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Smash the singular Ciphersuite trait into multiple

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This helps identify where the various functionalities are used, or rather, not
used. The `Ciphersuite` trait present in `patches/ciphersuite`, facilitating
the entire FCMP++ tree, only requires the markers _and_ canonical point
decoding. I've opened a PR to upstream such a trait into `group`
(https://github.com/zkcrypto/group/pull/68).

`WrappedGroup` is still justified for as long as `Group::generator` exists.
Moving `::generator()` to its own trait, on an independent structure (upstream)
would be massively appreciated. @tarcieri also wanted to update from
`fn generator()` to `const GENERATOR`, which would encourage further discussion
on https://github.com/zkcrypto/group/issues/32 and
https://github.com/zkcrypto/group/issues/45, which have been stagnant.

The `Id` trait is occasionally used yet really should be first off the chopping
block.

Finally, `WithPreferredHash` is only actually used around a third of the time,
which more than justifies it being a separate trait.

---

Updates `dalek_ff_group::Scalar` to directly re-export
`curve25519_dalek::Scalar`, as without issue. `dalek_ff_group::RistrettoPoint`
also could be replaced with an export of `curve25519_dalek::RistrettoPoint`,
yet the coordinator relies on how we implemented `Hash` on it for the hell of
it so it isn't worth it at this time. `dalek_ff_group::EdwardsPoint` can't be
replaced for an re-export of `curve25519_dalek::SubgroupPoint` as it doesn't
implement `zeroize`, `subtle` traits within a released, non-yanked version.
Relevance to https://github.com/serai-dex/serai/issues/201 and
https://github.com/dalek-cryptography/curve25519-dalek/issues/811#issuecomment-3247732746.

Also updates the `Ristretto` ciphersuite to prefer `Blake2b-512` over
`SHA2-512`. In order to maintain compliance with FROST's IETF standard,
`modular-frost` defines its own ciphersuite for Ristretto which still uses
`SHA2-512`.
This commit is contained in:
Luke Parker
2025-09-03 12:25:37 -04:00
parent 215e41fdb6
commit a141deaf36
124 changed files with 1003 additions and 1211 deletions
Download Patch File Download Diff File Expand all files Collapse all files

73
crypto/schnorr/src/aggregate.rs
View File

@@ -5,74 +5,34 @@ use std_shims::{
use zeroize::Zeroize;
use transcript::{Transcript, SecureDigest, DigestTranscript};
use transcript::{Transcript, DigestTranscript};
use ciphersuite::{
group::{
ff::{Field, PrimeField},
Group, GroupEncoding,
},
Ciphersuite,
FromUniformBytes, GroupIo, WithPreferredHash,
};
use multiexp::multiexp_vartime;
use crate::SchnorrSignature;
// Returns a unbiased scalar weight to use on a signature in order to prevent malleability
fn weight<D: Send + Clone + SecureDigest, F: PrimeField>(digest: &mut DigestTranscript<D>) -> F {
let mut bytes = digest.challenge(b"aggregation_weight");
debug_assert_eq!(bytes.len() % 8, 0);
// This should be guaranteed thanks to SecureDigest
debug_assert!(bytes.len() >= 32);
let mut res = F::ZERO;
let mut i = 0;
// Derive a scalar from enough bits of entropy that bias is < 2^128
// This can't be const due to its usage of a generic
// Also due to the usize::try_from, yet that could be replaced with an `as`
#[allow(non_snake_case)]
let BYTES: usize = usize::try_from((F::NUM_BITS + 128).div_ceil(8)).unwrap();
let mut remaining = BYTES;
// We load bits in as u64s
const WORD_LEN_IN_BITS: usize = 64;
const WORD_LEN_IN_BYTES: usize = WORD_LEN_IN_BITS / 8;
let mut first = true;
while i < remaining {
// Shift over the already loaded bits
if !first {
for _ in 0 .. WORD_LEN_IN_BITS {
res += res;
}
}
first = false;
// Add the next 64 bits
res += F::from(u64::from_be_bytes(bytes[i .. (i + WORD_LEN_IN_BYTES)].try_into().unwrap()));
i += WORD_LEN_IN_BYTES;
// If we've exhausted this challenge, get another
if i == bytes.len() {
bytes = digest.challenge(b"aggregation_weight_continued");
remaining -= i;
i = 0;
}
}
res
fn weight<C: WithPreferredHash>(digest: &mut DigestTranscript<C::H>) -> C::F {
let bytes = digest.challenge(b"aggregation_weight");
C::F::from_uniform_bytes(&bytes.into())
}
/// Aggregate Schnorr signature as defined in <https://eprint.iacr.org/2021/350>.
#[allow(non_snake_case)]
#[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
pub struct SchnorrAggregate<C: Ciphersuite> {
pub struct SchnorrAggregate<C: GroupIo + WithPreferredHash> {
Rs: Vec<C::G>,
s: C::F,
}
impl<C: Ciphersuite> SchnorrAggregate<C> {
impl<C: GroupIo + WithPreferredHash> SchnorrAggregate<C> {
/// Read a SchnorrAggregate from something implementing Read.
pub fn read<R: Read>(reader: &mut R) -> io::Result<Self> {
let mut len = [0; 4];
@@ -137,7 +97,7 @@ impl<C: Ciphersuite> SchnorrAggregate<C> {
let mut pairs = Vec::with_capacity((2 * keys_and_challenges.len()) + 1);
for (i, (key, challenge)) in keys_and_challenges.iter().enumerate() {
let z = weight(&mut digest);
let z = weight::<C>(&mut digest);
pairs.push((z, self.Rs[i]));
pairs.push((z * challenge, *key));
}
@@ -148,13 +108,22 @@ impl<C: Ciphersuite> SchnorrAggregate<C> {
/// A signature aggregator capable of consuming signatures in order to produce an aggregate.
#[allow(non_snake_case)]
#[derive(Clone, Debug, Zeroize)]
pub struct SchnorrAggregator<C: Ciphersuite> {
#[derive(Clone, Debug)]
pub struct SchnorrAggregator<C: GroupIo + WithPreferredHash> {
digest: DigestTranscript<C::H>,
sigs: Vec<SchnorrSignature<C>>,
}
impl<C: GroupIo + WithPreferredHash> Zeroize for SchnorrAggregator<C>
where
C::H: digest::block_api::BlockSizeUser,
{
fn zeroize(&mut self) {
self.digest.zeroize();
self.sigs.zeroize();
}
}
impl<C: Ciphersuite> SchnorrAggregator<C> {
impl<C: GroupIo + WithPreferredHash> SchnorrAggregator<C> {
/// Create a new aggregator.
///
/// The DST used here must prevent a collision with whatever hash function produced the
@@ -180,7 +149,7 @@ impl<C: Ciphersuite> SchnorrAggregator<C> {
let mut aggregate = SchnorrAggregate { Rs: Vec::with_capacity(self.sigs.len()), s: C::F::ZERO };
for i in 0 .. self.sigs.len() {
aggregate.Rs.push(self.sigs[i].R);
aggregate.s += self.sigs[i].s * weight::<_, C::F>(&mut self.digest);
aggregate.s += self.sigs[i].s * weight::<C>(&mut self.digest);
}
Some(aggregate)
}