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3.6.8 Simplify offset splitting

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This wasn't done prior to be 'leaderless', as now the participant with the
lowest ID has an extra step, yet this is still trivial. There's also notable
performance benefits to not taking the previous dividing approach, which
performed an exp.
This commit is contained in:
Luke Parker
2023-03-01 01:06:13 -05:00
parent a42a84e1e8
commit c6284b85a4
3 changed files with 23 additions and 21 deletions
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36
crypto/dkg/src/lib.rs
View File

@@ -401,31 +401,35 @@ impl<C: Ciphersuite> ThresholdKeys<C> {
self.core.serialize()
}
pub fn view(&self, included: &[Participant]) -> Result<ThresholdView<C>, DkgError<()>> {
pub fn view(&self, mut included: Vec<Participant>) -> Result<ThresholdView<C>, DkgError<()>> {
if (included.len() < self.params().t.into()) || (usize::from(self.params().n) < included.len())
{
Err(DkgError::InvalidSigningSet)?;
}
included.sort();
let offset_share = self.offset.unwrap_or_else(C::F::zero) *
C::F::from(included.len().try_into().unwrap()).invert().unwrap();
let offset_verification_share = C::generator() * offset_share;
let mut secret_share =
Zeroizing::new(lagrange::<C::F>(self.params().i, &included) * self.secret_share().deref());
let mut verification_shares = self.verification_shares();
for (i, share) in verification_shares.iter_mut() {
*share *= lagrange::<C::F>(*i, &included);
}
// The offset is included by adding it to the participant with the lowest ID
let offset = self.offset.unwrap_or_else(C::F::zero);
if included[0] == self.params().i() {
*secret_share += offset;
}
*verification_shares.get_mut(&included[0]).unwrap() += C::generator() * offset;
Ok(ThresholdView {
offset: self.offset.unwrap_or_else(C::F::zero),
offset,
group_key: self.group_key(),
secret_share: Zeroizing::new(
(lagrange::<C::F>(self.params().i, included) * self.secret_share().deref()) + offset_share,
),
secret_share,
original_verification_shares: self.verification_shares(),
verification_shares: self
.verification_shares()
.iter()
.map(|(l, share)| {
(*l, (*share * lagrange::<C::F>(*l, included)) + offset_verification_share)
})
.collect(),
included: included.to_vec(),
verification_shares,
included,
})
}
}