elliptic-curve: add MulByGeneratorVartime trait#2381
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tarcieri merged 1 commit intoApr 11, 2026
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Closes #2375 We now have variable-time precomputed basepoint tables that use wNAF when the `basepoint-table` and `alloc` features are enabled, which can be opportunistically used when these features are enabled to accelerate this operation. We use `Group::mul_by_generator` for the constant-time basepoint tables, however for an extension trait this is captured as `MulByGeneratorVartime::mul_by_generator_vartime`. As discussed in the above issue, and inspired by `curve25519-dalek`'s `EdwardsPoint::vartime_double_scalar_mul_basepoint` function, this adds `MulByGeneratorVartime::mul_by_generator_and_mul_add_point_vartime` as a provided method. This function is the core of many signature algorithms, and when the basepoint tables and alloc are unavailable it can fall back to a linear combination and still provide better performance than the naive constant time version.
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Implements the trait introduced in RustCrypto/traits#2381 which makes it possible to provide optimized implementations of multiplication by the generator. Currently this just naively calls `mul_vartime` on `ProjectivePoint::GENERATOR`, which still provides some optimization when the `alloc` feature is enabled: scalar operations/generator-scalar mul time: [122.08 µs 122.48 µs 122.97 µs] scalar operations/generator-scalar mul (variable-time) time: [105.83 µs 107.98 µs 111.45 µs] When `alloc` isn't available, it uses linear combinations to implement computing `aG * bB`, which should still provide a speedup in that case.
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Implements the trait introduced in RustCrypto/traits#2381 which makes it possible to provide optimized implementations of multiplication by the generator. Currently this just naively calls `mul_vartime` on `ProjectivePoint::GENERATOR`, which still provides some optimization when the `alloc` feature is enabled: scalar operations/generator-scalar mul time: [122.08 µs 122.48 µs 122.97 µs] scalar operations/generator-scalar mul (variable-time) time: [105.83 µs 107.98 µs 111.45 µs] When `alloc` isn't available, it uses linear combinations to implement computing `aG * bB`, which should still provide a speedup in that case.
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Like #1726 did for `primeorder`, this impls this new trait which was introduced in RustCrypto/traits#2381. Since `group::Wnaf` winds up being slower since it doesn't support the endomorphism optimization, this just calls into the constant-time operation.
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Like #1726 did for `primeorder`, this impls this new trait which was introduced in RustCrypto/traits#2381. Since `group::Wnaf` winds up being slower since it doesn't support the endomorphism optimization, this just calls into the constant-time operation.
tarcieri
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Apr 15, 2026
Like #1726 did for `primeorder` and #1728 did for `k256`, this impls this new trait which was introduced in RustCrypto/traits#2381. We don't actually have vartime support in this crate, so this just falls back to the constant-time implementation.
tarcieri
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Apr 15, 2026
Like #1726 did for `primeorder` and #1728 did for `k256`, this impls this new trait which was introduced in RustCrypto/traits#2381. We don't actually have vartime support in this crate, so this just falls back to the constant-time implementation.
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## Added - Implement `PartialEq + Eq` for `NonIdentity` and `NonZeroScalar` (#1834) - Implement `Zeroize` for `NonIdentity` (#1832) - `NonIdentity::mul_by_generator()` (#1833) - Implement `Mul<&NonZeroScalar>` for `NonIdentity` (#1852) - Implement `Mul<NonIdentity>` for `NonZeroScalar` (#1855) - Expose `AffineCoordinates::y` (#1891) - Scalar macros originall from `primeorder` (#1894) - Implement `BatchNormalize` for `NonIdentity` (#1896) - Re-export `group::Curve` as `CurveGroup` (#1902) - `NonIdentity`/`NonZeroScalar` casting methods (#1903) - `AffineCoordinates::from_coordinates` (#1996) - `getrandom` feature (#2085) - `ctutils` traits to `arithmetic` bounds (#2166) - `Retrieve` bound for `C::Scalar` (#2169) - `crypto_common::Generate` support (#2173, #2208) - Implement `crypto_common::TryKeyInit` for `SecretKey<C>` (#2174) - `dev::bench_projective!` macro (#2177) - Provide `Sec1Point::from/to_sec1_bytes` (#2221) - Implement `From<SecretKey<C>>` for `PublicKey<C>` (#2247) - `SecretKey::diffie_hellman` (#2248) - `LinearCombination::lincomb_vartime` method (#2286) - `ops::MulVartime` trait and bound `Scalar` (#2379) - `ops::MulByGeneratorVartime` trait ([#2381]) - `SecretKey::from_pem` (#2387) - `SecretKey::from_der` (#2408) - `hazmat` module with `FieldArithmetic` trait (#2458) - `Double::double_in_place` (#2464) ## Changed - Migrate from `generic-array` to `hybrid-array` (#1462) - Rename `LinearCombinationExt` => `LinearCombination`; replacing old trait (#1501) - Edition changed to 2024 and MSRV bumped to 1.85 (#1759) - Make `SecretKey::new` fallible (#1804) - Replace `ops::Invert` trait with `crypto_bigint::Invert` (#1839) - Rename `SecretKey::new` => `::from_scalar` (#1893) - Replace `Reduce` trait with `crypto_bigint::Reduce` (#1949) - Bump `serdect` dependency to v0.4 (#1978) - Use `crypto_bigint::Odd` to represent `Curve::ORDER` (#2006) - Bound `Curve::Uint` on `Unsigned` (#2007) - Rename `ScalarPrimitive` => `ScalarValue` (#2008) - Accept mixed-case hex-encoded strings in `FromStr` impl for `ScalarValue` (#2037) - Deprecate `SecretKey::random` (#2086) - Move `MockCurve` to `dev::mock_curve` (#2176) - Bump `rand_core` to v0.10 (#2250) - Rename `EncodedPoint` => `Sec1Point` (#2264) - Bump `crypto-bigint` to v0.7 (#2330) - Bump `digest` to v0.11 (#2331) - Bump `sec1` to v0.8 (#2339) - Bump `hkdf` dependency to v0.13 (#2349) - Use `*Vartime` as a suffix in names (#2378) - Bump `pkcs8` to v0.11 (#2397) - Bump `ff` and `group` to v0.14 (#2430, #2431) - Simplify `BatchInvert` trait (#2455) - Replace `FieldBytesEncoding` trait with `C::FIELD_ENDIANNESS` (#2457) - Move `Double` to `ops` module (#2465) ## Removed - `hazmat` feature (#1599) - `hash2curve` and `oprf` modules: moved to same-name crates (#1929) - PKCS#8 blanket impls for SEC1 private key traits (#1930) - `ShrAssign` bound on `Scalar`s (#1938) - JWK support: migrated to `jose-jwk` crate (#1963) - `weierstrass` module (#2005) - `bits` feature (#2417) ## Fixed - Include curve OID in SEC1 private keys (#1707, #1933)
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Closes #2375
We now have variable-time precomputed basepoint tables that use wNAF when the
basepoint-tableandallocfeatures are enabled, which can be opportunistically used when these features are enabled to accelerate this operation.We use
Group::mul_by_generatorfor the constant-time basepoint tables, however for an extension trait this is captured asMulByGeneratorVartime::mul_by_generator_vartime.As discussed in the above issue, and inspired by
curve25519-dalek'sEdwardsPoint::vartime_double_scalar_mul_basepointfunction, this addsMulByGeneratorVartime::mul_by_generator_and_mul_add_point_vartimeas a provided method. This function is the core of many signature algorithms, and when the basepoint tables and alloc are unavailable it can fall back to a linear combination and still provide better performance than the naive constant time version.