blip-0039: BOLT 11 Invoice Blinded Path Tagged Field #39

ellemouton · 2024-07-08T11:21:19Z

This bLIP defines a new tagged field, b, for the payment invoice
encoding described by BOLT 11 which can be used to communicate
encoded blinded path information to the payer of the invoice. It also
introduces a new feature bit for the I context to indicate the
presence of the new field in an invoice.

Delving Post: https://delvingbitcoin.org/t/blip-bolt-11-invoice-blinded-path-tagged-field/991
Implementation: lightningnetwork/lnd#8752

TheBlueMatt · 2024-07-08T12:25:25Z

blip-0039.md

+receiver being able to select paths it knows to be more reliable. This document 
+proposes a carve-out to the existing [BOLT 11][bolt11] invoice format so that 
+advantage can be taken of the blinded paths protocol in the context of payments 
+in a sooner time frame. This will be done by adding a new tagged-field type to 


I mean, it doesn't allow for a faster time frame given it's rolling out yet another invoice format, but if y'all want another lnd-specific invoice format, go for it?

timeframe 1: implement route blinding + implement b12 invoices format + implement onion messages + implement offers flow -> ok now we can make use of route blinding.

timeframe 2: implement route blinding + add new tagged field -> k now we can make use of route blinding.

timeframe 2 seems faster. It's also not a new invoice format, it's just adding a new tagged field.

implement route blinding + implement b12 invoices format + implement onion messages + implement offers flow -> ok now we can make use of route blinding.

Sure, just that everyone but lnd already did that so the total time there is now zero :)

It's also not a new invoice format, it's just adding a new tagged field.

For all intents and purposes its a new invoice format, just one that happens to share most of the same fields and format as BOLT 11. All existing senders won't support it so will fail to pay.

Sure, just that everyone but lnd already did that so the total time there is now zero :)

There's still quite a lot of existing work unfinished w.r.t the long tail of ensuring blinded paths works well in production, eg:

how many introduction nodes

how are they chosen, path finding algo changes, etc

dummy hop concerns

mpp over blinded paths

CLTV and other policy buffers

fixed path lengths

Having a set invoice format allows implementations to hone in on the questions above in isolation. Eg: IIUC some implementations only support creating/sending to a single blinded path. For us being able to test blinded paths in isolation has enabled us to find some interesting existing edge cases in spec/implementation, and also find some new higher order use cases.

For all intents and purposes its a new invoice format

That's quite an interpretation of the phrase "invoice format" 🙃

That's quite an interpretation of the phrase "invoice format" 🙃

Here I use the phrase to mean "a standard format that most, or really all, nodes can read". This is clearly a new format by that definition, just one that happens to share many of the same fields as the existing BOLT 11 one :)

updated this to say that it is for testing 👍

TheBlueMatt · 2024-07-08T12:27:53Z

blip-0039.md

+## Backwards Compatibility
+
+BOLT 11 states that the reader of an invoice "MUST skip over unknown fields". 
+This means that an un-updated reader of an invoice that includes the new tagged 


Huh? So the blinded path is informational? Wouldn't the invoice instead be signed by a random key so that you get blinding?

Not sure I understand the question?

In order for blinded paths in a BOLT 11 to be useful it has to be a required feature and we have to not reveal who the recipient node is via the existing BOLT 11 recipient fields (both the pubkey and the route hints). That is what I understood was going on, but here it says that existing senders will just ignore the blinded path fields?

Agreed, if you use a blinded path, but it's optional and the invoice contains identifying information for the recipient to fallback when not using blinded paths, then that blinded path doesn't provide any privacy?

Or maybe I got this wrong: there is no routing hint anyway, so a reader that doesn't know how to read the blinded path won't have a complete enough invoice and will simply fail without attempting the payment?

Or maybe I got this wrong: there is no routing hint anyway, so a reader that doesn't know how to read the blinded path won't have a complete enough invoice and will simply fail without attempting the payment?

Yeah there would be no routing hint, a required feature bit, and also the pubkey in the invoice would be random (not actually the node ID of the node creating the invoice).

So even assuming the parsing node ignores the feature bits, they would see a node ID that appears unconnected, as it isn't found in the main public graph.

Yea, okay, that's how I'd assumed it worked, can we clarify this in the bLIP though?

added some extra info at the end - lemme know if this looks ok

TheBlueMatt · 2024-07-08T12:30:57Z

blip-0039.md

+
+## Universality
+
+This proposal is a temporary measure that will allow users to start making use


You might want to call out that this is really just for testing and won't be broadly adopted - I don't think "temporary" means it shouldn't be in the BOLTs, but rather "not everyone can/will/should adopt this". "Temporary and most people won't adopt this cause it's for testing and everyone else already shipped offers" clearly meets that bar, "it's temporary" doesn't assuming there's some reason why everyone actually needs to adopt it.

I think "temporary" and "forecasted temporary use of the new field" implies this already no? Feels like writing "this wont be broadly adopted" is a bit to "hard" since we cant dictate via the spec that it wont be adopted broadly right? So here the wording implies: that this wasnt designed to be used long term but without actually making predictions re how it will be used. It does also say later on "Once the Offers protocol along with its new invoice format has been widely deployed, then there will be no use for this BOLT 11 carve-out."

