Merge pull request #344 from clearmatics/input-hashing-prepare

Changes in preparation for proof input hasing

client/test_commands/scenario.py

@@ -56,7 +56,6 @@ def wait_for_tx_update_mk_tree(
 def get_mix_parameters_components(
         zeth_client: MixerClient,
         prover_client: ProverClient,
-        zksnark: IZKSnarkProvider,
         mk_tree: MerkleTree,
         sender_ownership_keypair: OwnershipKeyPair,
         inputs: List[Tuple[int, ZethNote]],
@@ -79,8 +78,7 @@ def get_mix_parameters_components(
         compute_h_sig_cb)
     prover_inputs, signing_keypair = zeth_client.create_prover_inputs(
         mix_call_desc)
-    ext_proof_proto = prover_client.get_proof(prover_inputs)
-    ext_proof = zksnark.extended_proof_from_proto(ext_proof_proto)
+    ext_proof = prover_client.get_proof(prover_inputs)
     return (
         prover_inputs.js_outputs[0],
         prover_inputs.js_outputs[1],
@@ -262,7 +260,6 @@ def compute_h_sig_attack_nf(
         get_mix_parameters_components(
             zeth_client,
             prover_client,
-            zksnark,
             mk_tree,
             keystore["Charlie"].ownership_keypair(),  # sender
             [input1, input2],
@@ -370,7 +367,6 @@ def charlie_corrupt_bob_deposit(
         get_mix_parameters_components(
             zeth_client,
             prover_client,
-            zksnark,
             mk_tree,
             keystore["Bob"].ownership_keypair(),
             [input1, input2],

client/tests/test_input_hasher.py

@@ -0,0 +1,44 @@
+# Copyright (c) 2015-2021 Clearmatics Technologies Ltd
+#
+# SPDX-License-Identifier: LGPL-3.0+
+
+from zeth.core.mimc import MiMC7, MiMC31
+from zeth.core.input_hasher import InputHasher
+from unittest import TestCase
+
+DUMMY_INPUT_VALUES = [-1, 0, 1]
+
+
+class TestInputHasher(TestCase):
+
+    def test_input_hasher_simple(self) -> None:
+        # Some very simple cases
+        mimc = MiMC7()
+        input_hasher = InputHasher(mimc, 7)
+        self.assertEqual(mimc.hash_int(7, 0), input_hasher.hash([]))
+        self.assertEqual(
+            mimc.hash_int(mimc.hash_int(7, 1), 1), input_hasher.hash([1]))
+        self.assertEqual(
+            mimc.hash_int(
+                mimc.hash_int(
+                    mimc.hash_int(7, 1), 2),
+                2),
+            input_hasher.hash([1, 2]))
+
+    def test_input_hasher_mimc7(self) -> None:
+        mimc = MiMC7()
+        input_hasher = InputHasher(mimc)
+        values = [x % mimc.prime for x in DUMMY_INPUT_VALUES]
+        # pylint:disable=line-too-long
+        expect = 5568471640435576440988459485125198359192118312228711462978763973844457667180  # noqa
+        # pylint:enable=line-too-long
+        self.assertEqual(expect, input_hasher.hash(values))
+
+    def test_input_hasher_mimc31(self) -> None:
+        mimc = MiMC31()
+        input_hasher = InputHasher(mimc)
+        values = [x % mimc.prime for x in DUMMY_INPUT_VALUES]
+        # pylint: disable=line-too-long
+        expect = 1029772481427643815119825324071277815354972734622711297984795198139876181749  # noqa
+        # pylint: enable=line-too-long
+        self.assertEqual(expect, input_hasher.hash(values))

client/zeth/cli/zeth_get_verification_key.py

@@ -4,7 +4,6 @@
 
 from click import command, option, Context, pass_context
 
-from zeth.core.zksnark import get_zksnark_provider
 from zeth.cli.utils import create_prover_client
 import json
 from typing import Optional
@@ -21,12 +20,7 @@ def get_verification_key(ctx: Context, vk_out: Optional[str]) -> None:
     # Get the VK (proto object)
     client_ctx = ctx.obj
     prover_client = create_prover_client(client_ctx)
-    vk_proto = prover_client.get_verification_key()
-
-    # Get a zksnark provider and convert the VK to json
-    zksnark_name = prover_client.get_configuration().zksnark_name
-    zksnark = get_zksnark_provider(zksnark_name)
-    vk = zksnark.verification_key_from_proto(vk_proto)
+    vk = prover_client.get_verification_key()
     vk_json = vk.to_json_dict()
 
