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Move verify_share to return batch-verifiable statements

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While the previous construction achieved n/2 average detection,
this will run in log2(n). Unfortunately, the need to keep entropy
around (or take in an RNG here) remains.
This commit is contained in:
Luke Parker
2022-12-13 20:25:32 -05:00
parent 9c65518dc3
commit 25f1549c6c
14 changed files with 81 additions and 59 deletions
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39
crypto/schnorr/src/lib.rs
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@@ -7,10 +7,10 @@ use zeroize::{Zeroize, Zeroizing};
use group::{
ff::{Field, PrimeField},
GroupEncoding,
Group, GroupEncoding,
};
use multiexp::BatchVerifier;
use multiexp::{multiexp_vartime, BatchVerifier};
use ciphersuite::Ciphersuite;
@@ -59,10 +59,26 @@ impl<C: Ciphersuite> SchnorrSignature<C> {
}
}
/// Return the series of pairs whose products sum to zero for a valid signature.
/// This is inteded to be used with a multiexp.
pub fn batch_statements(&self, public_key: C::G, challenge: C::F) -> [(C::F, C::G); 3] {
// s = r + ca
// sG == R + cA
// R + cA - sG == 0
[
// R
(C::F::one(), self.R),
// cA
(challenge, public_key),
// -sG
(-self.s, C::generator()),
]
}
/// Verify a Schnorr signature for the given key with the specified challenge.
#[must_use]
pub fn verify(&self, public_key: C::G, challenge: C::F) -> bool {
(C::generator() * self.s) == (self.R + (public_key * challenge))
multiexp_vartime(&self.batch_statements(public_key, challenge)).is_identity().into()
}
/// Queue a signature for batch verification.
@@ -74,21 +90,6 @@ impl<C: Ciphersuite> SchnorrSignature<C> {
public_key: C::G,
challenge: C::F,
) {
// s = r + ca
// sG == R + cA
// R + cA - sG == 0
batch.queue(
rng,
id,
[
// R
(C::F::one(), self.R),
// cA
(challenge, public_key),
// -sG
(-self.s, C::generator()),
],
);
batch.queue(rng, id, self.batch_statements(public_key, challenge));
}
}