move implementation of x25519 into diffie_hellman

README.md

@@ -57,13 +57,13 @@ shared secret with Bob by doing:
 use x25519_dalek::EphemeralPublic;
 use x25519_dalek::EphemeralSecret;
 
-let shared_secret = EphemeralSecret::diffie_hellman(&alice_secret, &bob_public);
+let shared_secret = EphemeralSecret::diffie_hellman(alice_secret, &bob_public);
 ```
 
 Similarly, Bob computes the same shared secret by doing:
 
 ```rust
-let shared_secret = EphemeralSecret::diffie_hellman(&bob_secret, &alice_public);
+let shared_secret = EphemeralSecret::diffie_hellman(bob_secret, &alice_public);
 ```
 
 Voilá!  Alice and Bob can now use their shared secret to encrypt their

benches/x25519.rs

@@ -26,13 +26,14 @@ use x25519_dalek::EphemeralSecret;
 
 fn bench_diffie_hellman(c: &mut Criterion) {
     let mut csprng: OsRng = OsRng::new().unwrap();
-    let alice_secret: EphemeralSecret = EphemeralSecret::new(&mut csprng);
     let bob_secret: EphemeralSecret = EphemeralSecret::new(&mut csprng);
     let bob_public: EphemeralPublic = EphemeralPublic::from(&bob_secret);
 
     c.bench_function("diffie_hellman", move |b| {
-        b.iter(||
-               EphemeralSecret::diffie_hellman(&alice_secret, &bob_public)
+        let alice_secret: EphemeralSecret = EphemeralSecret::new(&mut csprng);
+        b.iter_with_setup(
+            || EphemeralSecret::new(&mut csprng),
+            |alice_secret| EphemeralSecret::diffie_hellman(alice_secret, &bob_public),
         )
     });
 }

src/lib.rs

@@ -89,7 +89,7 @@
 //! # let     bob_public = EphemeralPublic::from(&bob_secret);
 //! #
 //! #
-//! let shared_secret = EphemeralSecret::diffie_hellman(&alice_secret, &bob_public);
+//! let shared_secret = EphemeralSecret::diffie_hellman(alice_secret, &bob_public);
 //! # }
 //! ```
 //!
@@ -112,7 +112,7 @@
 //! # let     bob_secret = EphemeralSecret::new(&mut bob_csprng);
 //! # let     bob_public = EphemeralPublic::from(&bob_secret);
 //! #
-//! let shared_secret = EphemeralSecret::diffie_hellman(&bob_secret, &alice_public);
+//! let shared_secret = EphemeralSecret::diffie_hellman(bob_secret, &alice_public);
 //! # }
 //! ```
 //!

src/x25519.rs

@@ -38,11 +38,13 @@ impl Drop for EphemeralSecret {
 }
 
 impl EphemeralSecret {
-    /// Utility function to make it easier to call `x25519()` with
-    /// an ephemeral secret key and montegomery point as input and
-    /// a shared secret as the output.
-    pub fn diffie_hellman(&self, their_public: &EphemeralPublic) -> SharedSecret {
-        SharedSecret(x25519(&self.0, &MontgomeryPoint(*their_public.0.as_bytes())))
+    /// The diffie_hellman function performs scalar multipication on a montegomery point.
+    /// This is the implementation for the x25519 function, as specified in RFC7748.
+    pub fn diffie_hellman(self, their_public: &EphemeralPublic) -> SharedSecret {
+        let k: Scalar = clamp_scalar(self.0.as_bytes());
+        let point: MontgomeryPoint = MontgomeryPoint(*their_public.0.as_bytes());
+
+        SharedSecret(k * point)
     }
 
     /// Generate an x25519 `EphemeralSecret` key.
@@ -105,13 +107,6 @@ fn clamp_scalar(scalar: &[u8; 32]) -> Scalar {
     Scalar::from_bits(s)
 }
 
-/// The x25519 function, as specified in RFC7748.
-fn x25519(scalar: &Scalar, point: &MontgomeryPoint) -> MontgomeryPoint {
-    let k: Scalar = clamp_scalar(scalar.as_bytes());
-
-    (k * point)
-}
-
 #[cfg(test)]
 mod test {
     use super::*;
@@ -119,9 +114,9 @@ mod test {
     fn do_rfc7748_ladder_test1(input_scalar: &Scalar,
                                input_point: &MontgomeryPoint,
                                expected: &[u8; 32]) {
-        let result = x25519(&input_scalar, &input_point);
+        let result = EphemeralSecret::diffie_hellman(EphemeralSecret(*input_scalar), &EphemeralPublic(*input_point));
 
-        assert_eq!(result.0, *expected);
+        assert_eq!(result.0, MontgomeryPoint(*expected));
     }
 
     #[test]
@@ -173,12 +168,12 @@ mod test {
 
         let mut k: Scalar = Scalar::from_bits(X25519_BASEPOINT.0);
         let mut u: MontgomeryPoint = X25519_BASEPOINT;
-        let mut result: MontgomeryPoint;
+        let mut result: SharedSecret;
 
         macro_rules! do_iterations {
             ($n:expr) => (
                 for _ in 0..$n {
-                    result = x25519(&k, &u);
+                    result = EphemeralSecret::diffie_hellman(EphemeralSecret(k), &EphemeralPublic(u));
                     // OBVIOUS THING THAT I'M GOING TO NOTE ANYWAY BECAUSE I'VE
                     // SEEN PEOPLE DO THIS WITH GOLANG'S STDLIB AND YOU SURE AS
                     // HELL SHOULDN'T DO HORRIBLY STUPID THINGS LIKE THIS WITH
@@ -188,7 +183,7 @@ mod test {
                     //
                     //                ↓↓ DON'T DO THIS ↓↓
                     u = MontgomeryPoint(k.as_bytes().clone());
-                    k = Scalar::from_bits(result.to_bytes());
+                    k = Scalar::from_bits(result.0.to_bytes());
                 }
             )
         }