k256/p256/p384: Elliptic Curve Diffie-Hellman

Adds type aliases for the high-level generic Elliptic Curve
Diffie-Hellman (Ephemeral) implementation introduced in
RustCrypto/traits#251.

k256/Cargo.toml

@@ -30,12 +30,13 @@ criterion = "0.3"
 default = ["arithmetic", "oid", "std"]
 arithmetic = []
 digest = ["ecdsa-core/digest"]
+ecdh = ["elliptic-curve/ecdh"]
 ecdsa = ["arithmetic", "ecdsa-core/signer", "ecdsa-core/verifier", "rand", "sha256", "zeroize"]
 endomorphism-mul = []
 field-montgomery = []
 force-32-bit = []
 oid = ["elliptic-curve/oid"]
-rand = ["elliptic-curve/rand_core"]
+rand = ["elliptic-curve/rand"]
 sha256 = ["digest", "sha2"]
 test-vectors = []
 std = ["elliptic-curve/std"]

k256/src/ecdh.rs

@@ -0,0 +1,9 @@
+//! Elliptic Curve Diffie-Hellman (Ephemeral) Support.
+
+use crate::Secp256k1;
+
+/// NIST P-256 Ephemeral Diffie-Hellman Secret.
+pub type EphemeralSecret = elliptic_curve::ecdh::EphemeralSecret<Secp256k1>;
+
+/// Shared secret value computed via ECDH key agreement.
+pub type SharedSecret = elliptic_curve::ecdh::SharedSecret<Secp256k1>;

k256/src/lib.rs

@@ -19,6 +19,10 @@ mod arithmetic;
 #[cfg(feature = "arithmetic")]
 mod mul;
 
+#[cfg(feature = "ecdh")]
+#[cfg_attr(docsrs, doc(cfg(feature = "ecdh")))]
+pub mod ecdh;
+
 #[cfg(feature = "ecdsa-core")]
 #[cfg_attr(docsrs, doc(cfg(feature = "ecdsa-core")))]
 pub mod ecdsa;
@@ -59,7 +63,10 @@ impl elliptic_curve::Curve for Secp256k1 {
     type ElementSize = U32;
 }
 
-impl elliptic_curve::weierstrass::Curve for Secp256k1 {}
+impl elliptic_curve::weierstrass::Curve for Secp256k1 {
+    /// secp256k1 points are typically compressed.
+    const COMPRESS_POINTS: bool = true;
+}
 
 #[cfg(feature = "oid")]
 impl elliptic_curve::Identifier for Secp256k1 {
@@ -72,9 +79,9 @@ pub type SecretKey = elliptic_curve::SecretKey<Secp256k1>;
 /// K-256 (secp256k1) Public Key.
 pub type PublicKey = elliptic_curve::weierstrass::PublicKey<Secp256k1>;
 
-/// K-256 Scalar Bytes.
+/// K-256 Serialized Field Element.
 ///
-/// Byte array containing a serialized scalar value (i.e. an integer)
+/// Byte array containing a serialized field element value (base field or scalar).
 pub type ElementBytes = elliptic_curve::ElementBytes<Secp256k1>;
 
 /// K-256 Compressed Curve Point.

p256/Cargo.toml

@@ -25,9 +25,10 @@ proptest = "0.10"
 [features]
 default = ["arithmetic", "std"]
 arithmetic = []
+ecdh = ["elliptic-curve/ecdh"]
 ecdsa = ["arithmetic", "ecdsa-core/signer", "ecdsa-core/verifier", "rand", "sha256", "zeroize"]
 oid = ["elliptic-curve/oid"]
-rand = ["elliptic-curve/rand_core"]
+rand = ["elliptic-curve/rand"]
 sha256 = ["ecdsa-core/digest", "ecdsa-core/hazmat", "sha2"]
 test-vectors = []
 std = ["elliptic-curve/std"]

p256/src/ecdh.rs

@@ -0,0 +1,9 @@
+//! Elliptic Curve Diffie-Hellman (Ephemeral) Support.
+
+use crate::NistP256;
+
+/// NIST P-256 Ephemeral Diffie-Hellman Secret.
+pub type EphemeralSecret = elliptic_curve::ecdh::EphemeralSecret<NistP256>;
+
+/// Shared secret value computed via ECDH key agreement.
+pub type SharedSecret = elliptic_curve::ecdh::SharedSecret<NistP256>;

p256/src/lib.rs

@@ -16,6 +16,10 @@
 #[cfg(feature = "arithmetic")]
 mod arithmetic;
 
+#[cfg(feature = "ecdh")]
+#[cfg_attr(docsrs, doc(cfg(feature = "ecdh")))]
+pub mod ecdh;
+
 #[cfg(feature = "ecdsa-core")]
 #[cfg_attr(docsrs, doc(cfg(feature = "ecdsa-core")))]
 pub mod ecdsa;
@@ -67,7 +71,10 @@ impl elliptic_curve::Curve for NistP256 {
     type ElementSize = U32;
 }
 
-impl elliptic_curve::weierstrass::Curve for NistP256 {}
+impl elliptic_curve::weierstrass::Curve for NistP256 {
+    /// NIST P-256 points are typically uncompressed.
+    const COMPRESS_POINTS: bool = false;
+}
 
 #[cfg(feature = "oid")]
 impl elliptic_curve::Identifier for NistP256 {
@@ -80,9 +87,9 @@ pub type SecretKey = elliptic_curve::SecretKey<NistP256>;
 /// NIST P-256 Public Key
 pub type PublicKey = elliptic_curve::weierstrass::PublicKey<NistP256>;
 
-/// NIST P-256 Scalar Bytes.
+/// NIST P-256 Serialized Field Element.
 ///
-/// Byte array containing a serialized scalar value (i.e. an integer)
+/// Byte array containing a serialized field element value (base field or scalar).
 pub type ElementBytes = elliptic_curve::ElementBytes<NistP256>;
 
 /// NIST P-256 Compressed Curve Point

p384/src/lib.rs

@@ -57,7 +57,9 @@ impl elliptic_curve::Identifier for NistP384 {
     const OID: ObjectIdentifier = ObjectIdentifier::new(&[1, 3, 132, 0, 34]);
 }
 
-impl elliptic_curve::weierstrass::Curve for NistP384 {}
+impl elliptic_curve::weierstrass::Curve for NistP384 {
+    const COMPRESS_POINTS: bool = false;
+}
 
 /// NIST P-384 Secret Key
 pub type SecretKey = elliptic_curve::SecretKey<NistP384>;