primitives/commitments/
pedersen.rs

1use rand::SeedableRng;
2use subtle::ConstantTimeEq;
3
4use super::CommitmentScheme;
5use crate::{
6    algebra::elliptic_curve::{Curve, Point, ScalarAsExtension},
7    errors::PrimitiveError,
8    hashing::hash,
9    random::{BaseRng, CryptoRngCore, Random},
10};
11
12#[derive(Copy, Clone, Debug)]
13pub struct PedersenCommitment<C: Curve> {
14    pub g: Point<C>,
15    pub h: Point<C>,
16}
17
18impl<C: Curve> PedersenCommitment<C> {
19    // Create a new Pedersen commitment scheme by defining the two generators, using the curve's
20    // generator as the first generator (g) and the provided seed to derive the second generator
21    // (h). Use different seeds to instantiate separate sessions (e.g., with different SessionIds).
22    pub fn new<S: AsRef<[u8]>>(second_generator_seed: &S) -> Self {
23        let g = Point::generator();
24        let mut rng = BaseRng::from_seed(hash(&[second_generator_seed.as_ref()]).into());
25        let h = Point::random(&mut rng);
26        Self { g, h }
27    }
28}
29
30impl<C: Curve> CommitmentScheme<ScalarAsExtension<C>> for PedersenCommitment<C> {
31    type Commitment = Point<C>;
32    type Witness = ScalarAsExtension<C>;
33
34    fn commit<R: CryptoRngCore>(
35        &self,
36        input: &ScalarAsExtension<C>,
37        mut rng: R,
38    ) -> (Self::Commitment, Self::Witness) {
39        let witness = ScalarAsExtension::<C>::random(&mut rng);
40
41        let commitment = self.g * witness + self.h * input;
42        (commitment, witness)
43    }
44
45    fn open(
46        &self,
47        c: &Self::Commitment,
48        w: &Self::Witness,
49        input: &ScalarAsExtension<C>,
50    ) -> Result<(), PrimitiveError> {
51        let c_prime = self.g * w + self.h * input;
52        if bool::from(c.ct_eq(&c_prime)) {
53            Ok(())
54        } else {
55            Err(PrimitiveError::WrongOpening(
56                format!("{c:?}"),
57                format!("{c_prime:?}"),
58            ))
59        }
60    }
61}
primitives/commitments/pedersen.rs

primitives/commitments/
pedersen.rs
