elliptic-curve: add encoding module

elliptic-curve/src/encoding.rs

@@ -0,0 +1,23 @@
+//! Traits for decoding/encoding elliptic curve elements (i.e. base and scalar
+//! field elements) as bytes.
+
+use generic_array::{ArrayLength, GenericArray};
+use subtle::{ConditionallySelectable, CtOption};
+
+/// Try to decode the given bytes into a curve element
+pub trait FromBytes: ConditionallySelectable + Sized {
+    /// Size of the serialized byte array
+    type Size: ArrayLength<u8>;
+
+    /// Try to decode this object from bytes
+    fn from_bytes(bytes: &GenericArray<u8, Self::Size>) -> CtOption<Self>;
+}
+
+/// Encode this curve element as bytes
+pub trait ToBytes {
+    /// Size of the serialized byte array
+    type Size: ArrayLength<u8>;
+
+    /// Encode this object to bytes
+    fn to_bytes(&self) -> GenericArray<u8, Self::Size>;
+}

elliptic-curve/src/lib.rs

@@ -21,6 +21,7 @@
 #[cfg(feature = "std")]
 extern crate std;
 
+pub mod encoding;
 pub mod error;
 pub mod ops;
 pub mod point;
@@ -77,7 +78,7 @@ pub trait Arithmetic: Curve {
     type Scalar: ConditionallySelectable
         + ConstantTimeEq
         + Default
-        + secret_key::FromSecretKey<Self>;
+        + encoding::FromBytes<Size = Self::ElementSize>;
 
     /// Affine point type for a given curve
     type AffinePoint: ConditionallySelectable + Mul<scalar::NonZeroScalar<Self>> + point::Generator;

elliptic-curve/src/secret_key.rs

@@ -13,7 +13,6 @@ use core::{
     fmt::{self, Debug},
 };
 use generic_array::{typenum::Unsigned, GenericArray};
-use subtle::CtOption;
 
 #[cfg(feature = "rand_core")]
 use {
@@ -91,11 +90,3 @@ impl<C: Curve> Drop for SecretKey<C> {
         self.scalar.zeroize();
     }
 }
-
-/// Trait for deserializing a value from a secret key.
-///
-/// This is intended for use with the `Scalar` type for a given elliptic curve.
-pub trait FromSecretKey<C: Curve>: Sized {
-    /// Deserialize this value from a [`SecretKey`]
-    fn from_secret_key(secret_key: &SecretKey<C>) -> CtOption<Self>;
-}

elliptic-curve/src/weierstrass.rs

@@ -5,7 +5,7 @@ pub mod public_key;
 
 pub use self::{
     point::{CompressedPoint, CompressedPointSize, UncompressedPoint, UncompressedPointSize},
-    public_key::{FromPublicKey, PublicKey},
+    public_key::PublicKey,
 };
 
 /// Marker trait for elliptic curves in short Weierstrass form

elliptic-curve/src/weierstrass/public_key.rs

@@ -6,8 +6,7 @@ use super::{
     Curve,
 };
 use crate::{
-    point::Generator, scalar::NonZeroScalar, secret_key::FromSecretKey, Arithmetic, Error,
-    SecretKey,
+    encoding::FromBytes, point::Generator, scalar::NonZeroScalar, Arithmetic, Error, SecretKey,
 };
 use core::{
     fmt::{self, Debug},
@@ -17,7 +16,6 @@ use generic_array::{
     typenum::{Unsigned, U1},
     ArrayLength, GenericArray,
 };
-use subtle::CtOption;
 
 /// Size of an untagged point for given elliptic curve.
 pub type UntaggedPointSize<C> = <<C as crate::Curve>::ElementSize as Add>::Output;
@@ -133,7 +131,7 @@ where
     ///
     /// The `compress` flag requests point compression.
     pub fn from_secret_key(secret_key: &SecretKey<C>, compress: bool) -> Result<Self, Error> {
-        let ct_option = C::Scalar::from_secret_key(&secret_key).and_then(NonZeroScalar::new);
+        let ct_option = C::Scalar::from_bytes(secret_key.as_bytes()).and_then(NonZeroScalar::new);
 
         if ct_option.is_none().into() {
             return Err(Error);
@@ -208,21 +206,3 @@ where
         PublicKey::Uncompressed(point)
     }
 }
-
-/// Trait for deserializing a value from a public key.
-///
-/// This is intended for use with the `AffinePoint` type for a given elliptic curve.
-pub trait FromPublicKey<C: Curve>: Sized
-where
-    C::ElementSize: Add<U1>,
-    <C::ElementSize as Add>::Output: Add<U1>,
-    CompressedPointSize<C>: ArrayLength<u8>,
-    UncompressedPointSize<C>: ArrayLength<u8>,
-{
-    /// Deserialize this value from a [`PublicKey`]
-    ///
-    /// # Returns
-    ///
-    /// `None` if the public key is not on the curve.
-    fn from_public_key(public_key: &PublicKey<C>) -> CtOption<Self>;
-}