to be interpreted as described in +RFC 2119. [#RFC2119]_ + +The character § is used when referring to sections of the Zcash Protocol Specification +[#protocol]_. + + +Abstract +======== + +This proposal defines a new Zcash peer-to-peer transaction format, which includes data that supports the Orchard-ZSA protocol and all Zcash Shielded Assets (ZSAs) related operations. The +new transaction format defines well-bounded regions of the serialized form to +serve each of the existing pools of funds, and adds and describes a new elements +containing ZSA-specific elements. + +This ZIP also depends upon and defines modifications to the computation of the values +**TxId Digest**, **Signature Digest**, and **Authorizing Data Commitment** defined by ZIP +244 [#zip-0244]_. + + +Motivation +========== + +The Orchard-ZSA protocol requires serialized data elements that are distinct from +any previous Zcash transaction. Since ZIP 244 was activated in NU5, the +v5 and later serialized transaction formats are not consensus-critical. +Thus, this ZIP defines format that can easily accommodate future extensions, +where elements or a given pool are kept separate. + + +Requirements +============ + +The new format must fully support the Orchard-ZSA protocol. + +The new format should lend itself to future extension or pruning to add or remove +value pools. + +The computation of the non-malleable transaction identifier hash must include all +newly incorporated elements except those that attest to transaction validity. + +The computation of the commitment to authorizing data for a transaction must include +all newly incorporated elements that attest to transaction validity. + + +Non-requirements +================ + +More general forms of extensibility, such as definining a key/value format that +allows for parsers that are unaware of some components, are not required. + + +Specification +============= + +All fields in this specification are encoded as little-endian. + +The Zcash transaction format for transaction version 6 is as follows: + +Transaction Format +------------------ + ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++====================================+==========================+========================================+===========================================================================+ +| **Common Transaction Fields** | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``4`` |``header`` |``uint32`` |Contains: | +| | | | * ``fOverwintered`` flag (bit 31, always set) | +| | | | * ``version`` (bits 30 .. 0) – transaction version. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``4`` |``nVersionGroupId`` |``uint32`` |Version group ID (nonzero). | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``4`` |``nConsensusBranchId`` |``uint32`` |Consensus branch ID (nonzero). | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``4`` |``lock_time`` |``uint32`` |Unix-epoch UTC time or block height, encoded as in Bitcoin. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``4`` |``nExpiryHeight`` |``uint32`` |A block height in the range {1 .. 499999999} after which | +| | | |the transaction will expire, or 0 to disable expiry. | +| | | |[ZIP-203] | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``8`` |``fee`` |``int64`` |The fee to be paid by this transaction, in zatoshis. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| **Transparent Transaction Fields** | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``tx_in_count`` |``compactSize`` |Number of transparent inputs in ``tx_in``. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``tx_in`` |``tx_in`` |Transparent inputs, encoded as in Bitcoin. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``tx_out_count`` |``compactSize`` |Number of transparent outputs in ``tx_out``. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``tx_out`` |``tx_out`` |Transparent outputs, encoded as in Bitcoin. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| **Sapling Transaction Fields** | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``nSpendsSapling`` |``compactSize`` |Number of Sapling Spend descriptions in ``vSpendsSapling``. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``96 * nSpendsSapling`` |``vSpendsSapling`` |``SpendDescriptionV6[nSpendsSapling]`` |A sequence of Sapling Spend descriptions, encoded per | +| | | |protocol §7.3 ‘Spend Description Encoding and Consensus’. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``nOutputsSapling`` |``compactSize`` |Number of Sapling Output Decriptions in ``vOutputsSapling``. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``756 * nOutputsSapling`` |``vOutputsSapling`` |``OutputDescriptionV6[nOutputsSapling]``|A sequence of Sapling Output descriptions, encoded per | +| | | |protocol §7.4 ‘Output Description Encoding and Consensus’. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``8`` |``valueBalanceSapling`` |``int64`` |The net value of Sapling Spends minus Outputs | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``32`` |``anchorSapling`` |``byte[32]`` |A root of the Sapling note commitment tree | +| | | |at some block height in the past. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``192 * nSpendsSapling`` |``vSpendProofsSapling`` |``byte[192 * nSpendsSapling]`` |Encodings of the zk-SNARK proofs for each Sapling Spend. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``64 * nSpendsSapling`` |``vSpendAuthSigsSapling`` |``byte[64 * nSpendsSapling]`` |Authorizing signatures for each Sapling Spend. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``192 * nOutputsSapling`` |``vOutputProofsSapling`` |``byte[192 * nOutputsSapling]`` |Encodings of the zk-SNARK proofs for each Sapling Output. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``64`` |``bindingSigSapling`` |``byte[64]`` |A Sapling binding signature on the SIGHASH transaction hash. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| **Orchard-ZSA Transaction Fields** | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``nActionsOrchard`` |``compactSize`` |The number of Orchard-ZSA Action descriptions in | +| | | |``vActionsOrchard``. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``852 * nActionsOrchard`` |``vActionsOrchard`` |``OrchardZsaAction[nActionsOrchard]`` |A sequence of Orchard-ZSA Action descriptions, encoded per | +| | | |the `Orchard-ZSA Action Description Encoding`. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``1`` |``flagsOrchard`` |``byte`` |An 8-bit value representing a set of flags. Ordered from LSB to MSB: | +| | | | * ``enableSpendsOrchard`` | +| | | | * ``enableOutputsOrchard`` | +| | | | * ``enableZSAs`` | +| | | | * The remaining bits are set to ``0``. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``8`` |``valueBalanceOrchard`` |``int64`` |The net value of Orchard spends minus outputs. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``32`` |``anchorOrchard`` |``byte[32]`` |A root of the Orchard note commitment tree at some block | +| | | |height in the past. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``sizeProofsOrchardZSA`` |``compactSize`` |Length in bytes of ``proofsOrchardZSA``. Value is **(TO UPDATE)** | +| | | |:math:`2720 + 2272 \cdot \mathtt{nActionsOrchard}`. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``sizeProofsOrchardZSA`` |``proofsOrchardZSA`` |``byte[sizeProofsOrchardZSA]`` |Encoding of aggregated zk-SNARK proofs for Orchard-ZSA Actions. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``64 * nActionsOrchard`` |``vSpendAuthSigsOrchard`` |``byte[64 * nActionsOrchard]`` |Authorizing signatures for each Orchard-ZSA Action. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``64`` |``bindingSigOrchard`` |``byte[64]`` |An Orchard binding signature on the SIGHASH transaction hash. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| **Orchard-ZSA Burn Fields** | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| ``varies`` | ``nAssetBurn`` | ``compactSize`` | The number of Assets burnt. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| ``40 * nAssetBurn`` | ``vAssetBurn`` | ``AssetBurn[nAssetBurn]`` | A sequence of Asset Burn descriptions, | +| | | | encoded per `Orchard-ZSA Asset Burn Description`_. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +| **Orchard-ZSA Issuance Fields** | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``varies`` |``nIssueActions`` |``compactSize`` |The number of issuance actions in the bundle. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``IssueActionSize * nIssueActions`` |``vIssueActions`` |``IssueAction[nIssueActions]`` |A sequence of issuance action descriptions, where IssueActionSize is | +| | | |the size, in bytes, of an IssueAction description. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``32`` |``ik`` |``byte[32]`` |The issuance validating key of the issuer, used to validate the signature. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ +|``64`` |``issueAuthSig`` |``byte[64]`` |The signature of the transaction SIGHASH, signed by the issuer, | +| | | |validated as in Issuance Authorization Signature Scheme [#zip-0227]_. | ++------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ + + +* The fields ``valueBalanceSapling`` and ``bindingSigSapling`` are present if and only if + :math:`\mathtt{nSpendsSapling} + \mathtt{nOutputsSapling} > 0`. If ``valueBalanceSapling`` + is not present, then :math:`\mathsf{v^{balanceSapling}}`` is defined to be 0. + +* The field ``anchorSapling`` is present if and only if :math:`\mathtt{nSpendsSapling} > 0`. + +* The fields ``flagsOrchard``, ``valueBalanceOrchard``, ``anchorOrchard``, + ``sizeProofsOrchardZSA``, ``proofsOrchardZSA``, and ``bindingSigOrchard`` are present if and + only if :math:`\mathtt{nActionsOrchard} > 0`. If ``valueBalanceOrchard`` is not present, + then :math:`\mathsf{v^{balanceOrchard}}` is defined to be 0. + +* The elements of ``vSpendProofsSapling`` and ``vSpendAuthSigsSapling`` have a 1:1 + correspondence to the elements of ``vSpendsSapling`` and MUST be ordered such that the + proof or signature at a given index corresponds to the ``SpendDescriptionV6`` at the + same index. + +* The elements of ``vOutputProofsSapling`` have a 1:1 correspondence to the elements of + ``vOutputsSapling`` and MUST be ordered such that the proof at a given index corresponds + to the ``OutputDescriptionV6`` at the same index. + +* The proofs aggregated in ``proofsOrchardZSA``, and the elements of + ``vSpendAuthSigsOrchard``, each have a 1:1 correspondence to the elements of + ``vActionsOrchard`` and MUST be ordered such that the proof or signature at a given + index corresponds to the ``OrchardZsaAction`` at the same index. + +* For coinbase transactions, the ``enableSpendsOrchard`` and ``enableZSAs`` bits MUST be set to ``0``. + +The encodings of ``tx_in``, and ``tx_out`` are as in a version 4 transaction (i.e. +unchanged from Canopy). The encodings of ``SpendDescriptionV6``, ``OutputDescriptionV6`` +, ``OrchardZsaAction``, ``AssetBurn`` and ``IssueAction`` are described below. The encoding of Sapling Spends and Outputs has +changed relative to prior versions in order to better separate data that describe the +effects of the transaction from the proofs of and commitments to those effects, and for +symmetry with this separation in the Orchard-related parts of the transaction format. + +Sapling Spend Description (``SpendDescriptionV6``) +-------------------------------------------------- + ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=============================+==========================+======================================+============================================================+ +|``32`` |``cv`` |``byte[32]`` |A value commitment to the net value of the input note. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``nullifier`` |``byte[32]`` |The nullifier of the input note. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``rk`` |``byte[32]`` |The randomized validating key for the element of | +| | | |spendAuthSigsSapling corresponding to this Spend. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ + +The encodings of each of these elements are defined in §7.3 ‘Spend Description Encoding +and Consensus’ of the Zcash Protocol Specification [#protocol-spenddesc]_. + +Sapling Output Description (``OutputDescriptionV6``) +---------------------------------------------------- + ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=============================+==========================+======================================+============================================================+ +|``32`` |``cv`` |``byte[32]`` |A value commitment to the net value of the output note. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``cmu`` |``byte[32]`` |The u-coordinate of the note commitment for the output note.| ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``ephemeralKey`` |``byte[32]`` |An encoding of an ephemeral Jubjub public key. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``580`` |``encCiphertext`` |``byte[580]`` |The encrypted contents of the note plaintext. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``80`` |``outCiphertext`` |``byte[80]`` |The encrypted contents of the byte string created by | +| | | |concatenation of the transmission key with the ephemeral | +| | | |secret key. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ + +The encodings of each of these elements are defined in §7.4 ‘Output Description Encoding +and Consensus’ of the Zcash Protocol Specification [#protocol-outputdesc]_. + +Orchard-ZSA Action Description (``OrchardZsaAction``) +----------------------------------------------------- + ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=============================+==========================+======================================+============================================================+ +|``32`` |``cv`` |``byte[32]`` |A value commitment to the net value of the input note minus | +| | | |the output note. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``nullifier`` |``byte[32]`` |The nullifier of the input note. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``rk`` |``byte[32]`` |The randomized validating key for the element of | +| | | |spendAuthSigsOrchard corresponding to this Action. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``cmx`` |``byte[32]`` |The x-coordinate of the note commitment for the output note.| ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``32`` |``ephemeralKey`` |``byte[32]`` |An encoding of an ephemeral Pallas public key | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``612`` |``encCiphertext`` |``byte[580]`` |The encrypted contents of the note plaintext. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ +|``80`` |``outCiphertext`` |``byte[80]`` |The encrypted contents of the byte string created by | +| | | |concatenation of the transmission key with the ephemeral | +| | | |secret key. | ++-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ + +The encodings of each of these elements are defined in §7.5 ‘Action Description Encoding +and Consensus’ of the Zcash Protocol Specification [#protocol-actiondesc]_. + +Orchard-ZSA Asset Burn Description +---------------------------------- + +An Orchard-ZSA Asset Burn description is encoded in a transaction as an instance of an ``AssetBurn`` type: + ++-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=======+===============+=============================+===========================================================================================================================+ +| 32 | ``AssetBase`` | ``byte[32]`` | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. | ++-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ +| 8 | ``valueBurn`` | :math:`\{1 .. 2^{64} - 1\}` | The amount being burnt. | ++-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ + +The encodings of each of these elements are defined in ZIP 226 [#zip-0226]_. + +Issuance Action Description (``IssueAction``) +--------------------------------------------- + +An issuance action, ``IssueAction``, is the instance of issuing a specific Custom Asset, and contains the following fields: + ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=============================+==========================+===========================================+=====================================================================+ +|``2`` |``assetDescSize`` |``byte`` |The length of the asset description string in bytes. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``assetDescSize`` |``asset_desc`` |``byte[assetDescSize]`` |A byte sequence of length ``assetDescSize`` bytes which SHOULD be a | +| | | |well-formed UTF-8 code unit sequence according to Unicode 15.0.0 | +| | | |or later. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``varies`` |``nNotes`` |``compactSize`` |The number of notes in the issuance action. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``noteSize * nNotes`` |``vNotes`` |``Note[nNotes]`` |A sequence of note descriptions within the issuance action, | +| | | |where ``noteSize`` is the size, in bytes, of a Note. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ +|``1`` |``flagsIssuance`` |``byte`` |An 8-bit value representing a set of flags. Ordered from LSB to MSB: | +| | | | * :math:`\mathsf{finalize}` | +| | | | * The remaining bits are set to ``0``. | ++-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ + +The encodings of each of these elements are defined in ZIP 227 [#zip-0227]_. + +Reference implementation +======================== + +TODO + + +References +========== + +.. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels `_ +.. [#protocol] `Zcash Protocol Specification, Version 2021.2.16 or later [NU5 proposal] `_ +.. [#protocol-spenddesc] `Zcash Protocol Specification, Version 2021.2.16 [NU5 proposal]. Section 4.4: Spend Descriptions `_ +.. [#protocol-outputdesc] `Zcash Protocol Specification, Version 2021.2.16 [NU5 proposal]. Section 4.5: Output Descriptions `_ +.. [#protocol-actiondesc] `Zcash Protocol Specification, Version 2021.2.16 [NU5 proposal]. Section 4.6: Action Descriptions `_ +.. [#zip-0222] `ZIP 222: Transparent Zcash Extensions `_ +.. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ +.. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ +.. [#zip-0244] `ZIP 244: Transaction Identifier Non-Malleability `_ +.. [#zip-0307] `ZIP 307: Light Client Protocol for Payment Detection `_ From cea341ed7d73368566949ac6742982be73770d17 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 15:02:55 +0000 Subject: [PATCH 29/43] Switching the issuance authorization scheme to using Bitcoin Schnorr over `secp256k1`, as in BIP 340. (#40) We switch the `issueAuthSig` scheme from RedPallas without key re-randomization to the Bitcoin Schnorr signature (as described in bip340). 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This protocol is an extension of the Orchard protocol that enables the creation, transfer and burn of Custom Assets on the Zcash chain. The creation of such Assets is defined in this ZIP (ZIP 227), while the transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. This ZIP must only be implemented in conjuction with ZIP 226 [#zip-0226]_. The proposed issuance mechanism is only valid for the ZSA transfer protocol, because it produces notes that can only be transferred under ZSA. +This ZIP (ZIP 227) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunction with ZIP 226 [#zip-0226]_. This protocol is an extension of the Orchard protocol that enables the creation, transfer and burn of Custom Assets on the Zcash chain. The creation of such Assets is defined in this ZIP (ZIP 227), while the transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. This ZIP must only be implemented in conjuction with ZIP 226 [#zip-0226]_. The proposed issuance mechanism is only valid for the Orchard-ZSA transfer protocol, because it produces notes that can only be transferred under ZSA. Motivation ========== @@ -81,13 +81,11 @@ Requirements Specification: Issuance Keys and Issuance Authorization Signature Scheme ======================================================================== -The ZSA Protocol adds the following three keys to the key components [#protocol-addressesandkeys]_: +The Orchard-ZSA Protocol adds the following keys to the key components [#protocol-addressesandkeys]_: -1. The issuance master key, denoted as :math:`\mathsf{imk}`, is the key that is used to derive the other two keys. +1. The issuance master key, denoted as :math:`\mathsf{imk}`, is the key that is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. -2. The issuance authorizing key is the key that is used to sign the issuance transaction, and is denoted as :math:`\mathsf{isk}`. This key is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. - -3. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all blockchain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. +2. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all blockchain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. The relations between these keys are shown in the following diagram: @@ -96,20 +94,29 @@ The relations between these keys are shown in the following diagram: :align: center :figclass: align-center - Diagram of Issuance Key Components for the ZSA Protocol + Diagram of Issuance Key Components for the Orchard-ZSA Protocol Issuance Authorization Signature Scheme --------------------------------------- -We define the issuance authorization signature scheme :math:`\mathsf{IssueAuthSig}` similar to :math:`\mathsf{SpendAuthSig}^{\mathsf{Orchard}}`, the Orchard spend authorization signature scheme [#protocol-concretespendauthsig]_. -Specifically, we instantiate :math:`\mathsf{IssueAuthSig}` as :math:`\mathsf{RedPallas}` without key re-randomization using generator :math:`\mathcal{P}_{\mathbb{G}} = \mathcal{G}^{\mathsf{Issuance}} := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:ZSA"}, \texttt{"Issuance"})` where :math:`\mathsf{GroupHash}^\mathbb{P}` is defined as in the Zcash protocol specification [#protocol-concretegrouphashpallasandvesta]_. +We instantiate the issuance authorization signature scheme :math:`\mathsf{IssueAuthSig}` as a Schnorr signature over the :math:`\mathtt{secp256k1}` curve, as described in BIP-340 [#bip-0340]_. +We define the constants as per the :math:`\mathtt{secp256k1}` standard parameters, as described in BIP 340. + +The associated types of the :math:`\mathsf{IssueAuthSig}` signature scheme are as follows: + +* :math:`\mathsf{IssueAuthSig.Message} = \mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}` +* :math:`\mathsf{IssueAuthSig.Signature} = \mathbb{B}^{\mathbb{Y}^{[64]}} \cup \{\bot\}` +* :math:`\mathsf{IssueAuthSig.Public} = \mathbb{B}^{\mathbb{Y}^{[32]}} \cup \{\bot\}` +* :math:`\mathsf{IssueAuthSig.Private} = \mathbb{B}^{\mathbb{Y}^{[32]}}` + +where :math:`\mathbb{B}^{\mathbb{Y}^{[k]}}` denotes the set of sequences of :math:`k` bytes, and :math:`\mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}` denotes the type of byte sequences of arbitrary length, as defined in the Zcash protocol specification [#protocol-notation]_. + +The signing key generation algorithm and the validating key derivation algorithm are defined in the `Issuance Key Derivation`_ section, while the signing and validation algorithms are defined in the `Issuance Authorization Signing and Validation`_ section. Issuance Key Derivation ----------------------- -The issuance master key is generated by choosing a bit sequence uniformly at random from :math:`\mathbb{B}^{\mathbb{Y}[32]}`, like the Orchard spending key [#protocol-orchardkeycomponents]_. - Issuance master key generation for hierarchical deterministic wallets ````````````````````````````````````````````````````````````````````` @@ -129,27 +136,47 @@ We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD path From the generated :math:`(\mathsf{sk}, \mathsf{c})`, we set the issuance master key to be :math:`\mathsf{imk} := \mathsf{sk}`. -Derivation of issuance authorizing key and issuance validating key -`````````````````````````````````````````````````````````````````` +Derivation of issuance validating key +````````````````````````````````````` -The issuance authorizing key and issuance validating key are derived from the issuance master key in an analogous manner to the derivation of the Orchard spend authorizing key and Orchard spend validating key from the Orchard spending key [#protocol-orchardkeycomponents]_, as described below. +Define :math:`\mathsf{IssueAuthSig.DerivePublic}\: : \: (\mathsf{imk}\: : \: \mathsf{IssueAuthSig.Private}) \to \mathsf{IssueAuthSig.Public}` as: -- The issuance authorizing key is derived from the issuance master key, :math:`\mathsf{imk}`, as a private signature key. The function :math:`\mathsf{PRF^{expand}_{imk}}` is as defined in the Zcash protocol specification [#protocol-abstractprfs]_: +* :math:`\mathsf{ik} := \textit{PubKey}(\mathsf{imk})` +* Return :math:`\bot` if the :math:`\textit{PubKey}` algorithm invocation fails, otherwise return :math:`\mathsf{ik}`. -.. math:: \mathsf{isk} := \mathsf{ToScalar}^{\mathsf{Orchard}}(︀ \mathsf{PRF^{expand}_{imk}}([\mathtt{0x0a}]) ) +where the :math:`\textit{PubKey}` algorithm is defined in BIP 340 [#bip-0340]_. -- The issuance validating key is derived from the issuance authorizing key, :math:`\mathsf{isk}`, as a public verification key: - -.. math:: \mathsf{ik} := \mathsf{IssueAuthSig}.\mathsf{DerivePublic}(\mathsf{isk}) +It is possible for the :math:`\textit{PubKey}` algorithm to fail with very low probability, which means that :math:`\mathsf{IssueAuthSig.DerivePublic}` could return :math:`\bot` with very low probability. +If this happens, discard the keys and repeat with a different :math:`\mathsf{imk}`. This allows the issuer to use the same wallet it usually uses to transfer Assets, while keeping a disconnect from the other keys. Specifically, this method is aligned with the requirements and motivation of ZIP 32 [#zip-0032]_. It provides further anonymity and the ability to delegate issuance of an Asset (or in the future, generate a multi-signature protocol) while the rest of the keys remain in the wallet safe. +Issuance Authorization Signing and Validation +--------------------------------------------- + +Define :math:`\mathsf{IssueAuthSig.Sign}\: : \: (\mathsf{imk}\: : \: \mathsf{IssueAuthSig.Private}) \times (M\: : \: \mathsf{IssueAuthSig.Message}) \to \mathsf{IssueAuthSig.Signature}` as: + +* Let the auxiliary data :math:`a = \mathtt{[0x00]}^{32}`. +* Let :math:`\sigma = \mathsf{Sign}(\mathsf{imk},M)`. +* Return :math:`\bot` if the :math:`\mathsf{Sign}` algorithm fails in the previous step, otherwise return :math:`\sigma`. + +where the :math:`\mathsf{Sign}` algorithm is defined in BIP 340 and :math:`a` denotes the auxiliary data used in BIP 340 [#bip-0340]_. +Note that :math:`\mathsf{IssueAuthSig.Sign}` could return :math:`\bot` with very low probability. + + +Define :math:`\mathsf{IssueAuthSig.Validate}\: : \: (\mathsf{ik}\: : \: \mathsf{IssueAuthSig.Public}) \times (M\: : \: \mathsf{IssueAuthSig.Message}) \times (\sigma\: : \: \mathsf{IssueAuthSig.Signature}) \to \mathbb{B}` as: + +* Return :math:`0` if :math:`\sigma = \bot`. +* Return :math:`1` if :math:`\mathsf{Verify}(\mathsf{ik}, M, \sigma)` succeeds, otherwise :math:`0`. + +where the :math:`\mathsf{Verify}` algorithm is defined in BIP 340 [#bip-0340]_. + Specification: Asset Identifier =============================== For every new Asset, there must be a new and unique Asset Identifier, denoted :math:`\mathsf{AssetId}`. We define this to be a globally unique pair :math:`\mathsf{AssetId} := (\mathsf{ik}, \mathsf{asset\_desc})`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. -A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-based ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. +A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. From the Asset Digest, we derive a specific Asset Base within each shielded protocol using the applicable hash-to-curve algorithm. This Asset Base is included in shielded notes. Let @@ -164,7 +191,7 @@ where Define :math:`\mathsf{AssetBase_{\mathsf{AssetId}}} := \mathsf{ZSAValueBase}(\mathsf{AssetDigest}_{\mathsf{AssetId}})` -In the case of the Orchard-based ZSA protocol, we define :math:`\mathsf{ZSAValueBase}(\mathsf{AssetDigest}_{\mathsf{AssetId}}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{AssetDigest}_{\mathsf{AssetId}})` +In the case of the Orchard-ZSA protocol, we define :math:`\mathsf{ZSAValueBase}(\mathsf{AssetDigest}_{\mathsf{AssetId}}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{AssetDigest}_{\mathsf{AssetId}})` where :math:`\mathsf{GroupHash}^\mathbb{P}` is defined as in [#protocol-concretegrouphashpallasandvesta]_. The relations between the Asset Identifier, Asset Digest, and Asset Base are shown in the following diagram: @@ -239,7 +266,7 @@ It contains the following fields: - :math:`\mathsf{ik}`: the issuance validating key, that allows the validators to verify that the :math:`\mathsf{AssetId}` is properly associated with the issuer. - ``vIssueActions``: an array of issuance actions, of type ``IssueAction``. -- :math:`\mathsf{issueAuthSig}`: the signature of the transaction SIGHASH, signed by the issuance authorizing key, :math:`\mathsf{isk}`, that validates the issuance . +- :math:`\mathsf{issueAuthSig}`: the signature of the transaction SIGHASH, signed by the issuance master key, :math:`\mathsf{imk}`, that validates the issuance . The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-transactionstructure]_. @@ -259,25 +286,25 @@ The issuance bundle is then added within the transaction format as a new bundle. Issuance Protocol ----------------- -The issuer program performs the following operations +The issuer program performs the following operations: For all actions ``IssueAction``: - encode :math:`\mathsf{asset\_desc}` as a UTF-8 byte string of size up to 512. - compute :math:`\mathsf{AssetDigest}` from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as decribed in the `Specification: Asset Identifier`_ section. - compute :math:`\mathsf{AssetBase}` from :math:`\mathsf{AssetDigest}` as decribed in the `Specification: Asset Identifier`_ section. -- set the :math:`\mathsf{finalize}` boolean as desired (if more issuance actions are to be created for this Asset Identifier, set :math:`\mathsf{finalize} = 0`, otherwise set :math:`\mathsf{finalize} = 1`) -- For each recipient :math:`i`: +- set the :math:`\mathsf{finalize}` boolean as desired (if more issuance actions are to be created for this :math:`\mathsf{AssetBase}`, set :math:`\mathsf{finalize} = 0`, otherwise set :math:`\mathsf{finalize} = 1`). +- for each recipient :math:`i`: - - generate a ZSA output note that includes the Asset Base. For an Orchard-based ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d}_i}, \mathsf{v}_i, \rho_i, \mathsf{rseed}_i, \mathsf{AssetBase}, \mathsf{rcm}_i)\!`. + - generate a ZSA output note that includes the Asset Base. For an Orchard-ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d}_i}, \mathsf{v}_i, \rho_i, \mathsf{rseed}_i, \mathsf{AssetBase}, \mathsf{rcm}_i)\!`. - encode the ``IssueAction`` into the vector ``vIssueActions`` of the bundle. For the ``IssueBundle``: -- encode the ``vIssueActions`` vector -- encode the :math:`\mathsf{ik}` as 32 byte-string -- sign the SIGHASH transaction hash with the issuance authorizing key, :math:`\mathsf{isk}`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. +- encode the ``vIssueActions`` vector. +- encode the :math:`\mathsf{ik}` as 32 byte-string. +- sign the SIGHASH transaction hash with the issuance master key, :math:`\mathsf{imk}`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. **Note:** that the commitment is not included in the ``IssuanceAction`` itself. As explained below, it is computed later by the validators and added to the note commitment tree. @@ -288,7 +315,7 @@ Specification: Consensus Rule Changes For the ``IssueBundle``: -- Verify the RedPallas-based issuance authorization signature on the SIGHASH transaction hash, :math:`\mathsf{SigHash}`, :math:`\mathsf{issueAuthSig}`, is verified by invoking :math:`\mathsf{issueAuthSig.VerifySig(ik, SigHash)}` +- Validate the issuance authorization signature, :math:`\mathsf{issueAuthSig}`, on the SIGHASH transaction hash, :math:`\mathsf{SigHash}`, by invoking :math:`\mathsf{IssueAuthSig.Validate(ik, SigHash, issueAuthSig)}` For each ``IssueAction`` in ``IssueBundle``: @@ -349,7 +376,7 @@ TxId Digest - Issuance ====================== This section details the construction of the subtree of hashes in the transaction digest that corresponds to issuance transaction data. -Details of the overall changes to the transaction digest due to the ZSA protocol can be found in ZIP 226 [#zip-0226-txiddigest]_. +Details of the overall changes to the transaction digest due to the Orchard-ZSA protocol can be found in ZIP 226 [#zip-0226-txiddigest]_. As in ZIP 244 [#zip-0244]_, the digests are all personalized BLAKE2b-256 hashes, and in cases where no elements are available for hashing, a personalized hash of the empty byte array is used. A new issuance transaction digest algorithm is defined that constructs the subtree of the transaction digest tree of hashes for the issuance portion of a transaction. Each branch of the subtree will correspond to a specific subset of issuance transaction data. The overall structure of the hash is as follows; each name referenced here will be described in detail below:: @@ -446,7 +473,7 @@ Signature Digest The per-input transaction digest algorithm to generate the signature digest in ZIP 244 [#zip-0244-sigdigest]_ is modified so that a signature digest is produced for each transparent input, each Sapling input, each Orchard action, and additionally for each Issuance Action. For Issuance Actions, this algorithm has the exact same output as the transaction digest algorithm, thus the txid may be signed directly. -The overall structure of the hash is as follows. We highlight the changes for the ZSA protocol via the ``[ADDED FOR ZSA]`` text label, and we omit the descriptions of the sections that do not change for the ZSA protocol:: +The overall structure of the hash is as follows. We highlight the changes for the Orchard-ZSA protocol via the ``[ADDED FOR ZSA]`` text label, and we omit the descriptions of the sections that do not change for the Orchard-ZSA protocol:: signature_digest ├── header_digest @@ -474,8 +501,8 @@ Identical to that specified for the transaction identifier. Authorizing Data Commitment =========================== -The transaction digest algorithm defined in ZIP 244 [#zip-0244-authcommitment]_ which commits to the authorizing data of a transaction is modified by the ZSA protocol to have the following structure. -We highlight the changes for the ZSA protocol via the ``[ADDED FOR ZSA]`` text label, and we omit the descriptions of the sections that do not change for the ZSA protocol:: +The transaction digest algorithm defined in ZIP 244 [#zip-0244-authcommitment]_ which commits to the authorizing data of a transaction is modified by the Orchard-ZSA protocol to have the following structure. +We highlight the changes for the Orchard-ZSA protocol via the ``[ADDED FOR ZSA]`` text label, and we omit the descriptions of the sections that do not change for the Orchard-ZSA protocol:: auth_digest ├── transparent_scripts_digest @@ -523,7 +550,7 @@ Issuance Key Compromise The design of this protocol does not currently allow for rotation of the issuance validating key that would allow for replacing the key of a specific Asset. In case of compromise, the following actions are recommended: -- If an issuance validating key is compromised, the :math:`\mathsf{finalize}` boolean for all the Assets issued with that key should be set to :math:`1` and the issuer should change to a new issuance authorizing key, and issue new Assets, each with a new :math:`\mathsf{AssetId}`. +- If an issuance validating key is compromised, the :math:`\mathsf{finalize}` boolean for all the Assets issued with that key should be set to :math:`1` and the issuer should change to a new issuance master key, and issue new Assets, each with a new :math:`\mathsf{AssetId}`. Bridging Assets --------------- @@ -579,6 +606,8 @@ References .. [#zip-0032-key-path-levels] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Key path levels `_ .. [#zip-0032-orchard-key-path] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard key path `_ .. [#zip-0316] `ZIP 316: Unified Addresses and Unified Viewing Keys `_ +.. [#bip-0340] `BIP 340: Schnorr Signatures for secp256k1 `_ +.. [#protocol-Notation] `Zcash Protocol Specification, Version 2022.3.8. Section 2: Notation `_ .. [#protocol-addressesandkeys] `Zcash Protocol Specification, Version 2022.3.8. Section 3.1: Payment Addresses and Keys `_ .. [#protocol-concretegrouphashpallasandvesta] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.9.8: Group Hash into Pallas and Vesta `_ .. [#protocol-abstractprfs] `Zcash Protocol Specification, Version 2022.3.8. Section 4.1.2: Pseudo Random Functions `_ From 7aff6018380ce0dd8b49ab33e3cc4bd03a6ebfc2 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 15:03:29 +0000 Subject: [PATCH 30/43] updated burn description Minor addition to burn mechanism description --- zip-0226.rst | 1 + 1 file changed, 1 insertion(+) diff --git a/zip-0226.rst b/zip-0226.rst index 144ded774..56d310067 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -167,6 +167,7 @@ Burn Mechanism -------------- The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. +Burning makes it globally provable that a given amount of an Asset has been destroyed. The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `Orchard-ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). From eed714f30eca2181ee4683e2fb8de22b3a2121bb Mon Sep 17 00:00:00 2001 From: Vivek Arte <46618816+vivek-arte@users.noreply.github.com> Date: Wed, 18 Oct 2023 22:05:01 +0530 Subject: [PATCH 31/43] Suggestions from ZIP review: notation, typographical edits, and update Daira-Emma's name. Co-authored-by: Daira-Emma Hopwood --- README.template | 2 +- zip-0226.rst | 22 +++++++++++----------- zip-0227.rst | 15 +++++++++------ zip-0230.rst | 2 +- 4 files changed, 22 insertions(+), 19 deletions(-) diff --git a/README.template b/README.template index 3ceeb8e47..f838ffac0 100644 --- a/README.template +++ b/README.template @@ -37,7 +37,7 @@ Use ``make`` to check that you are using correct `reStructuredText `__ or `Markdown `__ syntax, and double-check the generated ``draft-*.html`` file before filing a Pull Request. - +See `here `__ for the project dependencies. NU5 ZIPs -------- diff --git a/zip-0226.rst b/zip-0226.rst index 56d310067..124aa64ac 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -54,13 +54,13 @@ These terms are formally defined in ZIP 227 [#zip-0227]_. The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-binding]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. -As was initially proposed by Jack Grigg and Daira Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}`, of the *net value* in an Orchard Action. +As was initially proposed by Jack Grigg and Daira-Emma Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}`, of the *net value* in an Orchard Action. Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same Asset Base is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point in the value commitment [#protocol-concretevaluecommit]_. This ensures (1) that the input and output notes are of the same Asset Base, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature. In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}` of the output note of that Split Action is the output of a valid :math:`\mathsf{ZSAValueBase}` computation defined in ZIP 227 [#zip-0227]_. -We include the ability to pause the ZSA functionality, via a :math:`\mathsf{enableZSA}` boolean flag. When this flag is set to false, it is not possible to perform transactions involving Custom Assets (the circuit will fail). +We include the ability to pause the ZSA functionality, via a :math:`\mathsf{enableZSA}` boolean flag. When this flag is set to false, it is not possible to perform transactions involving Custom Assets (the Action statement as modified for ZSAs will not be satisfied). Finally, in this ZIP we also describe the *burn* mechanism, which is a direct extension of the transfer mechanism. The burn process uses a similar mechanism to what is used in Orchard to unshield ZEC, by using the :math:`\mathsf{valueBalance}` of the Asset in question. Burning Assets is useful for many purposes, including bridging of Wrapped Assets and removing supply of Assets. @@ -85,26 +85,26 @@ Note Structure & Commitment --------------------------- Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. -:math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}*`. +:math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}^*`. An Orchard ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}})`, where -- :math:`\mathsf{AssetBase} : \mathbb{P}*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid non-bottom group element that is not the identity. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase})`. +- :math:`\mathsf{AssetBase} : \mathbb{P}^*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid group element that is not the identity and is not :math:`\bot`. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase})`. Note that the above assumes a canonical encoding, which is true for the Pallas group, but may not hold for future shielded protocols. We define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: -.. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \{0 .. 2^{\ell_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P}* \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Output} +.. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \{0 .. 2^{\ell_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P}^* \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Output} -where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and :math:`\mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor}, \mathsf{Orchard}.\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. +where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and where :math:`\mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor}` and :math:`\mathsf{Orchard}.\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. This note commitment scheme is instantiated using the Sinsemilla Commitment [#protocol-concretesinsemillacommit]_ as follows: .. math:: \begin{align} \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase})} :=\begin{cases} - \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ + \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}\star, pk_{d}\star, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ \mathsf{cm}_{\mathsf{ZSA}} &\text{otherwise} \end{cases} \end{align} @@ -113,7 +113,7 @@ where: .. math:: \begin{align} \mathsf{cm}_{\mathsf{ZSA}} :=&\ \mathsf{SinsemillaHashToPoint}( \texttt{"z.cash:ZSA-NoteCommit-M"}, \\ - &\ \ \ \mathsf{g_{d}*}\; \| \; \mathsf{pk_{d}*}\; \| \; \mathsf{I2LEBSP_{64}(v)}\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho)\; \| \; \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi)\; \| \; \mathsf{asset\_base}) \\ + &\ \ \ \mathsf{g_{d}*} \,||\, \mathsf{pk_{d}*} \,||\, \mathsf{I2LEBSP_{64}(v)} \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho) \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi) \,||\, \mathsf{asset\_base}) \\ &\ + [\mathsf{rcm}] \mathsf{GroupHash}^{\mathbb{P}}(\texttt{"z.cash:Orchard-NoteCommit-r"},\texttt{""}) \end{align} @@ -169,9 +169,9 @@ Burn Mechanism The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. Burning makes it globally provable that a given amount of an Asset has been destroyed. -The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `Orchard-ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (eg: to Sapling or Transparent). +The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `Orchard-ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (e.g. to Sapling or Transparent). -For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` vector the tuple :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. +For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` set the tuple :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. .. math:: \mathsf{assetBurn} = \{ (\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})\ |\ \forall\ \mathsf{AssetBase}_{\mathsf{AssetId}}\ \textit{s.t.}\ \mathsf{v_{AssetId}} \neq 0 \} @@ -241,7 +241,7 @@ Wallets and other clients have to choose from the following to ensure the Asset 2. The Split Input note could be a different unspent note containing the same Asset Base (note that the note will not actually be spent). 3. The Split Input note could be an already spent note containing the same Asset Base (note that by zeroing the value in the circuit, we prevent double spending). -For Split Notes, the nullifier is generated as follows +For Split Notes, the nullifier is generated as follows: .. math:: \mathsf{nf_{old}} = \mathsf{Extract}_{\mathbb{P}} ([(\mathsf{PRF^{nfOrchard}_{nk}} (\rho^{\mathsf{old}}) + \psi') \bmod q_{\mathbb{P}}] \mathcal{K}^\mathsf{Orchard} + \mathsf{cm^{old}} + \mathcal{L}^\mathsf{Orchard}) diff --git a/zip-0227.rst b/zip-0227.rst index baf25e5fa..6eceebb30 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -44,7 +44,7 @@ We define the following additional terms: Abstract ======== -This ZIP (ZIP 227) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunction with ZIP 226 [#zip-0226]_. This protocol is an extension of the Orchard protocol that enables the creation, transfer and burn of Custom Assets on the Zcash chain. The creation of such Assets is defined in this ZIP (ZIP 227), while the transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. This ZIP must only be implemented in conjuction with ZIP 226 [#zip-0226]_. The proposed issuance mechanism is only valid for the Orchard-ZSA transfer protocol, because it produces notes that can only be transferred under ZSA. +This ZIP (ZIP 227) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunction with ZIP 226 [#zip-0226]_. This protocol is an extension of the Orchard protocol that enables the creation, transfer and burn of Custom Assets on the Zcash chain. The creation of such Assets is defined in this ZIP (ZIP 227), while the transfer and burn of such Assets is defined in ZIP 226 [#zip-0226]_. This ZIP must only be implemented in conjunction with ZIP 226 [#zip-0226]_. The proposed issuance mechanism is only valid for the Orchard-ZSA transfer protocol, because it produces notes that can only be transferred under ZSA. Motivation ========== @@ -83,9 +83,9 @@ Specification: Issuance Keys and Issuance Authorization Signature Scheme The Orchard-ZSA Protocol adds the following keys to the key components [#protocol-addressesandkeys]_: -1. The issuance master key, denoted as :math:`\mathsf{imk}`, is the key that is used to authorize the issuance of a specific Asset Identifier, and is only used by the issuer. +1. The issuance master key, denoted as :math:`\mathsf{imk}`, is the key used to authorize the issuance of Asset Identifiers by a given issuer, and is only used by that issuer. -2. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate the issuance transaction. This key is used to validate the issuance of a specific Asset Identifier, and is used by all blockchain users (specifically the Asset owners and consensus validators) to associate the Asset in question with the issuer. +2. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate issuance transactions. This key is used to validate the issuance of Asset Identifiers by a given issuer, and is used by all blockchain users (specifically the owners of notes for that Asset, and consensus validators) to associate the Asset in question with the issuer. The relations between these keys are shown in the following diagram: @@ -100,8 +100,11 @@ The relations between these keys are shown in the following diagram: Issuance Authorization Signature Scheme --------------------------------------- -We instantiate the issuance authorization signature scheme :math:`\mathsf{IssueAuthSig}` as a Schnorr signature over the :math:`\mathtt{secp256k1}` curve, as described in BIP-340 [#bip-0340]_. -We define the constants as per the :math:`\mathtt{secp256k1}` standard parameters, as described in BIP 340. +We instantiate the issuance authorization signature scheme :math:`\mathsf{IssueAuthSig}` as a BIP-340 Schnorr signature over the secp256k1 curve. The signing and validation algorithms, signature encoding, and public key encoding MUST follow BIP 340 [#bip-0340]_. + +Batch verification MAY be used. Precomputation MAY be used if and only if it produces equivalent results; for example, for a given verification key :math:`pk`, :math:`\mathit{lift\_x}(\mathit{int}(pk))` MAY be precomputed. + +We define the constants as per the secp256k1 standard parameters, as described in BIP 340. The associated types of the :math:`\mathsf{IssueAuthSig}` signature scheme are as follows: @@ -112,7 +115,7 @@ The associated types of the :math:`\mathsf{IssueAuthSig}` signature scheme are a where :math:`\mathbb{B}^{\mathbb{Y}^{[k]}}` denotes the set of sequences of :math:`k` bytes, and :math:`\mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}` denotes the type of byte sequences of arbitrary length, as defined in the Zcash protocol specification [#protocol-notation]_. -The signing key generation algorithm and the validating key derivation algorithm are defined in the `Issuance Key Derivation`_ section, while the signing and validation algorithms are defined in the `Issuance Authorization Signing and Validation`_ section. +The issuance authorizing key generation algorithm and the issuance validating key derivation algorithm are defined in the `Issuance Key Derivation`_ section, while the corresponding signing and validation algorithms are defined in the `Issuance Authorization Signing and Validation`_ section. Issuance Key Derivation ----------------------- diff --git a/zip-0230.rst b/zip-0230.rst index 2ca7456db..462ccb3b7 100644 --- a/zip-0230.rst +++ b/zip-0230.rst @@ -2,7 +2,7 @@ ZIP: 230 Title: Version 6 Transaction Format - Owners: Daira Emma Hopwood + Owners: Daira-Emma Hopwood Jack Grigg Sean Bowe Kris Nuttycombe From de1235c2ce036e7c3047081d79387ec1163ed193 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 15:07:23 +0000 Subject: [PATCH 32/43] Rename of Issuance Keys (#44) This performs a rename of the Issuance keys as follows: - `imk : Issuance master key` is renamed to `isk: Issuance authorizing key` --- zip-0226.rst | 2 +- zip-0227-key-components-zsa.png | Bin 44217 -> 45907 bytes zip-0227-key-components-zsa.svg | 10 +++++----- zip-0227.rst | 30 +++++++++++++++--------------- 4 files changed, 21 insertions(+), 21 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 124aa64ac..63698e552 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -72,7 +72,7 @@ Most of the protocol is kept the same as the Orchard protocol released with NU5, Asset Identifiers ----------------- -For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}`) are derived as defined in ZIP 227 [#zip-0227]_. +For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance validating key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}`) are derived as defined in ZIP 227 [#zip-0227]_. This Asset Base will be the base point of the value commitment for the specific Custom Asset. 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z9+6INY#7tvn8=31vrKJX$h2B^jZ=-UKF}7L*86@lRW*}0783#bEOaBmDfh*%)cf`3SBq8R?kp%ubw7k zei}Vtwg&<^u1G*i`n3yeLwF&v@MIO@*QZ z9-3GOFutTi%FuWeaBIi@=Wd-v(q@LCj-Pnhu*s9o>4v6GiLZaWu51rZ6zBj%@gece zO)?w+DTmq(-VOg$cgwG^O8>`hrjAwdU<2PZDv=$L+((5RnLD~=3|;1mwdE`_59|D8s97~U}6N{xhfO0V4 zC(k0jpw*<@{7bqEf-JWhN1?P;b`-vWYQSqo6T7T}r#mJL<|V^c^T`=KDT37};pa`2 zLfnUxOFb$&4a#i{v?RhTX%-?)EuRTlNtG$>FM}?Up?=b@2q%{Rkg8fpd~#ESjDmMJ z;jJtg?fo*UU{D%@{vPPHoE=ynF&A?Kio@xHaU(I+dexItKqi$wY~daCPps+qm3BFG zk8ccD+s^>h36nytD#^##0$Sg;zek~gt{ zJ;Va|cQpC$7+-38 t;9s%yzb5|5PyYWeDeyn>za`0*V@+g|@23Jk*`N5~XI%a)Kka|({{V5JwWI(5 diff --git a/zip-0227-key-components-zsa.svg b/zip-0227-key-components-zsa.svg index 96f39ad74..eb38e4dcb 100644 --- a/zip-0227-key-components-zsa.svg +++ b/zip-0227-key-components-zsa.svg @@ -31,10 +31,10 @@ inkscape:document-units="px" inkscape:current-layer="layer1" showgrid="false" - inkscape:window-width="1158" + inkscape:window-width="1068" inkscape:window-height="916" - inkscape:window-x="381" - inkscape:window-y="81" + inkscape:window-x="222" + inkscape:window-y="102" inkscape:window-maximized="0" inkscape:showpageshadow="2" inkscape:pagecheckerboard="0" @@ -203,7 +203,7 @@ x="99.664932" id="tspan3757-7" sodipodi:role="line" - style="stroke-width:1.06667">imkiskIssuance master keyIssuance authorizing key Date: Wed, 7 Feb 2024 15:07:48 +0000 Subject: [PATCH 33/43] Updates to Security and Privacy Considerations section (#45) This adds some details to the ZIP 226 Security and Privacy Considerations section to address this [comment](https://github.com/zcash/zips/pull/680#discussion_r1377549364) --- zip-0226.rst | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/zip-0226.rst b/zip-0226.rst index 63698e552..fa6de250c 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -409,7 +409,9 @@ The details of the changes to these algorithms are in ZIP 227 [#zip-0227-sigdige Security and Privacy Considerations =================================== -- The notes generated via the ZSA protocol are different from those generated via the Orchard protocol. As with any protocol upgrade, it will be possible to distinguish between notes generated by each protocol. However, all ZEC notes will be fully spendable with the ZSA protocol transaction structure due to the built-in backward compatibility. +- After the protocol upgrade, the Orchard shielded pool will be shared by the Orchard protocol and the Orchard-ZSA protocol. +- Deploying the Orchard-ZSA protocol does not necessitate disabling the Orchard protocol. Both can co-exist and be addressed via different transaction versions (V5 for Orchard and V6 for Orchard-ZSA). Due to this, Orchard note commitments can be distinguished from Orchard-ZSA note commitments. This holds whether or not the two protocols are active simultaneously. +- Orchard-ZSA note commitments for the native asset (ZEC) are indistinguishable from Orchard-ZSA note commitments for non-native Assets. - When including new Assets we would like to maintain the amount and identifiers of Assets private, which is achieved with the design. - We prevent a potential malleability attack on the Asset Identifier by ensuring the output notes receive an Asset Base that exists on the global state. From 9eb00eeac3e96ca51a62cdc6ee79da8692ce6581 Mon Sep 17 00:00:00 2001 From: Vivek Arte Date: Wed, 7 Feb 2024 15:08:16 +0000 Subject: [PATCH 34/43] Clarifying the encoding of `ik` (#46) This makes it clear that the encoding of `ik` used in the Asset Base derivation is big-endian, as in the case of the underlying BIP 340 Schnorr signature scheme. It also adds a clarification about the version byte used in the Asset Base derivation. --- zip-0227.rst | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/zip-0227.rst b/zip-0227.rst index 66b632ae2..f46d1c526 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -148,6 +148,7 @@ Define :math:`\mathsf{IssueAuthSig.DerivePublic}\: : \: (\mathsf{isk}\: : \: \ma * Return :math:`\bot` if the :math:`\textit{PubKey}` algorithm invocation fails, otherwise return :math:`\mathsf{ik}`. where the :math:`\textit{PubKey}` algorithm is defined in BIP 340 [#bip-0340]_. +Note that the byte representation of :math:`\mathsf{ik}` is in big-endian order as defined in BIP 340. It is possible for the :math:`\textit{PubKey}` algorithm to fail with very low probability, which means that :math:`\mathsf{IssueAuthSig.DerivePublic}` could return :math:`\bot` with very low probability. If this happens, discard the keys and repeat with a different :math:`\mathsf{isk}`. @@ -190,7 +191,8 @@ Let Define :math:`\mathsf{AssetDigest_{\mathsf{AssetId}}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))`, where -- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathsf{ik}, \mathsf{asset\_desc})) := \mathsf{0x00} || \mathsf{repr}_{\mathbb{P}}(\mathsf{ik}) || \mathsf{asset\_desc}\!`. +- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathsf{ik}, \mathsf{asset\_desc})) := \mathsf{0x00} || \mathsf{ik} || \mathsf{asset\_desc}\!`. +- Note that the initial :math:`\mathsf{0x00}` byte is a version byte. Define :math:`\mathsf{AssetBase_{\mathsf{AssetId}}} := \mathsf{ZSAValueBase}(\mathsf{AssetDigest}_{\mathsf{AssetId}})` From a7a9c213db4fa19251694f2857e65be228728f72 Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 15:14:52 +0000 Subject: [PATCH 35/43] ZIPs 226 and 227: remove trailing spaces. Signed-off-by: Daira-Emma Hopwood --- zip-0226.rst | 44 ++++++++++++++++++++++---------------------- zip-0227.rst | 44 ++++++++++++++++++++++---------------------- zip-0230.rst | 4 ++-- 3 files changed, 46 insertions(+), 46 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index fa6de250c..5fac3cba9 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -48,7 +48,7 @@ This ZIP builds on the issuance mechanism introduced in ZIP 227 [#zip-0227]_. Overview ======== -In order to be able to represent different Assets, we need to define a data field that uniquely represents the Asset in question, which we call the Asset Identifier :math:`\mathsf{AssetId}`. +In order to be able to represent different Assets, we need to define a data field that uniquely represents the Asset in question, which we call the Asset Identifier :math:`\mathsf{AssetId}`. This Asset Identifier maps to an Asset Base :math:`\mathsf{AssetBase}` that is stored in Orchard-based ZSA notes. These terms are formally defined in ZIP 227 [#zip-0227]_. @@ -79,16 +79,16 @@ This Asset Base will be the base point of the value commitment for the specific Rationale for Asset Identifiers ``````````````````````````````` -In future network and protocol upgrades, the same Asset description string can be carried on, potentially mapping into a different shielded pool. In that case, nodes should know how to transform the Asset Identifier, the Asset Digest, and the Asset Base from one shielded pool to another, while ensuring there are no balance violations [#zip-0209]_. +In future network and protocol upgrades, the same Asset description string can be carried on, potentially mapping into a different shielded pool. In that case, nodes should know how to transform the Asset Identifier, the Asset Digest, and the Asset Base from one shielded pool to another, while ensuring there are no balance violations [#zip-0209]_. Note Structure & Commitment --------------------------- -Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. +Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. :math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}^*`. An Orchard ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}})`, -where +where - :math:`\mathsf{AssetBase} : \mathbb{P}^*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid group element that is not the identity and is not :math:`\bot`. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase})`. @@ -101,16 +101,16 @@ We define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and where :math:`\mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor}` and :math:`\mathsf{Orchard}.\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. This note commitment scheme is instantiated using the Sinsemilla Commitment [#protocol-concretesinsemillacommit]_ as follows: -.. math:: \begin{align} +.. math:: \begin{align} \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase})} - :=\begin{cases} - \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}\star, pk_{d}\star, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ + :=\begin{cases} + \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}\star, pk_{d}\star, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ \mathsf{cm}_{\mathsf{ZSA}} &\text{otherwise} \end{cases} \end{align} where: - + .. math:: \begin{align} \mathsf{cm}_{\mathsf{ZSA}} :=&\ \mathsf{SinsemillaHashToPoint}( \texttt{"z.cash:ZSA-NoteCommit-M"}, \\ &\ \ \ \mathsf{g_{d}*} \,||\, \mathsf{pk_{d}*} \,||\, \mathsf{I2LEBSP_{64}(v)} \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho) \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi) \,||\, \mathsf{asset\_base}) \\ @@ -122,22 +122,22 @@ Note that :math:`\mathsf{repr}_{\mathbb{P}}` and :math:`\mathsf{GroupHash}^{\mat The nullifier is generated in the same manner as in the Orchard protocol [#protocol-commitmentsandnullifiers]_. The ZSA note plaintext also includes the Asset Base in addition to the components in the Orchard note plaintext [#protocol-notept]_. -It consists of +It consists of .. math:: (\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[\ell_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{\ell_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]}) Rationale for Note Commitment ````````````````````````````` -In the ZSA protocol, the instance of the note commitment scheme, :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}`, differs from the Orchard note commitment :math:`\mathsf{NoteCommit^{Orchard}_{rcm}}` in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. -In the case where the Asset is the ZEC Asset, the commitment is computed identically to the Orchard note commitment, without making use of the ZEC Asset Base as an input. +In the ZSA protocol, the instance of the note commitment scheme, :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}`, differs from the Orchard note commitment :math:`\mathsf{NoteCommit^{Orchard}_{rcm}}` in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. +In the case where the Asset is the ZEC Asset, the commitment is computed identically to the Orchard note commitment, without making use of the ZEC Asset Base as an input. As we will see, the nested structure of the Sinsemilla-based commitment [#protocol-concretesinsemillacommit]_ allows us to add the Asset Base as a final recursive step. The note commitment output is still indistinguishable from the original Orchard ZEC note commitments, by definition of the Sinsemilla hash function [#protocol-concretesinsemillahash]_. ZSA note commitments will therefore be added to the same Orchard Note Commitment Tree. In essence, we have: .. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, \mathsf{AssetBase})} \in \mathsf{NoteCommit^{Orchard}.Output} -This definition can be viewed as a generalization of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes. +This definition can be viewed as a generalization of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes. Value Commitment ---------------- @@ -204,20 +204,20 @@ After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the bin Rationale for Value Balance Verification ```````````````````````````````````````` -We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of clarity) between Actions related to ZEC and Actions related to Custom Assets. +We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of clarity) between Actions related to ZEC and Actions related to Custom Assets. We denote by :math:`S_{\mathsf{ZEC}} \subseteq [1,n]` the set of indices of Actions that are related to ZEC, and by :math:`S_{\mathsf{CA}} = [1,n] \setminus S_{\mathsf{ZEC}}` the set of indices of Actions that are related to Custom Assets. The right hand side of the value balance verification equation can be expanded to: .. math:: ((\sum_{i \in S_{\mathsf{ZEC}}} \mathsf{cv^{net}}_{i}) + (\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv^{net}}_{j})) - ([\mathsf{v^{balanceOrchard}}]\mathcal{V}^{\mathsf{Orchard}} + [0]\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\mathsf{AssetBase} + [0]\mathcal{R}^{\mathsf{Orchard}}) - -This equation contains the balance check of the Orchard protocol [#protocol-binding]_. -With ZSA, transfer Actions for Custom Assets must also be balanced across Asset Bases. -All Custom Assets are contained within the shielded pool, and cannot be unshielded via a regular transfer. + +This equation contains the balance check of the Orchard protocol [#protocol-binding]_. +With ZSA, transfer Actions for Custom Assets must also be balanced across Asset Bases. +All Custom Assets are contained within the shielded pool, and cannot be unshielded via a regular transfer. Custom Assets can be burnt, the mechanism for which reveals the amount and identifier of the Asset being burnt, within the :math:`\mathsf{assetBurn}` set. As such, for a correctly constructed transaction, we will get :math:`\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv}_j^{\mathsf{net}} - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\mathsf{AssetBase} = \mathsf{\sum_{j \in S_{\mathsf{CA}}} rcv_{j}^{net}}\mathcal{R}^{\mathsf{Orchard}}`. -When the Asset is not being burnt, the net balance of the input and output values is zero, and there will be no addition to the :math:`\mathsf{assetBurn}` vector. +When the Asset is not being burnt, the net balance of the input and output values is zero, and there will be no addition to the :math:`\mathsf{assetBurn}` vector. Therefore, the relationship between :math:`\mathsf{bvk}` and :math:`\mathsf{bsk}` will hold if and only if, per Custom Asset, the sum of the net values of the relevant Actions equals the corresponding :math:`\mathsf{v}_k` value (or equals :math:`0` if that Asset is not in the :math:`\mathsf{assetBurn}` set), and for ZEC, the sum of the net values of the relevant Actions equals the :math:`\mathsf{v^{balanceOrchard}}` value. As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values must sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. @@ -237,7 +237,7 @@ When the number of input notes of a particular Asset Base is smaller than the re Wallets and other clients have to choose from the following to ensure the Asset Base is preserved for the output note of a Split Action: -1. The Split Input note could be another note containing the same Asset Base that is being spent by this transaction (but not by this Split Input). +1. The Split Input note could be another note containing the same Asset Base that is being spent by this transaction (but not by this Split Input). 2. The Split Input note could be a different unspent note containing the same Asset Base (note that the note will not actually be spent). 3. The Split Input note could be an already spent note containing the same Asset Base (note that by zeroing the value in the circuit, we prevent double spending). @@ -322,8 +322,8 @@ The transaction format for v6 transactions is described in ZIP 230 [#zip-0230]_. TxId Digest =========== -The transaction digest algorithm defined in ZIP 244 [#zip-0244]_ is modified by the ZSA protocol to add a new branch for issuance information, along with modifications within the ``orchard_digest`` to account for the inclusion of the Asset Base. -The details of these changes are described in this section, and highlighted using the ``[UPDATED FOR ZSA]`` or ``[ADDED FOR ZSA]`` text label. We omit the details of the sections that do not change for the ZSA protocol. +The transaction digest algorithm defined in ZIP 244 [#zip-0244]_ is modified by the ZSA protocol to add a new branch for issuance information, along with modifications within the ``orchard_digest`` to account for the inclusion of the Asset Base. +The details of these changes are described in this section, and highlighted using the ``[UPDATED FOR ZSA]`` or ``[ADDED FOR ZSA]`` text label. We omit the details of the sections that do not change for the ZSA protocol. txid_digest ----------- @@ -345,7 +345,7 @@ When Orchard Actions are present in the transaction, this digest is a BLAKE2b-25 T.4b: orchard_actions_memos_digest (32-byte hash output) [UPDATED FOR ZSA] T.4c: orchard_actions_noncompact_digest (32-byte hash output) [UPDATED FOR ZSA] T.4d: flagsOrchard (1 byte) - T.4e: valueBalanceOrchard (64-bit signed little-endian) + T.4e: valueBalanceOrchard (64-bit signed little-endian) T.4f: anchorOrchard (32 bytes) T.4a: orchard_actions_compact_digest diff --git a/zip-0227.rst b/zip-0227.rst index f46d1c526..a98b46707 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -51,7 +51,7 @@ Motivation This ZIP introduces the issuance mechanism for Custom Assets on the Zcash chain. While originally part of a same ZSA ZIP (ZIP 226 [#zip-0226]_) the issuance mechanism turned out to be substantial enough to stand on its own and justify the creation of this supporting ZIP for ZIP 226 [#zip-0226]_. -This ZIP only enables *transparent* issuance. As a first step, transparency will allow for proper testing of the applications that will be most used in the Zcash ecosystem, and will enable the supply of Assets to be tracked. +This ZIP only enables *transparent* issuance. As a first step, transparency will allow for proper testing of the applications that will be most used in the Zcash ecosystem, and will enable the supply of Assets to be tracked. The issuance mechanism described in this ZIP is broad enough for issuers to either create Assets on Zcash (i.e. Assets that originate on the Zcash blockchain), as well as for institutions to create bridges from other chains and import Wrapped Assets. This enables what we hope will be a useful set of applications. @@ -104,7 +104,7 @@ We instantiate the issuance authorization signature scheme :math:`\mathsf{IssueA Batch verification MAY be used. Precomputation MAY be used if and only if it produces equivalent results; for example, for a given verification key :math:`pk`, :math:`\mathit{lift\_x}(\mathit{int}(pk))` MAY be precomputed. -We define the constants as per the secp256k1 standard parameters, as described in BIP 340. +We define the constants as per the secp256k1 standard parameters, as described in BIP 340. The associated types of the :math:`\mathsf{IssueAuthSig}` signature scheme are as follows: @@ -128,7 +128,7 @@ The issuance authorizing key is generated using the Orchard master key derivatio Let :math:`S` be a seed byte sequence of a chosen length, which MUST be at least 32 and at most 252 bytes. We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssue_V1"}, S)`. -As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance authorizing key. +As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance authorizing key. We reuse the :math:`\mathsf{CDKsk}` function for Orchard child key derivation from ZIP 32. We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance authorizing key path as :math:`m_\mathsf{Issuance} / purpose' / coin\_type' / account'`. We fix the path levels as follows: @@ -147,10 +147,10 @@ Define :math:`\mathsf{IssueAuthSig.DerivePublic}\: : \: (\mathsf{isk}\: : \: \ma * :math:`\mathsf{ik} := \textit{PubKey}(\mathsf{isk})` * Return :math:`\bot` if the :math:`\textit{PubKey}` algorithm invocation fails, otherwise return :math:`\mathsf{ik}`. -where the :math:`\textit{PubKey}` algorithm is defined in BIP 340 [#bip-0340]_. +where the :math:`\textit{PubKey}` algorithm is defined in BIP 340 [#bip-0340]_. Note that the byte representation of :math:`\mathsf{ik}` is in big-endian order as defined in BIP 340. -It is possible for the :math:`\textit{PubKey}` algorithm to fail with very low probability, which means that :math:`\mathsf{IssueAuthSig.DerivePublic}` could return :math:`\bot` with very low probability. +It is possible for the :math:`\textit{PubKey}` algorithm to fail with very low probability, which means that :math:`\mathsf{IssueAuthSig.DerivePublic}` could return :math:`\bot` with very low probability. If this happens, discard the keys and repeat with a different :math:`\mathsf{isk}`. This allows the issuer to use the same wallet it usually uses to transfer Assets, while keeping a disconnect from the other keys. Specifically, this method is aligned with the requirements and motivation of ZIP 32 [#zip-0032]_. It provides further anonymity and the ability to delegate issuance of an Asset (or in the future, generate a multi-signature protocol) while the rest of the keys remain in the wallet safe. @@ -183,7 +183,7 @@ For every new Asset, there must be a new and unique Asset Identifier, denoted :m A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. From the Asset Digest, we derive a specific Asset Base within each shielded protocol using the applicable hash-to-curve algorithm. This Asset Base is included in shielded notes. -Let +Let - :math:`\mathsf{asset\_desc}` be the asset description, which includes any information pertaining to the issuance, and is a byte sequence of up to 512 bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later. - :math:`\mathsf{ik}` be the issuance validating key of the issuer, a public key used to verify the signature on the issuance transaction's SIGHASH. @@ -213,7 +213,7 @@ The relations between the Asset Identifier, Asset Digest, and Asset Base are sho Wallets MUST NOT display just the :math:`\mathsf{asset\_desc}` string to their users as the name of the Asset. Some possible alternatives include: -- Wallets could allow clients to provide an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers via a petname system. