ecdsa: use LinearCombination trait (#417)

Use the trait introduced in RustCrypto/traits#833 to implement ECDSA verification.
RustCrypto · Dec 4, 2021 · 8963704 · 8963704
1 parent bfb896f
commit 8963704
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Showing 4 changed files with 17 additions and 13 deletions.
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/ecdsa/Cargo.toml b/ecdsa/Cargo.toml
@@ -15,7 +15,7 @@ edition = "2021"
 rust-version = "1.56"
 
 [dependencies]
-elliptic-curve = { version = "0.11.1", default-features = false, features = ["sec1"] }
+elliptic-curve = { version = "0.11.4", default-features = false, features = ["sec1"] }
 signature = { version = ">= 1.3.1, <1.5", default-features = false, features = ["rand-preview"] }
 
 # optional dependencies

diff --git a/ecdsa/src/hazmat.rs b/ecdsa/src/hazmat.rs
@@ -16,7 +16,7 @@ use {
     core::borrow::Borrow,
     elliptic_curve::{
         group::Curve as _,
-        ops::{Invert, Reduce},
+        ops::{Invert, LinearCombination, Reduce},
         AffineArithmetic, AffineXCoordinate, Field, FieldBytes, Group, ProjectiveArithmetic,
         Scalar, ScalarArithmetic,
     },
@@ -112,7 +112,7 @@ where
 #[cfg_attr(docsrs, doc(cfg(feature = "arithmetic")))]
 pub trait VerifyPrimitive<C>: AffineXCoordinate<C> + Copy + Sized
 where
-    C: PrimeCurve + AffineArithmetic<AffinePoint = Self> + ProjectiveArithmetic,
+    C: PrimeCurve + AffineArithmetic<AffinePoint = Self> + LinearCombination + ProjectiveArithmetic,
     Scalar<C>: Reduce<C::UInt>,
     SignatureSize<C>: ArrayLength<u8>,
 {
@@ -127,10 +127,14 @@ where
         let s_inv = Option::<Scalar<C>>::from(s.invert()).ok_or_else(Error::new)?;
         let u1 = z * s_inv;
         let u2 = *r * s_inv;
-
-        let x = ((C::ProjectivePoint::generator() * u1) + (C::ProjectivePoint::from(*self) * u2))
-            .to_affine()
-            .x();
+        let x = C::lincomb(
+            &C::ProjectivePoint::generator(),
+            &u1,
+            &C::ProjectivePoint::from(*self),
+            &u2,
+        )
+        .to_affine()
+        .x();
 
         if Scalar::<C>::from_be_bytes_reduced(x) == *r {
             Ok(())

diff --git a/ecdsa/src/verify.rs b/ecdsa/src/verify.rs
@@ -7,7 +7,7 @@ use crate::{
 use core::{cmp::Ordering, fmt::Debug};
 use elliptic_curve::{
     generic_array::ArrayLength,
-    ops::Reduce,
+    ops::{LinearCombination, Reduce},
     sec1::{self, EncodedPoint, FromEncodedPoint, ToEncodedPoint},
     AffinePoint, FieldSize, PointCompression, PrimeCurve, ProjectiveArithmetic, PublicKey, Scalar,
 };
@@ -79,7 +79,7 @@ impl<C> Copy for VerifyingKey<C> where C: PrimeCurve + ProjectiveArithmetic {}
 
 impl<C, D> DigestVerifier<D, Signature<C>> for VerifyingKey<C>
 where
-    C: PrimeCurve + ProjectiveArithmetic,
+    C: PrimeCurve + ProjectiveArithmetic + LinearCombination,
     D: Digest<OutputSize = FieldSize<C>>,
     AffinePoint<C>: VerifyPrimitive<C>,
     Scalar<C>: Reduce<C::UInt>,
@@ -93,7 +93,7 @@ where
 
 impl<C> Verifier<Signature<C>> for VerifyingKey<C>
 where
-    C: PrimeCurve + ProjectiveArithmetic + DigestPrimitive,
+    C: PrimeCurve + ProjectiveArithmetic + DigestPrimitive + LinearCombination,
     C::Digest: Digest<OutputSize = FieldSize<C>>,
     AffinePoint<C>: VerifyPrimitive<C>,
     Scalar<C>: Reduce<C::UInt>,