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Move the generation of identifiers into a separate function

This commit is contained in:
Marek 2021-05-30 17:54:45 +01:00
parent 63ee073a82
commit f052e8f37f
1 changed files with 24 additions and 17 deletions
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41
src/frost.rs
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@ -230,6 +230,29 @@ fn verify_share(share: &Share) -> Result<(), &'static str> {
Ok(())
}
/// Generates the identifier for a given participant.
///
/// The identifier is generated as follows:
/// id = H("FROST_id", g^s, i), where:
/// - g is the basepoint,
/// - s is the secret chosen by the dealer, and
/// - i is the index of the participant.
///
/// The actual identifier consists of the first 64 bits of the resulting hash.
fn generate_id(secret: &Secret, index: u8) -> u64 {
use std::convert::TryInto;
let mut hasher = HStar::default();
hasher
.update("FROST_id".as_bytes())
.update(jubjub::AffinePoint::from(SpendAuth::basepoint() * secret.0).to_bytes())
.update(index.to_be_bytes());
let id_bytes = hasher.finalize().to_bytes();
u64::from_be_bytes(id_bytes[0..8].try_into().expect("slice of incorrect size"))
}
/// Creates secret shares for a given secret.
///
/// This function accepts a secret from which shares are generated. While in
@ -251,8 +274,6 @@ fn generate_shares<R: RngCore + CryptoRng>(
threshold: u8,
mut rng: R,
) -> Result<Vec<Share>, &'static str> {
use std::convert::TryInto;
if threshold < 1 {
return Err("Threshold cannot be 0");
}
@ -291,25 +312,11 @@ fn generate_shares<R: RngCore + CryptoRng>(
)));
}
// Participants' identifiers are generated as follows:
// id = H("FROST_id", g^s, i), where:
// g is the basepoint,
// s is the secret chosen by the dealer, and
// i is the index of the participant.
// The hash is finalized in the loop that follows.
let mut hasher = HStar::default();
hasher
.update("FROST_id".as_bytes())
.update(jubjub::AffinePoint::from(SpendAuth::basepoint() * secret.0).to_bytes());
// Evaluate the polynomial with `secret` as the constant term
// and `coeffs` as the other coefficients at the point x=share_index,
// using Horner's method.
for index in 1..numshares + 1 {
// The actual identifier consists of the first 64 bits of the resulting hash.
let id_bytes = hasher.update(index.to_be_bytes()).finalize().to_bytes();
let id = u64::from_be_bytes(id_bytes[0..8].try_into().expect("slice of incorrect size"));
let id = generate_id(secret, index);
let scalar_id = Scalar::from(id);
let mut value = Scalar::zero();