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Tweak multiexp to compile on core

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On `core`, it'll use a serial implementation of no benefit other than the fact
that when `alloc` _is_ enabled, it'll use the multi-scalar multiplication
algorithms.

`schnorr-signatures` was prior tweaked to include a shim for
`SchnorrSignature::verify` which didn't use `multiexp_vartime` yet this same
premise. Now, instead of callers writing these shims, it's within `multiexp`.
This commit is contained in:
Luke Parker
2025-09-15 22:37:59 -04:00
parent a82ccadbb0
commit 2be69b23b1
10 changed files with 161 additions and 189 deletions
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4
crypto/schnorr/Cargo.toml
View File

@@ -27,7 +27,7 @@ digest = { version = "0.11.0-rc.1", default-features = false, features = ["block
transcript = { package = "flexible-transcript", path = "../transcript", version = "^0.3.2", default-features = false, optional = true }
ciphersuite = { path = "../ciphersuite", version = "^0.4.1", default-features = false }
multiexp = { path = "../multiexp", version = "0.4", default-features = false, features = ["batch"], optional = true }
multiexp = { path = "../multiexp", version = "0.4", default-features = false }
[dev-dependencies]
hex = "0.4"
@@ -40,7 +40,7 @@ dalek-ff-group = { path = "../dalek-ff-group" }
ciphersuite = { path = "../ciphersuite" }
[features]
alloc = ["zeroize/alloc", "digest/alloc", "ciphersuite/alloc", "multiexp"]
alloc = ["zeroize/alloc", "digest/alloc", "ciphersuite/alloc", "multiexp/alloc", "multiexp/batch"]
aggregate = ["alloc", "transcript"]
std = ["alloc", "std-shims/std", "rand_core/std", "zeroize/std", "transcript?/std", "ciphersuite/std", "multiexp/std"]
default = ["std"]

10
crypto/schnorr/src/lib.rs
View File

@@ -23,8 +23,9 @@ use ciphersuite::{
},
GroupIo,
};
use multiexp::multiexp_vartime;
#[cfg(feature = "alloc")]
use multiexp::{multiexp_vartime, BatchVerifier};
use multiexp::BatchVerifier;
/// Half-aggregation from <https://eprint.iacr.org/2021/350>.
#[cfg(feature = "aggregate")]
@@ -109,12 +110,7 @@ impl<C: GroupIo> SchnorrSignature<C> {
/// different keys/messages.
#[must_use]
pub fn verify(&self, public_key: C::G, challenge: C::F) -> bool {
let statements = self.batch_statements(public_key, challenge);
#[cfg(feature = "alloc")]
let res = multiexp_vartime(&statements);
#[cfg(not(feature = "alloc"))]
let res = statements.into_iter().map(|(scalar, point)| point * scalar).sum::<C::G>();
res.is_identity().into()
multiexp_vartime(&self.batch_statements(public_key, challenge)).is_identity().into()
}
/// Queue a signature for batch verification.