From 8963704ae413aca54012debe0c24243c579b8b6e Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sat, 4 Dec 2021 10:27:37 -0700
Subject: [PATCH] ecdsa: use `LinearCombination` trait (#417)

Use the trait introduced in RustCrypto/traits#833 to implement ECDSA
verification.
---
 Cargo.lock          |  6 +++---
 ecdsa/Cargo.toml    |  2 +-
 ecdsa/src/hazmat.rs | 16 ++++++++++------
 ecdsa/src/verify.rs |  6 +++---
 4 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 243da467..54b6b4ac 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -161,7 +161,7 @@ name = "ecdsa"
 version = "0.13.1"
 dependencies = [
  "der 0.5.1",
- "elliptic-curve 0.11.3",
+ "elliptic-curve 0.11.4",
  "hex-literal",
  "rfc6979",
  "sha2",
@@ -221,9 +221,9 @@ dependencies = [
 
 [[package]]
 name = "elliptic-curve"
-version = "0.11.3"
+version = "0.11.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4c4c31bb557a73d165c838b614521f888112f9d4fcff7421d35646376dd17caf"
+checksum = "d9be7b065e66163fd97787a4cadc56625f948e22e914a0deab1d22b1f48fde25"
 dependencies = [
  "crypto-bigint 0.3.2",
  "der 0.5.1",
diff --git a/ecdsa/Cargo.toml b/ecdsa/Cargo.toml
index ba0eb78b..2e40988c 100644
--- 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
index 95801bd7..2db9b5a7 100644
--- 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
index fd05b9ef..16c67915 100644
--- 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>,