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. +- Wallets could allow clients to provide an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers via a petname system. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients. - The Asset Digest could be used as a more compact bytestring to uniquely determine an Asset, and wallets could support clients scanning QR codes to load Asset information into their wallets. Specification: Global Issuance State @@ -238,12 +238,12 @@ An issuance action, ``IssueAction``, is the instance of issuing a specific Custo - ``flagsIssuance``: a byte that stores the :math:`\mathsf{finalize}` boolean that defines whether the issuance of that specific Custom Asset is finalized or not. An asset's :math:`\mathsf{AssetDigest}` is added to the :math:`\mathsf{previously\_finalized}` set after a block that contains any issuance transaction for that asset with :math:`\mathsf{finalize} = 1`. It then cannot be removed from this set. For Assets with :math:`\mathsf{AssetDigest} \in \mathsf{previously\_finalized}`, no further tokens can be issued, so as seen below, the validators will reject the transaction. For Assets with :math:`\mathsf{AssetDigest} \not\in \mathsf{previously\_finalized}`, new issuance actions can be issued in future transactions. These must use the same Asset description, :math:`\mathsf{asset\_desc}`, and can either maintain :math:`\mathsf{finalize} = 0` or change it to :math:`\mathsf{finalize} = 1`, denoting that this Custom Asset cannot be issued after the containing block. - + +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ | Bytes | Name | Data Type | Description | +=============================+==========================+===========================================+=====================================================================+ -|``2`` |``assetDescSize`` |``byte`` |The length of the :math:`\mathsf{asset\_desc}` string in bytes. | +|``2`` |``assetDescSize`` |``byte`` |The length of the :math:`\mathsf{asset\_desc}` string in bytes. | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ |``assetDescSize`` |``asset_desc`` |``byte[assetDescSize]`` |A byte sequence of length ``assetDescSize`` bytes which SHOULD be a | | | | |well-formed UTF-8 code unit sequence according to Unicode 15.0.0 | @@ -259,14 +259,14 @@ An asset's :math:`\mathsf{AssetDigest}` is added to the :math:`\mathsf{previousl | | | | * The remaining bits are set to ``0``. | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ -We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the note commitment tree as a shielded note. +We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the note commitment tree as a shielded note. This prevents future usage of the note from being linked to the issuance transaction, as the nullifier key is not known to the validators and chain observers. Issuance Bundle --------------- -An issuance bundle, ``IssueBundle``, is the aggregate of all the issuance-related information. -Specifically, contains all the issuance actions and the issuer signature on the transaction SIGHASH that validates the issuance itself. +An issuance bundle, ``IssueBundle``, is the aggregate of all the issuance-related information. +Specifically, contains all the issuance actions and the issuer signature on the transaction SIGHASH that validates the issuance itself. It contains the following fields: - :math:`\mathsf{ik}`: the issuance validating key, that allows the validators to verify that the :math:`\mathsf{AssetId}` is properly associated with the issuer. @@ -354,7 +354,7 @@ The following is a list of rationale for different decisions made in the proposa - information to be committed by the issuer, though not enforceable by the protocol. - We require a check whether the :math:`\mathsf{finalize}` flag only has been set in a previous block rather than a previous transaction in the same block. In other words, we only update the :math:`\mathsf{previously\_finalized}`` set at the block boundary. This is in keeping with the current property which allows for a miner to reorder transactions in a block without changing the meaning, which we aim to preserve. -- We require non-zero fees in the presence of an issue bundle, in order to preclude the possibility of a transaction containing only an issue bundle. If a transaction includes only an issue bundle, the SIGHASH transaction hash would be computed solely based on the issue bundle. A duplicate bundle would have the same SIGHASH transaction hash, potentially allowing for a replay attack. +- We require non-zero fees in the presence of an issue bundle, in order to preclude the possibility of a transaction containing only an issue bundle. If a transaction includes only an issue bundle, the SIGHASH transaction hash would be computed solely based on the issue bundle. A duplicate bundle would have the same SIGHASH transaction hash, potentially allowing for a replay attack. Concrete Applications --------------------- @@ -369,7 +369,7 @@ Concrete Applications - issuing a last set of tokens of that specific :math:`\mathsf{AssetId}`, for which :math:`\mathsf{finalize} = 1`, or by - issuing a transaction with a single note in the issuance action pertaining to that :math:`\mathsf{AssetId}`, where the note will contain a ``value = 0``. This can be used for application-specific purposes (NFT collections) or for security purposes to revoke the Asset issuance (see Security and Privacy Considerations). - - Note in the above cases, that the setting of the :math:`\mathsf{finalize}` flag will take effect at the block boundary, that is, after all the transactions in the block. + - Note in the above cases, that the setting of the :math:`\mathsf{finalize}` flag will take effect at the block boundary, that is, after all the transactions in the block. - The issuance and burn mechanisms can be used in conjunction to determine the supply of Assets on the Zcash ecosystem. This allows for the bridging of Assets defined on other chains. @@ -387,11 +387,11 @@ As in ZIP 244 [#zip-0244]_, the digests are all personalized BLAKE2b-256 hashes, A new issuance transaction digest algorithm is defined that constructs the subtree of the transaction digest tree of hashes for the issuance portion of a transaction. Each branch of the subtree will correspond to a specific subset of issuance transaction data. The overall structure of the hash is as follows; each name referenced here will be described in detail below:: issuance_digest - ├── issue_actions_digest - │   ├── issue_notes_digest - │   ├── assetDescription - │   └── flagsIssuance - └── issuanceValidatingKey + ├── issue_actions_digest + │   ├── issue_notes_digest + │   ├── assetDescription + │   └── flagsIssuance + └── issuanceValidatingKey In the specification below, nodes of the tree are presented in depth-first order. @@ -407,7 +407,7 @@ The personalization field of this hash is set to:: "ZTxIdSAIssueHash" In case the transaction has no issuance components, ''issue_actions_digest'' is:: - + BLAKE2b-256("ZTxIdSAIssueHash", []) T.5a: issue_actions_digest @@ -506,7 +506,7 @@ Identical to that specified for the transaction identifier. Authorizing Data Commitment =========================== -The transaction digest algorithm defined in ZIP 244 [#zip-0244-authcommitment]_ which commits to the authorizing data of a transaction is modified by the Orchard-ZSA protocol to have the following structure. +The transaction digest algorithm defined in ZIP 244 [#zip-0244-authcommitment]_ which commits to the authorizing data of a transaction is modified by the Orchard-ZSA protocol to have the following structure. We highlight the changes for the Orchard-ZSA protocol via the ``[ADDED FOR ZSA]`` text label, and we omit the descriptions of the sections that do not change for the Orchard-ZSA protocol:: auth_digest @@ -548,7 +548,7 @@ Security and Privacy Considerations Displaying Asset Identifier information to users ------------------------------------------------ -Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are provided in the `Specification: Asset Identifier`_ section. +Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are provided in the `Specification: Asset Identifier`_ section. Issuance Key Compromise ----------------------- diff --git a/zip-0230.rst b/zip-0230.rst index 462ccb3b7..4d7829404 100644 --- a/zip-0230.rst +++ b/zip-0230.rst @@ -46,7 +46,7 @@ Motivation The Orchard-ZSA protocol requires serialized data elements that are distinct from any previous Zcash transaction. Since ZIP 244 was activated in NU5, the -v5 and later serialized transaction formats are not consensus-critical. +v5 and later serialized transaction formats are not consensus-critical. Thus, this ZIP defines format that can easily accommodate future extensions, where elements or a given pool are kept separate. @@ -312,7 +312,7 @@ An issuance action, ``IssueAction``, is the instance of issuing a specific Custo +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ | Bytes | Name | Data Type | Description | +=============================+==========================+===========================================+=====================================================================+ -|``2`` |``assetDescSize`` |``byte`` |The length of the asset description string in bytes. | +|``2`` |``assetDescSize`` |``byte`` |The length of the asset description string in bytes. | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ |``assetDescSize`` |``asset_desc`` |``byte[assetDescSize]`` |A byte sequence of length ``assetDescSize`` bytes which SHOULD be a | | | | |well-formed UTF-8 code unit sequence according to Unicode 15.0.0 | From 865469aadb75b18a1b178fe45b45598b404678d2 Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 15:16:30 +0000 Subject: [PATCH 36/43] ZIP 226: use `\star` instead of `*` for bit representations. Signed-off-by: Daira-Emma Hopwood --- zip-0226.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 5fac3cba9..43246fd08 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -102,7 +102,7 @@ where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for t This note commitment scheme is instantiated using the Sinsemilla Commitment [#protocol-concretesinsemillacommit]_ as follows: .. math:: \begin{align} - \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}*, pk_{d}*, v, \rho, \psi, \mathsf{AssetBase})} + \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}\star, pk_{d}\star, v, \rho, \psi, \mathsf{AssetBase})} :=\begin{cases} \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}\star, pk_{d}\star, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ \mathsf{cm}_{\mathsf{ZSA}} &\text{otherwise} @@ -113,7 +113,7 @@ where: .. math:: \begin{align} \mathsf{cm}_{\mathsf{ZSA}} :=&\ \mathsf{SinsemillaHashToPoint}( \texttt{"z.cash:ZSA-NoteCommit-M"}, \\ - &\ \ \ \mathsf{g_{d}*} \,||\, \mathsf{pk_{d}*} \,||\, \mathsf{I2LEBSP_{64}(v)} \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho) \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi) \,||\, \mathsf{asset\_base}) \\ + &\ \ \ \mathsf{g_{d}\star} \,||\, \mathsf{pk_{d}\star} \,||\, \mathsf{I2LEBSP_{64}(v)} \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho) \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi) \,||\, \mathsf{asset\_base}) \\ &\ + [\mathsf{rcm}] \mathsf{GroupHash}^{\mathbb{P}}(\texttt{"z.cash:Orchard-NoteCommit-r"},\texttt{""}) \end{align} From 3b98ae5e05ab309ec2d2a00317e789b60a281d09 Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 16:39:41 +0000 Subject: [PATCH 37/43] ZIPs 226, 227, and 230: update references and key words to latest ZIP conventions and protocol spec. Signed-off-by: Daira-Emma Hopwood --- zip-0226.rst | 54 ++++++++++++++++++++++++---------------------------- zip-0227.rst | 34 +++++++++++++++------------------ zip-0230.rst | 16 +++++++--------- 3 files changed, 47 insertions(+), 57 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 43246fd08..19ad029f4 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -21,7 +21,7 @@ Terminology =========== -The key word "MUST" in this document is to be interpreted as described in RFC 2119 [#RFC2119]_. +The key word "MUST" in this document is to be interpreted as described in BCP 14 [#BCP14]_ when, and only when, it appears in all capitals. The term "network upgrade" in this document is to be interpreted as described in ZIP 200 [#zip-0200]_. @@ -52,13 +52,12 @@ In order to be able to represent different Assets, we need to define a data fiel This Asset Identifier maps to an Asset Base :math:`\mathsf{AssetBase}` that is stored in Orchard-based ZSA notes. These terms are formally defined in ZIP 227 [#zip-0227]_. -The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-binding]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. +The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ [#protocol-actionencodingandconsensus]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-orchardbalance]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. As was initially proposed by Jack Grigg and Daira-Emma Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}`, of the *net value* in an Orchard Action. -Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same Asset Base is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point in the value commitment [#protocol-concretevaluecommit]_. This ensures (1) that the input and output notes are of the same Asset Base, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature. +Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same Asset Base is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point in the value commitment [#protocol-concretehomomorphiccommit]_. This ensures (1) that the input and output notes are of the same Asset Base, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature. -In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-dummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}` of the output note of that Split Action is the output of a valid :math:`\mathsf{ZSAValueBase}` computation defined in ZIP 227 [#zip-0227]_. We include the ability to pause the ZSA functionality, via a :math:`\mathsf{enableZSA}` boolean flag. When this flag is set to false, it is not possible to perform transactions involving Custom Assets (the Action statement as modified for ZSAs will not be satisfied). @@ -159,7 +158,7 @@ For ZEC, we define :math:`\mathsf{AssetBase}_{\mathsf{AssetId}} :=\mathcal{V}^{\ Rationale for Value Commitment `````````````````````````````` -The Orchard Protocol uses a Homomorphic Pedersen Commitment [#protocol-concretevaluecommit]_ to perform the value commitment, with fixed base points :math:`\mathcal{V}^{\mathsf{Orchard}}` and :math:`\mathcal{R}^{\mathsf{Orchard}}` as the values represent the amount of ZEC being transferred. +The Orchard Protocol uses a Homomorphic Pedersen Commitment [#protocol-concretehomomorphiccommit]_ to perform the value commitment, with fixed base points :math:`\mathcal{V}^{\mathsf{Orchard}}` and :math:`\mathcal{R}^{\mathsf{Orchard}}` as the values represent the amount of ZEC being transferred. The use of different value base points for different Assets enables the final balance of the transaction to be securely computed, such that each Asset Identifier is balanced independently, which is required as different Assets are not meant to be mutually fungible. @@ -189,7 +188,7 @@ Additional Consensus Rules Value Balance Verification -------------------------- -In order to verify the balance of the different Assets, the verifier MUST perform a similar process as for the Orchard protocol [#protocol-binding]_, with the addition of the burn information. +In order to verify the balance of the different Assets, the verifier MUST perform a similar process as for the Orchard protocol [#protocol-orchardbalance]_, with the addition of the burn information. For a total of :math:`n` Actions in a transfer, the prover MUST still sign the SIGHASH transaction hash using the binding signature key :math:`\mathsf{bsk} = \sum_{i=1}^{n} \mathsf{rcv}_{i}`. @@ -211,7 +210,7 @@ The right hand side of the value balance verification equation can be expanded t .. math:: ((\sum_{i \in S_{\mathsf{ZEC}}} \mathsf{cv^{net}}_{i}) + (\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv^{net}}_{j})) - ([\mathsf{v^{balanceOrchard}}]\mathcal{V}^{\mathsf{Orchard}} + [0]\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\mathsf{AssetBase} + [0]\mathcal{R}^{\mathsf{Orchard}}) -This equation contains the balance check of the Orchard protocol [#protocol-binding]_. +This equation contains the balance check of the Orchard protocol [#protocol-orchardbalance]_. With ZSA, transfer Actions for Custom Assets must also be balanced across Asset Bases. All Custom Assets are contained within the shielded pool, and cannot be unshielded via a regular transfer. Custom Assets can be burnt, the mechanism for which reveals the amount and identifier of the Asset being burnt, within the :math:`\mathsf{assetBurn}` set. @@ -250,7 +249,7 @@ where :math:`\psi'` is sampled uniformly at random on :math:`\mathbb{F}_{q_{\mat Rationale for Split Notes ````````````````````````` -In the Orchard protocol, since each Action represents an input and an output, the transaction that wants to send one input to multiple outputs must have multiple inputs. The Orchard protocol gives *dummy spend notes* [#protocol-dummynotes]_ to the Actions that have not been assigned input notes. +In the Orchard protocol, since each Action represents an input and an output, the transaction that wants to send one input to multiple outputs must have multiple inputs. The Orchard protocol gives *dummy spend notes* [#protocol-orcharddummynotes]_ to the Actions that have not been assigned input notes. The Orchard technique requires modification for the ZSA protocol with multiple Asset Identifiers, as the output note of the split Actions *cannot* contain *any* Asset Base. We must enforce it to be an actual output of a GroupHash computation (in fact, we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). Without this enforcement the prover could input a multiple (or linear combination) of an existing Asset Base, and thereby attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds. @@ -453,37 +452,34 @@ Reference Implementation References ========== -.. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels `_ +.. [#BCP14] `Information on BCP 14 — "RFC 2119: Key words for use in RFCs to Indicate Requirement Levels" and "RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words" `_ .. [#zip-0200] `ZIP 200: Network Upgrade Mechanism `_ .. [#zip-0209] `ZIP 209: Prohibit Negative Shielded Chain Value Pool Balances `_ .. [#zip-0224] `ZIP 224: Orchard `_ -.. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ -.. [#zip-0230] `ZIP 230: Version 6 Transaction Format `_ .. [#zip-0227-assetidentifier] `ZIP 227: Issuance of Zcash Shielded Assets: Specification: Asset Identifier `_ .. [#zip-0227-txiddigest] `ZIP 227: Issuance of Zcash Shielded Assets: TxId Digest - Issuance `_ .. [#zip-0227-sigdigest] `ZIP 227: Issuance of Zcash Shielded Assets: Signature Digest `_ .. [#zip-0227-authcommitment] `ZIP 227: Issuance of Zcash Shielded Assets: Authorizing Data Commitment `_ +.. [#zip-0230] `ZIP 230: Version 6 Transaction Format `_ .. [#zip-0244] `ZIP 244: Transaction Identifier Non-Malleability `_ .. [#zip-0307] `ZIP 307: Light Client Protocol for Payment Detection `_ -.. [#protocol-notes] `Zcash Protocol Specification, Version 2022.3.8. Section 3.2: Notes `_ -.. [#protocol-notept] `Zcash Protocol Specification, Version 2022.3.8. Section 5.5: Encodings of Note Plaintexts and Memo Fields `_ -.. [#protocol-actions] `Zcash Protocol Specification, Version 2022.3.8. Section 3.7: Action Transfers and their Descriptions `_ -.. [#protocol-abstractcommit] `Zcash Protocol Specification, Version 2022.3.8. Section 4.1.8: Commitment `_ -.. [#protocol-binding] `Zcash Protocol Specification, Version 2022.3.8. Section 4.14: Balance and Binding Signature (Orchard) `_ -.. [#protocol-commitmentsandnullifiers] `Zcash Protocol Specification, Version 2022.3.8. Section 4.16: Note Commitments and Nullifiers `_ -.. [#protocol-endian] `Zcash Protocol Specification, Version 2022.3.8. Section 5.1: Integers, Bit Sequences, and Endianness `_ -.. [#protocol-constants] `Zcash Protocol Specification, Version 2022.3.8. Section 5.3: Constants `_ -.. [#protocol-pallasandvesta] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.9.6: Pallas and Vesta `_ -.. [#pasta-evidence] `Pallas/Vesta supporting evidence `_ -.. [#protocol-concretesinsemillahash] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.1.9: Sinsemilla hash function `_ -.. [#protocol-concretesinsemillacommit] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.8.4: Sinsemilla commitments `_ -.. [#protocol-concretevaluecommit] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.8.3: Homomorphic Pedersen commitments (Sapling and Orchard) `_ -.. [#protocol-dummynotes] `Zcash Protocol Specification, Version 2022.3.8. Section 4.8.3: Dummy Notes (Orchard) `_ -.. [#protocol-actionstatement] `Zcash Protocol Specification, Version 2022.3.8. Section 4.17.4: Action Statement (Orchard) `_ -.. [#protocol-transactionstructure] `Zcash Protocol Specification, Version 2022.3.8. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5) `_ -.. [#protocol-actionencodingandconsensus] `Zcash Protocol Specification, Version 2022.3.8. Section 7.5: Action Description Encoding and Consensus `_ +.. [#zip-0317b] `ZIP 317: Proportional Transfer Fee Mechanism - Pull Request #667 for ZSA Protocol ZIPs `_ +.. [#protocol-notes] `Zcash Protocol Specification, Version 2023.4.0. Section 3.2: Notes `_ +.. [#protocol-actions] `Zcash Protocol Specification, Version 2023.4.0. Section 3.7: Action Transfers and their Descriptions `_ +.. [#protocol-abstractcommit] `Zcash Protocol Specification, Version 2023.4.0. Section 4.1.8: Commitment `_ +.. [#protocol-orcharddummynotes] `Zcash Protocol Specification, Version 2023.4.0. Section 4.8.3: Dummy Notes (Orchard) `_ +.. [#protocol-orchardbalance] `Zcash Protocol Specification, Version 2023.4.0. Section 4.14: Balance and Binding Signature (Orchard) `_ +.. [#protocol-commitmentsandnullifiers] `Zcash Protocol Specification, Version 2023.4.0. Section 4.16: Note Commitments and Nullifiers `_ +.. [#protocol-actionstatement] `Zcash Protocol Specification, Version 2023.4.0. Section 4.17.4: Action Statement (Orchard) `_ +.. [#protocol-endian] `Zcash Protocol Specification, Version 2023.4.0. Section 5.1: Integers, Bit Sequences, and Endianness `_ +.. [#protocol-constants] `Zcash Protocol Specification, Version 2023.4.0. Section 5.3: Constants `_ +.. [#protocol-concretesinsemillahash] `Zcash Protocol Specification, Version 2023.4.0. Section 5.4.1.9: Sinsemilla hash function `_ +.. [#protocol-concretehomomorphiccommit] `Zcash Protocol Specification, Version 2023.4.0. Section 5.4.8.3: Homomorphic Pedersen commitments (Sapling and Orchard) `_ +.. [#protocol-concretesinsemillacommit] `Zcash Protocol Specification, Version 2023.4.0. Section 5.4.8.4: Sinsemilla commitments `_ +.. [#protocol-pallasandvesta] `Zcash Protocol Specification, Version 2023.4.0. Section 5.4.9.6: Pallas and Vesta `_ +.. [#protocol-notept] `Zcash Protocol Specification, Version 2023.4.0. Section 5.5: Encodings of Note Plaintexts and Memo Fields `_ +.. [#protocol-actionencodingandconsensus] `Zcash Protocol Specification, Version 2023.4.0. Section 7.5: Action Description Encoding and Consensus `_ .. [#initial-zsa-issue] `User-Defined Assets and Wrapped Assets `_ .. [#generalized-value-commitments] `Comment on Generalized Value Commitments `_ -.. [#zip-0317b] `ZIP 317: Proportional Transfer Fee Mechanism - Pull Request #667 for ZSA Protocol ZIPs `_ .. [#circuit-modifications] `Modifications to the Orchard circuit for the ZSA Protocol `_ diff --git a/zip-0227.rst b/zip-0227.rst index a98b46707..fa61b0e53 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -21,7 +21,7 @@ Terminology =========== -The key word "MUST" in this document is to be interpreted as described in RFC 2119 [#RFC2119]_. +The key words "MUST", "MUST NOT", "SHOULD", "RECOMMENDED", and "MAY" in this document are to be interpreted as described in BCP 14 [#BCP14]_ when, and only when, they appear in all capitals. The term "network upgrade" in this document is to be interpreted as described in ZIP 200 [#zip-0200]_. @@ -81,7 +81,7 @@ Requirements Specification: Issuance Keys and Issuance Authorization Signature Scheme ======================================================================== -The Orchard-ZSA Protocol adds the following keys to the key components [#protocol-addressesandkeys]_: +The Orchard-ZSA Protocol adds the following keys to the key components [#protocol-addressesandkeys]_ [#protocol-orchardkeycomponents]_: 1. The issuance authorizing key, denoted as :math:`\mathsf{isk}`, is the key used to authorize the issuance of Asset Identifiers by a given issuer, and is only used by that issuer. @@ -273,7 +273,7 @@ It contains the following fields: - ``vIssueActions``: an array of issuance actions, of type ``IssueAction``. - :math:`\mathsf{issueAuthSig}`: the signature of the transaction SIGHASH, signed by the issuance authorizing key, :math:`\mathsf{isk}`, that validates the issuance . -The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-transactionstructure]_. +The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-txnencoding]_. +------------------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------------+ | Bytes | Name | Data Type | Description | @@ -595,7 +595,12 @@ This ZIP is proposed to activate with Network Upgrade 6. References ========== -.. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels `_ +.. [#BCP14] `Information on BCP 14 — "RFC 2119: Key words for use in RFCs to Indicate Requirement Levels" and "RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words" `_ +.. [#zip-0032] `ZIP 32: Shielded Hierarchical Deterministic Wallets `_ +.. [#zip-0032-orchard-master] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard master key generation `_ +.. [#zip-0032-orchard-child-key-derivation] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard child key derivation `_ +.. [#zip-0032-key-path-levels] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Key path levels `_ +.. [#zip-0032-orchard-key-path] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard key path `_ .. [#zip-0200] `ZIP 200: Network Upgrade Mechanism `_ .. [#zip-0224] `ZIP 224: Orchard `_ .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ @@ -605,19 +610,10 @@ References .. [#zip-0244-sigdigest] `ZIP 244: Transaction Identifier Non-Malleability: Signature Digest `_ .. [#zip-0244-authcommitment] `ZIP 244: Transaction Identifier Non-Malleability: Authorizing Data Commitment `_ .. [#zip-0317b] `ZIP 317: Proportional Transfer Fee Mechanism `_ -.. [#zip-0032] `ZIP 32: Shielded Hierarchical Deterministic Wallets `_ -.. [#zip-0032-orchard-master] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard master key generation `_ -.. [#zip-0032-orchard-child-key-derivation] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard child key derivation `_ -.. [#zip-0032-key-path-levels] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Key path levels `_ -.. [#zip-0032-orchard-key-path] `ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard key path `_ -.. [#zip-0316] `ZIP 316: Unified Addresses and Unified Viewing Keys `_ .. [#bip-0340] `BIP 340: Schnorr Signatures for secp256k1 `_ -.. [#protocol-Notation] `Zcash Protocol Specification, Version 2022.3.8. Section 2: Notation `_ -.. [#protocol-addressesandkeys] `Zcash Protocol Specification, Version 2022.3.8. Section 3.1: Payment Addresses and Keys `_ -.. [#protocol-concretegrouphashpallasandvesta] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.9.8: Group Hash into Pallas and Vesta `_ -.. [#protocol-abstractprfs] `Zcash Protocol Specification, Version 2022.3.8. Section 4.1.2: Pseudo Random Functions `_ -.. [#protocol-orchardkeycomponents] `Zcash Protocol Specification, Version 2022.3.8. Section 4.2.3: Orchard Key Components `_ -.. [#protocol-spendauthsig] `Zcash Protocol Specification, Version 2022.3.8. Section 4.15: Spend Authorization Signature (Sapling and Orchard) `_ -.. [#protocol-concretespendauthsig] `Zcash Protocol Specification, Version 2022.3.8. Section 5.4.7.1: Spend Authorization Signature (Sapling and Orchard) `_ -.. [#protocol-orchardpaymentaddrencoding] `Zcash Protocol Specification, Version 2022.3.8. Section 5.6.4.2: Orchard Raw Payment Addresses `_ -.. [#protocol-transactionstructure] `Zcash Protocol Specification, Version 2022.3.8. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5) `_ +.. [#protocol-notation] `Zcash Protocol Specification, Version 2023.4.0. Section 2: Notation `_ +.. [#protocol-addressesandkeys] `Zcash Protocol Specification, Version 2023.4.0. Section 3.1: Payment Addresses and Keys `_ +.. [#protocol-orchardkeycomponents] `Zcash Protocol Specification, Version 2023.4.0. Section 4.2.3: Orchard Key Components `_ +.. [#protocol-concretegrouphashpallasandvesta] `Zcash Protocol Specification, Version 2023.4.0. Section 5.4.9.8: Group Hash into Pallas and Vesta `_ +.. [#protocol-orchardpaymentaddrencoding] `Zcash Protocol Specification, Version 2023.4.0. Section 5.6.4.2: Orchard Raw Payment Addresses `_ +.. [#protocol-txnencoding] `Zcash Protocol Specification, Version 2023.4.0. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5) `_ diff --git a/zip-0230.rst b/zip-0230.rst index 4d7829404..3354be4dc 100644 --- a/zip-0230.rst +++ b/zip-0230.rst @@ -21,8 +21,8 @@ Terminology =========== -The key words "MUST" and "MAY" in this document are to be interpreted as described in -RFC 2119. [#RFC2119]_ +The key words "MUST", "SHOULD", and "MAY" in this document are to be interpreted as +described in BCP 14 [#BCP14]_ when, and only when, they appear in all capitals. The character § is used when referring to sections of the Zcash Protocol Specification [#protocol]_. @@ -339,13 +339,11 @@ TODO References ========== -.. [#RFC2119] `RFC 2119: Key words for use in RFCs to Indicate Requirement Levels `_ -.. [#protocol] `Zcash Protocol Specification, Version 2021.2.16 or later [NU5 proposal] `_ -.. [#protocol-spenddesc] `Zcash Protocol Specification, Version 2021.2.16 [NU5 proposal]. Section 4.4: Spend Descriptions `_ -.. [#protocol-outputdesc] `Zcash Protocol Specification, Version 2021.2.16 [NU5 proposal]. Section 4.5: Output Descriptions `_ -.. [#protocol-actiondesc] `Zcash Protocol Specification, Version 2021.2.16 [NU5 proposal]. Section 4.6: Action Descriptions `_ -.. [#zip-0222] `ZIP 222: Transparent Zcash Extensions `_ +.. [#BCP14] `Information on BCP 14 — "RFC 2119: Key words for use in RFCs to Indicate Requirement Levels" and "RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words" `_ +.. [#protocol] `Zcash Protocol Specification, Version 2023.4.0 or later [NU5 proposal] `_ +.. [#protocol-spenddesc] `Zcash Protocol Specification, Version 2023.4.0 [NU5 proposal]. Section 4.4: Spend Descriptions `_ +.. [#protocol-outputdesc] `Zcash Protocol Specification, Version 2023.4.0 [NU5 proposal]. Section 4.5: Output Descriptions `_ +.. [#protocol-actiondesc] `Zcash Protocol Specification, Version 2023.4.0 [NU5 proposal]. Section 4.6: Action Descriptions `_ .. [#zip-0226] `ZIP 226: Transfer and Burn of Zcash Shielded Assets `_ .. [#zip-0227] `ZIP 227: Issuance of Zcash Shielded Assets `_ .. [#zip-0244] `ZIP 244: Transaction Identifier Non-Malleability `_ -.. [#zip-0307] `ZIP 307: Light Client Protocol for Payment Detection `_ From 15118ac4c03354348afd5983020fa5fe9ab22840 Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 18:33:46 +0000 Subject: [PATCH 38/43] ZIPs 226, 227, and 230: cosmetic math formatting improvements. Signed-off-by: Daira-Emma Hopwood --- zip-0226.rst | 103 ++++++++++++++++++++++++------------------------ zip-0227.rst | 108 +++++++++++++++++++++++++-------------------------- zip-0230.rst | 38 +++++++++--------- 3 files changed, 126 insertions(+), 123 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 19ad029f4..6f8966c1b 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -48,16 +48,17 @@ This ZIP builds on the issuance mechanism introduced in ZIP 227 [#zip-0227]_. Overview ======== -In order to be able to represent different Assets, we need to define a data field that uniquely represents the Asset in question, which we call the Asset Identifier :math:`\mathsf{AssetId}`. +In order to be able to represent different Assets, we need to define a data field that uniquely represents the Asset in question, which we call the Asset Identifier :math:`\mathsf{AssetId}\!`. This Asset Identifier maps to an Asset Base :math:`\mathsf{AssetBase}` that is stored in Orchard-based ZSA notes. These terms are formally defined in ZIP 227 [#zip-0227]_. -The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ [#protocol-actionencodingandconsensus]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-orchardbalance]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}-value^{new}}`, must be balanced **only with respect to the same Asset Identifier**. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. +The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description [#protocol-actions]_ [#protocol-actionencodingandconsensus]_ is preserved across Assets (see the Orchard Binding Signature [#protocol-orchardbalance]_), and by extension the balance of an Orchard transaction. That is, the sum of all the :math:`\mathsf{value^{net}}` from each Action Description, computed as :math:`\mathsf{value^{old}} - \mathsf{value^{new}}\!`, must be balanced **only with respect to the same Asset Identifier**. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred. -As was initially proposed by Jack Grigg and Daira-Emma Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}`, of the *net value* in an Orchard Action. +As was initially proposed by Jack Grigg and Daira-Emma Hopwood [#initial-zsa-issue]_ [#generalized-value-commitments]_, we propose to make this happen by changing the value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}\!`, in the Homomorphic Pedersen Commitment that derives the value commitment, :math:`\mathsf{cv^{net}}\!`, of the *net value* in an Orchard Action. Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base an auxiliary input to the proof for each Action statement [#protocol-actionstatement]_, represented already as a point on the Pallas curve. The circuit then should check that the same Asset Base is used in the old note commitment and the new note commitment [#protocol-concretesinsemillacommit]_, **and** as the base point in the value commitment [#protocol-concretehomomorphiccommit]_. This ensures (1) that the input and output notes are of the same Asset Base, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature. +In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes [#protocol-orcharddummynotes]_ for Custom Assets, as we need to enforce that the :math:`\mathsf{AssetBase}` of the output note of that Split Action is the output of a valid :math:`\mathsf{ZSAValueBase}` computation defined in ZIP 227 [#zip-0227]_. We include the ability to pause the ZSA functionality, via a :math:`\mathsf{enableZSA}` boolean flag. When this flag is set to false, it is not possible to perform transactions involving Custom Assets (the Action statement as modified for ZSAs will not be satisfied). @@ -71,9 +72,9 @@ Most of the protocol is kept the same as the Orchard protocol released with NU5, Asset Identifiers ----------------- -For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance validating key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}`) are derived as defined in ZIP 227 [#zip-0227]_. +For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an *Asset description*, :math:`\mathsf{asset\_desc}\!`, which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance validating key of the issuer, the specific Asset Identifier, :math:`\mathsf{AssetId}\!`, the Asset Digest, and the Asset Base (:math:`\mathsf{AssetBase}\!`) are derived as defined in ZIP 227 [#zip-0227]_. -This Asset Base will be the base point of the value commitment for the specific Custom Asset. Note that the Asset Base of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^\mathsf{Orchard}`. +This Asset Base will be the base point of the value commitment for the specific Custom Asset. Note that the Asset Base of the ZEC Asset will be kept as the original value base point, :math:`\mathcal{V}^{\mathsf{Orchard}}\!`. Rationale for Asset Identifiers ``````````````````````````````` @@ -84,36 +85,36 @@ Note Structure & Commitment --------------------------- Let :math:`\mathsf{Note^{OrchardZSA}}` be the type of a ZSA note, i.e. -:math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}^*`. +:math:`\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}^*\!`. -An Orchard ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}`. So a ZSA note is a tuple :math:`(\mathsf{g_d, pk_d, v, \rho, \psi, \mathsf{AssetBase}})`, +An Orchard ZSA note differs from an Orchard note [#protocol-notes]_ by additionally including the Asset Base, :math:`\mathsf{AssetBase}\!`. So a ZSA note is a tuple :math:`(\mathsf{g_d}, \mathsf{pk_d}, \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase})\!`, where -- :math:`\mathsf{AssetBase} : \mathbb{P}^*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid group element that is not the identity and is not :math:`\bot`. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase})`. +- :math:`\mathsf{AssetBase} : \mathbb{P}^*` is the unique element of the Pallas group [#protocol-pallasandvesta]_ that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 [#zip-0227]_, a valid group element that is not the identity and is not :math:`\bot\!`. The byte representation of the Asset Base is defined as :math:`\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase})\!`. Note that the above assumes a canonical encoding, which is true for the Pallas group, but may not hold for future shielded protocols. We define the note commitment scheme :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}` as follows: -.. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \{0 .. 2^{\ell_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P}^* \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Output} +.. math:: \mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\!\mathsf{Trapdoor} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \{0 .. 2^{\ell_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P}^* \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\!\mathsf{Output} -where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and where :math:`\mathsf{NoteCommit}^{\mathsf{Orchard}}.\mathsf{Trapdoor}` and :math:`\mathsf{Orchard}.\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. +where :math:`\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, and where :math:`\mathsf{NoteCommit^{Orchard}}.\!\mathsf{Trapdoor}` and :math:`\mathsf{Orchard}.\!\mathsf{Output}` are as defined in the Zcash protocol specification [#protocol-abstractcommit]_. This note commitment scheme is instantiated using the Sinsemilla Commitment [#protocol-concretesinsemillacommit]_ as follows: .. math:: \begin{align} - \mathsf{NoteCommit^{OrchardZSA}_{rcm}(g_{d}\star, pk_{d}\star, v, \rho, \psi, \mathsf{AssetBase})} - :=\begin{cases} - \mathsf{NoteCommit^{Orchard}_{rcm}(g_{d}\star, pk_{d}\star, v, \rho, \psi)}, &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ - \mathsf{cm}_{\mathsf{ZSA}} &\text{otherwise} - \end{cases} + \mathsf{NoteCommit^{OrchardZSA}_{rcm}}(\mathsf{g_d}\star, \mathsf{pk_d}\star, \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase}) + := \begin{cases} + \mathsf{NoteCommit^{Orchard}_{rcm}}(\mathsf{g_d}\star, \mathsf{pk_d}\star, \mathsf{v}, \text{ρ}, \text{ψ}), &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ + \mathsf{cm_{ZSA}} &\text{otherwise} + \end{cases} \end{align} where: .. math:: \begin{align} - \mathsf{cm}_{\mathsf{ZSA}} :=&\ \mathsf{SinsemillaHashToPoint}( \texttt{"z.cash:ZSA-NoteCommit-M"}, \\ - &\ \ \ \mathsf{g_{d}\star} \,||\, \mathsf{pk_{d}\star} \,||\, \mathsf{I2LEBSP_{64}(v)} \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\rho) \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\psi) \,||\, \mathsf{asset\_base}) \\ - &\ + [\mathsf{rcm}] \mathsf{GroupHash}^{\mathbb{P}}(\texttt{"z.cash:Orchard-NoteCommit-r"},\texttt{""}) + \mathsf{cm_{ZSA}} :=&\;\;\mathsf{SinsemillaHashToPoint}(\texttt{"z.cash:ZSA-NoteCommit-M"}, \\ + &\;\;\;\;\;\mathsf{g_{d}\star} \,||\, \mathsf{pk_{d}\star} \,||\, \mathsf{I2LEBSP_{64}(v)} \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\text{ρ}) \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\text{ψ}) \,||\, \mathsf{asset\_base}) \\ + &\;\;+\;\;[\mathsf{rcm}]\,\mathsf{GroupHash}^{\mathbb{P}}(\texttt{"z.cash:Orchard-NoteCommit-r"}, \texttt{""}) \end{align} Note that :math:`\mathsf{repr}_{\mathbb{P}}` and :math:`\mathsf{GroupHash}^{\mathbb{P}}` are as defined for the Pallas curve [#protocol-pallasandvesta]_, :math:`\ell^{\mathsf{Orchard}}_{\mathsf{base}}` is as defined in §5.3 [#protocol-constants]_, and :math:`\mathsf{I2LEBSP}` is as defined in §5.1 [#protocol-endian]_ of the Zcash protocol specification. @@ -128,13 +129,13 @@ It consists of Rationale for Note Commitment ````````````````````````````` -In the ZSA protocol, the instance of the note commitment scheme, :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}`, differs from the Orchard note commitment :math:`\mathsf{NoteCommit^{Orchard}_{rcm}}` in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. +In the ZSA protocol, the instance of the note commitment scheme, :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm}}\!`, differs from the Orchard note commitment :math:`\mathsf{NoteCommit^{Orchard}_{rcm}}` in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. In the case where the Asset is the ZEC Asset, the commitment is computed identically to the Orchard note commitment, without making use of the ZEC Asset Base as an input. As we will see, the nested structure of the Sinsemilla-based commitment [#protocol-concretesinsemillacommit]_ allows us to add the Asset Base as a final recursive step. The note commitment output is still indistinguishable from the original Orchard ZEC note commitments, by definition of the Sinsemilla hash function [#protocol-concretesinsemillahash]_. ZSA note commitments will therefore be added to the same Orchard Note Commitment Tree. In essence, we have: -.. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, \mathsf{AssetBase})} \in \mathsf{NoteCommit^{Orchard}.Output} +.. math:: \mathsf{NoteCommit^{OrchardZSA}_{rcm}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d}), \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase}) \in \mathsf{NoteCommit^{Orchard}}.\!\mathsf{Output} This definition can be viewed as a generalization of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes. @@ -143,17 +144,17 @@ Value Commitment In the case of the Orchard-based ZSA protocol, the value of different Asset Identifiers in a given transaction will be committed using a **different value base point**. The value commitment becomes: -.. math:: \mathsf{cv^{net}:=ValueCommit^{OrchardZSA}_{rcv}(\mathsf{AssetBase}_{\mathsf{AssetId}}, v^{net}_{AssetId})}:= \mathsf{[v^{net}_{AssetId}]}\mathsf{AssetBase}_{\mathsf{AssetId}} + [\mathsf{rcv}]\mathcal{R}^{\mathsf{Orchard}} +.. math:: \mathsf{cv^{net}} := \mathsf{ValueCommit^{OrchardZSA}_{rcv}}(\mathsf{AssetBase_{AssetId}}, \mathsf{v^{net}_{AssetId}}) = [\mathsf{v^{net}_{AssetId}}]\,\mathsf{AssetBase_{AssetId}} + [\mathsf{rcv}]\,\mathcal{R}^{\mathsf{Orchard}} -where :math:`\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId} - v^{new}_{AssetId}}` such that :math:`\mathsf{v^{old}_{AssetId}}` and :math:`\mathsf{v^{new}_{AssetId}}` are the values of the old and new notes of Asset Identifier :math:`\mathsf{AssetId}` respectively, +where :math:`\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId}} - \mathsf{v^{new}_{AssetId}}` such that :math:`\mathsf{v^{old}_{AssetId}}` and :math:`\mathsf{v^{new}_{AssetId}}` are the values of the old and new notes of Asset Identifier :math:`\mathsf{AssetId}` respectively, .. _`asset base`: -:math:`\mathsf{AssetBase}_{\mathsf{AssetId}}` is defined in ZIP 227 [#zip-0227]_, and +:math:`\mathsf{AssetBase_{AssetId}}` is defined in ZIP 227 [#zip-0227]_, and -:math:`\mathcal{R}^{\mathsf{Orchard}}:=\mathsf{GroupHash^{\mathbb{P}}}\texttt{("z.cash:Orchard-cv", "r")}`, as in the Orchard protocol. +:math:`\mathcal{R}^{\mathsf{Orchard}} := \mathsf{GroupHash^{\mathbb{P}}}(\texttt{"z.cash:Orchard-cv"}, \texttt{"r"})\!`, as in the Orchard protocol. -For ZEC, we define :math:`\mathsf{AssetBase}_{\mathsf{AssetId}} :=\mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. As such :math:`\mathsf{ValueCommit^{Orchard}_{rcv}(v)}` as defined in [#zip-0224]_ is used as :math:`\mathsf{ValueCommit^{OrchardZSA}_{rcv}(\mathcal{V}^{\mathsf{Orchard}}, v)}` here. +For ZEC, we define :math:`\mathsf{AssetBase}_{\mathsf{AssetId}} := \mathcal{V}^{\mathsf{Orchard}}` so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 [#zip-0224]_. As such :math:`\mathsf{ValueCommit^{Orchard}_{rcv}}(\mathsf{v})` as defined in [#zip-0224]_ is used as :math:`\mathsf{ValueCommit^{OrchardZSA}_{rcv}}(\mathcal{V}^{\mathsf{Orchard}}, \mathsf{v})` here. Rationale for Value Commitment `````````````````````````````` @@ -168,9 +169,9 @@ Burn Mechanism The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. Burning makes it globally provable that a given amount of an Asset has been destroyed. -The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `Orchard-ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^Orchard}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (e.g. to Sapling or Transparent). +The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the `Orchard-ZSA Transaction Structure`_, this is separate from the regular :math:`\mathsf{valueBalance^{Orchard}}` that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (e.g. to Sapling or Transparent). -For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` set the tuple :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. +For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` set the tuple :math:`(\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. .. math:: \mathsf{assetBurn} = \{ (\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})\ |\ \forall\ \mathsf{AssetBase}_{\mathsf{AssetId}}\ \textit{s.t.}\ \mathsf{v_{AssetId}} \neq 0 \} @@ -179,9 +180,9 @@ We denote by :math:`L` the cardinality of the :math:`\mathsf{assetBurn}` set. Additional Consensus Rules `````````````````````````` -1. We require that for every :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}}) \in \mathsf{assetBurn}\ ,\ \mathsf{AssetBase}_{\mathsf{AssetId}} \neq \mathcal{V}^{\mathsf{Orchard}}`. That is, ZEC or TAZ is not allowed to be burnt. -2. We require that for every :math:`(\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}}) \in \mathsf{assetBurn}\ ,\ \mathsf{v_{AssetId}} \neq 0`. -3. We require that there be no duplication of Custom Assets in the :math:`\mathsf{assetBurn}` set. That is, every :math:`\mathsf{AssetBase}_{\mathsf{AssetId}}` has at most one entry in :math:`\mathsf{assetBurn}`. +1. We require that for every :math:`(\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}}) \in \mathsf{assetBurn}, \mathsf{AssetBase_{AssetId}} \neq \mathcal{V}^{\mathsf{Orchard}}\!`. That is, ZEC or TAZ is not allowed to be burnt. +2. We require that for every :math:`(\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}}) \in \mathsf{assetBurn}, \mathsf{v_{AssetId}} \neq 0\!`. +3. We require that there be no duplication of Custom Assets in the :math:`\mathsf{assetBurn}` set. That is, every :math:`\mathsf{AssetBase_{AssetId}}` has at most one entry in :math:`\mathsf{assetBurn}\!`. **Note:** Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets. @@ -191,35 +192,35 @@ Value Balance Verification In order to verify the balance of the different Assets, the verifier MUST perform a similar process as for the Orchard protocol [#protocol-orchardbalance]_, with the addition of the burn information. For a total of :math:`n` Actions in a transfer, the prover MUST still sign the SIGHASH transaction hash using the binding signature key -:math:`\mathsf{bsk} = \sum_{i=1}^{n} \mathsf{rcv}_{i}`. +:math:`\mathsf{bsk} = \sum_{i=1}^{n} \mathsf{rcv}_i\!`. The verifier MUST compute the value balance verification equation: -.. math:: \mathsf{bvk} =(\sum_{i=1}^{n} \mathsf{cv^{net}}_{i}) - \mathsf{ValueCommit_0^{OrchardZSA}(\mathcal{V}^{\mathsf{Orchard}}, v^{balanceOrchard})} - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{AssetBase}, \mathsf{v}) +.. math:: \mathsf{bvk} = (\sum_{i=1}^{n} \mathsf{cv}^{\mathsf{net}}_i) - \mathsf{ValueCommit_0^{OrchardZSA}(\mathcal{V}^{\mathsf{Orchard}}, v^{balanceOrchard})} - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{AssetBase}, \mathsf{v}) -After computing :math:`\mathsf{bvk}`, the verifier MUST use it to verify the binding signature on the SIGHASH transaction hash. +After computing :math:`\mathsf{bvk}\!`, the verifier MUST use it to verify the binding signature on the SIGHASH transaction hash. Rationale for Value Balance Verification ```````````````````````````````````````` We assume :math:`n` Actions in a transfer. Out of these :math:`n` Actions, we further distinguish (for the sake of clarity) between Actions related to ZEC and Actions related to Custom Assets. -We denote by :math:`S_{\mathsf{ZEC}} \subseteq [1,n]` the set of indices of Actions that are related to ZEC, and by :math:`S_{\mathsf{CA}} = [1,n] \setminus S_{\mathsf{ZEC}}` the set of indices of Actions that are related to Custom Assets. +We denote by :math:`S_{\mathsf{ZEC}} \subseteq \{1 .. n\}` the set of indices of Actions that are related to ZEC, and by :math:`S_{\mathsf{CA}} = \{1 .. n\} \setminus S_{\mathsf{ZEC}}` the set of indices of Actions that are related to Custom Assets. The right hand side of the value balance verification equation can be expanded to: -.. math:: ((\sum_{i \in S_{\mathsf{ZEC}}} \mathsf{cv^{net}}_{i}) + (\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv^{net}}_{j})) - ([\mathsf{v^{balanceOrchard}}]\mathcal{V}^{\mathsf{Orchard}} + [0]\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\mathsf{AssetBase} + [0]\mathcal{R}^{\mathsf{Orchard}}) +.. math:: ((\sum_{i \in S_{\mathsf{ZEC}}} \mathsf{cv}^{\mathsf{net}}_i) + (\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv}^{\mathsf{net}}_j)) - ([\mathsf{v^{balanceOrchard}}]\,\mathcal{V}^{\mathsf{Orchard}} + [0]\,\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\,\mathsf{AssetBase} + [0]\,\mathcal{R}^{\mathsf{Orchard}}) This equation contains the balance check of the Orchard protocol [#protocol-orchardbalance]_. With ZSA, transfer Actions for Custom Assets must also be balanced across Asset Bases. All Custom Assets are contained within the shielded pool, and cannot be unshielded via a regular transfer. Custom Assets can be burnt, the mechanism for which reveals the amount and identifier of the Asset being burnt, within the :math:`\mathsf{assetBurn}` set. -As such, for a correctly constructed transaction, we will get :math:`\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv}_j^{\mathsf{net}} - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\mathsf{AssetBase} = \mathsf{\sum_{j \in S_{\mathsf{CA}}} rcv_{j}^{net}}\mathcal{R}^{\mathsf{Orchard}}`. +As such, for a correctly constructed transaction, we will get :math:`\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv}^{\mathsf{net}}_j - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\,\mathsf{AssetBase} = \sum_{j \in S_{\mathsf{CA}}} [\mathsf{rcv}^{\mathsf{net}}_j]\,\mathcal{R}^{\mathsf{Orchard}}\!`. When the Asset is not being burnt, the net balance of the input and output values is zero, and there will be no addition to the :math:`\mathsf{assetBurn}` vector. Therefore, the relationship between :math:`\mathsf{bvk}` and :math:`\mathsf{bsk}` will hold if and only if, per Custom Asset, the sum of the net values of the relevant Actions equals the corresponding :math:`\mathsf{v}_k` value (or equals :math:`0` if that Asset is not in the :math:`\mathsf{assetBurn}` set), and for ZEC, the sum of the net values of the relevant Actions equals the :math:`\mathsf{v^{balanceOrchard}}` value. -As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values must sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. +As in the Orchard protocol, the binding signature verification key, :math:`\mathsf{bvk}\!`, will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values must sum to zero **per Asset Base**, as the Pedersen commitments add up homomorphically only with respect to the same value base point. Split Notes @@ -242,9 +243,9 @@ Wallets and other clients have to choose from the following to ensure the Asset For Split Notes, the nullifier is generated as follows: -.. math:: \mathsf{nf_{old}} = \mathsf{Extract}_{\mathbb{P}} ([(\mathsf{PRF^{nfOrchard}_{nk}} (\rho^{\mathsf{old}}) + \psi') \bmod q_{\mathbb{P}}] \mathcal{K}^\mathsf{Orchard} + \mathsf{cm^{old}} + \mathcal{L}^\mathsf{Orchard}) +.. math:: \mathsf{nf_{old}} = \mathsf{Extract}_{\mathbb{P}} ([(\mathsf{PRF^{nfOrchard}_{nk}} (\text{ρ}^{\mathsf{old}}) + \text{ψ}') \bmod q_{\mathbb{P}}]\,\mathcal{K}^\mathsf{Orchard} + \mathsf{cm^{old}} + \mathcal{L}^\mathsf{Orchard}) -where :math:`\psi'` is sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}`, :math:`\mathcal{K}^{\mathsf{Orchard}}` is the Orchard Nullifier Base as defined in [#protocol-commitmentsandnullifiers]_, and :math:`\mathcal{L}^{\mathsf{Orchard}} := \mathsf{GroupHash^{\mathbb{P}}}\texttt{("z.cash:Orchard", "L")}`. +where :math:`\text{ψ}'` is sampled uniformly at random on :math:`\mathbb{F}_{q_{\mathbb{P}}}\!`, :math:`\mathcal{K}^{\mathsf{Orchard}}` is the Orchard Nullifier Base as defined in [#protocol-commitmentsandnullifiers]_, and :math:`\mathcal{L}^{\mathsf{Orchard}} := \mathsf{GroupHash^{\mathbb{P}}}(\texttt{"z.cash:Orchard"}, \texttt{"L"})\!`. Rationale for Split Notes ````````````````````````` @@ -269,28 +270,28 @@ All modifications in the Circuit are detailed in [#circuit-modifications]_. Asset Base Equality ``````````````````` -The following constraints must be added to ensure that the input and output note are of the same :math:`\mathsf{AssetBase}`: +The following constraints must be added to ensure that the input and output note are of the same :math:`\mathsf{AssetBase}\!`: -- The Asset Base, :math:`\mathsf{AssetBase}_{\mathsf{AssetId}}`, for the note is witnessed once, as an auxiliary input. -- In the Old note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}(repr_{\mathbb{P}}(g_d^{old}), repr_{\mathbb{P}}(pk_d^{old}), v^{old}, \rho^{old}, \psi^{old}, \mathsf{AssetBase}_{\mathsf{AssetId}})}`. -- In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new})}` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}(repr_{\mathbb{P}}(g_d^{new}), repr_{\mathbb{P}}(pk_d^{new}), v^{new}, \rho^{new}, \psi^{new}, \mathsf{AssetBase}_{\mathsf{AssetId}})}`. +- The Asset Base, :math:`\mathsf{AssetBase_{AssetId}}\!`, for the note is witnessed once, as an auxiliary input. +- In the Old note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{old}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{old}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{old}}), \mathsf{v^{old}}, \text{ρ}^{\mathsf{old}}, \text{ψ}^{\mathsf{old}})` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{old}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{old}}), \mathsf{v^{old}}, \text{ρ}^{\mathsf{old}}, \text{ψ}^{\mathsf{old}}, \mathsf{AssetBase_{AssetId}})\!`. +- In the New note commitment integrity constraint in the Orchard Action statement [#protocol-actionstatement]_, :math:`\mathsf{NoteCommit^{Orchard}_{rcm^{new}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{new}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{new}}), \mathsf{v^{new}}, \text{ρ}^{\mathsf{new}}, \text{ψ}^{\mathsf{new}})` is replaced with :math:`\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{new}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{new}}), \mathsf{v^{new}}, \text{ρ}^{\mathsf{new}}, \text{ψ}^{\mathsf{new}}, \mathsf{AssetBase_{AssetId}})\!`. -To make the evaluation of the note commitment easier, we add a boolean :math:`\mathsf{is\_native\_asset}` as an auxiliary witness. We also add some constraints to verify that this variable is activated (i.e. :math:`\mathsf{is\_native\_asset} = 1`) if the Asset Base is equal to :math:`\mathcal{V}^\mathsf{Orchard}` and this variable is not activated (i.e. :math:`\mathsf{is\_native\_asset} = 0`) if the Asset Base is not equal to :math:`\mathcal{V}^\mathsf{Orchard}`. +To make the evaluation of the note commitment easier, we add a boolean :math:`\mathsf{is\_native\_asset}` as an auxiliary witness. We also add some constraints to verify that this variable is activated (i.e. :math:`\mathsf{is\_native\_asset} = 1\!`) if the Asset Base is equal to :math:`\mathcal{V}^{\mathsf{Orchard}}` and this variable is not activated (i.e. :math:`\mathsf{is\_native\_asset} = 0\!`) if the Asset Base is not equal to :math:`\mathcal{V}^{\mathsf{Orchard}}\!`. The :math:`\mathsf{enableZSA}` Flag ````````````````````````````````````` The following constraints must be added to disable transactions involving Custom Assets when the :math:`\mathsf{enableZSA}` flag is set to false: -- if :math:`\mathsf{enableZSA}` is not activated (i.e. :math:`\mathsf{enableZSA} = 0`), then constrain :math:`\mathsf{is\_native\_asset} = 1`, since the :math:`\mathsf{AsssetBase}` must be equal to the native asset. +- if :math:`\mathsf{enableZSA}` is not activated (i.e. :math:`\mathsf{enableZSA} = 0\!`), then constrain :math:`\mathsf{is\_native\_asset} = 1\!`, since the :math:`\mathsf{AsssetBase}` must be equal to the native asset. Value Commitment Correctness ```````````````````````````` The following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base: -- The fixed-base multiplication constraints between the value and the value base point of the value commitment, :math:`\mathsf{cv}`, is replaced with a variable-base multiplication between the two. -- The witness to the value base point (as defined in the `asset base`_ equation) is the auxiliary input :math:`\mathsf{AssetBase}_{\mathsf{AssetId}}`. +- The fixed-base multiplication constraint between the value and the value base point of the value commitment, :math:`\mathsf{cv}\!`, is replaced with a variable-base multiplication between the two. +- The witness to the value base point (as defined in the `asset base`_ equation) is the auxiliary input :math:`\mathsf{AssetBase_{AssetId}}\!`. Asset Identifier Consistency for Split Actions `````````````````````````````````````````````` @@ -298,13 +299,13 @@ Asset Identifier Consistency for Split Actions Senders must not be able to change the Asset Base for the output note in a Split Action. We do this via the following constraints: - The Value Commitment Integrity should be changed: - - Replace the input note value by a generic value, :math:`\mathsf{v}'`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}(\mathsf{AssetBase}_{\mathsf{AssetId}}, v’ - v^new)}` + - Replace the input note value by a generic value, :math:`\mathsf{v}'\!`, as :math:`\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}}(\mathsf{AssetBase_{AssetId}}, \mathsf{v}' - \mathsf{v^{new}})` - Add a boolean :math:`\mathsf{split\_flag}` variable as an auxiliary witness. This variable is to be activated :math:`\mathsf{split\_flag} = 1` if the Action in question has a Split Input and :math:`\mathsf{split\_flag} = 0` if the Action is actually spending an input note: - - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{v}' = 0` otherwise constrain :math:`\mathsf{v}'=\mathsf{v^{old}}` from the auxiliary input. + - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{v}' = 0` otherwise constrain :math:`\mathsf{v}' = \mathsf{v^{old}}` from the auxiliary input. - If :math:`\mathsf{split\_flag} = 1` then constrain :math:`\mathsf{is\_native\_asset} = 0` because split notes are only available for Custom Assets. - The Merkle Path Validity should check the existence of the note commitment as usual (and not like with dummy notes): - - Check for all notes except dummy notes that (path, pos) is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^Orchard}`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}`. - - The new constraint is :math:`\underbrace{(\mathsf{v^{old}} = 0 \land \mathsf{is\_native\_asset} = 1)}_\text{It is a dummy note} \lor \underbrace{(\mathsf{Valid\,Merkle\,Path})}_\text{The Merkle Path is valid}`. + - Check for all notes except dummy notes that :math:`(\mathsf{path}, \mathsf{pos})` is a valid Merkle path of depth :math:`\mathsf{MerkleDepth^{Orchard}}\!`, from :math:`\mathsf{cm^{old}}` to the anchor :math:`\mathsf{rt^{Orchard}}\!`. + - The new constraint is :math:`\underbrace{(\mathsf{v^{old}} = 0 \land \mathsf{is\_native\_asset} = 1)}_\text{It is a dummy note} \lor \underbrace{(\mathsf{Valid\,Merkle\,Path})}_\text{The Merkle Path is valid}\!`. - The Nullifier Integrity will be changed to prevent the identification of notes as defined in the `Split Notes`_ section. Backwards Compatibility with ZEC Notes diff --git a/zip-0227.rst b/zip-0227.rst index fa61b0e53..1f519c203 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -83,9 +83,9 @@ Specification: Issuance Keys and Issuance Authorization Signature Scheme The Orchard-ZSA Protocol adds the following keys to the key components [#protocol-addressesandkeys]_ [#protocol-orchardkeycomponents]_: -1. The issuance authorizing key, denoted as :math:`\mathsf{isk}`, is the key used to authorize the issuance of Asset Identifiers by a given issuer, and is only used by that issuer. +1. The issuance authorizing key, denoted as :math:`\mathsf{isk}\!`, is the key used to authorize the issuance of Asset Identifiers by a given issuer, and is only used by that issuer. -2. The issuance validating key, denoted as :math:`\mathsf{ik}`, is the key that is used to validate issuance transactions. This key is used to validate the issuance of Asset Identifiers by a given issuer, and is used by all blockchain users (specifically the owners of notes for that Asset, and consensus validators) to associate the Asset in question with the issuer. +2. The issuance validating key, denoted as :math:`\mathsf{ik}\!`, is the key that is used to validate issuance transactions. This key is used to validate the issuance of Asset Identifiers by a given issuer, and is used by all blockchain users (specifically the owners of notes for that Asset, and consensus validators) to associate the Asset in question with the issuer. The relations between these keys are shown in the following diagram: @@ -102,16 +102,16 @@ Issuance Authorization Signature Scheme We instantiate the issuance authorization signature scheme :math:`\mathsf{IssueAuthSig}` as a BIP-340 Schnorr signature over the secp256k1 curve. The signing and validation algorithms, signature encoding, and public key encoding MUST follow BIP 340 [#bip-0340]_. -Batch verification MAY be used. Precomputation MAY be used if and only if it produces equivalent results; for example, for a given verification key :math:`pk`, :math:`\mathit{lift\_x}(\mathit{int}(pk))` MAY be precomputed. +Batch verification MAY be used. Precomputation MAY be used if and only if it produces equivalent results; for example, for a given verification key :math:`pk` and :math:`\mathit{lift\_x}(\mathit{int}(pk))` MAY be precomputed. We define the constants as per the secp256k1 standard parameters, as described in BIP 340. The associated types of the :math:`\mathsf{IssueAuthSig}` signature scheme are as follows: -* :math:`\mathsf{IssueAuthSig.Message} = \mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}` -* :math:`\mathsf{IssueAuthSig.Signature} = \mathbb{B}^{\mathbb{Y}^{[64]}} \cup \{\bot\}` -* :math:`\mathsf{IssueAuthSig.Public} = \mathbb{B}^{\mathbb{Y}^{[32]}} \cup \{\bot\}` -* :math:`\mathsf{IssueAuthSig.Private} = \mathbb{B}^{\mathbb{Y}^{[32]}}` +* :math:`\mathsf{IssueAuthSig}.\!\mathsf{Message} = \mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}` +* :math:`\mathsf{IssueAuthSig}.\!\mathsf{Signature} = \mathbb{B}^{\mathbb{Y}^{[64]}} \cup \{\bot\}` +* :math:`\mathsf{IssueAuthSig}.\!\mathsf{Public} = \mathbb{B}^{\mathbb{Y}^{[32]}} \cup \{\bot\}` +* :math:`\mathsf{IssueAuthSig}.\!\mathsf{Private} = \mathbb{B}^{\mathbb{Y}^{[32]}}` where :math:`\mathbb{B}^{\mathbb{Y}^{[k]}}` denotes the set of sequences of :math:`k` bytes, and :math:`\mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}` denotes the type of byte sequences of arbitrary length, as defined in the Zcash protocol specification [#protocol-notation]_. @@ -126,61 +126,61 @@ Issuance authorizing key generation for hierarchical deterministic wallets The issuance authorizing key is generated using the Orchard master key derivation procedure defined in ZIP 32 [#zip-0032-orchard-master]_. We reuse the functions defined there in what follows in this section. Let :math:`S` be a seed byte sequence of a chosen length, which MUST be at least 32 and at most 252 bytes. -We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssue_V1"}, S)`. +We define the master extended issuance key :math:`m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssue_V1"}, S)\!`. As in ZIP 32 for Orchard [#zip-0032-orchard-child-key-derivation]_, we only use hardened child key derivation for the issuance authorizing key. We reuse the :math:`\mathsf{CDKsk}` function for Orchard child key derivation from ZIP 32. -We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance authorizing key path as :math:`m_\mathsf{Issuance} / purpose' / coin\_type' / account'`. We fix the path levels as follows: +We use the notation of ZIP 32 [#zip-0032-orchard-key-path]_ for shielded HD paths, and define the issuance authorizing key path as :math:`m_{\mathsf{Issuance}} / \mathit{purpose}' / \mathit{coin\_type}' / \mathit{account}'\!`. We fix the path levels as follows: -- :math:`purpose`: a constant set to :math:`227` (i.e. :math:`\texttt{0xe3}`). :math:`purpose'` is thus :math:`227'` (or :math:`\texttt{0x800000e3}`) following the BIP 43 recommendation. -- :math:`coin\_type`: Defined as in ZIP 32 [#zip-0032-key-path-levels]_. -- :math:`account`: fixed to index :math:`0`. +- :math:`\mathit{purpose}`: a constant set to :math:`227` (i.e. :math:`\mathtt{0xe3}\!`). :math:`\mathit{purpose}'` is thus :math:`227'` (or :math:`\mathtt{0x800000e3}\!`) following the BIP 43 recommendation. +- :math:`\mathit{coin\_type}`: Defined as in ZIP 32 [#zip-0032-key-path-levels]_. +- :math:`\mathit{account}`: fixed to index :math:`0\!`. -From the generated :math:`(\mathsf{sk}, \mathsf{c})`, we set the issuance authorizing key to be :math:`\mathsf{isk} := \mathsf{sk}`. +From the generated :math:`(\mathsf{sk}, \mathsf{c})\!`, we set the issuance authorizing key to be :math:`\mathsf{isk} := \mathsf{sk}\!`. Derivation of issuance validating key ````````````````````````````````````` -Define :math:`\mathsf{IssueAuthSig.DerivePublic}\: : \: (\mathsf{isk}\: : \: \mathsf{IssueAuthSig.Private}) \to \mathsf{IssueAuthSig.Public}` as: +Define :math:`\mathsf{IssueAuthSig}.\!\mathsf{DerivePublic}\; : \; (\mathsf{isk}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Private}) \to \mathsf{IssueAuthSig}.\!\mathsf{Public}` as: * :math:`\mathsf{ik} := \textit{PubKey}(\mathsf{isk})` -* Return :math:`\bot` if the :math:`\textit{PubKey}` algorithm invocation fails, otherwise return :math:`\mathsf{ik}`. +* Return :math:`\bot` if the :math:`\textit{PubKey}` algorithm invocation fails, otherwise return :math:`\mathsf{ik}\!`. where the :math:`\textit{PubKey}` algorithm is defined in BIP 340 [#bip-0340]_. Note that the byte representation of :math:`\mathsf{ik}` is in big-endian order as defined in BIP 340. -It is possible for the :math:`\textit{PubKey}` algorithm to fail with very low probability, which means that :math:`\mathsf{IssueAuthSig.DerivePublic}` could return :math:`\bot` with very low probability. -If this happens, discard the keys and repeat with a different :math:`\mathsf{isk}`. +It is possible for the :math:`\textit{PubKey}` algorithm to fail with very low probability, which means that :math:`\mathsf{IssueAuthSig}.\!\mathsf{DerivePublic}` could return :math:`\bot` with very low probability. +If this happens, discard the keys and repeat with a different :math:`\mathsf{isk}\!`. This allows the issuer to use the same wallet it usually uses to transfer Assets, while keeping a disconnect from the other keys. Specifically, this method is aligned with the requirements and motivation of ZIP 32 [#zip-0032]_. It provides further anonymity and the ability to delegate issuance of an Asset (or in the future, generate a multi-signature protocol) while the rest of the keys remain in the wallet safe. Issuance Authorization Signing and Validation --------------------------------------------- -Define :math:`\mathsf{IssueAuthSig.Sign}\: : \: (\mathsf{isk}\: : \: \mathsf{IssueAuthSig.Private}) \times (M\: : \: \mathsf{IssueAuthSig.Message}) \to \mathsf{IssueAuthSig.Signature}` as: +Define :math:`\mathsf{IssueAuthSig}.\!\mathsf{Sign}\; : \; (\mathsf{isk}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Private}) \times (M\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Message}) \to \mathsf{IssueAuthSig}.\!\mathsf{Signature}` as: -* Let the auxiliary data :math:`a = \mathtt{[0x00]}^{32}`. -* Let :math:`\sigma = \mathsf{Sign}(\mathsf{isk},M)`. -* Return :math:`\bot` if the :math:`\mathsf{Sign}` algorithm fails in the previous step, otherwise return :math:`\sigma`. +* Let the auxiliary data :math:`a = [\mathtt{0x00}]^{32}\!`. +* Let :math:`\text{σ} = \mathsf{Sign}(\mathsf{isk}, M)\!`. +* Return :math:`\bot` if the :math:`\mathsf{Sign}` algorithm fails in the previous step, otherwise return :math:`\text{σ}\!`. where the :math:`\mathsf{Sign}` algorithm is defined in BIP 340 and :math:`a` denotes the auxiliary data used in BIP 340 [#bip-0340]_. -Note that :math:`\mathsf{IssueAuthSig.Sign}` could return :math:`\bot` with very low probability. +Note that :math:`\mathsf{IssueAuthSig}.