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Switch RO to use the one in the Group trait (#54)

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* switch to RO in the Group trait

* simplify compression

* absorb IO as bignum for relaxedR1CS
This commit is contained in:
Srinath Setty
2022-05-13 14:19:34 +05:30
committed by GitHub
parent 82b7fabd9d
commit 677fe23673
7 changed files with 144 additions and 80 deletions
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62
src/lib.rs
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@@ -16,12 +16,11 @@ pub mod traits;
use commitments::CompressedCommitment;
use errors::NovaError;
use merlin::Transcript;
use r1cs::{
R1CSGens, R1CSInstance, R1CSShape, R1CSWitness, RelaxedR1CSInstance, RelaxedR1CSWitness,
};
use std::marker::PhantomData;
use traits::{AppendToTranscriptTrait, ChallengeTrait, Group};
use traits::{AbsorbInROTrait, Group, HashFuncConstantsTrait, HashFuncTrait};
/// A SNARK that holds the proof of a step of an incremental computation
pub struct StepSNARK<G: Group> {
@@ -30,10 +29,6 @@ pub struct StepSNARK<G: Group> {
}
impl<G: Group> StepSNARK<G> {
fn protocol_name() -> &'static [u8] {
b"NovaStepSNARK"
}
/// Takes as input a Relaxed R1CS instance-witness tuple `(U1, W1)` and
/// an R1CS instance-witness tuple `(U2, W2)` with the same structure `shape`
/// and defined with respect to the same `gens`, and outputs
@@ -47,7 +42,6 @@ impl<G: Group> StepSNARK<G> {
W1: &RelaxedR1CSWitness<G>,
U2: &R1CSInstance<G>,
W2: &R1CSWitness<G>,
transcript: &mut Transcript,
) -> Result<
(
StepSNARK<G>,
@@ -55,24 +49,27 @@ impl<G: Group> StepSNARK<G> {
),
NovaError,
> {
// append the protocol name to the transcript
transcript.append_message(b"protocol-name", StepSNARK::<G>::protocol_name());
// initialize a new RO
let mut ro = G::HashFunc::new(<<G as traits::Group>::HashFunc as HashFuncTrait<
G::Base,
G::Scalar,
>>::Constants::new());
// append S to the transcript
S.append_to_transcript(b"S", transcript);
S.absorb_in_ro(&mut ro);
// append U1 and U2 to transcript
U1.append_to_transcript(b"U1", transcript);
U2.append_to_transcript(b"U2", transcript);
U1.absorb_in_ro(&mut ro);
U2.absorb_in_ro(&mut ro);
// compute a commitment to the cross-term
let (T, comm_T) = S.commit_T(gens, U1, W1, U2, W2)?;
// append `comm_T` to the transcript and obtain a challenge
comm_T.append_to_transcript(b"comm_T", transcript);
comm_T.absorb_in_ro(&mut ro);
// compute a challenge from the transcript
let r = G::Scalar::challenge(b"r", transcript);
// compute a challenge from the RO
let r = ro.get_challenge();
// fold the instance using `r` and `comm_T`
let U = U1.fold(U2, &comm_T, &r)?;
@@ -83,7 +80,7 @@ impl<G: Group> StepSNARK<G> {
// return the folded instance and witness
Ok((
StepSNARK {
comm_T,
comm_T: comm_T.compress(),
_p: Default::default(),
},
(U, W),
@@ -100,26 +97,29 @@ impl<G: Group> StepSNARK<G> {
S: &R1CSShape<G>,
U1: &RelaxedR1CSInstance<G>,
U2: &R1CSInstance<G>,
transcript: &mut Transcript,
) -> Result<RelaxedR1CSInstance<G>, NovaError> {
// append the protocol name to the transcript
transcript.append_message(b"protocol-name", StepSNARK::<G>::protocol_name());
// initialize a new RO
let mut ro = G::HashFunc::new(<<G as traits::Group>::HashFunc as HashFuncTrait<
G::Base,
G::Scalar,
>>::Constants::new());
// append S to the transcript
S.append_to_transcript(b"S", transcript);
S.absorb_in_ro(&mut ro);
// append U1 and U2 to transcript
U1.append_to_transcript(b"U1", transcript);
U2.append_to_transcript(b"U2", transcript);
U1.absorb_in_ro(&mut ro);
U2.absorb_in_ro(&mut ro);
// append `comm_T` to the transcript and obtain a challenge
self.comm_T.append_to_transcript(b"comm_T", transcript);
let comm_T = self.comm_T.decompress()?;
comm_T.absorb_in_ro(&mut ro);
// compute a challenge from the transcript
let r = G::Scalar::challenge(b"r", transcript);
// compute a challenge from the RO
let r = ro.get_challenge();
// fold the instance using `r` and `comm_T`
let U = U1.fold(U2, &self.comm_T, &r)?;
let U = U1.fold(U2, &comm_T, &r)?;
// return the folded instance
Ok(U)
@@ -239,14 +239,12 @@ mod tests {
let mut r_U = RelaxedR1CSInstance::default(gens, shape);
// produce a step SNARK with (W1, U1) as the first incoming witness-instance pair
let mut prover_transcript = Transcript::new(b"StepSNARKExample");
let res = StepSNARK::prove(gens, shape, &r_U, &r_W, U1, W1, &mut prover_transcript);
let res = StepSNARK::prove(gens, shape, &r_U, &r_W, U1, W1);
assert!(res.is_ok());
let (step_snark, (_U, W)) = res.unwrap();
// verify the step SNARK with U1 as the first incoming instance
let mut verifier_transcript = Transcript::new(b"StepSNARKExample");
let res = step_snark.verify(shape, &r_U, U1, &mut verifier_transcript);
let res = step_snark.verify(shape, &r_U, U1);
assert!(res.is_ok());
let U = res.unwrap();
@@ -257,12 +255,12 @@ mod tests {
r_U = U;
// produce a step SNARK with (W2, U2) as the second incoming witness-instance pair
let res = StepSNARK::prove(gens, shape, &r_U, &r_W, U2, W2, &mut prover_transcript);
let res = StepSNARK::prove(gens, shape, &r_U, &r_W, U2, W2);
assert!(res.is_ok());
let (step_snark, (_U, W)) = res.unwrap();
// verify the step SNARK with U1 as the first incoming instance
let res = step_snark.verify(shape, &r_U, U2, &mut verifier_transcript);
let res = step_snark.verify(shape, &r_U, U2);
assert!(res.is_ok());
let U = res.unwrap();