     # Write the json to stdout or a file

client/zeth/core/input_hasher.py

@@ -0,0 +1,36 @@
+# Copyright (c) 2015-2021 Clearmatics Technologies Ltd
+#
+# SPDX-License-Identifier: LGPL-3.0+
+
+from zeth.core.mimc import MiMCBase
+from typing import List
+
+
+# Default seed, generated as:
+#   zeth.core.mimc._keccak_256(
+#       zeth.core.mimc._str_to_bytes("clearmatics_hash_seed"))
+DEFAULT_IV_UINT256 = \
+    13196537064117388418196223856311987714388543839552400408340921397545324034315
+
+
+class InputHasher:
+    """
+    Note that this is currently experimental code. Hash a series of field
+    elements via the Merkle-Damgard construction on a MiMC compression
+    function. Note that since this function only accepts whole numbers of
+    scalar field elements, there is no ambiguity w.r.t to padding and we could
+    technically omit the finalization step. It has been kept for now, to allow
+    time for further consideration, and in case the form of the hasher changes
+    (e.g. in case we want to be able to hash arbitrary bit strings in the
+    future).
+    """
+    def __init__(self, compression_fn: MiMCBase, iv: int = DEFAULT_IV_UINT256):
+        assert compression_fn.prime < (2 << 256)
+        self._compression_fn = compression_fn
+        self._iv = iv % compression_fn.prime
+
+    def hash(self, values: List[int]) -> int:
+        current = self._iv
+        for m in values:
+            current = self._compression_fn.hash_int(current, m)
+        return self._compression_fn.hash_int(current, len(values))

client/zeth/core/mimc.py

@@ -61,8 +61,15 @@ def hash(self, left: bytes, right: bytes) -> bytes:
         """
         x = int.from_bytes(left, byteorder='big') % self.prime
         y = int.from_bytes(right, byteorder='big') % self.prime
-        result = (self.encrypt(x, y) + x + y) % self.prime
-        return result.to_bytes(32, byteorder='big')
+        return self.hash_int(x, y).to_bytes(32, byteorder='big')
+
+    def hash_int(self, x: int, y: int) -> int:
+        """
+        Similar to hash, but use field elements directly.
+        """
+        assert x < self.prime
+        assert y < self.prime
+        return (self.encrypt(x, y) + x + y) % self.prime
 
     @abstractmethod
     def mimc_round(self, message: int, key: int, rc: int) -> int:

client/zeth/core/mixer_client.py

@@ -276,13 +276,12 @@ def deploy(
         Deploy Zeth contracts.
         """
         prover_config = prover_client.get_configuration()
-        zksnark = get_zksnark_provider(prover_config.zksnark_name)
-        vk_proto = prover_client.get_verification_key()
-        pp = prover_config.pairing_parameters
-        vk = zksnark.verification_key_from_proto(vk_proto)
+        vk = prover_client.get_verification_key()
         deploy_gas = deploy_gas or constants.DEPLOYMENT_GAS_WEI
 
         contracts_dir = get_contracts_dir()
+        zksnark = get_zksnark_provider(prover_config.zksnark_name)
+        pp = prover_config.pairing_parameters
         mixer_name = zksnark.get_contract_name(pp)
         mixer_src = os.path.join(contracts_dir, mixer_name + ".sol")
 
@@ -581,11 +580,8 @@ def create_mix_parameters_and_signing_key(
         prover_inputs, signing_keypair = MixerClient.create_prover_inputs(
             mix_call_desc)
 
-        zksnark = get_zksnark_provider(self.prover_config.zksnark_name)
-
         # Query the prover_server for the related proof
-        ext_proof_proto = prover_client.get_proof(prover_inputs)
-        ext_proof = zksnark.extended_proof_from_proto(ext_proof_proto)
+        ext_proof = prover_client.get_proof(prover_inputs)
 
         # Create the final MixParameters object
         mix_params = self.create_mix_parameters_from_proof(

client/zeth/core/prover_client.py

@@ -5,9 +5,10 @@
 # SPDX-License-Identifier: LGPL-3.0+
 
 from __future__ import annotations
-from .pairing import PairingParameters, pairing_parameters_from_proto
+from zeth.core.zksnark import IZKSnarkProvider, get_zksnark_provider, \
+    IVerificationKey, ExtendedProof
+from zeth.core.pairing import PairingParameters, pairing_parameters_from_proto
 from zeth.api.zeth_messages_pb2 import ProofInputs
-from zeth.api.snark_messages_pb2 import VerificationKey, ExtendedProof
 from zeth.api import prover_pb2  # type: ignore
 from zeth.api import prover_pb2_grpc  # type: ignore
 import grpc  # type: ignore
@@ -93,14 +94,22 @@ def get_configuration(self) -> ProverConfiguration:
 
         return self.prover_config
 
-    def get_verification_key(self) -> VerificationKey:
+    def get_zksnark_provider(self) -> IZKSnarkProvider:
+        """
+        Get the appropriate zksnark provider, based on the server configuration.
+        """
+        config = self.get_configuration()
+        return get_zksnark_provider(config.zksnark_name)
+
+    def get_verification_key(self) -> IVerificationKey:
         """
         Fetch the verification key from the proving service
         """
         with grpc.insecure_channel(self.endpoint) as channel:
             stub = prover_pb2_grpc.ProverStub(channel)  # type: ignore
-            verificationkey = stub.GetVerificationKey(_make_empty_message())
-            return verificationkey
+            vk_proto = stub.GetVerificationKey(_make_empty_message())
+            zksnark = self.get_zksnark_provider()
+            return zksnark.verification_key_from_proto(vk_proto)
 
