elliptic-curve: consolidate CurveArithmetic trait

Consolidates the following former three traits into a single trait:

- `AffineArithmetic`
- `ProjectiveArithmetic`
- `ScalarArithmetic`

It doesn't make sense to impl one of these traits without impl'ing them
all, so this commit combines them into a single trait.

Author: tarcieri

elliptic-curve/src/arithmetic.rs

@@ -7,8 +7,8 @@ use core::fmt::Debug;
 use subtle::{ConditionallySelectable, ConstantTimeEq};
 use zeroize::DefaultIsZeroes;
 
-/// Elliptic curve with affine arithmetic implementation.
-pub trait AffineArithmetic: Curve + ScalarArithmetic {
+/// Elliptic curve with an arithmetic implementation.
+pub trait CurveArithmetic: Curve {
     /// Elliptic curve point in affine coordinates.
     type AffinePoint: 'static
         + AffineXCoordinate<Self>
@@ -23,18 +23,7 @@ pub trait AffineArithmetic: Curve + ScalarArithmetic {
         + Sized
         + Send
         + Sync;
-}
-
-/// Prime order elliptic curve with projective arithmetic implementation.
-pub trait PrimeCurveArithmetic:
-    PrimeCurve + ProjectiveArithmetic<ProjectivePoint = Self::CurveGroup>
-{
-    /// Prime order elliptic curve group.
-    type CurveGroup: group::prime::PrimeCurve<Affine = <Self as AffineArithmetic>::AffinePoint>;
-}
 
-/// Elliptic curve with projective arithmetic implementation.
-pub trait ProjectiveArithmetic: Curve + AffineArithmetic {
     /// Elliptic curve point in projective coordinates.
     ///
     /// Note: the following bounds are provided by [`group::Group`]:
@@ -55,12 +44,8 @@ pub trait ProjectiveArithmetic: Curve + AffineArithmetic {
         + LinearCombination
         + group::Curve<AffineRepr = Self::AffinePoint>
         + group::Group<Scalar = Self::Scalar>;
-}
 
-/// Scalar arithmetic.
-#[cfg(feature = "arithmetic")]
-pub trait ScalarArithmetic: Curve {
-    /// Scalar field type.
+    /// Scalar field modulo this curve's order.
     ///
     /// Note: the following bounds are provided by [`ff::Field`]:
     /// - `'static`
@@ -80,3 +65,11 @@ pub trait ScalarArithmetic: Curve {
         + ff::Field
         + ff::PrimeField<Repr = FieldBytes<Self>>;
 }
+
+/// Prime order elliptic curve with projective arithmetic implementation.
+pub trait PrimeCurveArithmetic:
+    PrimeCurve + CurveArithmetic<ProjectivePoint = Self::CurveGroup>
+{
+    /// Prime order elliptic curve group.
+    type CurveGroup: group::prime::PrimeCurve<Affine = <Self as CurveArithmetic>::AffinePoint>;
+}

elliptic-curve/src/dev.rs

@@ -12,8 +12,7 @@ use crate::{
     sec1::{CompressedPoint, FromEncodedPoint, ToEncodedPoint},
     subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption},
     zeroize::DefaultIsZeroes,
-    AffineArithmetic, AffineXCoordinate, Curve, IsHigh, PrimeCurve, ProjectiveArithmetic,
-    ScalarArithmetic,
+    AffineXCoordinate, Curve, CurveArithmetic, IsHigh, PrimeCurve,
 };
 use core::{
     iter::{Product, Sum},
@@ -73,15 +72,9 @@ impl Curve for MockCurve {
 
 impl PrimeCurve for MockCurve {}
 
-impl AffineArithmetic for MockCurve {
+impl CurveArithmetic for MockCurve {
     type AffinePoint = AffinePoint;
-}
-
-impl ProjectiveArithmetic for MockCurve {
     type ProjectivePoint = ProjectivePoint;
-}
-
-impl ScalarArithmetic for MockCurve {
     type Scalar = Scalar;
 }
 

