implement transcript methods for various types (#49)

* implement transcript methods for various types

* address clippy

* add shape to transcript

Cargo.toml

@@ -27,6 +27,9 @@ neptune = "6.1"
 generic-array = "0.14.4"
 bellperson-nonnative = { version = "0.2.1", default-features = false, features = ["wasm"] }
 rug = { version = "1.10", default-features = false, features = ["integer", "serde", "rand"] }
+serde = { version = "1.0", features = ["derive"] }
+bincode = "1.2.1"
+flate2 = "1.0"
 
 [features]
 default = [ "bellperson/default", "bellperson-nonnative/default" ]

src/commitments.rs

@@ -1,6 +1,6 @@
 use super::{
   errors::NovaError,
-  traits::{CompressedGroup, Group},
+  traits::{AppendToTranscriptTrait, CompressedGroup, Group},
 };
 use core::{
   fmt::Debug,
@@ -80,10 +80,6 @@ impl CommitTrait for [G::Scalar] {
   }
 }
 
-pub trait AppendToTranscriptTrait {
-  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript);
-}
-
 impl<G: Group> AppendToTranscriptTrait for Commitment<G> {
   fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript) {
     transcript.append_message(label, self.comm.compress().as_bytes());

src/lib.rs

@@ -16,13 +16,13 @@ pub mod traits;
 
 use std::marker::PhantomData;
 
-use commitments::{AppendToTranscriptTrait, CompressedCommitment};
+use commitments::CompressedCommitment;
 use errors::NovaError;
 use merlin::Transcript;
 use r1cs::{
   R1CSGens, R1CSInstance, R1CSShape, R1CSWitness, RelaxedR1CSInstance, RelaxedR1CSWitness,
 };
-use traits::{ChallengeTrait, Group};
+use traits::{AppendToTranscriptTrait, ChallengeTrait, Group};
 
 /// A SNARK that holds the proof of a step of an incremental computation
 pub struct StepSNARK<G: Group> {
@@ -59,6 +59,13 @@ impl StepSNARK {
     // append the protocol name to the transcript
     transcript.append_message(b"protocol-name", StepSNARK::<G>::protocol_name());
 
+    // append S to the transcript
+    S.append_to_transcript(b"S", transcript);
+
+    // append U1 and U2 to transcript
+    U1.append_to_transcript(b"U1", transcript);
+    U2.append_to_transcript(b"U2", transcript);
+
     // compute a commitment to the cross-term
     let (T, comm_T) = S.commit_T(gens, U1, W1, U2, W2)?;
 
@@ -91,6 +98,7 @@ impl StepSNARK {
   /// if and only if `U1` and `U2` are satisfiable.
   pub fn verify(
     &self,
+    S: &R1CSShape<G>,
     U1: &RelaxedR1CSInstance<G>,
     U2: &R1CSInstance<G>,
     transcript: &mut Transcript,
@@ -98,6 +106,13 @@ impl StepSNARK {
     // append the protocol name to the transcript
     transcript.append_message(b"protocol-name", StepSNARK::<G>::protocol_name());
 
+    // append S to the transcript
+    S.append_to_transcript(b"S", transcript);
+
+    // append U1 and U2 to transcript
+    U1.append_to_transcript(b"U1", transcript);
+    U2.append_to_transcript(b"U2", transcript);
+
     // append `comm_T` to the transcript and obtain a challenge
     self.comm_T.append_to_transcript(b"comm_T", transcript);
 
@@ -232,7 +247,7 @@ mod tests {
 
     // verify the step SNARK with U1 as the first incoming instance
     let mut verifier_transcript = Transcript::new(b"StepSNARKExample");
-    let res = step_snark.verify(&r_U, U1, &mut verifier_transcript);
+    let res = step_snark.verify(shape, &r_U, U1, &mut verifier_transcript);
     assert!(res.is_ok());
     let U = res.unwrap();
 
@@ -248,7 +263,7 @@ mod tests {
     let (step_snark, (_U, W)) = res.unwrap();
 
     // verify the step SNARK with U1 as the first incoming instance
-    let res = step_snark.verify(&r_U, U2, &mut verifier_transcript);
+    let res = step_snark.verify(shape, &r_U, U2, &mut verifier_transcript);
     assert!(res.is_ok());
     let U = res.unwrap();
 

src/r1cs.rs

@@ -3,11 +3,14 @@
 use super::{
   commitments::{CommitGens, CommitTrait, Commitment, CompressedCommitment},
   errors::NovaError,
-  traits::Group,
+  traits::{AppendToTranscriptTrait, Group},
 };
-use ff::Field;
+use ff::{Field, PrimeField};
+use flate2::{write::ZlibEncoder, Compression};
 use itertools::concat;
+use merlin::Transcript;
 use rayon::prelude::*;
+use serde::{Deserialize, Serialize};
 