     def get_proof(
             self,
@@ -111,8 +120,9 @@ def get_proof(
         with grpc.insecure_channel(self.endpoint) as channel:
             stub = prover_pb2_grpc.ProverStub(channel)  # type: ignore
             print("-------------- Get the proof --------------")
-            proof = stub.Prove(proof_inputs)
-            return proof
+            extproof_proto = stub.Prove(proof_inputs)
+            zksnark = self.get_zksnark_provider()
+            return zksnark.extended_proof_from_proto(extproof_proto)
 
 
 def _make_empty_message() -> empty_pb2.Empty:

libzeth/circuits/circuit_wrapper.hpp

@@ -25,26 +25,27 @@ template<
     size_t TreeDepth>
 class circuit_wrapper
 {
-private:
-    std::shared_ptr<joinsplit_gadget<
-        libff::Fr<ppT>,
+public:
+    using Field = libff::Fr<ppT>;
+    // Both `joinsplit` and `joinsplit_gadget` are already used in the
+    // namespace.
+    using joinsplit_type = joinsplit_gadget<
+        Field,
         HashT,
         HashTreeT,
         NumInputs,
         NumOutputs,
-        TreeDepth>>
-        joinsplit_g;
-
-public:
-    using Field = libff::Fr<ppT>;
+        TreeDepth>;
 
     circuit_wrapper();
+    circuit_wrapper(const circuit_wrapper &) = delete;
+    circuit_wrapper &operator=(const circuit_wrapper &) = delete;
 
     // Generate the trusted setup
     typename snarkT::keypair generate_trusted_setup() const;
 
     // Retrieve the constraint system (intended for debugging purposes).
-    libsnark::protoboard<Field> get_constraint_system() const;
+    const libsnark::protoboard<Field> &get_constraint_system() const;
 
     // Generate a proof and returns an extended proof
     extended_proof<ppT, snarkT> prove(
@@ -56,6 +57,10 @@ class circuit_wrapper
         const bits256 &h_sig_in,
         const bits256 &phi_in,
         const typename snarkT::proving_key &proving_key) const;
+
+private:
+    libsnark::protoboard<Field> pb;
+    std::shared_ptr<joinsplit_type> joinsplit;
 };
 
 } // namespace libzeth

libzeth/circuits/circuit_wrapper.tcc

@@ -27,6 +27,14 @@ circuit_wrapper<
     NumOutputs,
     TreeDepth>::circuit_wrapper()
 {
+    // Joinsplit gadget internally allocates its public data first.
+    // TODO: joinsplit_gadget should be refactored to be properly composable.
+    joinsplit = std::make_shared<joinsplit_type>(pb);
+    const size_t num_public_elements = joinsplit->get_num_public_elements();
+    pb.set_input_sizes(num_public_elements);
+
+    // Generate constraints
+    joinsplit->generate_r1cs_constraints();
 }
 
 template<
@@ -46,11 +54,6 @@ typename snarkT::keypair circuit_wrapper<
     NumOutputs,
     TreeDepth>::generate_trusted_setup() const
 {
-    libsnark::protoboard<Field> pb;
-    joinsplit_gadget<Field, HashT, HashTreeT, NumInputs, NumOutputs, TreeDepth>
-        g(pb);
-    g.generate_r1cs_constraints();
-
     // Generate a verification and proving key (trusted setup) and write them
     // in a file
     return snarkT::generate_setup(pb);
@@ -64,7 +67,7 @@ template<
     size_t NumInputs,
     size_t NumOutputs,
     size_t TreeDepth>
-libsnark::protoboard<libff::Fr<ppT>> circuit_wrapper<
+const libsnark::protoboard<libff::Fr<ppT>> &circuit_wrapper<
     HashT,
     HashTreeT,
     ppT,
@@ -73,10 +76,6 @@ libsnark::protoboard<libff::Fr<ppT>> circuit_wrapper<
     NumOutputs,
     TreeDepth>::get_constraint_system() const
 {
-    libsnark::protoboard<Field> pb;
-    joinsplit_gadget<Field, HashT, HashTreeT, NumInputs, NumOutputs, TreeDepth>
-        g(pb);
-    g.generate_r1cs_constraints();
     return pb;
 }
 
@@ -128,12 +127,7 @@ extended_proof<ppT, snarkT> circuit_wrapper<
         throw std::invalid_argument("invalid joinsplit balance");
     }
 
-    libsnark::protoboard<Field> pb;
-
-    joinsplit_gadget<Field, HashT, HashTreeT, NumInputs, NumOutputs, TreeDepth>
-        g(pb);
-    g.generate_r1cs_constraints();
-    g.generate_r1cs_witness(
+    joinsplit->generate_r1cs_witness(
         root, inputs, outputs, vpub_in, vpub_out, h_sig_in, phi_in);
 
     bool is_valid_witness = pb.is_satisfied();