\!\mathsf{Sign}` could return :math:`\bot` with very low probability. -Define :math:`\mathsf{IssueAuthSig.Validate}\: : \: (\mathsf{ik}\: : \: \mathsf{IssueAuthSig.Public}) \times (M\: : \: \mathsf{IssueAuthSig.Message}) \times (\sigma\: : \: \mathsf{IssueAuthSig.Signature}) \to \mathbb{B}` as: +Define :math:`\mathsf{IssueAuthSig}.\!\mathsf{Validate}\; : \; (\mathsf{ik}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Public}) \times (M\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Message}) \times (\text{σ}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Signature}) \to \mathbb{B}` as: -* Return :math:`0` if :math:`\sigma = \bot`. -* Return :math:`1` if :math:`\mathsf{Verify}(\mathsf{ik}, M, \sigma)` succeeds, otherwise :math:`0`. +* Return :math:`0` if :math:`\text{σ} = \bot\!`. +* Return :math:`1` if :math:`\mathsf{Verify}(\mathsf{ik}, M, \text{σ})` succeeds, otherwise :math:`0\!`. where the :math:`\mathsf{Verify}` algorithm is defined in BIP 340 [#bip-0340]_. Specification: Asset Identifier =============================== -For every new Asset, there must be a new and unique Asset Identifier, denoted :math:`\mathsf{AssetId}`. We define this to be a globally unique pair :math:`\mathsf{AssetId} := (\mathsf{ik}, \mathsf{asset\_desc})`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. +For every new Asset, there must be a new and unique Asset Identifier, denoted :math:`\mathsf{AssetId}\!`. We define this to be a globally unique pair :math:`\mathsf{AssetId} := (\mathsf{ik}, \mathsf{asset\_desc})\!`, where :math:`\mathsf{ik}` is the issuance key and :math:`\mathsf{asset\_desc}` is a byte string. -A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. +A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, :math:`\mathsf{AssetDigest}\!`, which is simply is a :math:`\textsf{BLAKE2b-512}` hash of the Asset Identifier. From the Asset Digest, we derive a specific Asset Base within each shielded protocol using the applicable hash-to-curve algorithm. This Asset Base is included in shielded notes. Let @@ -188,15 +188,15 @@ Let - :math:`\mathsf{asset\_desc}` be the asset description, which includes any information pertaining to the issuance, and is a byte sequence of up to 512 bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later. - :math:`\mathsf{ik}` be the issuance validating key of the issuer, a public key used to verify the signature on the issuance transaction's SIGHASH. -Define :math:`\mathsf{AssetDigest_{\mathsf{AssetId}}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))`, +Define :math:`\mathsf{AssetDigest_{AssetId}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))\!`, where -- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathsf{ik}, \mathsf{asset\_desc})) := \mathsf{0x00} || \mathsf{ik} || \mathsf{asset\_desc}\!`. -- Note that the initial :math:`\mathsf{0x00}` byte is a version byte. +- :math:`\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathsf{ik}, \mathsf{asset\_desc})) := \mathtt{0x00} || \mathsf{ik} || \mathsf{asset\_desc}\!\!`. +- Note that the initial :math:`\mathtt{0x00}` byte is a version byte. -Define :math:`\mathsf{AssetBase_{\mathsf{AssetId}}} := \mathsf{ZSAValueBase}(\mathsf{AssetDigest}_{\mathsf{AssetId}})` +Define :math:`\mathsf{AssetBase_{AssetId}} := \mathsf{ZSAValueBase}(\mathsf{AssetDigest_{AssetId}})` -In the case of the Orchard-ZSA protocol, we define :math:`\mathsf{ZSAValueBase}(\mathsf{AssetDigest}_{\mathsf{AssetId}}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{AssetDigest}_{\mathsf{AssetId}})` +In the case of the Orchard-ZSA protocol, we define :math:`\mathsf{ZSAValueBase}(\mathsf{AssetDigest_{AssetId}}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{AssetDigest_{AssetId}})` where :math:`\mathsf{GroupHash}^\mathbb{P}` is defined as in [#protocol-concretegrouphashpallasandvesta]_. The relations between the Asset Identifier, Asset Digest, and Asset Base are shown in the following diagram: @@ -209,7 +209,7 @@ The relations between the Asset Identifier, Asset Digest, and Asset Base are sho Diagram relating the Asset Identifier, Asset Digest, and Asset Base in the ZSA Protocol -**Note:** To keep notations light and concise, we may omit :math:`\mathsf{AssetId}` (resp. :math:`\mathsf{Protocol}`) in the subscript (resp. superscript) when the Asset Identifier (resp. Protocol) is clear from the context. +**Note:** To keep notations light and concise, we may omit :math:`\mathsf{AssetId}` (resp. :math:`\mathsf{Protocol}\!`) in the subscript (resp. superscript) when the Asset Identifier (resp. Protocol) is clear from the context. Wallets MUST NOT display just the :math:`\mathsf{asset\_desc}` string to their users as the name of the Asset. Some possible alternatives include: @@ -221,7 +221,7 @@ Specification: Global Issuance State Issuance requires the following additions to the global state defined at block boundaries: -- :math:`\mathsf{previously\_finalized}`, a set of :math:`\mathsf{AssetId}` that have been finalized (i.e.: the :math:`\mathsf{finalize}` flag has been set to :math:`1` in some issuance transaction preceding the block boundary). +- :math:`\mathsf{previously\_finalized}\!`, a set of :math:`\mathsf{AssetId}` that have been finalized (i.e.: the :math:`\mathsf{finalize}` flag has been set to :math:`1` in some issuance transaction preceding the block boundary). Specification: Issuance Action, Issuance Bundle and Issuance Protocol @@ -232,18 +232,18 @@ Issuance Action Description An issuance action, ``IssueAction``, is the instance of issuing a specific Custom Asset, and contains the following fields: -- :math:`\mathsf{assetDescSize}`: the size of the Asset description, a number between :math:`0` and :math:`512`, stored in two bytes. -- :math:`\mathsf{asset\_desc}`: the Asset description, a byte string of up to 512 bytes as defined in the `Specification: Asset Identifier`_ section. +- ``assetDescSize``: the size of the Asset description, a number between :math:`0` and :math:`512\!`, stored in two bytes. +- ``asset_desc``: the Asset description, a byte string of up to 512 bytes as defined in the `Specification: Asset Identifier`_ section. - ``vNotes``: an array of ``Note`` containing the unencrypted output notes of the recipients of the Asset. - ``flagsIssuance``: a byte that stores the :math:`\mathsf{finalize}` boolean that defines whether the issuance of that specific Custom Asset is finalized or not. -An asset's :math:`\mathsf{AssetDigest}` is added to the :math:`\mathsf{previously\_finalized}` set after a block that contains any issuance transaction for that asset with :math:`\mathsf{finalize} = 1`. It then cannot be removed from this set. For Assets with :math:`\mathsf{AssetDigest} \in \mathsf{previously\_finalized}`, no further tokens can be issued, so as seen below, the validators will reject the transaction. For Assets with :math:`\mathsf{AssetDigest} \not\in \mathsf{previously\_finalized}`, new issuance actions can be issued in future transactions. These must use the same Asset description, :math:`\mathsf{asset\_desc}`, and can either maintain :math:`\mathsf{finalize} = 0` or change it to :math:`\mathsf{finalize} = 1`, denoting that this Custom Asset cannot be issued after the containing block. +An asset's :math:`\mathsf{AssetDigest}` is added to the :math:`\mathsf{previously\_finalized}` set after a block that contains any issuance transaction for that asset with :math:`\mathsf{finalize} = 1\!`. It then cannot be removed from this set. For Assets with :math:`\mathsf{AssetDigest} \in \mathsf{previously\_finalized}\!`, no further tokens can be issued, so as seen below, the validators will reject the transaction. For Assets with :math:`\mathsf{AssetDigest} \not\in \mathsf{previously\_finalized}\!`, new issuance actions can be issued in future transactions. These must use the same Asset description, :math:`\mathsf{asset\_desc}\!`, and can either maintain :math:`\mathsf{finalize} = 0` or change it to :math:`\mathsf{finalize} = 1\!`, denoting that this Custom Asset cannot be issued after the containing block. +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ | Bytes | Name | Data Type | Description | +=============================+==========================+===========================================+=====================================================================+ -|``2`` |``assetDescSize`` |``byte`` |The length of the :math:`\mathsf{asset\_desc}` string in bytes. | +|``2`` |``assetDescSize`` |``byte`` |The length of the ``asset_desc`` string in bytes. | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ |``assetDescSize`` |``asset_desc`` |``byte[assetDescSize]`` |A byte sequence of length ``assetDescSize`` bytes which SHOULD be a | | | | |well-formed UTF-8 code unit sequence according to Unicode 15.0.0 | @@ -256,7 +256,7 @@ An asset's :math:`\mathsf{AssetDigest}` is added to the :math:`\mathsf{previousl +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ |``1`` |``flagsIssuance`` |``byte`` |An 8-bit value representing a set of flags. Ordered from LSB to MSB: | | | | | * :math:`\mathsf{finalize}` | -| | | | * The remaining bits are set to ``0``. | +| | | | * The remaining bits are set to :math:`0\!`. | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the note commitment tree as a shielded note. @@ -271,7 +271,7 @@ It contains the following fields: - :math:`\mathsf{ik}`: the issuance validating key, that allows the validators to verify that the :math:`\mathsf{AssetId}` is properly associated with the issuer. - ``vIssueActions``: an array of issuance actions, of type ``IssueAction``. -- :math:`\mathsf{issueAuthSig}`: the signature of the transaction SIGHASH, signed by the issuance authorizing key, :math:`\mathsf{isk}`, that validates the issuance . +- :math:`\mathsf{issueAuthSig}`: the signature of the transaction SIGHASH, signed by the issuance authorizing key, :math:`\mathsf{isk}\!`, that validates the issuance. The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format [#protocol-txnencoding]_. @@ -298,10 +298,10 @@ For all actions ``IssueAction``: - encode :math:`\mathsf{asset\_desc}` as a UTF-8 byte string of size up to 512. - compute :math:`\mathsf{AssetDigest}` from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as decribed in the `Specification: Asset Identifier`_ section. - compute :math:`\mathsf{AssetBase}` from :math:`\mathsf{AssetDigest}` as decribed in the `Specification: Asset Identifier`_ section. -- set the :math:`\mathsf{finalize}` boolean as desired (if more issuance actions are to be created for this :math:`\mathsf{AssetBase}`, set :math:`\mathsf{finalize} = 0`, otherwise set :math:`\mathsf{finalize} = 1`). +- set the :math:`\mathsf{finalize}` boolean as desired (if more issuance actions are to be created for this :math:`\mathsf{AssetBase}\!`, set :math:`\mathsf{finalize} = 0\!`, otherwise set :math:`\mathsf{finalize} = 1\!`). - for each recipient :math:`i`: - - generate a ZSA output note that includes the Asset Base. For an Orchard-ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d}_i}, \mathsf{v}_i, \rho_i, \mathsf{rseed}_i, \mathsf{AssetBase}, \mathsf{rcm}_i)\!`. + - generate a ZSA output note that includes the Asset Base. For an Orchard-ZSA note this is :math:`\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d}_i}, \mathsf{v}_i, \text{ρ}_i, \mathsf{rseed}_i, \mathsf{AssetBase}, \mathsf{rcm}_i)\!`. - encode the ``IssueAction`` into the vector ``vIssueActions`` of the bundle. @@ -309,7 +309,7 @@ For the ``IssueBundle``: - encode the ``vIssueActions`` vector. - encode the :math:`\mathsf{ik}` as 32 byte-string. -- sign the SIGHASH transaction hash with the issuance authorizing key, :math:`\mathsf{isk}`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. +- sign the SIGHASH transaction hash with the issuance authorizing key, :math:`\mathsf{isk}\!`, using the :math:`\mathsf{IssueAuthSig}` signature scheme. The signature is then added to the issuance bundle. **Note:** that the commitment is not included in the ``IssuanceAction`` itself. As explained below, it is computed later by the validators and added to the note commitment tree. @@ -320,22 +320,22 @@ Specification: Consensus Rule Changes For the ``IssueBundle``: -- Validate the issuance authorization signature, :math:`\mathsf{issueAuthSig}`, on the SIGHASH transaction hash, :math:`\mathsf{SigHash}`, by invoking :math:`\mathsf{IssueAuthSig.Validate(ik, SigHash, issueAuthSig)}` +- Validate the issuance authorization signature, :math:`\mathsf{issueAuthSig}\!`, on the SIGHASH transaction hash, :math:`\mathsf{SigHash}\!`, by invoking :math:`\mathsf{IssueAuthSig}.\!\mathsf{Validate}(\mathsf{ik}, \mathsf{SigHash}, \mathsf{issueAuthSig})\!`. For each ``IssueAction`` in ``IssueBundle``: -- check that :math:`0 < \mathtt{assetDescSize} <= 512`. +- check that :math:`0 < \mathtt{assetDescSize} \leq 512\!`. - check that :math:`\mathsf{asset\_desc}` is a string of length :math:`\mathtt{assetDescSize}` bytes. - retrieve :math:`\mathsf{AssetBase}` from the first note in the sequence and check that :math:`\mathsf{AssetBase}` is derived from the issuance validating key :math:`\mathsf{ik}` and :math:`\mathsf{asset\_desc}` as described in the `Specification: Asset Identifier`_ section. - check that the :math:`\mathsf{AssetDigest}` does not exist in the :math:`\mathsf{previously\_finalized}` set in the global state. -- check that every note in the ``IssueAction`` contains the same :math:`\mathsf{AssetBase}` and is properly constructed as :math:`\mathsf{note} = (\mathsf{g_d, pk_d, v, \rho, rseed, AssetBase})`. +- check that every note in the ``IssueAction`` contains the same :math:`\mathsf{AssetBase}` and is properly constructed as :math:`\mathsf{note} = (\mathsf{g_d}, \mathsf{pk_d}, \mathsf{v}, \text{ρ}, \mathsf{rseed}, \mathsf{AssetBase})\!`. If all of the above checks pass, do the following: -- For each note, compute the note commitment as :math:`\mathsf{cm} = \mathsf{NoteCommit^{OrchardZSA}_{rcm}(repr_{\mathbb{P}}(g_d), repr_{\mathbb{P}}(pk_d), v, \rho, \psi, AssetBase)}` as defined in the Note Structure and Commitment section of ZIP 226 [#zip-0226-notestructure]_ and +- For each note, compute the note commitment as :math:`\mathsf{cm} = \mathsf{NoteCommit^{OrchardZSA}_{rcm}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d}), \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase})` as defined in the Note Structure and Commitment section of ZIP 226 [#zip-0226-notestructure]_ and - Add :math:`\mathsf{cm}` to the Merkle tree of note commitments. -- If :math:`\mathsf{finalize} = 1`, add :math:`\mathsf{AssetDigest}` to the :math:`\mathsf{previously\_finalized}` set immediately after the block in which this transaction occurs. +- If :math:`\mathsf{finalize} = 1\!`, add :math:`\mathsf{AssetDigest}` to the :math:`\mathsf{previously\_finalized}` set immediately after the block in which this transaction occurs. - (Replay Protection) If issue bundle is present, the fees MUST be greater than zero. @@ -367,13 +367,13 @@ Concrete Applications - Issuers can also stop the existing supply production of any Asset associated to their issuer keys. This could be done by - - issuing a last set of tokens of that specific :math:`\mathsf{AssetId}`, for which :math:`\mathsf{finalize} = 1`, or by - - issuing a transaction with a single note in the issuance action pertaining to that :math:`\mathsf{AssetId}`, where the note will contain a ``value = 0``. This can be used for application-specific purposes (NFT collections) or for security purposes to revoke the Asset issuance (see Security and Privacy Considerations). + - issuing a last set of tokens of that specific :math:`\mathsf{AssetId}\!`, for which :math:`\mathsf{finalize} = 1\!`, or by + - issuing a transaction with a single note in the issuance action pertaining to that :math:`\mathsf{AssetId}\!`, where the note will contain a :math:`\mathsf{value} = 0\!`. This can be used for application-specific purposes (NFT collections) or for security purposes to revoke the Asset issuance (see Security and Privacy Considerations). - Note in the above cases, that the setting of the :math:`\mathsf{finalize}` flag will take effect at the block boundary, that is, after all the transactions in the block. - The issuance and burn mechanisms can be used in conjunction to determine the supply of Assets on the Zcash ecosystem. This allows for the bridging of Assets defined on other chains. -- Furthermore, NFT issuance is enabled by issuing in a single bundle several issuance actions, where each :math:`\mathsf{AssetId}` corresponds to ``value = 1`` at the fundamental unit level. Issuers and users should make sure that :math:`\mathsf{finalize} = 1` for each of the actions in this scenario. +- Furthermore, NFT issuance is enabled by issuing in a single bundle several issuance actions, where each :math:`\mathsf{AssetId}` corresponds to :math:`\mathsf{value} = 1` at the fundamental unit level. Issuers and users should make sure that :math:`\mathsf{finalize} = 1` for each of the actions in this scenario. @@ -465,7 +465,7 @@ T.5a.iii: flagsIssuance An 8-bit value representing a set of flags. Ordered from LSB to MSB: - :math:`\mathsf{finalize}` -- The remaining bits are set to `0`. +- The remaining bits are set to `0\!`. T.5b: issuanceValidatingKey @@ -555,7 +555,7 @@ Issuance Key Compromise The design of this protocol does not currently allow for rotation of the issuance validating key that would allow for replacing the key of a specific Asset. In case of compromise, the following actions are recommended: -- If an issuance validating key is compromised, the :math:`\mathsf{finalize}` boolean for all the Assets issued with that key should be set to :math:`1` and the issuer should change to a new issuance authorizing key, and issue new Assets, each with a new :math:`\mathsf{AssetId}`. +- If an issuance validating key is compromised, the :math:`\mathsf{finalize}` boolean for all the Assets issued with that key should be set to :math:`1` and the issuer should change to a new issuance authorizing key, and issue new Assets, each with a new :math:`\mathsf{AssetId}\!`. Bridging Assets --------------- @@ -568,7 +568,7 @@ Other Considerations Implementing Zcash Nodes ------------------------ -Although not enforced in the global state, it is RECOMMENDED that Zcash full validators keep track of the total supply of Assets as a mutable mapping :math:`\mathsf{issuanceSupplyInfoMap}` from :math:`\mathsf{AssetId}` to :math:`\mathsf{(totalSupply, finalize)}` in order to properly keep track of the total supply for different Asset Identifiers. This is useful for wallets and other applications that need to keep track of the total supply of Assets. +Although not enforced in the global state, it is RECOMMENDED that Zcash full validators keep track of the total supply of Assets as a mutable mapping :math:`\mathsf{issuanceSupplyInfoMap}` from :math:`\mathsf{AssetId}` to :math:`(\mathsf{totalSupply}, \mathsf{finalize})` in order to properly keep track of the total supply for different Asset Identifiers. This is useful for wallets and other applications that need to keep track of the total supply of Assets. Fee Structures -------------- diff --git a/zip-0230.rst b/zip-0230.rst index 3354be4dc..a4fbd1f75 100644 --- a/zip-0230.rst +++ b/zip-0230.rst @@ -151,7 +151,7 @@ Transaction Format | | | | * ``enableSpendsOrchard`` | | | | | * ``enableOutputsOrchard`` | | | | | * ``enableZSAs`` | -| | | | * The remaining bits are set to ``0``. | +| | | | * The remaining bits are set to :math:`0\!`. | +------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ |``8`` |``valueBalanceOrchard`` |``int64`` |The net value of Orchard spends minus outputs. | +------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ @@ -159,7 +159,7 @@ Transaction Format | | | |height in the past. | +------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ |``varies`` |``sizeProofsOrchardZSA`` |``compactSize`` |Length in bytes of ``proofsOrchardZSA``. Value is **(TO UPDATE)** | -| | | |:math:`2720 + 2272 \cdot \mathtt{nActionsOrchard}`. | +| | | |:math:`2720 + 2272 \cdot \mathtt{nActionsOrchard}\!`. | +------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ |``sizeProofsOrchardZSA`` |``proofsOrchardZSA`` |``byte[sizeProofsOrchardZSA]`` |Encoding of aggregated zk-SNARK proofs for Orchard-ZSA Actions. | +------------------------------------+--------------------------+----------------------------------------+---------------------------------------------------------------------------+ @@ -189,15 +189,15 @@ Transaction Format * The fields ``valueBalanceSapling`` and ``bindingSigSapling`` are present if and only if - :math:`\mathtt{nSpendsSapling} + \mathtt{nOutputsSapling} > 0`. If ``valueBalanceSapling`` - is not present, then :math:`\mathsf{v^{balanceSapling}}`` is defined to be 0. + :math:`\mathtt{nSpendsSapling} + \mathtt{nOutputsSapling} > 0\!`. If ``valueBalanceSapling`` + is not present, then :math:`\mathsf{v^{balanceSapling}}`` is defined to be :math:`0\!`. -* The field ``anchorSapling`` is present if and only if :math:`\mathtt{nSpendsSapling} > 0`. +* The field ``anchorSapling`` is present if and only if :math:`\mathtt{nSpendsSapling} > 0\!`. * The fields ``flagsOrchard``, ``valueBalanceOrchard``, ``anchorOrchard``, ``sizeProofsOrchardZSA``, ``proofsOrchardZSA``, and ``bindingSigOrchard`` are present if and - only if :math:`\mathtt{nActionsOrchard} > 0`. If ``valueBalanceOrchard`` is not present, - then :math:`\mathsf{v^{balanceOrchard}}` is defined to be 0. + only if :math:`\mathtt{nActionsOrchard} > 0\!`. If ``valueBalanceOrchard`` is not present, + then :math:`\mathsf{v^{balanceOrchard}}` is defined to be :math:`0\!`. * The elements of ``vSpendProofsSapling`` and ``vSpendAuthSigsSapling`` have a 1:1 correspondence to the elements of ``vSpendsSapling`` and MUST be ordered such that the @@ -213,7 +213,7 @@ Transaction Format ``vActionsOrchard`` and MUST be ordered such that the proof or signature at a given index corresponds to the ``OrchardZsaAction`` at the same index. -* For coinbase transactions, the ``enableSpendsOrchard`` and ``enableZSAs`` bits MUST be set to ``0``. +* For coinbase transactions, the ``enableSpendsOrchard`` and ``enableZSAs`` bits MUST be set to :math:`0\!`. The encodings of ``tx_in``, and ``tx_out`` are as in a version 4 transaction (i.e. unchanged from Canopy). The encodings of ``SpendDescriptionV6``, ``OutputDescriptionV6`` @@ -247,7 +247,8 @@ Sapling Output Description (``OutputDescriptionV6``) +=============================+==========================+======================================+============================================================+ |``32`` |``cv`` |``byte[32]`` |A value commitment to the net value of the output note. | +-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ -|``32`` |``cmu`` |``byte[32]`` |The u-coordinate of the note commitment for the output note.| +|``32`` |``cmu`` |``byte[32]`` |The :math:`u\!`-coordinate of the note commitment for the | +| | | |output note. | +-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ |``32`` |``ephemeralKey`` |``byte[32]`` |An encoding of an ephemeral Jubjub public key. | +-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ @@ -275,7 +276,8 @@ Orchard-ZSA Action Description (``OrchardZsaAction``) |``32`` |``rk`` |``byte[32]`` |The randomized validating key for the element of | | | | |spendAuthSigsOrchard corresponding to this Action. | +-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ -|``32`` |``cmx`` |``byte[32]`` |The x-coordinate of the note commitment for the output note.| +|``32`` |``cmx`` |``byte[32]`` |The :math:`x\!`-coordinate of the note commitment for the | +| | | |output note. | +-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ |``32`` |``ephemeralKey`` |``byte[32]`` |An encoding of an ephemeral Pallas public key | +-----------------------------+--------------------------+--------------------------------------+------------------------------------------------------------+ @@ -294,13 +296,13 @@ Orchard-ZSA Asset Burn Description An Orchard-ZSA Asset Burn description is encoded in a transaction as an instance of an ``AssetBurn`` type: -+-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ -| Bytes | Name | Data Type | Description | -+=======+===============+=============================+===========================================================================================================================+ -| 32 | ``AssetBase`` | ``byte[32]`` | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase}^{\mathsf{Orchard}}`. | -+-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ -| 8 | ``valueBurn`` | :math:`\{1 .. 2^{64} - 1\}` | The amount being burnt. | -+-------+---------------+-----------------------------+---------------------------------------------------------------------------------------------------------------------------+ ++-------+---------------+-----------------------------+--------------------------------------------------------------------------------------------------------------------+ +| Bytes | Name | Data Type | Description | ++=======+===============+=============================+====================================================================================================================+ +| 32 | ``AssetBase`` | ``byte[32]`` | For the Orchard-based ZSA protocol, this is the encoding of the Asset Base :math:`\mathsf{AssetBase^{Orchard}}\!`. | ++-------+---------------+-----------------------------+--------------------------------------------------------------------------------------------------------------------+ +| 8 | ``valueBurn`` | :math:`\{1 .. 2^{64} - 1\}` | The amount being burnt. | ++-------+---------------+-----------------------------+--------------------------------------------------------------------------------------------------------------------+ The encodings of each of these elements are defined in ZIP 226 [#zip-0226]_. @@ -325,7 +327,7 @@ An issuance action, ``IssueAction``, is the instance of issuing a specific Custo +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ |``1`` |``flagsIssuance`` |``byte`` |An 8-bit value representing a set of flags. Ordered from LSB to MSB: | | | | | * :math:`\mathsf{finalize}` | -| | | | * The remaining bits are set to ``0``. | +| | | | * The remaining bits are set to :math:`0\!`. | +-----------------------------+--------------------------+-------------------------------------------+---------------------------------------------------------------------+ The encodings of each of these elements are defined in ZIP 227 [#zip-0227]_. From c67f8d0359ccd0f31db6e8d145d1be05c6137ebe Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 12:49:42 +0000 Subject: [PATCH 39/43] ZIP 226: editorial clarifications. Signed-off-by: Daira-Emma Hopwood --- zip-0226.rst | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/zip-0226.rst b/zip-0226.rst index 6f8966c1b..4d0e1c2f3 100644 --- a/zip-0226.rst +++ b/zip-0226.rst @@ -173,14 +173,14 @@ The sender includes a :math:`\mathsf{v_{AssetId}}` variable for every Asset Iden For every Custom Asset that is burnt, we add to the :math:`\mathsf{assetBurn}` set the tuple :math:`(\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}})` such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer. -.. math:: \mathsf{assetBurn} = \{ (\mathsf{AssetBase}_{\mathsf{AssetId}},\mathsf{v_{AssetId}})\ |\ \forall\ \mathsf{AssetBase}_{\mathsf{AssetId}}\ \textit{s.t.}\ \mathsf{v_{AssetId}} \neq 0 \} +.. math:: \mathsf{assetBurn} := \{ (\mathsf{AssetBase}_{\mathsf{AssetId}} : \mathbb{P}^*, \mathsf{v_{AssetId}} : \{1 .. 2^{\ell_{\mathsf{value}}} - 1\}) \,|\, \mathsf{AssetId} \in \mathsf{AssetIdsToBurn} \} We denote by :math:`L` the cardinality of the :math:`\mathsf{assetBurn}` set. Additional Consensus Rules `````````````````````````` -1. We require that for every :math:`(\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}}) \in \mathsf{assetBurn}, \mathsf{AssetBase_{AssetId}} \neq \mathcal{V}^{\mathsf{Orchard}}\!`. That is, ZEC or TAZ is not allowed to be burnt. +1. We require that for every :math:`(\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}}) \in \mathsf{assetBurn}, \mathsf{AssetBase_{AssetId}} \neq \mathcal{V}^{\mathsf{Orchard}}\!`. That is, ZEC or TAZ is not allowed to be burnt by this mechanism. 2. We require that for every :math:`(\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}}) \in \mathsf{assetBurn}, \mathsf{v_{AssetId}} \neq 0\!`. 3. We require that there be no duplication of Custom Assets in the :math:`\mathsf{assetBurn}` set. That is, every :math:`\mathsf{AssetBase_{AssetId}}` has at most one entry in :math:`\mathsf{assetBurn}\!`. @@ -252,7 +252,7 @@ Rationale for Split Notes In the Orchard protocol, since each Action represents an input and an output, the transaction that wants to send one input to multiple outputs must have multiple inputs. The Orchard protocol gives *dummy spend notes* [#protocol-orcharddummynotes]_ to the Actions that have not been assigned input notes. -The Orchard technique requires modification for the ZSA protocol with multiple Asset Identifiers, as the output note of the split Actions *cannot* contain *any* Asset Base. We must enforce it to be an actual output of a GroupHash computation (in fact, we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). Without this enforcement the prover could input a multiple (or linear combination) of an existing Asset Base, and thereby attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds. +The Orchard technique requires modification for the ZSA protocol with multiple Asset Identifiers, as the output note of the split Actions *cannot* contain *just any* Asset Base. We must enforce it to be an actual output of a GroupHash computation (in fact, we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). Without this enforcement the prover could input a multiple (or linear combination) of an existing Asset Base, and thereby attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds. Therefore, for Custom Assets we enforce that *every* input note to an ZSA Action must be proven to exist in the set of note commitments in the note commitment tree. We then enforce this real note to be “unspendable” in the sense that its value will be zeroed in split Actions and the nullifier will be randomized, making the note not spendable in the specific Action. Then, the proof itself ensures that the output note is of the same Asset Base as the input note. In the circuit, the split note functionality will be activated by a boolean private input to the proof (aka the :math:`\mathsf{split\_flag}` boolean). This ensures that the value base points of all output notes of a transfer are actual outputs of a GroupHash, as they originate in the Issuance protocol which is publicly verified. From 30bf5c966686e822fef92715b854bcd2ed708a2c Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 16:41:34 +0000 Subject: [PATCH 40/43] ZIP 227: minor rewording. Signed-off-by: Daira-Emma Hopwood --- zip-0227.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/zip-0227.rst b/zip-0227.rst index 1f519c203..89e837f4a 100644 --- a/zip-0227.rst +++ b/zip-0227.rst @@ -49,7 +49,7 @@ This ZIP (ZIP 227) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunc Motivation ========== -This ZIP introduces the issuance mechanism for Custom Assets on the Zcash chain. While originally part of a same ZSA ZIP (ZIP 226 [#zip-0226]_) the issuance mechanism turned out to be substantial enough to stand on its own and justify the creation of this supporting ZIP for ZIP 226 [#zip-0226]_. +This ZIP introduces the issuance mechanism for Custom Assets on the Zcash chain. While originally part of a single ZSA ZIP, the issuance mechanism turned out to be substantial enough to stand on its own and justify the creation of this supporting ZIP for ZIP 226 [#zip-0226]_. This ZIP only enables *transparent* issuance. As a first step, transparency will allow for proper testing of the applications that will be most used in the Zcash ecosystem, and will enable the supply of Assets to be tracked. From 46a885f1cda9e0ea3719c64f7372194cdb02772e Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 16:40:52 +0000 Subject: [PATCH 41/43] ZIP 230: reword and wrap abstract. Signed-off-by: Daira-Emma Hopwood --- zip-0230.rst | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/zip-0230.rst b/zip-0230.rst index a4fbd1f75..e807d6140 100644 --- a/zip-0230.rst +++ b/zip-0230.rst @@ -31,14 +31,15 @@ The character § is used when referring to sections of the Zcash Protocol Specif Abstract ======== -This proposal defines a new Zcash peer-to-peer transaction format, which includes data that supports the Orchard-ZSA protocol and all Zcash Shielded Assets (ZSAs) related operations. The -new transaction format defines well-bounded regions of the serialized form to -serve each of the existing pools of funds, and adds and describes a new elements -containing ZSA-specific elements. +This proposal defines a new Zcash peer-to-peer transaction format, which includes +data that supports the Orchard-ZSA protocol and all operations related to Zcash +Shielded Assets (ZSAs). The new format adds and describes new fields containing +ZSA-specific elements. Like the existing v5 transaction format, it keeps well-bounded +regions of the serialized form to serve each pool of funds. This ZIP also depends upon and defines modifications to the computation of the values -**TxId Digest**, **Signature Digest**, and **Authorizing Data Commitment** defined by ZIP -244 [#zip-0244]_. +**TxId Digest**, **Signature Digest**, and **Authorizing Data Commitment** defined by +ZIP 244 [#zip-0244]_. Motivation From 406b7e86d99f8e47a683b6900bdd8885aced83c1 Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 16:51:19 +0000 Subject: [PATCH 42/43] CSS: Improve the font weight and size of code in headings. Signed-off-by: Daira-Emma Hopwood --- css/style.css | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/css/style.css b/css/style.css index 692e988e3..1eee84aa0 100644 --- a/css/style.css +++ b/css/style.css @@ -186,17 +186,28 @@ h1 { margin-bottom: 1.5rem; } +h1 code { + font-size: 2.25rem; + font-weight: 300; +} + h2 { font-size: 2.125rem; margin-bottom: 1.125rem; } +h2 code { + font-size: 1.9rem; + font-weight: 300; +} + h3 { font-size: 1.85rem; } h3 code { - font-size: 1.5rem; + font-size: 1.65rem; + font-weight: 300; } h4 { @@ -205,6 +216,7 @@ h4 { h4 code { font-size: 1.35rem; + font-weight: 200; } h5 { From 21cf12456a48770bd4fa99bebe7aa95f7cb4339b Mon Sep 17 00:00:00 2001 From: Daira-Emma Hopwood Date: Wed, 7 Feb 2024 18:43:35 +0000 Subject: [PATCH 43/43] ZIPs 226, 227 and 230: regenerate HTML. Signed-off-by: Daira-Emma Hopwood --- README.rst | 6 +- index.html | 8 +- zip-0226.html | 779 +++++++++++++++++++++++++++++++++++++++- zip-0227.html | 968 +++++++++++++++++++++++++++++++++++++++++++++++++- zip-0230.html | 627 +++++++++++++++++++++++++++++++- 5 files changed, 2375 insertions(+), 13 deletions(-) diff --git a/README.rst b/README.rst index 6d9e6b8d3..292f69850 100644 --- a/README.rst +++ b/README.rst @@ -107,10 +107,10 @@ Index of ZIPs 222 Transparent Zcash Extensions Draft 224 Orchard Shielded Protocol Final 225 Version 5 Transaction Format Final - 226 Transfer and Burn of Zcash Shielded Assets Reserved - 227 Issuance of Zcash Shielded Assets Reserved + 226 Transfer and Burn of Zcash Shielded Assets Draft + 227 Issuance of Zcash Shielded Assets Draft 228 Asset Swaps for Zcash Shielded Assets Reserved - 230 Version 6 Transaction Format Reserved + 230 Version 6 Transaction Format Draft 231 Decouple Memos from Transaction Outputs Reserved 239 Relay of Version 5 Transactions Final 243 Transaction Signature Validation for Sapling Final diff --git a/index.html b/index.html index 885fe2608..f2f0bafe0 100644 --- a/index.html +++ b/index.html @@ -22,7 +22,7 @@