 /// Public parameters for a given R1CS
 pub struct R1CSGens<G: Group> {
@@ -292,6 +295,46 @@ impl R1CSShape {
   }
 }
 
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+struct R1CSShapeSerialized {
+  num_cons: usize,
+  num_vars: usize,
+  num_io: usize,
+  A: Vec<(usize, usize, Vec<u8>)>,
+  B: Vec<(usize, usize, Vec<u8>)>,
+  C: Vec<(usize, usize, Vec<u8>)>,
+}
+
+impl<G: Group> AppendToTranscriptTrait for R1CSShape<G> {
+  fn append_to_transcript(&self, _label: &'static [u8], transcript: &mut Transcript) {
+    let shape_serialized = R1CSShapeSerialized {
+      num_cons: self.num_cons,
+      num_vars: self.num_vars,
+      num_io: self.num_io,
+      A: self
+        .A
+        .iter()
+        .map(|(i, j, v)| (*i, *j, v.to_repr().as_ref().to_vec()))
+        .collect(),
+      B: self
+        .B
+        .iter()
+        .map(|(i, j, v)| (*i, *j, v.to_repr().as_ref().to_vec()))
+        .collect(),
+      C: self
+        .C
+        .iter()
+        .map(|(i, j, v)| (*i, *j, v.to_repr().as_ref().to_vec()))
+        .collect(),
+    };
+
+    let mut encoder = ZlibEncoder::new(Vec::new(), Compression::default());
+    bincode::serialize_into(&mut encoder, &shape_serialized).unwrap();
+    let shape_bytes = encoder.finish().unwrap();
+    transcript.append_message(b"R1CSShape", &shape_bytes);
+  }
+}
+
 impl<G: Group> R1CSWitness<G> {
   /// A method to create a witness object using a vector of scalars
   pub fn new(S: &R1CSShape<G>, W: &[G::Scalar]) -> Result<R1CSWitness<G>, NovaError> {
@@ -326,6 +369,13 @@ impl R1CSInstance {
   }
 }
 
+impl<G: Group> AppendToTranscriptTrait for R1CSInstance<G> {
+  fn append_to_transcript(&self, _label: &'static [u8], transcript: &mut Transcript) {
+    self.comm_W.append_to_transcript(b"comm_W", transcript);
+    self.X.append_to_transcript(b"X", transcript);
+  }
+}
+
 impl<G: Group> RelaxedR1CSWitness<G> {
   /// Produces a default RelaxedR1CSWitness given an R1CSShape
   pub fn default(S: &R1CSShape<G>) -> RelaxedR1CSWitness<G> {
@@ -427,3 +477,12 @@ impl RelaxedR1CSInstance {
     })
   }
 }
+
+impl<G: Group> AppendToTranscriptTrait for RelaxedR1CSInstance<G> {
+  fn append_to_transcript(&self, _label: &'static [u8], transcript: &mut Transcript) {
+    self.comm_W.append_to_transcript(b"comm_W", transcript);
+    self.comm_E.append_to_transcript(b"comm_E", transcript);
+    self.X.append_to_transcript(b"X", transcript);
+    self.u.append_to_transcript(b"u", transcript);
+  }
+}

src/traits.rs

@@ -68,6 +68,12 @@ pub trait CompressedGroup: Clone + Copy + Debug + Eq + Sized + Send + Sync + 'st
   fn as_bytes(&self) -> &[u8];
 }
 
+/// A helper trait to append different types to the transcript
+pub trait AppendToTranscriptTrait {
+  /// appends the value to the transcript under the provided label
+  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript);
+}
+
 /// A helper trait to generate challenges using a transcript object
 pub trait ChallengeTrait {
   /// Returns a Scalar representing the challenge using the transcript
@@ -133,3 +139,17 @@ pub trait StepCircuit {
     z: AllocatedNum<F>,
   ) -> Result<AllocatedNum<F>, SynthesisError>;
 }
+
+impl<F: PrimeField> AppendToTranscriptTrait for F {
+  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript) {
+    transcript.append_message(label, self.to_repr().as_ref());
+  }
+}
+
+impl<F: PrimeField> AppendToTranscriptTrait for [F] {
+  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut Transcript) {
+    for s in self {
+      s.append_to_transcript(label, transcript);
+    }
+  }
+}