Simon Wicky
58 lines
1.7 KiB
Rust
58 lines
1.7 KiB
Rust
// Copyright 2024 - Nym Technologies SA <contact@nymtech.net>
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// SPDX-License-Identifier: Apache-2.0
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use std::borrow::Borrow;
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use digest::generic_array::typenum::Unsigned;
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use digest::Digest;
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use nym_bls12_381_fork::Scalar;
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use sha2::Sha256;
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pub mod proof_spend;
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pub mod proof_withdrawal;
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type ChallengeDigest = Sha256;
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/// Generates a Scalar [or Fp] challenge by hashing a number of elliptic curve points.
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fn compute_challenge<D, I, B>(iter: I) -> Scalar
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where
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D: Digest,
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I: Iterator<Item = B>,
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B: AsRef<[u8]>,
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{
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let mut h = D::new();
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for point_representation in iter {
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h.update(point_representation);
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}
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let digest = h.finalize();
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// TODO: I don't like the 0 padding here (though it's what we've been using before,
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// but we never had a security audit anyway...)
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// instead we could maybe use the `from_bytes` variant and adding some suffix
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// when computing the digest until we produce a valid scalar.
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let mut bytes = [0u8; 64];
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let pad_size = 64usize.saturating_sub(D::OutputSize::to_usize());
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bytes[pad_size..].copy_from_slice(&digest);
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Scalar::from_bytes_wide(&bytes)
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}
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fn produce_response(witness_replacement: &Scalar, challenge: &Scalar, secret: &Scalar) -> Scalar {
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witness_replacement - challenge * secret
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}
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// note: it's caller's responsibility to ensure witnesses.len() = secrets.len()
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fn produce_responses<S>(witnesses: &[Scalar], challenge: &Scalar, secrets: &[S]) -> Vec<Scalar>
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where
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S: Borrow<Scalar>,
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{
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debug_assert_eq!(witnesses.len(), secrets.len());
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witnesses
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.iter()
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.zip(secrets.iter())
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.map(|(w, x)| produce_response(w, challenge, x.borrow()))
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.collect()
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}
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