Participation in the Zcash project is subject to a Code of Conduct.

The Zcash protocol is documented in its Protocol Specification.

To start contributing, first read ZIP 0 which documents the ZIP process. Then clone this repo from GitHub, and start adding your draft ZIP, formatted either as reStructuredText or as Markdown.

-

For example, if using reStructuredText, use a filename matching draft-*.rst. Use make to check that you are using correct reStructuredText or Markdown syntax, and double-check the generated draft-*.html file before filing a Pull Request.

+

For example, if using reStructuredText, use a filename matching draft-*.rst. Use make to check that you are using correct reStructuredText or Markdown syntax, and double-check the generated draft-*.html file before filing a Pull Request. See here for the project dependencies.

NU5 ZIPs

This is the list of ZIPs relevant to the NU5 Upgrade, which activated on 31st May 2022:

@@ -81,10 +81,10 @@ 222 Transparent Zcash Extensions Draft 224 Orchard Shielded Protocol Final 225 Version 5 Transaction Format Final - 226 Transfer and Burn of Zcash Shielded Assets Reserved - 227 Issuance of Zcash Shielded Assets Reserved + 226 Transfer and Burn of Zcash Shielded Assets Draft + 227 Issuance of Zcash Shielded Assets Draft 228 Asset Swaps for Zcash Shielded Assets Reserved - 230 Version 6 Transaction Format Reserved + 230 Version 6 Transaction Format Draft 231 Decouple Memos from Transaction Outputs Reserved 239 Relay of Version 5 Transactions Final 243 Transaction Signature Validation for Sapling Final diff --git a/zip-0226.html b/zip-0226.html index 3c6fca54b..4ebbc36b4 100644 --- a/zip-0226.html +++ b/zip-0226.html @@ -3,6 +3,7 @@ ZIP 226: Transfer and Burn of Zcash Shielded Assets +
@@ -15,10 +16,784 @@ Credits: Daniel Benarroch Aurelien Nicolas Deirdre Connolly -Status: Reserved + Teor +Status: Draft Category: Consensus +Created: 2022-05-01 +License: MIT Discussions-To: <https://github.com/zcash/zips/issues/618> -Pull-Request: <https://github.com/zcash/zips/pull/649> +Pull-Request: <https://github.com/zcash/zips/pull/680> +

Terminology

+

The key word "MUST" in this document is to be interpreted as described in BCP 14 1 when, and only when, it appears in all capitals.

+

The term "network upgrade" in this document is to be interpreted as described in ZIP 200 2.

+

The terms "Orchard" and "Action" in this document are to be interpreted as described in ZIP 224 4.

+

The terms "Asset", "Custom Asset" and "Wrapped Asset" in this document are to be interpreted as described in ZIP 227 5.

+

We define the following additional terms:

+
    +
  • Split Input: an Action input used to ensure that the output note of that Action is of a validly issued + \(\mathsf{AssetBase}\) + (see 6) when there is no corresponding real input note, in situations where the number of outputs are larger than the number of inputs. See formal definition in Split Notes.
    • +
  • Split Action: an Action that contains a Split Input.
    • +
+
+

Abstract

+

This ZIP (ZIP 226) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunction with ZIP 227 5. The ZSA protocol is an extension of the Orchard protocol that enables the issuance, transfer and burn of custom Assets on the Zcash chain. The issuance of such Assets is defined in ZIP 227 5, while the transfer and burn of such Assets is defined in this ZIP (ZIP 226). While the proposed ZSA protocol is a modification to the Orchard protocol, it has been designed with adaptation to possible future shielded protocols in mind.

+
+

Motivation

+

None of the currently deployed Zcash transfer protocols support Custom Assets. Enabling multi-asset support on the Zcash chain will open the door for a host of applications, and enhance the ecosystem with application developers and Asset custody institutions for issuance and bridging purposes. This ZIP builds on the issuance mechanism introduced in ZIP 227 5.

+
+

Overview

+

In order to be able to represent different Assets, we need to define a data field that uniquely represents the Asset in question, which we call the Asset Identifier + \(\mathsf{AssetId}\!\) + . This Asset Identifier maps to an Asset Base + \(\mathsf{AssetBase}\) + that is stored in Orchard-based ZSA notes. These terms are formally defined in ZIP 227 5.

+

The Asset Identifier (via means of the Asset Digest and Asset Base) will be used to enforce that the balance of an Action Description 15 28 is preserved across Assets (see the Orchard Binding Signature 18), and by extension the balance of an Orchard transaction. That is, the sum of all the + \(\mathsf{value^{net}}\) + from each Action Description, computed as + \(\mathsf{value^{old}} - \mathsf{value^{new}}\!\) + , must be balanced only with respect to the same Asset Identifier. This is especially important since we will allow different Action Descriptions to transfer notes of different Asset Identifiers, where the overall balance is checked without revealing which (or how many distinct) Assets are being transferred.

+

As was initially proposed by Jack Grigg and Daira-Emma Hopwood 29 30, we propose to make this happen by changing the value base point, + \(\mathcal{V}^{\mathsf{Orchard}}\!\) + , in the Homomorphic Pedersen Commitment that derives the value commitment, + \(\mathsf{cv^{net}}\!\) + , of the net value in an Orchard Action.

+

Because in a single transaction all value commitments are balanced, there must be as many different value base points as there are Asset Identifiers for a given shielded protocol used in a transaction. We propose to make the Asset Base an auxiliary input to the proof for each Action statement 20, represented already as a point on the Pallas curve. The circuit then should check that the same Asset Base is used in the old note commitment and the new note commitment 25, and as the base point in the value commitment 24. This ensures (1) that the input and output notes are of the same Asset Base, and (2) that only Actions with the same Asset Base will balance out in the Orchard binding signature.

+

In order to ensure the security of the transfers, and as we will explain below, we are redefining input dummy notes 17 for Custom Assets, as we need to enforce that the + \(\mathsf{AssetBase}\) + of the output note of that Split Action is the output of a valid + \(\mathsf{ZSAValueBase}\) + computation defined in ZIP 227 5.

+

We include the ability to pause the ZSA functionality, via a + \(\mathsf{enableZSA}\) + boolean flag. When this flag is set to false, it is not possible to perform transactions involving Custom Assets (the Action statement as modified for ZSAs will not be satisfied).

+

Finally, in this ZIP we also describe the burn mechanism, which is a direct extension of the transfer mechanism. The burn process uses a similar mechanism to what is used in Orchard to unshield ZEC, by using the + \(\mathsf{valueBalance}\) + of the Asset in question. Burning Assets is useful for many purposes, including bridging of Wrapped Assets and removing supply of Assets.

+
+

Specification

+

Most of the protocol is kept the same as the Orchard protocol released with NU5, except for the following.

+

Asset Identifiers

+

For every new Asset, there must be a new and unique Asset Identifier. Every Asset is defined by an Asset description, + \(\mathsf{asset\_desc}\!\) + , which is a global byte string (scoped across all future versions of Zcash). From this Asset description and the issuance validating key of the issuer, the specific Asset Identifier, + \(\mathsf{AssetId}\!\) + , the Asset Digest, and the Asset Base ( + \(\mathsf{AssetBase}\!\) + ) are derived as defined in ZIP 227 5.

+

This Asset Base will be the base point of the value commitment for the specific Custom Asset. Note that the Asset Base of the ZEC Asset will be kept as the original value base point, + \(\mathcal{V}^{\mathsf{Orchard}}\!\) + .

+

Rationale for Asset Identifiers

+

In future network and protocol upgrades, the same Asset description string can be carried on, potentially mapping into a different shielded pool. In that case, nodes should know how to transform the Asset Identifier, the Asset Digest, and the Asset Base from one shielded pool to another, while ensuring there are no balance violations 3.

+
+
+

Note Structure & Commitment

+

Let + \(\mathsf{Note^{OrchardZSA}}\) + be the type of a ZSA note, i.e. + \(\mathsf{Note^{OrchardZSA}} := \mathsf{Note^{Orchard}} \times \mathbb{P}^*\!\) + .

+

An Orchard ZSA note differs from an Orchard note 14 by additionally including the Asset Base, + \(\mathsf{AssetBase}\!\) + . So a ZSA note is a tuple + \((\mathsf{g_d}, \mathsf{pk_d}, \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase})\!\) + , where

+
    +
  • + \(\mathsf{AssetBase} : \mathbb{P}^*\) + is the unique element of the Pallas group 26 that identifies each Asset in the Orchard protocol, defined as the Asset Base in ZIP 227 5, a valid group element that is not the identity and is not + \(\bot\!\) + . The byte representation of the Asset Base is defined as + \(\mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]} := \mathsf{repr}_{\mathbb{P}}(\mathsf{AssetBase})\!\) + .
    • +
+

Note that the above assumes a canonical encoding, which is true for the Pallas group, but may not hold for future shielded protocols.

+

We define the note commitment scheme + \(\mathsf{NoteCommit^{OrchardZSA}_{rcm}}\) + as follows:

+
\(\mathsf{NoteCommit}^{\mathsf{OrchardZSA}} : \mathsf{NoteCommit}^{\mathsf{Orchard}}.\!\mathsf{Trapdoor} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \mathbb{B}^{[\ell_{\mathbb{P}}]} \times \{0 .. 2^{\ell_{\mathsf{value}}} - 1\} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{F}_{q_{\mathbb{P}}} \times \mathbb{P}^* \to \mathsf{NoteCommit}^{\mathsf{Orchard}}.\!\mathsf{Output}\)
+

where + \(\mathbb{P}, \ell_{\mathbb{P}}, q_{\mathbb{P}}\) + are as defined for the Pallas curve 26, and where + \(\mathsf{NoteCommit^{Orchard}}.\!\mathsf{Trapdoor}\) + and + \(\mathsf{Orchard}.\!\mathsf{Output}\) + are as defined in the Zcash protocol specification 16. This note commitment scheme is instantiated using the Sinsemilla Commitment 25 as follows:

+
\(\begin{align} +\mathsf{NoteCommit^{OrchardZSA}_{rcm}}(\mathsf{g_d}\star, \mathsf{pk_d}\star, \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase}) +:= \begin{cases} + \mathsf{NoteCommit^{Orchard}_{rcm}}(\mathsf{g_d}\star, \mathsf{pk_d}\star, \mathsf{v}, \text{ρ}, \text{ψ}), &\text{if } \mathsf{AssetBase} = \mathcal{V}^{\mathsf{Orchard}} \\ + \mathsf{cm_{ZSA}} &\text{otherwise} + \end{cases} +\end{align}\)
+

where:

+
\(\begin{align} +\mathsf{cm_{ZSA}} :=&\;\;\mathsf{SinsemillaHashToPoint}(\texttt{"z.cash:ZSA-NoteCommit-M"}, \\ +&\;\;\;\;\;\mathsf{g_{d}\star} \,||\, \mathsf{pk_{d}\star} \,||\, \mathsf{I2LEBSP_{64}(v)} \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\text{ρ}) \,||\, \mathsf{I2LEBSP}_{\ell^{\mathsf{Orchard}}_{\mathsf{base}}}(\text{ψ}) \,||\, \mathsf{asset\_base}) \\ +&\;\;+\;\;[\mathsf{rcm}]\,\mathsf{GroupHash}^{\mathbb{P}}(\texttt{"z.cash:Orchard-NoteCommit-r"}, \texttt{""}) +\end{align}\)
+

Note that + \(\mathsf{repr}_{\mathbb{P}}\) + and + \(\mathsf{GroupHash}^{\mathbb{P}}\) + are as defined for the Pallas curve 26, + \(\ell^{\mathsf{Orchard}}_{\mathsf{base}}\) + is as defined in §5.3 22, and + \(\mathsf{I2LEBSP}\) + is as defined in §5.1 21 of the Zcash protocol specification.

+

The nullifier is generated in the same manner as in the Orchard protocol 19.

+

The ZSA note plaintext also includes the Asset Base in addition to the components in the Orchard note plaintext 27. It consists of

+
\((\mathsf{leadByte} : \mathbb{B}^{\mathbb{Y}}, \mathsf{d} : \mathbb{B}^{[\ell_{\mathsf{d}}]}, \mathsf{v} : \{0 .. 2^{\ell_{\mathsf{value}}} - 1\}, \mathsf{rseed} : \mathbb{B}^{\mathbb{Y}[32]}, \mathsf{asset\_base} : \mathbb{B}^{[\ell_{\mathbb{P}}]}, \mathsf{memo} : \mathbb{B}^{\mathbb{Y}[512]})\)
+

Rationale for Note Commitment

+

In the ZSA protocol, the instance of the note commitment scheme, + \(\mathsf{NoteCommit^{OrchardZSA}_{rcm}}\!\) + , differs from the Orchard note commitment + \(\mathsf{NoteCommit^{Orchard}_{rcm}}\) + in that for Custom Assets, the Asset Base will be added as an input to the commitment computation. In the case where the Asset is the ZEC Asset, the commitment is computed identically to the Orchard note commitment, without making use of the ZEC Asset Base as an input. As we will see, the nested structure of the Sinsemilla-based commitment 25 allows us to add the Asset Base as a final recursive step.

+

The note commitment output is still indistinguishable from the original Orchard ZEC note commitments, by definition of the Sinsemilla hash function 23. ZSA note commitments will therefore be added to the same Orchard Note Commitment Tree. In essence, we have:

+
\(\mathsf{NoteCommit^{OrchardZSA}_{rcm}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d}), \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase}) \in \mathsf{NoteCommit^{Orchard}}.\!\mathsf{Output}\)
+

This definition can be viewed as a generalization of the Orchard note commitment, and will allow maintaining a single commitment instance for the note commitment, which will be used both for pre-ZSA Orchard and ZSA notes.

+
+
+

Value Commitment

+

In the case of the Orchard-based ZSA protocol, the value of different Asset Identifiers in a given transaction will be committed using a different value base point. The value commitment becomes:

+
\(\mathsf{cv^{net}} := \mathsf{ValueCommit^{OrchardZSA}_{rcv}}(\mathsf{AssetBase_{AssetId}}, \mathsf{v^{net}_{AssetId}}) = [\mathsf{v^{net}_{AssetId}}]\,\mathsf{AssetBase_{AssetId}} + [\mathsf{rcv}]\,\mathcal{R}^{\mathsf{Orchard}}\)
+

where + \(\mathsf{v^{net}_{AssetId}} = \mathsf{v^{old}_{AssetId}} - \mathsf{v^{new}_{AssetId}}\) + such that + \(\mathsf{v^{old}_{AssetId}}\) + and + \(\mathsf{v^{new}_{AssetId}}\) + are the values of the old and new notes of Asset Identifier + \(\mathsf{AssetId}\) + respectively,

+

+ \(\mathsf{AssetBase_{AssetId}}\) + is defined in ZIP 227 5, and

+

+ \(\mathcal{R}^{\mathsf{Orchard}} := \mathsf{GroupHash^{\mathbb{P}}}(\texttt{"z.cash:Orchard-cv"}, \texttt{"r"})\!\) + , as in the Orchard protocol.

+

For ZEC, we define + \(\mathsf{AssetBase}_{\mathsf{AssetId}} := \mathcal{V}^{\mathsf{Orchard}}\) + so that the value commitment for ZEC notes is computed identically to the Orchard protocol deployed in NU5 4. As such + \(\mathsf{ValueCommit^{Orchard}_{rcv}}(\mathsf{v})\) + as defined in 4 is used as + \(\mathsf{ValueCommit^{OrchardZSA}_{rcv}}(\mathcal{V}^{\mathsf{Orchard}}, \mathsf{v})\) + here.

+

Rationale for Value Commitment

+

The Orchard Protocol uses a Homomorphic Pedersen Commitment 24 to perform the value commitment, with fixed base points + \(\mathcal{V}^{\mathsf{Orchard}}\) + and + \(\mathcal{R}^{\mathsf{Orchard}}\) + as the values represent the amount of ZEC being transferred.

+

The use of different value base points for different Assets enables the final balance of the transaction to be securely computed, such that each Asset Identifier is balanced independently, which is required as different Assets are not meant to be mutually fungible.

+
+
+

Burn Mechanism

+

The burn mechanism is a transparent extension to the transfer protocol that enables a specific amount of any Asset Identifier to be "destroyed". The burn mechanism does NOT send Assets to a non-spendable address, it simply reduces the total number of units of a given Custom Asset in circulation at the consensus level. It is enforced at the consensus level, by using an extension of the value balance mechanism used for ZEC Assets. Burning makes it globally provable that a given amount of an Asset has been destroyed.

+

The sender includes a + \(\mathsf{v_{AssetId}}\) + variable for every Asset Identifier that is being burnt, which represents the amount of that Asset being burnt. As described in the Orchard-ZSA Transaction Structure, this is separate from the regular + \(\mathsf{valueBalance^{Orchard}}\) + that is the default transparent value for the ZEC Asset, and represents either the transaction fee, or the amount of ZEC changing pools (e.g. to Sapling or Transparent).

+

For every Custom Asset that is burnt, we add to the + \(\mathsf{assetBurn}\) + set the tuple + \((\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}})\) + such that the validator of the transaction can compute the value commitment with the corresponding value base point of that Asset. This ensures that the values are all balanced out with respect to the Asset Identifiers in the transfer.

+
\(\mathsf{assetBurn} := \{ (\mathsf{AssetBase}_{\mathsf{AssetId}} : \mathbb{P}^*, \mathsf{v_{AssetId}} : \{1 .. 2^{\ell_{\mathsf{value}}} - 1\}) \,|\, \mathsf{AssetId} \in \mathsf{AssetIdsToBurn} \}\)
+

We denote by + \(L\) + the cardinality of the + \(\mathsf{assetBurn}\) + set.

+

Additional Consensus Rules

+
    +
  1. We require that for every + \((\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}}) \in \mathsf{assetBurn}, \mathsf{AssetBase_{AssetId}} \neq \mathcal{V}^{\mathsf{Orchard}}\!\) + . That is, ZEC or TAZ is not allowed to be burnt by this mechanism.
    2. +
  2. We require that for every + \((\mathsf{AssetBase_{AssetId}}, \mathsf{v_{AssetId}}) \in \mathsf{assetBurn}, \mathsf{v_{AssetId}} \neq 0\!\) + .
    3. +
  3. We require that there be no duplication of Custom Assets in the + \(\mathsf{assetBurn}\) + set. That is, every + \(\mathsf{AssetBase_{AssetId}}\) + has at most one entry in + \(\mathsf{assetBurn}\!\) + .
    4. +
+

Note: Even if this mechanism allows having transparent ↔ shielded Asset transfers in theory, the transparent protocol will not be changed with this ZIP to adapt to a multiple Asset structure. This means that unless future consensus rules changes do allow it, unshielding will not be possible for Custom Assets.

+
+
+

Value Balance Verification

+

In order to verify the balance of the different Assets, the verifier MUST perform a similar process as for the Orchard protocol 18, with the addition of the burn information.

+

For a total of + \(n\) + Actions in a transfer, the prover MUST still sign the SIGHASH transaction hash using the binding signature key + \(\mathsf{bsk} = \sum_{i=1}^{n} \mathsf{rcv}_i\!\) + .

+

The verifier MUST compute the value balance verification equation:

+
\(\mathsf{bvk} = (\sum_{i=1}^{n} \mathsf{cv}^{\mathsf{net}}_i) - \mathsf{ValueCommit_0^{OrchardZSA}(\mathcal{V}^{\mathsf{Orchard}}, v^{balanceOrchard})} - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} \mathsf{ValueCommit_0^{OrchardZSA}}(\mathsf{AssetBase}, \mathsf{v})\)
+

After computing + \(\mathsf{bvk}\!\) + , the verifier MUST use it to verify the binding signature on the SIGHASH transaction hash.

+

Rationale for Value Balance Verification

+

We assume + \(n\) + Actions in a transfer. Out of these + \(n\) + Actions, we further distinguish (for the sake of clarity) between Actions related to ZEC and Actions related to Custom Assets. We denote by + \(S_{\mathsf{ZEC}} \subseteq \{1 .. n\}\) + the set of indices of Actions that are related to ZEC, and by + \(S_{\mathsf{CA}} = \{1 .. n\} \setminus S_{\mathsf{ZEC}}\) + the set of indices of Actions that are related to Custom Assets.

+

The right hand side of the value balance verification equation can be expanded to:

+
\(((\sum_{i \in S_{\mathsf{ZEC}}} \mathsf{cv}^{\mathsf{net}}_i) + (\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv}^{\mathsf{net}}_j)) - ([\mathsf{v^{balanceOrchard}}]\,\mathcal{V}^{\mathsf{Orchard}} + [0]\,\mathcal{R}^{\mathsf{Orchard}}) - (\sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\,\mathsf{AssetBase} + [0]\,\mathcal{R}^{\mathsf{Orchard}})\)
+

This equation contains the balance check of the Orchard protocol 18. With ZSA, transfer Actions for Custom Assets must also be balanced across Asset Bases. All Custom Assets are contained within the shielded pool, and cannot be unshielded via a regular transfer. Custom Assets can be burnt, the mechanism for which reveals the amount and identifier of the Asset being burnt, within the + \(\mathsf{assetBurn}\) + set. As such, for a correctly constructed transaction, we will get + \(\sum_{j \in S_{\mathsf{CA}}} \mathsf{cv}^{\mathsf{net}}_j - \sum_{(\mathsf{AssetBase}, \mathsf{v}) \in \mathsf{assetBurn}} [\mathsf{v}]\,\mathsf{AssetBase} = \sum_{j \in S_{\mathsf{CA}}} [\mathsf{rcv}^{\mathsf{net}}_j]\,\mathcal{R}^{\mathsf{Orchard}}\!\) + .

+

When the Asset is not being burnt, the net balance of the input and output values is zero, and there will be no addition to the + \(\mathsf{assetBurn}\) + vector. Therefore, the relationship between + \(\mathsf{bvk}\) + and + \(\mathsf{bsk}\) + will hold if and only if, per Custom Asset, the sum of the net values of the relevant Actions equals the corresponding + \(\mathsf{v}_k\) + value (or equals + \(0\) + if that Asset is not in the + \(\mathsf{assetBurn}\) + set), and for ZEC, the sum of the net values of the relevant Actions equals the + \(\mathsf{v^{balanceOrchard}}\) + value.

+

As in the Orchard protocol, the binding signature verification key, + \(\mathsf{bvk}\!\) + , will only be valid (and hence verify the signature correctly), as long as the committed values sum to zero. In contrast, in this protocol, the committed values must sum to zero per Asset Base, as the Pedersen commitments add up homomorphically only with respect to the same value base point.

+
+
+

Split Notes

+

A Split Input is a copy of a previously issued input note (that is, a note that has previously been included in the Merkle tree), with the following changes:

+
    +
  • A + \(\mathsf{split\_flag}\) + boolean is set to 1.
    • +
  • The value of the note is replaced with the value 0 during the computation of the value commitment.
    • +
+

Input notes are sometimes split in two (or more) output notes, as in most cases, not all the value in a single note is sent to a single output.

+

When the number of input notes of a particular Asset Base is smaller than the required number of output notes for the same Asset Base, the sender creates Split Inputs of the same Asset Base as padding for the input-less Actions. Note that we do not care about whether the previously issued note copied to create a Split Input is owned by the sender, or whether it was nullified before.

+

Wallets and other clients have to choose from the following to ensure the Asset Base is preserved for the output note of a Split Action:

+
    +
  1. The Split Input note could be another note containing the same Asset Base that is being spent by this transaction (but not by this Split Input).
    2. +
  2. The Split Input note could be a different unspent note containing the same Asset Base (note that the note will not actually be spent).
    3. +
  3. The Split Input note could be an already spent note containing the same Asset Base (note that by zeroing the value in the circuit, we prevent double spending).
    4. +
+

For Split Notes, the nullifier is generated as follows:

+
\(\mathsf{nf_{old}} = \mathsf{Extract}_{\mathbb{P}} ([(\mathsf{PRF^{nfOrchard}_{nk}} (\text{ρ}^{\mathsf{old}}) + \text{ψ}') \bmod q_{\mathbb{P}}]\,\mathcal{K}^\mathsf{Orchard} + \mathsf{cm^{old}} + \mathcal{L}^\mathsf{Orchard})\)
+

where + \(\text{ψ}'\) + is sampled uniformly at random on + \(\mathbb{F}_{q_{\mathbb{P}}}\!\) + , + \(\mathcal{K}^{\mathsf{Orchard}}\) + is the Orchard Nullifier Base as defined in 19, and + \(\mathcal{L}^{\mathsf{Orchard}} := \mathsf{GroupHash^{\mathbb{P}}}(\texttt{"z.cash:Orchard"}, \texttt{"L"})\!\) + .

+

Rationale for Split Notes

+

In the Orchard protocol, since each Action represents an input and an output, the transaction that wants to send one input to multiple outputs must have multiple inputs. The Orchard protocol gives dummy spend notes 17 to the Actions that have not been assigned input notes.

+

The Orchard technique requires modification for the ZSA protocol with multiple Asset Identifiers, as the output note of the split Actions cannot contain just any Asset Base. We must enforce it to be an actual output of a GroupHash computation (in fact, we want it to be of the same Asset Base as the original input note, but the binding signature takes care that the proper balancing is performed). Without this enforcement the prover could input a multiple (or linear combination) of an existing Asset Base, and thereby attack the network by overflowing the ZEC value balance and hence counterfeiting ZEC funds.

+

Therefore, for Custom Assets we enforce that every input note to an ZSA Action must be proven to exist in the set of note commitments in the note commitment tree. We then enforce this real note to be “unspendable” in the sense that its value will be zeroed in split Actions and the nullifier will be randomized, making the note not spendable in the specific Action. Then, the proof itself ensures that the output note is of the same Asset Base as the input note. In the circuit, the split note functionality will be activated by a boolean private input to the proof (aka the + \(\mathsf{split\_flag}\) + boolean). This ensures that the value base points of all output notes of a transfer are actual outputs of a GroupHash, as they originate in the Issuance protocol which is publicly verified.

+

Note that the Orchard dummy note functionality remains in use for ZEC notes, and the Split Input technique is used in order to support Custom Assets.

+
+
+

Circuit Statement

+

Every ZSA Action statement is closely similar to the Orchard Action statement 20, except for a few additions that ensure the security of the Asset Identifier system. We detail these changes below.

+

All modifications in the Circuit are detailed in 31.

+

Asset Base Equality

+

The following constraints must be added to ensure that the input and output note are of the same + \(\mathsf{AssetBase}\!\) + :

+
    +
  • The Asset Base, + \(\mathsf{AssetBase_{AssetId}}\!\) + , for the note is witnessed once, as an auxiliary input.
    • +
  • In the Old note commitment integrity constraint in the Orchard Action statement 20, + \(\mathsf{NoteCommit^{Orchard}_{rcm^{old}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{old}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{old}}), \mathsf{v^{old}}, \text{ρ}^{\mathsf{old}}, \text{ψ}^{\mathsf{old}})\) + is replaced with + \(\mathsf{NoteCommit^{OrchardZSA}_{rcm^{old}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{old}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{old}}), \mathsf{v^{old}}, \text{ρ}^{\mathsf{old}}, \text{ψ}^{\mathsf{old}}, \mathsf{AssetBase_{AssetId}})\!\) + .
    • +
  • In the New note commitment integrity constraint in the Orchard Action statement 20, + \(\mathsf{NoteCommit^{Orchard}_{rcm^{new}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{new}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{new}}), \mathsf{v^{new}}, \text{ρ}^{\mathsf{new}}, \text{ψ}^{\mathsf{new}})\) + is replaced with + \(\mathsf{NoteCommit^{OrchardZSA}_{rcm^{new}}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d^{new}}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d^{new}}), \mathsf{v^{new}}, \text{ρ}^{\mathsf{new}}, \text{ψ}^{\mathsf{new}}, \mathsf{AssetBase_{AssetId}})\!\) + .
    • +
+

To make the evaluation of the note commitment easier, we add a boolean + \(\mathsf{is\_native\_asset}\) + as an auxiliary witness. We also add some constraints to verify that this variable is activated (i.e. + \(\mathsf{is\_native\_asset} = 1\!\) + ) if the Asset Base is equal to + \(\mathcal{V}^{\mathsf{Orchard}}\) + and this variable is not activated (i.e. + \(\mathsf{is\_native\_asset} = 0\!\) + ) if the Asset Base is not equal to + \(\mathcal{V}^{\mathsf{Orchard}}\!\) + .

