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Merged
davxy merged 3 commits into from
May 23, 2025
Merged

Improve secret scalar generation #62

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Improve secret scalar generation
davxy May 22, 2025
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davxy May 22, 2025
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davxy May 22, 2025
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32 changes: 24 additions & 8 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -126,7 +126,7 @@
#![deny(unsafe_code)]

use ark_ec::{AffineRepr, CurveGroup};
use ark_ff::{One, PrimeField, Zero};
use ark_ff::{PrimeField, Zero};
use ark_serialize::{CanonicalDeserialize, CanonicalSerialize};
use ark_std::vec::Vec;

Expand Down Expand Up @@ -323,15 +323,31 @@ impl<S: Suite> Secret<S> {
Self { scalar, public }
}

/// Construct a `Secret` from the given seed.
/// Derives a `Secret` scalar deterministically from a seed.
///
/// The `seed` is hashed using the `Suite::hash` to construct the secret scalar.
/// The seed is hashed using `Suite::Hasher`, and the output is reduced
/// modulo the curve's order to produce a valid scalar in the range
/// `[1, n - 1]`. No clamping or multiplication by the cofactor is
/// performed, regardless of the curve.
///
/// The caller is responsible for ensuring that the resulting scalar is
/// used safely with respect to the target curve's cofactor and subgroup
/// properties.
pub fn from_seed(seed: &[u8]) -> Self {
let bytes = utils::hash::<S::Hasher>(seed);
let mut scalar = ScalarField::<S>::from_le_bytes_mod_order(&bytes[..]);
if scalar.is_zero() {
scalar.set_one();
}
let mut cnt = 0_u8;
let scalar = loop {
let mut hasher = S::Hasher::new();
hasher.update(seed);
if cnt > 0 {
hasher.update([cnt]);
}
let bytes = hasher.finalize();
let scalar = ScalarField::<S>::from_le_bytes_mod_order(&bytes[..]);
if !scalar.is_zero() {
break scalar;
}
cnt += 1;
};
Self::from_scalar(scalar)
}

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