I understood this was really more for testing (ie it makes sense that its just gonna be an lnd thing cause its for lnd users to test blinded paths or for use in other contexts where everyone involved is running lnd and they know everyone supports this feature via some prenegotiation), is that not the intent?

added a piece at the end re this being for testing - lemme know if that looks ok?

ellemouton

Thanks for taking an initial look at this @TheBlueMatt 🙏 responded to your comments. One comment was unclear to me.

ellemouton · 2024-07-10T15:58:13Z

blip-0039.md

+receiver being able to select paths it knows to be more reliable. This document 
+proposes a carve-out to the existing [BOLT 11][bolt11] invoice format so that 
+advantage can be taken of the blinded paths protocol in the context of payments 
+in a sooner time frame. This will be done by adding a new tagged-field type to 


timeframe 1: implement route blinding + implement b12 invoices format + implement onion messages + implement offers flow -> ok now we can make use of route blinding.

timeframe 2: implement route blinding + add new tagged field -> k now we can make use of route blinding.

timeframe 2 seems faster. It's also not a new invoice format, it's just adding a new tagged field.

ellemouton · 2024-07-10T15:59:08Z

blip-0039.md

+## Backwards Compatibility
+
+BOLT 11 states that the reader of an invoice "MUST skip over unknown fields". 
+This means that an un-updated reader of an invoice that includes the new tagged 


Not sure I understand the question?

ellemouton · 2024-07-10T16:03:32Z

blip-0039.md

+
+## Universality
+
+This proposal is a temporary measure that will allow users to start making use


I think "temporary" and "forecasted temporary use of the new field" implies this already no? Feels like writing "this wont be broadly adopted" is a bit to "hard" since we cant dictate via the spec that it wont be adopted broadly right? So here the wording implies: that this wasnt designed to be used long term but without actually making predictions re how it will be used. It does also say later on "Once the Offers protocol along with its new invoice format has been widely deployed, then there will be no use for this BOLT 11 carve-out."

ellemouton

Addressed the concerns :)

ellemouton · 2024-07-29T09:50:04Z

blip-0039.md

+receiver being able to select paths it knows to be more reliable. This document 
+proposes a carve-out to the existing [BOLT 11][bolt11] invoice format so that 
+advantage can be taken of the blinded paths protocol in the context of payments 
+in a sooner time frame. This will be done by adding a new tagged-field type to 


updated this to say that it is for testing 👍

ellemouton · 2024-07-29T09:53:12Z

blip-0039.md

+
+## Universality
+
+This proposal is a temporary measure that will allow users to start making use


added a piece at the end re this being for testing - lemme know if that looks ok?

ellemouton · 2024-07-29T09:57:19Z

blip-0039.md

+## Backwards Compatibility
+
+BOLT 11 states that the reader of an invoice "MUST skip over unknown fields". 
+This means that an un-updated reader of an invoice that includes the new tagged 


added some extra info at the end - lemme know if this looks ok

TheBlueMatt

Seems like a well-formed spec that is not targeting broad adoption, which meets the requirements for a bLIP. Didn't carefully read all of it but there's enough here someone could probably implement it, so makes sense to land.

carlaKC · 2024-08-07T17:50:05Z

blip-0002.md

+| 54/55   | `keysend`             | A form of spontaneous payment                            | N       | `var_onion_optin`       | [bLIP 3](./blip-0003.md)  |
+| 256/257 | `hosted_channels`     | This node accepts requests for hosted channels           | IN      |                         | [bLIP 17](./blip-0017.md) |
+| 258/259 | `dns_resolver`        | This node accepts DNSSEC proof requests                  | N       |                         | [bLIP 32](./blip-0032.md) |
+| 260/261 | `bolt11_blinded_path` | This invoice may contain a new blinded path tagged field | I       | `option_route_blinding` | [bLIP 39](./blip-0039.md) |


Conflicts with the feature bits in #27!

oooo great catch! thank you!

ellemouton · 2024-08-07T18:13:18Z

updated to 262/263 - thanks @carlaKC 🙏

Roasbeef

LGTM 🎍

ellemouton mentioned this pull request Jul 8, 2024

[1/4] Route Blinding Receives: Groundwork lightningnetwork/lnd#8752

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ellemouton changed the title ~~blip-39: BOLT 11 Invoice Blinded Path Tagged Field~~ blip-0039: BOLT 11 Invoice Blinded Path Tagged Field Jul 8, 2024

TheBlueMatt reviewed Jul 8, 2024

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ellemouton commented Jul 10, 2024

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ellemouton force-pushed the bolt11-blinded-path branch from d4e6787 to 599759c Compare July 29, 2024 09:58

ellemouton commented Jul 29, 2024

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TheBlueMatt approved these changes Aug 6, 2024

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carlaKC reviewed Aug 7, 2024

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carlaKC mentioned this pull request Aug 7, 2024

blip-0004: experimental endorsement signaling in update_add_htlc #27

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blip-39: BOLT 11 Invoice Blinded Path Tagged Field

8415112

ellemouton force-pushed the bolt11-blinded-path branch from bb06b52 to 8415112 Compare August 12, 2024 08:42

Roasbeef approved these changes Aug 14, 2024

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Roasbeef merged commit 9a1bd0a into lightning:master Aug 14, 2024

ellemouton deleted the bolt11-blinded-path branch August 14, 2024 04:21

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blip-0039: BOLT 11 Invoice Blinded Path Tagged Field #39

blip-0039: BOLT 11 Invoice Blinded Path Tagged Field #39

ellemouton commented Jul 8, 2024

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		## Universality

		This proposal is a temporary measure that will allow users to start making use

blip-0039: BOLT 11 Invoice Blinded Path Tagged Field #39

blip-0039: BOLT 11 Invoice Blinded Path Tagged Field #39

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