elliptic-curve/src/ecdh.rs

@@ -27,8 +27,8 @@
 //! [SIGMA]: https://webee.technion.ac.il/~hugo/sigma-pdf.pdf
 
 use crate::{
-    AffineArithmetic, AffinePoint, AffineXCoordinate, Curve, FieldBytes, NonZeroScalar,
-    ProjectiveArithmetic, ProjectivePoint, PublicKey,
+    AffinePoint, AffineXCoordinate, Curve, CurveArithmetic, FieldBytes, NonZeroScalar,
+    ProjectivePoint, PublicKey,
 };
 use core::borrow::Borrow;
 use digest::{crypto_common::BlockSizeUser, Digest};
@@ -62,7 +62,7 @@ pub fn diffie_hellman<C>(
     public_key: impl Borrow<AffinePoint<C>>,
 ) -> SharedSecret<C>
 where
-    C: Curve + ProjectiveArithmetic,
+    C: CurveArithmetic,
 {
     let public_point = ProjectivePoint::<C>::from(*public_key.borrow());
     let secret_point = (public_point * secret_key.borrow().as_ref()).to_affine();
@@ -92,14 +92,14 @@ where
 /// takes further steps to authenticate the peers in a key exchange.
 pub struct EphemeralSecret<C>
 where
-    C: Curve + ProjectiveArithmetic,
+    C: CurveArithmetic,
 {
     scalar: NonZeroScalar<C>,
 }
 
 impl<C> EphemeralSecret<C>
 where
-    C: Curve + ProjectiveArithmetic,
+    C: CurveArithmetic,
 {
     /// Generate a cryptographically random [`EphemeralSecret`].
     pub fn random(rng: impl CryptoRng + RngCore) -> Self {
@@ -124,7 +124,7 @@ where
 
 impl<C> From<&EphemeralSecret<C>> for PublicKey<C>
 where
-    C: Curve + ProjectiveArithmetic,
+    C: CurveArithmetic,
 {
     fn from(ephemeral_secret: &EphemeralSecret<C>) -> Self {
         ephemeral_secret.public_key()
@@ -133,18 +133,18 @@ where
 
 impl<C> Zeroize for EphemeralSecret<C>
 where
-    C: Curve + ProjectiveArithmetic,
+    C: CurveArithmetic,
 {
     fn zeroize(&mut self) {
         self.scalar.zeroize()
     }
 }
 
-impl<C> ZeroizeOnDrop for EphemeralSecret<C> where C: Curve + ProjectiveArithmetic {}
+impl<C> ZeroizeOnDrop for EphemeralSecret<C> where C: CurveArithmetic {}
 
 impl<C> Drop for EphemeralSecret<C>
 where
-    C: Curve + ProjectiveArithmetic,
+    C: CurveArithmetic,
 {
     fn drop(&mut self) {
         self.zeroize();
@@ -162,7 +162,7 @@ impl<C: Curve> SharedSecret<C> {
     #[inline]
     fn new(point: AffinePoint<C>) -> Self
     where
-        C: AffineArithmetic,
+        C: CurveArithmetic,
     {
         Self {
             secret_bytes: point.x(),

elliptic-curve/src/hash2curve/group_digest.rs

@@ -1,11 +1,11 @@
 //! Traits for handling hash to curve.
 
 use super::{hash_to_field, ExpandMsg, FromOkm, MapToCurve};
-use crate::{ProjectiveArithmetic, ProjectivePoint, Result};
+use crate::{CurveArithmetic, ProjectivePoint, Result};
 use group::cofactor::CofactorGroup;
 
 /// Adds hashing arbitrary byte sequences to a valid group element
-pub trait GroupDigest: ProjectiveArithmetic
+pub trait GroupDigest: CurveArithmetic
 where
     ProjectivePoint<Self>: CofactorGroup,
 {

elliptic-curve/src/jwk.rs

@@ -26,7 +26,7 @@ use zeroize::{Zeroize, ZeroizeOnDrop};
 use crate::{
     public_key::PublicKey,
     sec1::{FromEncodedPoint, ToEncodedPoint},
-    AffinePoint, ProjectiveArithmetic,
+    AffinePoint, CurveArithmetic,
 };
 
