use ark_ec::AffineRepr;
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use ark_std::{
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rand::{Rng, RngCore},
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UniformRand,
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};
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use std::marker::PhantomData;
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use crate::transcript::Transcript;
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use crate::utils::{naive_msm, vec_add, vector_elem_product};
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pub struct Proof_elem<C: AffineRepr> {
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R: C,
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t1: C::ScalarField,
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t2: C::ScalarField,
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}
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pub struct Proof<C: AffineRepr> {
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R: C,
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u_: Vec<C::ScalarField>,
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ru_: C::ScalarField,
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}
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pub struct Params<C: AffineRepr> {
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g: C,
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h: C,
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pub r_vec: Vec<C>,
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}
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pub struct Pedersen<C: AffineRepr> {
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_phantom: PhantomData<C>,
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}
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impl<C: AffineRepr> Pedersen<C> {
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pub fn new_params<R: Rng>(rng: &mut R, max: usize) -> Params<C> {
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let h_scalar = C::ScalarField::rand(rng);
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let g: C = C::generator();
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let r_vec: Vec<C> = vec![C::rand(rng); max];
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let params: Params<C> = Params::<C> {
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g,
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h: g.mul(h_scalar).into(),
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r_vec, // will need 2 r: rE, rW
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};
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params
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}
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pub fn commit_elem<R: RngCore>(
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rng: &mut R,
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params: &Params<C>,
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v: &C::ScalarField,
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) -> CommitmentElem<C> {
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let r = C::ScalarField::rand(rng);
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let cm: C = (params.g.mul(v) + params.h.mul(r)).into();
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CommitmentElem::<C> { cm, r }
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}
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pub fn commit(
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params: &Params<C>,
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v: &Vec<C::ScalarField>,
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r: &C::ScalarField, // random value is provided, in order to be choosen by other parts of the protocol
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) -> Commitment<C> {
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let cm = params.h.mul(r) + naive_msm(v, ¶ms.r_vec);
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Commitment::<C>(cm.into())
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}
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pub fn prove_elem(
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params: &Params<C>,
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transcript: &mut Transcript<C::ScalarField>,
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cm: C,
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v: C::ScalarField,
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r: C::ScalarField,
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) -> Proof_elem<C> {
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let r1 = transcript.get_challenge(b"r_1");
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let r2 = transcript.get_challenge(b"r_2");
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let R: C = (params.g.mul(r1) + params.h.mul(r2)).into();
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transcript.add(b"cm", &cm);
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transcript.add(b"R", &R);
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let e = transcript.get_challenge(b"e");
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let t1 = r1 + v * e;
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let t2 = r2 + r * e;
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Proof_elem::<C> { R, t1, t2 }
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}
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pub fn prove(
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params: &Params<C>,
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transcript: &mut Transcript<C::ScalarField>,
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cm: &Commitment<C>, // TODO maybe it makes sense to not have a type wrapper and use directly C
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v: &Vec<C::ScalarField>,
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r: &C::ScalarField,
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) -> Proof<C> {
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let r1 = transcript.get_challenge(b"r_1");
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let d = transcript.get_challenge_vec(b"d", v.len());
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let R: C = (params.h.mul(r1) + naive_msm(&d, ¶ms.r_vec)).into();
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transcript.add(b"cm", &cm.0);
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transcript.add(b"R", &R);
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let e = transcript.get_challenge(b"e");
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let u_ = vec_add(&vector_elem_product(&v, &e), &d);
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let ru_ = e * r + r1;
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Proof::<C> { R, u_, ru_ }
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}
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pub fn verify(
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params: &Params<C>,
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transcript: &mut Transcript<C::ScalarField>,
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cm: Commitment<C>,
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proof: Proof<C>,
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) -> bool {
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// r1, d just to match Prover's transcript
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transcript.get_challenge(b"r_1");
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transcript.get_challenge_vec(b"d", proof.u_.len());
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transcript.add(b"cm", &cm.0);
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transcript.add(b"R", &proof.R);
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let e = transcript.get_challenge(b"e");
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let lhs = proof.R + cm.0.mul(e);
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let rhs = params.h.mul(proof.ru_) + naive_msm(&proof.u_, ¶ms.r_vec);
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if lhs != rhs {
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return false;
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}
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true
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}
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pub fn verify_elem(
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params: &Params<C>,
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transcript: &mut Transcript<C::ScalarField>,
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cm: C,
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proof: Proof_elem<C>,
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) -> bool {
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// s1, s2 just to match Prover's transcript
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transcript.get_challenge(b"r_1");
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transcript.get_challenge(b"r_2");
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transcript.add(b"cm", &cm);
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transcript.add(b"R", &proof.R);
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let e = transcript.get_challenge(b"e");
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let lhs = proof.R + cm.mul(e);
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let rhs = params.g.mul(proof.t1) + params.h.mul(proof.t2);
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if lhs != rhs {
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return false;
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}
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true
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}
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}
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pub struct Commitment<C: AffineRepr>(pub C);
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pub struct CommitmentElem<C: AffineRepr> {
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pub cm: C,
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pub r: C::ScalarField,
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}
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impl<C: AffineRepr> CommitmentElem<C> {
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pub fn prove(
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&self,
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params: &Params<C>,
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transcript: &mut Transcript<C::ScalarField>,
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v: C::ScalarField,
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) -> Proof_elem<C> {
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Pedersen::<C>::prove_elem(params, transcript, self.cm, v, self.r)
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use ark_bn254::{g1::G1Affine, Fr};
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use ark_ec::CurveGroup;
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use std::ops::Mul;
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#[test]
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fn test_pedersen_single_element() {
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let mut rng = ark_std::test_rng();
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// setup params
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let params = Pedersen::<G1Affine>::new_params(
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&mut rng, 0, /* 0, as here we don't use commit_vec */
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);
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// init Prover's transcript
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let mut transcript_p: Transcript<Fr> = Transcript::<Fr>::new();
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// init Verifier's transcript
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let mut transcript_v: Transcript<Fr> = Transcript::<Fr>::new();
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let v = Fr::rand(&mut rng);
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let cm = Pedersen::commit_elem(&mut rng, ¶ms, &v);
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let proof = cm.prove(¶ms, &mut transcript_p, v);
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// also can use:
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// let proof = Pedersen::prove_elem(¶ms, &mut transcript_p, cm.cm, v, cm.r);
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let v = Pedersen::verify_elem(¶ms, &mut transcript_v, cm.cm, proof);
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assert!(v);
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}
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#[test]
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fn test_pedersen_vector() {
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let mut rng = ark_std::test_rng();
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const n: usize = 10;
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// setup params
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let params = Pedersen::<G1Affine>::new_params(&mut rng, n);
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// init Prover's transcript
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let mut transcript_p: Transcript<Fr> = Transcript::<Fr>::new();
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// init Verifier's transcript
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let mut transcript_v: Transcript<Fr> = Transcript::<Fr>::new();
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let v: Vec<Fr> = vec![Fr::rand(&mut rng); n];
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let r: Fr = Fr::rand(&mut rng);
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let cm = Pedersen::commit(¶ms, &v, &r);
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let proof = Pedersen::prove(¶ms, &mut transcript_p, &cm, &v, &r);
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let v = Pedersen::verify(¶ms, &mut transcript_v, cm, proof);
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assert!(v);
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}
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}
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