+
+
+

The + \(\mathsf{enableZSA}\) + Flag

+

The following constraints must be added to disable transactions involving Custom Assets when the + \(\mathsf{enableZSA}\) + flag is set to false:

+
    +
  • if + \(\mathsf{enableZSA}\) + is not activated (i.e. + \(\mathsf{enableZSA} = 0\!\) + ), then constrain + \(\mathsf{is\_native\_asset} = 1\!\) + , since the + \(\mathsf{AsssetBase}\) + must be equal to the native asset.
    • +
+
+

Value Commitment Correctness

+

The following constraints must be added to ensure that the value commitment is computed using the witnessed Asset Base:

+
    +
  • The fixed-base multiplication constraint between the value and the value base point of the value commitment, + \(\mathsf{cv}\!\) + , is replaced with a variable-base multiplication between the two.
    • +
  • The witness to the value base point (as defined in the asset base equation) is the auxiliary input + \(\mathsf{AssetBase_{AssetId}}\!\) + .
    • +
+
+

Asset Identifier Consistency for Split Actions

+

Senders must not be able to change the Asset Base for the output note in a Split Action. We do this via the following constraints:

+
    +
  • +
    +
    The Value Commitment Integrity should be changed:
    +
    +
      +
    • Replace the input note value by a generic value, + \(\mathsf{v}'\!\) + , as + \(\mathsf{cv^{net}} = \mathsf{ValueCommit_rcv^{OrchardZSA}}(\mathsf{AssetBase_{AssetId}}, \mathsf{v}' - \mathsf{v^{new}})\) +
      • +
    +
    +
    +
    • +
  • +
    +
    Add a boolean + \(\mathsf{split\_flag}\) + variable as an auxiliary witness. This variable is to be activated + \(\mathsf{split\_flag} = 1\) + if the Action in question has a Split Input and + \(\mathsf{split\_flag} = 0\) + if the Action is actually spending an input note:
    +
    +
      +
    • If + \(\mathsf{split\_flag} = 1\) + then constrain + \(\mathsf{v}' = 0\) + otherwise constrain + \(\mathsf{v}' = \mathsf{v^{old}}\) + from the auxiliary input.
      • +
    • If + \(\mathsf{split\_flag} = 1\) + then constrain + \(\mathsf{is\_native\_asset} = 0\) + because split notes are only available for Custom Assets.
      • +
    +
    +
    +
    • +
  • +
    +
    The Merkle Path Validity should check the existence of the note commitment as usual (and not like with dummy notes):
    +
    +
      +
    • Check for all notes except dummy notes that + \((\mathsf{path}, \mathsf{pos})\) + is a valid Merkle path of depth + \(\mathsf{MerkleDepth^{Orchard}}\!\) + , from + \(\mathsf{cm^{old}}\) + to the anchor + \(\mathsf{rt^{Orchard}}\!\) + .
      • +
    • The new constraint is + \(\underbrace{(\mathsf{v^{old}} = 0 \land \mathsf{is\_native\_asset} = 1)}_\text{It is a dummy note} \lor \underbrace{(\mathsf{Valid\,Merkle\,Path})}_\text{The Merkle Path is valid}\!\) + .
      • +
    +
    +
    +
    • +
  • The Nullifier Integrity will be changed to prevent the identification of notes as defined in the Split Notes section.
    • +
+
+

Backwards Compatibility with ZEC Notes

+

The input note in the old note commitment integrity check must either include an Asset Base (ZSA note) or not (pre-ZSA Orchard note). If the note is a pre-ZSA Orchard note, the note commitment is computed in the original Orchard fashion 16. If the note is a ZSA note, the note commitment is computed as defined in the Note Structure & Commitment section.

+
+
+
+

Orchard-ZSA Transaction Structure

+

The transaction format for v6 transactions is described in ZIP 230 10.

+
+

TxId Digest

+

The transaction digest algorithm defined in ZIP 244 11 is modified by the ZSA protocol to add a new branch for issuance information, along with modifications within the orchard_digest to account for the inclusion of the Asset Base. The details of these changes are described in this section, and highlighted using the [UPDATED FOR ZSA] or [ADDED FOR ZSA] text label. We omit the details of the sections that do not change for the ZSA protocol.

+

txid_digest

+

A BLAKE2b-256 hash of the following values

+ 
T.1: header_digest       (32-byte hash output)
+T.2: transparent_digest  (32-byte hash output)
+T.3: sapling_digest      (32-byte hash output)
+T.4: orchard_digest      (32-byte hash output)  [UPDATED FOR ZSA]
+T.5: issuance_digest     (32-byte hash output)  [ADDED FOR ZSA]
+

The personalization field remains the same as in ZIP 244 11.

+

T.4: orchard_digest

+

When Orchard Actions are present in the transaction, this digest is a BLAKE2b-256 hash of the following values

+ 
T.4a: orchard_actions_compact_digest      (32-byte hash output)          [UPDATED FOR ZSA]
+T.4b: orchard_actions_memos_digest        (32-byte hash output)          [UPDATED FOR ZSA]
+T.4c: orchard_actions_noncompact_digest   (32-byte hash output)          [UPDATED FOR ZSA]
+T.4d: flagsOrchard                        (1 byte)
+T.4e: valueBalanceOrchard                 (64-bit signed little-endian)
+T.4f: anchorOrchard                       (32 bytes)
+
T.4a: orchard_actions_compact_digest
+

A BLAKE2b-256 hash of the subset of Orchard Action information intended to be included in an updated version of the ZIP-307 12 CompactBlock format for all Orchard Actions belonging to the transaction. For each Action, the following elements are included in the hash:

+ 
T.4a.i  : nullifier            (field encoding bytes)
+T.4a.ii : cmx                  (field encoding bytes)
+T.4a.iii: ephemeralKey         (field encoding bytes)
+T.4a.iv : encCiphertext[..84]  (First 84 bytes of field encoding)  [UPDATED FOR ZSA]
+

The personalization field of this hash is the same as in ZIP 244:

+ 
"ZTxIdOrcActCHash"
+
+
T.4b: orchard_actions_memos_digest
+

A BLAKE2b-256 hash of the subset of Orchard shielded memo field data for all Orchard Actions belonging to the transaction. For each Action, the following elements are included in the hash:

+ 
T.4b.i: encCiphertext[84..596] (contents of the encrypted memo field)  [UPDATED FOR ZSA]
+

The personalization field of this hash remains identical to ZIP 244:

+ 
"ZTxIdOrcActMHash"
+
+
T.4c: orchard_actions_noncompact_digest
+

A BLAKE2b-256 hash of the remaining subset of Orchard Action information not intended for inclusion in an updated version of the the ZIP 307 12 CompactBlock format, for all Orchard Actions belonging to the transaction. For each Action, the following elements are included in the hash:

+ 
T.4d.i  : cv                    (field encoding bytes)
+T.4d.ii : rk                    (field encoding bytes)
+T.4d.iii: encCiphertext[596..]  (post-memo suffix of field encoding)  [UPDATED FOR ZSA]
+T.4d.iv : outCiphertext         (field encoding bytes)
+

The personalization field of this hash is defined identically to ZIP 244:

+ 
"ZTxIdOrcActNHash"
+
+
+

T.5: issuance_digest

+

The details of the computation of this value are in ZIP 227 7.

+
+
+
+

Signature Digest and Authorizing Data Commitment

+

The details of the changes to these algorithms are in ZIP 227 8 9.

+
+

Security and Privacy Considerations

+
    +
  • After the protocol upgrade, the Orchard shielded pool will be shared by the Orchard protocol and the Orchard-ZSA protocol.
    • +
  • Deploying the Orchard-ZSA protocol does not necessitate disabling the Orchard protocol. Both can co-exist and be addressed via different transaction versions (V5 for Orchard and V6 for Orchard-ZSA). Due to this, Orchard note commitments can be distinguished from Orchard-ZSA note commitments. This holds whether or not the two protocols are active simultaneously.
    • +
  • Orchard-ZSA note commitments for the native asset (ZEC) are indistinguishable from Orchard-ZSA note commitments for non-native Assets.
    • +
  • When including new Assets we would like to maintain the amount and identifiers of Assets private, which is achieved with the design.
    • +
  • We prevent a potential malleability attack on the Asset Identifier by ensuring the output notes receive an Asset Base that exists on the global state.
    • +
+
+

Other Considerations

+

Transaction Fees

+

The fee mechanism for the upgrades proposed in this ZIP will follow the mechanism described in ZIP 317 for the ZSA protocol upgrade 13.

+
+

Backward Compatibility

+

In order to have backward compatibility with the ZEC notes, we have designed the circuit to support both ZEC and ZSA notes. As we specify above, there are three main reasons we can do this:

+
    +
  • Note commitments for ZEC notes will remain the same, while note commitments for Custom Assets will be computed taking into account the + \(\mathsf{AssetBase}\) + value as well.
    • +
  • The existing Orchard shielded pool will continue to be used for the new ZSA notes post the upgrade.
    • +
  • The value commitment is abstracted to allow for the value base-point as a variable private input to the proof.
    • +
  • The ZEC-based Actions will still include dummy input notes, whereas the ZSA-based Actions will include split input notes and will not include dummy input notes.
    • +
+
+

Deployment

+

The Zcash Shielded Assets protocol will be deployed in a subsequent Network Upgrade.

+
+
+

Test Vectors

+ +
+

Reference Implementation

+ +
+

References

+ + + + + + + +
1Information on BCP 14 — "RFC 2119: Key words for use in RFCs to Indicate Requirement Levels" and "RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"
+ + + + + + + +
2ZIP 200: Network Upgrade Mechanism
+ + + + + + + +
3ZIP 209: Prohibit Negative Shielded Chain Value Pool Balances
+ + + + + + + +
4ZIP 224: Orchard
+ + + + + + + +
5ZIP 227: Issuance of Zcash Shielded Assets
+ + + + + + + +
6ZIP 227: Issuance of Zcash Shielded Assets: Specification: Asset Identifier
+ + + + + + + +
7ZIP 227: Issuance of Zcash Shielded Assets: TxId Digest - Issuance
+ + + + + + + +
8ZIP 227: Issuance of Zcash Shielded Assets: Signature Digest
+ + + + + + + +
9ZIP 227: Issuance of Zcash Shielded Assets: Authorizing Data Commitment
+ + + + + + + +
10ZIP 230: Version 6 Transaction Format
+ + + + + + + +
11ZIP 244: Transaction Identifier Non-Malleability
+ + + + + + + +
12ZIP 307: Light Client Protocol for Payment Detection
+ + + + + + + +
13ZIP 317: Proportional Transfer Fee Mechanism - Pull Request #667 for ZSA Protocol ZIPs
+ + + + + + + +
14Zcash Protocol Specification, Version 2023.4.0. Section 3.2: Notes
+ + + + + + + +
15Zcash Protocol Specification, Version 2023.4.0. Section 3.7: Action Transfers and their Descriptions
+ + + + + + + +
16Zcash Protocol Specification, Version 2023.4.0. Section 4.1.8: Commitment
+ + + + + + + +
17Zcash Protocol Specification, Version 2023.4.0. Section 4.8.3: Dummy Notes (Orchard)
+ + + + + + + +
18Zcash Protocol Specification, Version 2023.4.0. Section 4.14: Balance and Binding Signature (Orchard)
+ + + + + + + +
19Zcash Protocol Specification, Version 2023.4.0. Section 4.16: Note Commitments and Nullifiers
+ + + + + + + +
20Zcash Protocol Specification, Version 2023.4.0. Section 4.17.4: Action Statement (Orchard)
+ + + + + + + +
21Zcash Protocol Specification, Version 2023.4.0. Section 5.1: Integers, Bit Sequences, and Endianness
+ + + + + + + +
22Zcash Protocol Specification, Version 2023.4.0. Section 5.3: Constants
+ + + + + + + +
23Zcash Protocol Specification, Version 2023.4.0. Section 5.4.1.9: Sinsemilla hash function
+ + + + + + + +
24Zcash Protocol Specification, Version 2023.4.0. Section 5.4.8.3: Homomorphic Pedersen commitments (Sapling and Orchard)
+ + + + + + + +
25Zcash Protocol Specification, Version 2023.4.0. Section 5.4.8.4: Sinsemilla commitments
+ + + + + + + +
26Zcash Protocol Specification, Version 2023.4.0. Section 5.4.9.6: Pallas and Vesta
+ + + + + + + +
27Zcash Protocol Specification, Version 2023.4.0. Section 5.5: Encodings of Note Plaintexts and Memo Fields
+ + + + + + + +
28Zcash Protocol Specification, Version 2023.4.0. Section 7.5: Action Description Encoding and Consensus
+ + + + + + + +
29User-Defined Assets and Wrapped Assets
+ + + + + + + +
30Comment on Generalized Value Commitments
+ + + + + + + +
31Modifications to the Orchard circuit for the ZSA Protocol
+
\ No newline at end of file diff --git a/zip-0227.html b/zip-0227.html index 9db3dcd41..86a06c336 100644 --- a/zip-0227.html +++ b/zip-0227.html @@ -3,6 +3,7 @@ ZIP 227: Issuance of Zcash Shielded Assets +
@@ -15,10 +16,973 @@ Credits: Daniel Benarroch Aurelien Nicolas Deirdre Connolly -Status: Reserved + Teor +Status: Draft Category: Consensus +Created: 2022-05-01 +License: MIT Discussions-To: <https://github.com/zcash/zips/issues/618> -Pull-Request: <https://github.com/zcash/zips/pull/649> +Pull-Request: <https://github.com/zcash/zips/pull/680> +

Terminology

+

The key words "MUST", "MUST NOT", "SHOULD", "RECOMMENDED", and "MAY" in this document are to be interpreted as described in BCP 14 1 when, and only when, they appear in all capitals.

+

The term "network upgrade" in this document is to be interpreted as described in ZIP 200 7.

+

The terms "Orchard" and "Action" in this document are to be interpreted as described in ZIP 224 8.

+

We define the following additional terms:

+
    +
  • Asset: A type of note that can be transferred on the Zcash blockchain. Each Asset is identified by an Asset Identifier Specification: Asset Identifier. +
      +
    • ZEC is the default (and currently the only defined) Asset for the Zcash mainnet.
      • +
    • TAZ is the default (and currently the only defined) Asset for the Zcash testnet.
      • +
    • We use the term "Custom Asset" to refer to any Asset other than ZEC and TAZ.
      • +
    +
    • +
  • Native Asset: a Custom Asset with issuance defined on the Zcash blockchain.
    • +
  • Wrapped Asset: a Custom Asset with native issuance defined outside the Zcash blockchain.
    • +
  • Issuance Action: an instance of a single issuance of a Zcash Shielded Asset. It defines the issuance of a single Asset Identifier.
    • +
  • Issuance Bundle: the bundle in the transaction that contains all the issuance actions of that transaction.
    • +
+
+

Abstract

+

This ZIP (ZIP 227) proposes the Zcash Shielded Assets (ZSA) protocol, in conjunction with ZIP 226 9. This protocol is an extension of the Orchard protocol that enables the creation, transfer and burn of Custom Assets on the Zcash chain. The creation of such Assets is defined in this ZIP (ZIP 227), while the transfer and burn of such Assets is defined in ZIP 226 9. This ZIP must only be implemented in conjunction with ZIP 226 9. The proposed issuance mechanism is only valid for the Orchard-ZSA transfer protocol, because it produces notes that can only be transferred under ZSA.

+
+

Motivation

+

This ZIP introduces the issuance mechanism for Custom Assets on the Zcash chain. While originally part of a single ZSA ZIP, the issuance mechanism turned out to be substantial enough to stand on its own and justify the creation of this supporting ZIP for ZIP 226 9.

+

This ZIP only enables transparent issuance. As a first step, transparency will allow for proper testing of the applications that will be most used in the Zcash ecosystem, and will enable the supply of Assets to be tracked.

+

The issuance mechanism described in this ZIP is broad enough for issuers to either create Assets on Zcash (i.e. Assets that originate on the Zcash blockchain), as well as for institutions to create bridges from other chains and import Wrapped Assets. This enables what we hope will be a useful set of applications.

+
+

Use Cases

+

The design presented in this ZIP enables issuance of shielded Assets in various modes:

+
    +
  • The issuer may or may not know the receivers of the issued Asset in advance.
    • +
  • The Asset can be of non-fungible type, where each Asset type can be made part of a single “series”.
    • +
  • The supply of the Asset can be limited in advance or not.
    • +
  • The Asset can be a wrapped version of an Asset issued by another chain (as long as there is a bridge that supports transfer of that Asset between chains).
    • +
+

See the Concrete Applications section for more details.

+
+

Requirements

+
    +
  • Any user of the Zcash blockchain can issue Custom Assets on chain.
    • +
  • The issuance mechanism should enable public tracking of the supply of the Assets on the Zcash blockchain.
    • +
  • Issuing or changing the attributes of a specific Asset should require cryptographic authorization.
    • +
  • The Asset identification should be unique (among all shielded pools) and different issuer public keys should not be able to generate the same Asset Identifier.
    • +
  • An issuer should be able to issue different Assets in the same transaction. In other words, in a single "issuance bundle", the issuer should be able publish many "issuance actions", potentially creating multiple Custom Assets.
    • +
  • Every "issuance action" should contain a + \(\mathsf{finalize}\) + boolean that defines whether the specific Custom Asset can have further tokens issued or not.
    • +
+
+

Specification: Issuance Keys and Issuance Authorization Signature Scheme

+

The Orchard-ZSA Protocol adds the following keys to the key components 18 19:

+
    +
  1. The issuance authorizing key, denoted as + \(\mathsf{isk}\!\) + , is the key used to authorize the issuance of Asset Identifiers by a given issuer, and is only used by that issuer.
    2. +
  2. The issuance validating key, denoted as + \(\mathsf{ik}\!\) + , is the key that is used to validate issuance transactions. This key is used to validate the issuance of Asset Identifiers by a given issuer, and is used by all blockchain users (specifically the owners of notes for that Asset, and consensus validators) to associate the Asset in question with the issuer.
    3. +
+

The relations between these keys are shown in the following diagram:

+
+ +
Diagram of Issuance Key Components for the Orchard-ZSA Protocol
+
+

Issuance Authorization Signature Scheme

+

We instantiate the issuance authorization signature scheme + \(\mathsf{IssueAuthSig}\) + as a BIP-340 Schnorr signature over the secp256k1 curve. The signing and validation algorithms, signature encoding, and public key encoding MUST follow BIP 340 16.

+

Batch verification MAY be used. Precomputation MAY be used if and only if it produces equivalent results; for example, for a given verification key + \(pk\) + and + \(\mathit{lift\_x}(\mathit{int}(pk))\) + MAY be precomputed.

+

We define the constants as per the secp256k1 standard parameters, as described in BIP 340.

+

The associated types of the + \(\mathsf{IssueAuthSig}\) + signature scheme are as follows:

+
    +
  • + \(\mathsf{IssueAuthSig}.\!\mathsf{Message} = \mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}\) +
    • +
  • + \(\mathsf{IssueAuthSig}.\!\mathsf{Signature} = \mathbb{B}^{\mathbb{Y}^{[64]}} \cup \{\bot\}\) +
    • +
  • + \(\mathsf{IssueAuthSig}.\!\mathsf{Public} = \mathbb{B}^{\mathbb{Y}^{[32]}} \cup \{\bot\}\) +
    • +
  • + \(\mathsf{IssueAuthSig}.\!\mathsf{Private} = \mathbb{B}^{\mathbb{Y}^{[32]}}\) +
    • +
+

where + \(\mathbb{B}^{\mathbb{Y}^{[k]}}\) + denotes the set of sequences of + \(k\) + bytes, and + \(\mathbb{B}^{\mathbb{Y}^{[\mathbb{N}]}}\) + denotes the type of byte sequences of arbitrary length, as defined in the Zcash protocol specification 17.

+

The issuance authorizing key generation algorithm and the issuance validating key derivation algorithm are defined in the Issuance Key Derivation section, while the corresponding signing and validation algorithms are defined in the Issuance Authorization Signing and Validation section.

+
+

Issuance Key Derivation

+

Issuance authorizing key generation for hierarchical deterministic wallets

+

The issuance authorizing key is generated using the Orchard master key derivation procedure defined in ZIP 32 3. We reuse the functions defined there in what follows in this section.

+

Let + \(S\) + be a seed byte sequence of a chosen length, which MUST be at least 32 and at most 252 bytes. We define the master extended issuance key + \(m_{\mathsf{Issuance}} := \mathsf{MasterKeyGen}(\texttt{"ZIP32ZSAIssue_V1"}, S)\!\) + .

+

As in ZIP 32 for Orchard 4, we only use hardened child key derivation for the issuance authorizing key. We reuse the + \(\mathsf{CDKsk}\) + function for Orchard child key derivation from ZIP 32.

+

We use the notation of ZIP 32 6 for shielded HD paths, and define the issuance authorizing key path as + \(m_{\mathsf{Issuance}} / \mathit{purpose}' / \mathit{coin\_type}' / \mathit{account}'\!\) + . We fix the path levels as follows:

+
    +
  • + \(\mathit{purpose}\) + : a constant set to + \(227\) + (i.e. + \(\mathtt{0xe3}\!\) + ). + \(\mathit{purpose}'\) + is thus + \(227'\) + (or + \(\mathtt{0x800000e3}\!\) + ) following the BIP 43 recommendation.
    • +
  • + \(\mathit{coin\_type}\) + : Defined as in ZIP 32 5.
    • +
  • + \(\mathit{account}\) + : fixed to index + \(0\!\) + .
    • +
+

From the generated + \((\mathsf{sk}, \mathsf{c})\!\) + , we set the issuance authorizing key to be + \(\mathsf{isk} := \mathsf{sk}\!\) + .

+
+

Derivation of issuance validating key

+

Define + \(\mathsf{IssueAuthSig}.\!\mathsf{DerivePublic}\; : \; (\mathsf{isk}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Private}) \to \mathsf{IssueAuthSig}.\!\mathsf{Public}\) + as:

+
    +
  • + \(\mathsf{ik} := \textit{PubKey}(\mathsf{isk})\) +
    • +
  • Return + \(\bot\) + if the + \(\textit{PubKey}\) + algorithm invocation fails, otherwise return + \(\mathsf{ik}\!\) + .
    • +
+

where the + \(\textit{PubKey}\) + algorithm is defined in BIP 340 16. Note that the byte representation of + \(\mathsf{ik}\) + is in big-endian order as defined in BIP 340.

+

It is possible for the + \(\textit{PubKey}\) + algorithm to fail with very low probability, which means that + \(\mathsf{IssueAuthSig}.\!\mathsf{DerivePublic}\) + could return + \(\bot\) + with very low probability. If this happens, discard the keys and repeat with a different + \(\mathsf{isk}\!\) + .

+

This allows the issuer to use the same wallet it usually uses to transfer Assets, while keeping a disconnect from the other keys. Specifically, this method is aligned with the requirements and motivation of ZIP 32 2. It provides further anonymity and the ability to delegate issuance of an Asset (or in the future, generate a multi-signature protocol) while the rest of the keys remain in the wallet safe.

+
+
+

Issuance Authorization Signing and Validation

+

Define + \(\mathsf{IssueAuthSig}.\!\mathsf{Sign}\; : \; (\mathsf{isk}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Private}) \times (M\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Message}) \to \mathsf{IssueAuthSig}.\!\mathsf{Signature}\) + as:

+
    +
  • Let the auxiliary data + \(a = [\mathtt{0x00}]^{32}\!\) + .
    • +
  • Let + \(\text{σ} = \mathsf{Sign}(\mathsf{isk}, M)\!\) + .
    • +
  • Return + \(\bot\) + if the + \(\mathsf{Sign}\) + algorithm fails in the previous step, otherwise return + \(\text{σ}\!\) + .
    • +
+

where the + \(\mathsf{Sign}\) + algorithm is defined in BIP 340 and + \(a\) + denotes the auxiliary data used in BIP 340 16. Note that + \(\mathsf{IssueAuthSig}.\!\mathsf{Sign}\) + could return + \(\bot\) + with very low probability.

+

Define + \(\mathsf{IssueAuthSig}.\!\mathsf{Validate}\; : \; (\mathsf{ik}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Public}) \times (M\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Message}) \times (\text{σ}\; : \; \mathsf{IssueAuthSig}.\!\mathsf{Signature}) \to \mathbb{B}\) + as:

+
    +
  • Return + \(0\) + if + \(\text{σ} = \bot\!\) + .
    • +
  • Return + \(1\) + if + \(\mathsf{Verify}(\mathsf{ik}, M, \text{σ})\) + succeeds, otherwise + \(0\!\) + .
    • +
+

where the + \(\mathsf{Verify}\) + algorithm is defined in BIP 340 16.

+
+
+

Specification: Asset Identifier

+

For every new Asset, there must be a new and unique Asset Identifier, denoted + \(\mathsf{AssetId}\!\) + . We define this to be a globally unique pair + \(\mathsf{AssetId} := (\mathsf{ik}, \mathsf{asset\_desc})\!\) + , where + \(\mathsf{ik}\) + is the issuance key and + \(\mathsf{asset\_desc}\) + is a byte string.

+

A given Asset Identifier is used across all Zcash protocols that support ZSAs -- that is, the Orchard-ZSA protocol and potentially future Zcash shielded protocols. For this Asset Identifier, we derive an Asset Digest, + \(\mathsf{AssetDigest}\!\) + , which is simply is a + \(\textsf{BLAKE2b-512}\) + hash of the Asset Identifier. From the Asset Digest, we derive a specific Asset Base within each shielded protocol using the applicable hash-to-curve algorithm. This Asset Base is included in shielded notes.

+

Let

+
    +
  • + \(\mathsf{asset\_desc}\) + be the asset description, which includes any information pertaining to the issuance, and is a byte sequence of up to 512 bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later.
    • +
  • + \(\mathsf{ik}\) + be the issuance validating key of the issuer, a public key used to verify the signature on the issuance transaction's SIGHASH.
    • +
+

Define + \(\mathsf{AssetDigest_{AssetId}} := \textsf{BLAKE2b-512}(\texttt{"ZSA-Asset-Digest"},\; \mathsf{EncodeAssetId}(\mathsf{AssetId}))\!\) + , where

+
    +
  • + \(\mathsf{EncodeAssetId}(\mathsf{AssetId}) = \mathsf{EncodeAssetId}((\mathsf{ik}, \mathsf{asset\_desc})) := \mathtt{0x00} || \mathsf{ik} || \mathsf{asset\_desc}\!\!\) + .
    • +
  • Note that the initial + \(\mathtt{0x00}\) + byte is a version byte.
    • +
+

Define + \(\mathsf{AssetBase_{AssetId}} := \mathsf{ZSAValueBase}(\mathsf{AssetDigest_{AssetId}})\) +

+

In the case of the Orchard-ZSA protocol, we define + \(\mathsf{ZSAValueBase}(\mathsf{AssetDigest_{AssetId}}) := \mathsf{GroupHash}^\mathbb{P}(\texttt{"z.cash:OrchardZSA"}, \mathsf{AssetDigest_{AssetId}})\) + where + \(\mathsf{GroupHash}^\mathbb{P}\) + is defined as in 20.

+

The relations between the Asset Identifier, Asset Digest, and Asset Base are shown in the following diagram:

+
+ +
Diagram relating the Asset Identifier, Asset Digest, and Asset Base in the ZSA Protocol
+
+

Note: To keep notations light and concise, we may omit + \(\mathsf{AssetId}\) + (resp. + \(\mathsf{Protocol}\!\) + ) in the subscript (resp. superscript) when the Asset Identifier (resp. Protocol) is clear from the context.

+

Wallets MUST NOT display just the + \(\mathsf{asset\_desc}\) + string to their users as the name of the Asset. Some possible alternatives include:

+
    +
  • Wallets could allow clients to provide an additional configuration file that stores a one-to-one mapping of names to Asset Identifiers via a petname system. This allows clients to rename the Assets in a way they find useful. Default versions of this file with well-known Assets listed can be made available online as a starting point for clients.
    • +
  • The Asset Digest could be used as a more compact bytestring to uniquely determine an Asset, and wallets could support clients scanning QR codes to load Asset information into their wallets.
    • +
+
+

Specification: Global Issuance State

+

Issuance requires the following additions to the global state defined at block boundaries:

+
    +
  • + \(\mathsf{previously\_finalized}\!\) + , a set of + \(\mathsf{AssetId}\) + that have been finalized (i.e.: the + \(\mathsf{finalize}\) + flag has been set to + \(1\) + in some issuance transaction preceding the block boundary).
    • +
+
+

Specification: Issuance Action, Issuance Bundle and Issuance Protocol

+

Issuance Action Description

+

An issuance action, IssueAction, is the instance of issuing a specific Custom Asset, and contains the following fields:

+
    +
  • assetDescSize: the size of the Asset description, a number between + \(0\) + and + \(512\!\) + , stored in two bytes.
    • +
  • asset_desc: the Asset description, a byte string of up to 512 bytes as defined in the Specification: Asset Identifier section.
    • +
  • vNotes: an array of Note containing the unencrypted output notes of the recipients of the Asset.
    • +
  • flagsIssuance: a byte that stores the + \(\mathsf{finalize}\) + boolean that defines whether the issuance of that specific Custom Asset is finalized or not.
    • +
+

An asset's + \(\mathsf{AssetDigest}\) + is added to the + \(\mathsf{previously\_finalized}\) + set after a block that contains any issuance transaction for that asset with + \(\mathsf{finalize} = 1\!\) + . It then cannot be removed from this set. For Assets with + \(\mathsf{AssetDigest} \in \mathsf{previously\_finalized}\!\) + , no further tokens can be issued, so as seen below, the validators will reject the transaction. For Assets with + \(\mathsf{AssetDigest} \not\in \mathsf{previously\_finalized}\!\) + , new issuance actions can be issued in future transactions. These must use the same Asset description, + \(\mathsf{asset\_desc}\!\) + , and can either maintain + \(\mathsf{finalize} = 0\) + or change it to + \(\mathsf{finalize} = 1\!\) + , denoting that this Custom Asset cannot be issued after the containing block.

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
BytesNameData TypeDescription
2assetDescSizebyteThe length of the asset_desc string in bytes.
assetDescSizeasset_descbyte[assetDescSize]A byte sequence of length assetDescSize bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later.
variesnNotescompactSizeThe number of notes in the issuance action.
noteSize * nNotesvNotesNote[nNotes]A sequence of note descriptions within the issuance action, where noteSize is the size, in bytes, of a Note.
1flagsIssuancebyte +
+
An 8-bit value representing a set of flags. Ordered from LSB to MSB:
+
+
    +
  • + \(\mathsf{finalize}\) +
    • +
  • The remaining bits are set to + \(0\!\) + .
    • +
+
+
+
+

We note that the output note commitment of the recipient's notes are not included in the actual transaction, but when added to the global state of the chain, they will be added to the note commitment tree as a shielded note. This prevents future usage of the note from being linked to the issuance transaction, as the nullifier key is not known to the validators and chain observers.

+
+

Issuance Bundle

+

An issuance bundle, IssueBundle, is the aggregate of all the issuance-related information. Specifically, contains all the issuance actions and the issuer signature on the transaction SIGHASH that validates the issuance itself. It contains the following fields:

+
    +
  • + \(\mathsf{ik}\) + : the issuance validating key, that allows the validators to verify that the + \(\mathsf{AssetId}\) + is properly associated with the issuer.
    • +
  • vIssueActions: an array of issuance actions, of type IssueAction.
    • +
  • + \(\mathsf{issueAuthSig}\) + : the signature of the transaction SIGHASH, signed by the issuance authorizing key, + \(\mathsf{isk}\!\) + , that validates the issuance.
    • +
+

The issuance bundle is then added within the transaction format as a new bundle. That is, issuance requires the addition of the following information to the transaction format 22.