 /// Key Type (`kty`) for elliptic curve keys.
@@ -110,7 +110,7 @@ impl JwkEcKey {
     #[cfg(feature = "arithmetic")]
     pub fn to_public_key<C>(&self) -> Result<PublicKey<C>>
     where
-        C: Curve + JwkParameters + ProjectiveArithmetic,
+        C: CurveArithmetic + JwkParameters,
         AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
         FieldSize<C>: ModulusSize,
     {
@@ -213,7 +213,7 @@ where
 #[cfg(feature = "arithmetic")]
 impl<C> From<SecretKey<C>> for JwkEcKey
 where
-    C: Curve + JwkParameters + ProjectiveArithmetic,
+    C: CurveArithmetic + JwkParameters,
     AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
     FieldSize<C>: ModulusSize,
 {
@@ -225,7 +225,7 @@ where
 #[cfg(feature = "arithmetic")]
 impl<C> From<&SecretKey<C>> for JwkEcKey
 where
-    C: Curve + JwkParameters + ProjectiveArithmetic,
+    C: CurveArithmetic + JwkParameters,
     AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
     FieldSize<C>: ModulusSize,
 {
@@ -241,7 +241,7 @@ where
 #[cfg(feature = "arithmetic")]
 impl<C> TryFrom<JwkEcKey> for PublicKey<C>
 where
-    C: Curve + JwkParameters + ProjectiveArithmetic,
+    C: CurveArithmetic + JwkParameters,
     AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
     FieldSize<C>: ModulusSize,
 {
@@ -255,7 +255,7 @@ where
 #[cfg(feature = "arithmetic")]
 impl<C> TryFrom<&JwkEcKey> for PublicKey<C>
 where
-    C: Curve + JwkParameters + ProjectiveArithmetic,
+    C: CurveArithmetic + JwkParameters,
     AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
     FieldSize<C>: ModulusSize,
 {
@@ -269,7 +269,7 @@ where
 #[cfg(feature = "arithmetic")]
 impl<C> From<PublicKey<C>> for JwkEcKey
 where
-    C: Curve + JwkParameters + ProjectiveArithmetic,
+    C: CurveArithmetic + JwkParameters,
     AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
     FieldSize<C>: ModulusSize,
 {
@@ -281,7 +281,7 @@ where
 #[cfg(feature = "arithmetic")]
 impl<C> From<&PublicKey<C>> for JwkEcKey
 where
-    C: Curve + JwkParameters + ProjectiveArithmetic,
+    C: CurveArithmetic + JwkParameters,
     AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
     FieldSize<C>: ModulusSize,
 {

elliptic-curve/src/lib.rs

@@ -104,9 +104,7 @@ pub use zeroize;
 #[cfg(feature = "arithmetic")]
 pub use {
     crate::{
-        arithmetic::{
-            AffineArithmetic, PrimeCurveArithmetic, ProjectiveArithmetic, ScalarArithmetic,
-        },
+        arithmetic::{CurveArithmetic, PrimeCurveArithmetic},
         public_key::PublicKey,
         scalar::{nonzero::NonZeroScalar, Scalar},
     },
@@ -175,12 +173,12 @@ pub type FieldBytes<C> = GenericArray<u8, FieldSize<C>>;
 /// Affine point type for a given curve with a [`ProjectiveArithmetic`]
 /// implementation.
 #[cfg(feature = "arithmetic")]
-pub type AffinePoint<C> = <C as AffineArithmetic>::AffinePoint;
+pub type AffinePoint<C> = <C as CurveArithmetic>::AffinePoint;
 
 /// Projective point type for a given curve with a [`ProjectiveArithmetic`]
 /// implementation.
 #[cfg(feature = "arithmetic")]
-pub type ProjectivePoint<C> = <C as ProjectiveArithmetic>::ProjectivePoint;
+pub type ProjectivePoint<C> = <C as CurveArithmetic>::ProjectivePoint;
 
 /// Elliptic curve parameters used by VOPRF.
 #[cfg(feature = "voprf")]