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DRY the interpolating value derivation code #7

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DRY the interpolating value derivation code #7

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50 changes: 24 additions & 26 deletions frost-core/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -341,15 +341,29 @@ fn derive_interpolating_value<C: Ciphersuite>(
signer_id: &Identifier<C>,
signing_package: &SigningPackage<C>,
) -> Result<Scalar<C>, Error<C>> {
compute_lagrange_coefficient(
&signing_package
.signing_commitments()
.keys()
.cloned()
.collect(),
None,
*signer_id,
)
match &signing_package.signing_participants_groups {
Some(signing_participants_groups) => {
let signing_participants_group = signing_participants_groups.iter().find(|g| g.contains(signer_id));

match signing_participants_group {
Some(group) => compute_lagrange_coefficient(
group,
None,
*signer_id,
),
None => Err(Error::UnknownIdentifier),
}
}
None => compute_lagrange_coefficient(
&signing_package
.signing_commitments()
.keys()
.cloned()
.collect(),
None,
*signer_id,
),
}
}

/// Generated by the coordinator of the signing operation and distributed to
Expand Down Expand Up @@ -874,23 +888,7 @@ fn verify_signature_share_precomputed<C: Ciphersuite>(
verifying_share: &keys::VerifyingShare<C>,
challenge: Challenge<C>,
) -> Result<(), Error<C>> {
let lambda_i = match signing_package.signing_participants_groups.clone() {
Some(signing_participants_groups) => {
let mut result: Result<Scalar<C>, Error<C>> = Err(Error::UnknownIdentifier);
for signing_participants_group in signing_participants_groups {
if signing_participants_group.contains(&signature_share_identifier) {
result = compute_lagrange_coefficient(
&signing_participants_group,
None,
signature_share_identifier,
);
break;
}
}
result?
}
None => derive_interpolating_value(&signature_share_identifier, signing_package)?,
};
let lambda_i = derive_interpolating_value(&signature_share_identifier, signing_package)?;

let binding_factor = binding_factor_list
.get(&signature_share_identifier)
Expand Down
18 changes: 1 addition & 17 deletions frost-core/src/round2.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -160,23 +160,7 @@ pub fn sign<C: Ciphersuite>(
let group_commitment = compute_group_commitment(&signing_package, &binding_factor_list)?;

// Compute Lagrange coefficient.
let lambda_i = match signing_package.signing_participants_groups.clone() {
Some(signing_participants_groups) => {
let mut result: Result<Scalar<C>, Error<C>> = Err(Error::UnknownIdentifier);
for signing_participants_group in signing_participants_groups {
if signing_participants_group.contains(key_package.identifier()) {
result = frost::compute_lagrange_coefficient(
&signing_participants_group,
None,
*key_package.identifier(),
);
break;
}
}
result?
}
None => frost::derive_interpolating_value(key_package.identifier(), &signing_package)?,
};
let lambda_i = frost::derive_interpolating_value(key_package.identifier(), &signing_package)?;

// Compute the per-message challenge.
let challenge = <C>::challenge(
Expand Down