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
BytesNameData TypeDescription
variesnIssueActionscompactSizeThe number of issuance actions in the bundle.
IssueActionSize * nIssueActionsvIssueActionsIssueAction[nIssueActions]A sequence of issuance action descriptions, where IssueActionSize is the size, in bytes, of an IssueAction description.
32ikbyte[32]The issuance validating key of the issuer, used to validate the signature.
64issueAuthSigbyte[64]The signature of the transaction SIGHASH, signed by the issuer, validated as in Issuance Authorization Signature Scheme.
+
+

Issuance Protocol

+

The issuer program performs the following operations:

+

For all actions IssueAction:

+
    +
  • encode + \(\mathsf{asset\_desc}\) + as a UTF-8 byte string of size up to 512.
    • +
  • compute + \(\mathsf{AssetDigest}\) + from the issuance validating key + \(\mathsf{ik}\) + and + \(\mathsf{asset\_desc}\) + as decribed in the Specification: Asset Identifier section.
    • +
  • compute + \(\mathsf{AssetBase}\) + from + \(\mathsf{AssetDigest}\) + as decribed in the Specification: Asset Identifier section.
    • +
  • set the + \(\mathsf{finalize}\) + boolean as desired (if more issuance actions are to be created for this + \(\mathsf{AssetBase}\!\) + , set + \(\mathsf{finalize} = 0\!\) + , otherwise set + \(\mathsf{finalize} = 1\!\) + ).
    • +
  • for each recipient + \(i\) + : +
      +
    • generate a ZSA output note that includes the Asset Base. For an Orchard-ZSA note this is + \(\mathsf{note}_i = (\mathsf{d}_i, \mathsf{pk}_{\mathsf{d}_i}, \mathsf{v}_i, \text{ρ}_i, \mathsf{rseed}_i, \mathsf{AssetBase}, \mathsf{rcm}_i)\!\) + .
      • +
    +
    • +
  • encode the IssueAction into the vector vIssueActions of the bundle.
    • +
+

For the IssueBundle:

+
    +
  • encode the vIssueActions vector.
    • +
  • encode the + \(\mathsf{ik}\) + as 32 byte-string.
    • +
  • sign the SIGHASH transaction hash with the issuance authorizing key, + \(\mathsf{isk}\!\) + , using the + \(\mathsf{IssueAuthSig}\) + signature scheme. The signature is then added to the issuance bundle.
    • +
+

Note: that the commitment is not included in the IssuanceAction itself. As explained below, it is computed later by the validators and added to the note commitment tree.

+
+
+

Specification: Consensus Rule Changes

+

For the IssueBundle:

+
    +
  • Validate the issuance authorization signature, + \(\mathsf{issueAuthSig}\!\) + , on the SIGHASH transaction hash, + \(\mathsf{SigHash}\!\) + , by invoking + \(\mathsf{IssueAuthSig}.\!\mathsf{Validate}(\mathsf{ik}, \mathsf{SigHash}, \mathsf{issueAuthSig})\!\) + .
    • +
+

For each IssueAction in IssueBundle:

+
    +
  • check that + \(0 < \mathtt{assetDescSize} \leq 512\!\) + .
    • +
  • check that + \(\mathsf{asset\_desc}\) + is a string of length + \(\mathtt{assetDescSize}\) + bytes.
    • +
  • retrieve + \(\mathsf{AssetBase}\) + from the first note in the sequence and check that + \(\mathsf{AssetBase}\) + is derived from the issuance validating key + \(\mathsf{ik}\) + and + \(\mathsf{asset\_desc}\) + as described in the Specification: Asset Identifier section.
    • +
  • check that the + \(\mathsf{AssetDigest}\) + does not exist in the + \(\mathsf{previously\_finalized}\) + set in the global state.
    • +
  • check that every note in the IssueAction contains the same + \(\mathsf{AssetBase}\) + and is properly constructed as + \(\mathsf{note} = (\mathsf{g_d}, \mathsf{pk_d}, \mathsf{v}, \text{ρ}, \mathsf{rseed}, \mathsf{AssetBase})\!\) + .
    • +
+

If all of the above checks pass, do the following:

+
    +
  • For each note, compute the note commitment as + \(\mathsf{cm} = \mathsf{NoteCommit^{OrchardZSA}_{rcm}}(\mathsf{repr}_{\mathbb{P}}(\mathsf{g_d}), \mathsf{repr}_{\mathbb{P}}(\mathsf{pk_d}), \mathsf{v}, \text{ρ}, \text{ψ}, \mathsf{AssetBase})\) + as defined in the Note Structure and Commitment section of ZIP 226 10 and
    • +
  • Add + \(\mathsf{cm}\) + to the Merkle tree of note commitments.
    • +
  • If + \(\mathsf{finalize} = 1\!\) + , add + \(\mathsf{AssetDigest}\) + to the + \(\mathsf{previously\_finalized}\) + set immediately after the block in which this transaction occurs.
    • +
  • (Replay Protection) If issue bundle is present, the fees MUST be greater than zero.
    • +
+
+

Rationale

+

The following is a list of rationale for different decisions made in the proposal:

+
    +
  • The issuance key structure is independent of the original key tree, but derived in an analogous manner (via ZIP 32). This is in order to keep the issuance details and the Asset Identifiers consistent across multiple shielded pools.
    • +
  • The design decision is not to have a chosen name to describe the Custom Asset, but to delegate it to an off-chain mapping, as this would imply a land-grab “war”.
    • +
  • The + \(\mathsf{asset\_desc}\) + is a general byte string in order to allow for a wide range of information type to be included that may be associated with the Assets. Some are: +
      +
    • links for storage such as for NFTs.
      • +
    • metadata for Assets, encoded in any format.
      • +
    • bridging information for Wrapped Assets (chain of origin, issuer name, etc)
      • +
    • information to be committed by the issuer, though not enforceable by the protocol.
      • +
    +
    • +
  • We require a check whether the + \(\mathsf{finalize}\) + flag only has been set in a previous block rather than a previous transaction in the same block. In other words, we only update the + \(\mathsf{previously\_finalized}`\) + set at the block boundary. This is in keeping with the current property which allows for a miner to reorder transactions in a block without changing the meaning, which we aim to preserve.
    • +
  • We require non-zero fees in the presence of an issue bundle, in order to preclude the possibility of a transaction containing only an issue bundle. If a transaction includes only an issue bundle, the SIGHASH transaction hash would be computed solely based on the issue bundle. A duplicate bundle would have the same SIGHASH transaction hash, potentially allowing for a replay attack.
    • +
+

Concrete Applications

+

Asset Features

+
    +
  • By using the + \(\mathsf{finalize}\) + boolean and the burning mechanism defined in 9, issuers can control the supply production of any Asset associated to their issuer keys. For example, +
      +
    • by setting + \(\mathsf{finalize} = 1\) + from the first issuance action for that Asset Identifier, the issuer is in essence creating a one-time issuance transaction. This is useful when the max supply is capped from the beginning and the distribution is known in advance. All tokens are issued at once and distributed as needed.
      • +
    +
    • +
  • Issuers can also stop the existing supply production of any Asset associated to their issuer keys. This could be done by +
      +
    • issuing a last set of tokens of that specific + \(\mathsf{AssetId}\!\) + , for which + \(\mathsf{finalize} = 1\!\) + , or by
      • +
    • issuing a transaction with a single note in the issuance action pertaining to that + \(\mathsf{AssetId}\!\) + , where the note will contain a + \(\mathsf{value} = 0\!\) + . This can be used for application-specific purposes (NFT collections) or for security purposes to revoke the Asset issuance (see Security and Privacy Considerations).
      • +
    • Note in the above cases, that the setting of the + \(\mathsf{finalize}\) + flag will take effect at the block boundary, that is, after all the transactions in the block.
      • +
    +
    • +
  • The issuance and burn mechanisms can be used in conjunction to determine the supply of Assets on the Zcash ecosystem. This allows for the bridging of Assets defined on other chains.
    • +
  • Furthermore, NFT issuance is enabled by issuing in a single bundle several issuance actions, where each + \(\mathsf{AssetId}\) + corresponds to + \(\mathsf{value} = 1\) + at the fundamental unit level. Issuers and users should make sure that + \(\mathsf{finalize} = 1\) + for each of the actions in this scenario.
    • +
+
+
+

TxId Digest - Issuance

+

This section details the construction of the subtree of hashes in the transaction digest that corresponds to issuance transaction data. Details of the overall changes to the transaction digest due to the Orchard-ZSA protocol can be found in ZIP 226 11. As in ZIP 244 12, the digests are all personalized BLAKE2b-256 hashes, and in cases where no elements are available for hashing, a personalized hash of the empty byte array is used.

+

A new issuance transaction digest algorithm is defined that constructs the subtree of the transaction digest tree of hashes for the issuance portion of a transaction. Each branch of the subtree will correspond to a specific subset of issuance transaction data. The overall structure of the hash is as follows; each name referenced here will be described in detail below:

+ 
issuance_digest
+├── issue_actions_digest
+│   ├── issue_notes_digest
+│   ├── assetDescription
+│   └── flagsIssuance
+└── issuanceValidatingKey
+

In the specification below, nodes of the tree are presented in depth-first order.

+

T.5: issuance_digest

+

A BLAKE2b-256 hash of the following values

+ 
T.5a: issue_actions_digest    (32-byte hash output)
+T.5b: issuanceValidatingKey   (32 bytes)
+

The personalization field of this hash is set to:

+ 
"ZTxIdSAIssueHash"
+

In case the transaction has no issuance components, ''issue_actions_digest'' is:

+ 
BLAKE2b-256("ZTxIdSAIssueHash", [])
+

T.5a: issue_actions_digest

+

A BLAKE2b-256 hash of Issue Action information for all Issuance Actions belonging to the transaction. For each Action, the following elements are included in the hash:

+ 
T.5a.i  : notes_digest            (32-byte hash output)
+T.5a.ii : assetDescription        (field encoding bytes)
+T.5a.iii: flagsIssuance           (1 byte)
+

The personalization field of this hash is set to:

+ 
"ZTxIdIssuActHash"
+
T.5a.i: issue_notes_digest
+

A BLAKE2b-256 hash of Note information for all Notes belonging to the Issuance Action. For each Note, the following elements are included in the hash:

+ 
T.5a.i.1: recipient                    (field encoding bytes)
+T.5a.i.2: value                        (field encoding bytes)
+T.5a.i.3: assetBase                    (field encoding bytes)
+T.5a.i.4: rho                          (field encoding bytes)
+T.5a.i.5: rseed                        (field encoding bytes)
+

The personalization field of this hash is set to:

+ 
"ZTxIdIAcNoteHash"
+
T.5a.i.1: recipient
+

This is the raw encoding of an Orchard shielded payment address as defined in the protocol specification 21.

+
+
T.5a.i.2: value
+

Note value encoded as little-endian 8-byte representation of 64-bit unsigned integer (e.g. u64 in Rust) raw value.

+
+
T.5a.i.3: assetBase
+

Asset Base encoded as the 32-byte representation of a point on the Pallas curve.

+
+
T.5a.i.4: rho
+

Nullifier encoded as 32-byte representation of a point on the Pallas curve.

+
+
T.5a.i.5: rseed
+

The ZIP 212 32-byte seed randomness for a note.

+
+
+
T.5a.ii: assetDescription
+

The Asset description byte string.

+
+
T.5a.iii: flagsIssuance
+

An 8-bit value representing a set of flags. Ordered from LSB to MSB:

+
    +
  • + \(\mathsf{finalize}\) +
    • +
  • The remaining bits are set to 0!.
    • +
+
+
+

T.5b: issuanceValidatingKey

+

A byte encoding of issuance validating key for the bundle as defined in the Issuance Key Derivation section.

+
+
+
+

Signature Digest

+

The per-input transaction digest algorithm to generate the signature digest in ZIP 244 13 is modified so that a signature digest is produced for each transparent input, each Sapling input, each Orchard action, and additionally for each Issuance Action. For Issuance Actions, this algorithm has the exact same output as the transaction digest algorithm, thus the txid may be signed directly.

+

The overall structure of the hash is as follows. We highlight the changes for the Orchard-ZSA protocol via the [ADDED FOR ZSA] text label, and we omit the descriptions of the sections that do not change for the Orchard-ZSA protocol:

+ 
signature_digest
+├── header_digest
+├── transparent_sig_digest
+├── sapling_digest
+├── orchard_digest
+└── issuance_digest         [ADDED FOR ZSA]
+

signature_digest

+

A BLAKE2b-256 hash of the following values

+ 
S.1: header_digest          (32-byte hash output)
+S.2: transparent_sig_digest (32-byte hash output)
+S.3: sapling_digest         (32-byte hash output)
+S.4: orchard_digest         (32-byte hash output)
+S.5: issuance_digest        (32-byte hash output)  [ADDED FOR ZSA]
+

The personalization field remains the same as in ZIP 244 12.

+

S.5: issuance_digest

+

Identical to that specified for the transaction identifier.

+
+
+
+

Authorizing Data Commitment

+

The transaction digest algorithm defined in ZIP 244 14 which commits to the authorizing data of a transaction is modified by the Orchard-ZSA protocol to have the following structure. We highlight the changes for the Orchard-ZSA protocol via the [ADDED FOR ZSA] text label, and we omit the descriptions of the sections that do not change for the Orchard-ZSA protocol:

+ 
auth_digest
+├── transparent_scripts_digest
+├── sapling_auth_digest
+├── orchard_auth_digest
+└── issuance_auth_digest        [ADDED FOR ZSA]
+

The pair (Transaction Identifier, Auth Commitment) constitutes a commitment to all the data of a serialized transaction that may be included in a block.

+

auth_digest

+

A BLAKE2b-256 hash of the following values

+ 
A.1: transparent_scripts_digest (32-byte hash output)
+A.2: sapling_auth_digest        (32-byte hash output)
+A.3: orchard_auth_digest        (32-byte hash output)
+A.4: issuance_auth_digest       (32-byte hash output)  [ADDED FOR ZSA]
+

The personalization field of this hash remains the same as in ZIP 244.

+

A.4: issuance_auth_digest

+

In the case that Issuance Actions are present, this is a BLAKE2b-256 hash of the field encoding of the issueAuthSig field of the transaction:

+ 
A.4a: issueAuthSig            (field encoding bytes)
+

The personalization field of this hash is set to:

+ 
"ZTxAuthZSAOrHash"
+

In the case that the transaction has no Orchard Actions, issuance_auth_digest is

+ 
BLAKE2b-256("ZTxAuthZSAOrHash", [])
+
+
+
+

Security and Privacy Considerations

+

Displaying Asset Identifier information to users

+

Wallets need to communicate the names of the Assets in a non-confusing way to users, since the byte representation of the Asset Identifier would be hard to read for an end user. Possible solutions are provided in the Specification: Asset Identifier section.

+
+

Issuance Key Compromise

+

The design of this protocol does not currently allow for rotation of the issuance validating key that would allow for replacing the key of a specific Asset. In case of compromise, the following actions are recommended:

+
    +
  • If an issuance validating key is compromised, the + \(\mathsf{finalize}\) + boolean for all the Assets issued with that key should be set to + \(1\) + and the issuer should change to a new issuance authorizing key, and issue new Assets, each with a new + \(\mathsf{AssetId}\!\) + .
    • +
+
+

Bridging Assets

+

For bridging purposes, the secure method of off-boarding Assets is to burn an Asset with the burning mechanism in ZIP 226 9. Users should be aware of issuers that demand the Assets be sent to a specific address on the Zcash chain to be redeemed elsewhere, as this may not reflect the real reserve value of the specific Wrapped Asset.

+
+
+

Other Considerations

+

Implementing Zcash Nodes

+

Although not enforced in the global state, it is RECOMMENDED that Zcash full validators keep track of the total supply of Assets as a mutable mapping + \(\mathsf{issuanceSupplyInfoMap}\) + from + \(\mathsf{AssetId}\) + to + \((\mathsf{totalSupply}, \mathsf{finalize})\) + in order to properly keep track of the total supply for different Asset Identifiers. This is useful for wallets and other applications that need to keep track of the total supply of Assets.

+
+

Fee Structures

+

The fee mechanism described in this ZIP will follow the mechanism described in ZIP 317 15.

+
+
+

Test Vectors

+
    +
  • LINK TBD
    • +
+
+

Reference Implementation

+
    +
  • LINK TBD
    • +
  • LINK TBD
    • +
+
+

Deployment

+

This ZIP is proposed to activate with Network Upgrade 6.

+
+

References

+ + + + + + + +
1Information on BCP 14 — "RFC 2119: Key words for use in RFCs to Indicate Requirement Levels" and "RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"
+ + + + + + + +
2ZIP 32: Shielded Hierarchical Deterministic Wallets
+ + + + + + + +
3ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard master key generation
+ + + + + + + +
4ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard child key derivation
+ + + + + + + +
5ZIP 32: Shielded Hierarchical Deterministic Wallets - Key path levels
+ + + + + + + +
6ZIP 32: Shielded Hierarchical Deterministic Wallets - Orchard key path
+ + + + + + + +
7ZIP 200: Network Upgrade Mechanism
+ + + + + + + +
8ZIP 224: Orchard
+ + + + + + + +
9ZIP 226: Transfer and Burn of Zcash Shielded Assets
+ + + + + + + +
10ZIP 226: Transfer and Burn of Zcash Shielded Assets - Note Structure & Commitment
+ + + + + + + +
11ZIP 226: Transfer and Burn of Zcash Shielded Assets - TxId Digest
+ + + + + + + +
12ZIP 244: Transaction Identifier Non-Malleability
+ + + + + + + +
13ZIP 244: Transaction Identifier Non-Malleability: Signature Digest
+ + + + + + + +
14ZIP 244: Transaction Identifier Non-Malleability: Authorizing Data Commitment
+ + + + + + + +
15ZIP 317: Proportional Transfer Fee Mechanism
+ + + + + + + +
16BIP 340: Schnorr Signatures for secp256k1
+ + + + + + + +
17Zcash Protocol Specification, Version 2023.4.0. Section 2: Notation
+ + + + + + + +
18Zcash Protocol Specification, Version 2023.4.0. Section 3.1: Payment Addresses and Keys
+ + + + + + + +
19Zcash Protocol Specification, Version 2023.4.0. Section 4.2.3: Orchard Key Components
+ + + + + + + +
20Zcash Protocol Specification, Version 2023.4.0. Section 5.4.9.8: Group Hash into Pallas and Vesta
+ + + + + + + +
21Zcash Protocol Specification, Version 2023.4.0. Section 5.6.4.2: Orchard Raw Payment Addresses
+ + + + + + + +
22Zcash Protocol Specification, Version 2023.4.0. Section 7.1: Transaction Encoding and Consensus (Transaction Version 5)
+
\ No newline at end of file diff --git a/zip-0230.html b/zip-0230.html index 130594ab9..dc1547dcd 100644 --- a/zip-0230.html +++ b/zip-0230.html @@ -3,21 +3,644 @@ ZIP 230: Version 6 Transaction Format + 
ZIP: 230
 Title: Version 6 Transaction Format
-Owners: Daira Emma Hopwood <daira@electriccoin.co>
+Owners: Daira-Emma Hopwood <daira@electriccoin.co>
         Jack Grigg <jack@electriccoin.co>
         Sean Bowe <sean@electriccoin.co>
         Kris Nuttycombe <kris@electriccoin.co>
+        Pablo Kogan <pablo@qed-it.com>
+        Vivek Arte <vivek@qed-it.com>
 Original-Authors: Greg Pfeil
                   Deirdre Connolly
 Credits: Ying Tong Lai
-Status: Reserved
+Status: Draft
 Category: Consensus
+Created: 2023-04-18
+License: MIT
 Discussions-To: <https://github.com/zcash/zips/issues/686>
+

Terminology

+

The key words "MUST", "SHOULD", and "MAY" in this document are to be interpreted as described in BCP 14 1 when, and only when, they appear in all capitals.

+

The character § is used when referring to sections of the Zcash Protocol Specification 2.

+
+

Abstract

+

This proposal defines a new Zcash peer-to-peer transaction format, which includes data that supports the Orchard-ZSA protocol and all operations related to Zcash Shielded Assets (ZSAs). The new format adds and describes new fields containing ZSA-specific elements. Like the existing v5 transaction format, it keeps well-bounded regions of the serialized form to serve each pool of funds.

+

This ZIP also depends upon and defines modifications to the computation of the values TxId Digest, Signature Digest, and Authorizing Data Commitment defined by ZIP 244 8.

+
+

Motivation

+

The Orchard-ZSA protocol requires serialized data elements that are distinct from any previous Zcash transaction. Since ZIP 244 was activated in NU5, the v5 and later serialized transaction formats are not consensus-critical. Thus, this ZIP defines format that can easily accommodate future extensions, where elements or a given pool are kept separate.

+
+

Requirements

+

The new format must fully support the Orchard-ZSA protocol.

+

The new format should lend itself to future extension or pruning to add or remove value pools.

+

The computation of the non-malleable transaction identifier hash must include all newly incorporated elements except those that attest to transaction validity.

+

The computation of the commitment to authorizing data for a transaction must include all newly incorporated elements that attest to transaction validity.

+
+

Non-requirements

+

More general forms of extensibility, such as definining a key/value format that allows for parsers that are unaware of some components, are not required.

+
+

Specification

+

All fields in this specification are encoded as little-endian.

+

The Zcash transaction format for transaction version 6 is as follows:

+

Transaction Format

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
BytesNameData TypeDescription
Common Transaction Fields
4headeruint32 +
+
Contains:
+
+
    +
  • fOverwintered flag (bit 31, always set)
    • +
  • version (bits 30 .. 0) – transaction version.
    • +
+
+
+
4nVersionGroupIduint32Version group ID (nonzero).
4nConsensusBranchIduint32Consensus branch ID (nonzero).
4lock_timeuint32Unix-epoch UTC time or block height, encoded as in Bitcoin.
4nExpiryHeightuint32A block height in the range {1 .. 499999999} after which the transaction will expire, or 0 to disable expiry. [ZIP-203]
8feeint64The fee to be paid by this transaction, in zatoshis.
Transparent Transaction Fields
variestx_in_countcompactSizeNumber of transparent inputs in tx_in.
variestx_intx_inTransparent inputs, encoded as in Bitcoin.
variestx_out_countcompactSizeNumber of transparent outputs in tx_out.
variestx_outtx_outTransparent outputs, encoded as in Bitcoin.
Sapling Transaction Fields
variesnSpendsSaplingcompactSizeNumber of Sapling Spend descriptions in vSpendsSapling.
96 * nSpendsSaplingvSpendsSaplingSpendDescriptionV6[nSpendsSapling]A sequence of Sapling Spend descriptions, encoded per protocol §7.3 ‘Spend Description Encoding and Consensus’.
variesnOutputsSaplingcompactSizeNumber of Sapling Output Decriptions in vOutputsSapling.
756 * nOutputsSaplingvOutputsSaplingOutputDescriptionV6[nOutputsSapling]A sequence of Sapling Output descriptions, encoded per protocol §7.4 ‘Output Description Encoding and Consensus’.
8valueBalanceSaplingint64The net value of Sapling Spends minus Outputs
32anchorSaplingbyte[32]A root of the Sapling note commitment tree at some block height in the past.
192 * nSpendsSaplingvSpendProofsSaplingbyte[192 * nSpendsSapling]Encodings of the zk-SNARK proofs for each Sapling Spend.
64 * nSpendsSaplingvSpendAuthSigsSaplingbyte[64 * nSpendsSapling]Authorizing signatures for each Sapling Spend.
192 * nOutputsSaplingvOutputProofsSaplingbyte[192 * nOutputsSapling]Encodings of the zk-SNARK proofs for each Sapling Output.
64bindingSigSaplingbyte[64]A Sapling binding signature on the SIGHASH transaction hash.
Orchard-ZSA Transaction Fields
variesnActionsOrchardcompactSizeThe number of Orchard-ZSA Action descriptions in vActionsOrchard.
852 * nActionsOrchardvActionsOrchardOrchardZsaAction[nActionsOrchard]A sequence of Orchard-ZSA Action descriptions, encoded per the Orchard-ZSA Action Description Encoding.
1flagsOrchardbyte +
+
An 8-bit value representing a set of flags. Ordered from LSB to MSB:
+
+
    +
  • enableSpendsOrchard
    • +
  • enableOutputsOrchard
    • +
  • enableZSAs
    • +
  • The remaining bits are set to + \(0\!\) + .
    • +
+
+
+
8valueBalanceOrchardint64The net value of Orchard spends minus outputs.
32anchorOrchardbyte[32]A root of the Orchard note commitment tree at some block height in the past.
variessizeProofsOrchardZSAcompactSizeLength in bytes of proofsOrchardZSA. Value is (TO UPDATE) + \(2720 + 2272 \cdot \mathtt{nActionsOrchard}\!\) + .
sizeProofsOrchardZSAproofsOrchardZSAbyte[sizeProofsOrchardZSA]Encoding of aggregated zk-SNARK proofs for Orchard-ZSA Actions.
64 * nActionsOrchardvSpendAuthSigsOrchardbyte[64 * nActionsOrchard]Authorizing signatures for each Orchard-ZSA Action.
64bindingSigOrchardbyte[64]An Orchard binding signature on the SIGHASH transaction hash.
Orchard-ZSA Burn Fields
variesnAssetBurncompactSizeThe number of Assets burnt.
40 * nAssetBurnvAssetBurnAssetBurn[nAssetBurn]A sequence of Asset Burn descriptions, encoded per Orchard-ZSA Asset Burn Description.
Orchard-ZSA Issuance Fields
variesnIssueActionscompactSizeThe number of issuance actions in the bundle.
IssueActionSize * nIssueActionsvIssueActionsIssueAction[nIssueActions]A sequence of issuance action descriptions, where IssueActionSize is the size, in bytes, of an IssueAction description.
32ikbyte[32]The issuance validating key of the issuer, used to validate the signature.
64issueAuthSigbyte[64]The signature of the transaction SIGHASH, signed by the issuer, validated as in Issuance Authorization Signature Scheme 7.
+
    +
  • The fields valueBalanceSapling and bindingSigSapling are present if and only if + \(\mathtt{nSpendsSapling} + \mathtt{nOutputsSapling} > 0\!\) + . If valueBalanceSapling is not present, then + \(\mathsf{v^{balanceSapling}}`\) + is defined to be + \(0\!\) + .
    • +
  • The field anchorSapling is present if and only if + \(\mathtt{nSpendsSapling} > 0\!\) + .
    • +
  • The fields flagsOrchard, valueBalanceOrchard, anchorOrchard, sizeProofsOrchardZSA, proofsOrchardZSA, and bindingSigOrchard are present if and only if + \(\mathtt{nActionsOrchard} > 0\!\) + . If valueBalanceOrchard is not present, then + \(\mathsf{v^{balanceOrchard}}\) + is defined to be + \(0\!\) + .
    • +
  • The elements of vSpendProofsSapling and vSpendAuthSigsSapling have a 1:1 correspondence to the elements of vSpendsSapling and MUST be ordered such that the proof or signature at a given index corresponds to the SpendDescriptionV6 at the same index.
    • +
  • The elements of vOutputProofsSapling have a 1:1 correspondence to the elements of vOutputsSapling and MUST be ordered such that the proof at a given index corresponds to the OutputDescriptionV6 at the same index.
    • +
  • The proofs aggregated in proofsOrchardZSA, and the elements of vSpendAuthSigsOrchard, each have a 1:1 correspondence to the elements of vActionsOrchard and MUST be ordered such that the proof or signature at a given index corresponds to the OrchardZsaAction at the same index.
    • +
  • For coinbase transactions, the enableSpendsOrchard and enableZSAs bits MUST be set to + \(0\!\) + .
    • +
+

The encodings of tx_in, and tx_out are as in a version 4 transaction (i.e. unchanged from Canopy). The encodings of SpendDescriptionV6, OutputDescriptionV6 , OrchardZsaAction, AssetBurn and IssueAction are described below. The encoding of Sapling Spends and Outputs has changed relative to prior versions in order to better separate data that describe the effects of the transaction from the proofs of and commitments to those effects, and for symmetry with this separation in the Orchard-related parts of the transaction format.

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+

Sapling Spend Description (SpendDescriptionV6)

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BytesNameData TypeDescription
32cvbyte[32]A value commitment to the net value of the input note.
32nullifierbyte[32]The nullifier of the input note.
32rkbyte[32]The randomized validating key for the element of spendAuthSigsSapling corresponding to this Spend.
+

The encodings of each of these elements are defined in §7.3 ‘Spend Description Encoding and Consensus’ of the Zcash Protocol Specification 3.

+
+

Sapling Output Description (OutputDescriptionV6)

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
BytesNameData TypeDescription
32cvbyte[32]A value commitment to the net value of the output note.
32cmubyte[32]The + \(u\!\) + -coordinate of the note commitment for the output note.
32ephemeralKeybyte[32]An encoding of an ephemeral Jubjub public key.
580encCiphertextbyte[580]The encrypted contents of the note plaintext.
80outCiphertextbyte[80]The encrypted contents of the byte string created by concatenation of the transmission key with the ephemeral secret key.
+

The encodings of each of these elements are defined in §7.4 ‘Output Description Encoding and Consensus’ of the Zcash Protocol Specification 4.

+
+

Orchard-ZSA Action Description (OrchardZsaAction)

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
BytesNameData TypeDescription
32cvbyte[32]A value commitment to the net value of the input note minus the output note.
32nullifierbyte[32]The nullifier of the input note.
32rkbyte[32]The randomized validating key for the element of spendAuthSigsOrchard corresponding to this Action.
32cmxbyte[32]The + \(x\!\) + -coordinate of the note commitment for the output note.
32ephemeralKeybyte[32]An encoding of an ephemeral Pallas public key
612encCiphertextbyte[580]The encrypted contents of the note plaintext.
80outCiphertextbyte[80]The encrypted contents of the byte string created by concatenation of the transmission key with the ephemeral secret key.
+

The encodings of each of these elements are defined in §7.5 ‘Action Description Encoding and Consensus’ of the Zcash Protocol Specification 5.

+
+

Orchard-ZSA Asset Burn Description

+

An Orchard-ZSA Asset Burn description is encoded in a transaction as an instance of an AssetBurn type:

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BytesNameData TypeDescription
32AssetBasebyte[32]For the Orchard-based ZSA protocol, this is the encoding of the Asset Base + \(\mathsf{AssetBase^{Orchard}}\!\) + .
8valueBurn + \(\{1 .. 2^{64} - 1\}\) + The amount being burnt.
+

The encodings of each of these elements are defined in ZIP 226 6.

+
+

Issuance Action Description (IssueAction)

+

An issuance action, IssueAction, is the instance of issuing a specific Custom Asset, and contains the following fields:

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BytesNameData TypeDescription
2assetDescSizebyteThe length of the asset description string in bytes.
assetDescSizeasset_descbyte[assetDescSize]A byte sequence of length assetDescSize bytes which SHOULD be a well-formed UTF-8 code unit sequence according to Unicode 15.0.0 or later.
variesnNotescompactSizeThe number of notes in the issuance action.
noteSize * nNotesvNotesNote[nNotes]A sequence of note descriptions within the issuance action, where noteSize is the size, in bytes, of a Note.
1flagsIssuancebyte +
+
An 8-bit value representing a set of flags. Ordered from LSB to MSB:
+
+
    +
  • + \(\mathsf{finalize}\) +
    • +
  • The remaining bits are set to + \(0\!\) + .
    • +
+
+
+
+

The encodings of each of these elements are defined in ZIP 227 7.

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+
+

Reference implementation

+

TODO

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+

References

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1Information on BCP 14 — "RFC 2119: Key words for use in RFCs to Indicate Requirement Levels" and "RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"
+ + + + + + + +
2Zcash Protocol Specification, Version 2023.4.0 or later [NU5 proposal]
+ + + + + + + +
3Zcash Protocol Specification, Version 2023.4.0 [NU5 proposal]. Section 4.4: Spend Descriptions
+ + + + + + + +
4Zcash Protocol Specification, Version 2023.4.0 [NU5 proposal]. Section 4.5: Output Descriptions
+ + + + + + + +
5Zcash Protocol Specification, Version 2023.4.0 [NU5 proposal]. Section 4.6: Action Descriptions
+ + + + + + + +
6ZIP 226: Transfer and Burn of Zcash Shielded Assets
+ + + + + + + +
7ZIP 227: Issuance of Zcash Shielded Assets
+ + + + + + + +
8ZIP 244: Transaction Identifier Non-Malleability
+
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