Updated to curve25519-dalek rc0

Cargo.toml

@@ -35,10 +35,10 @@ travis-ci = { repository = "dalek-cryptography/x25519-dalek", branch = "master"}
 features = ["nightly", "reusable_secrets", "serde"]
 
 [dependencies]
-curve25519-dalek = { version = "4.0.0-pre.2", default-features = false }
+curve25519-dalek = { version = "4.0.0-rc.0", default-features = false }
 rand_core = { version = "0.6", default-features = false, features = ["getrandom"] }
 serde = { version = "1", default-features = false, optional = true, features = ["derive"] }
-zeroize = { version = "1", default-features = false, features = ["zeroize_derive"] }
+zeroize = { version = "1", default-features = false, optional = true, features = ["zeroize_derive"] }
 
 [dev-dependencies]
 bincode = "1"
@@ -49,11 +49,9 @@ name = "x25519"
 harness = false
 
 [features]
-default = ["alloc"]
+default = ["alloc", "precomputed-tables", "zeroize"]
+zeroize = ["dep:zeroize", "curve25519-dalek/zeroize"]
 serde = ["dep:serde", "curve25519-dalek/serde"]
-alloc = ["curve25519-dalek/alloc", "serde?/alloc"]
+alloc = ["curve25519-dalek/alloc", "serde?/alloc", "zeroize?/alloc"]
+precomputed-tables = ["curve25519-dalek/precomputed-tables"]
 reusable_secrets = []
-
-
-[patch.crates-io]
-curve25519-dalek = { git = "https://github.com/dalek-cryptography/curve25519-dalek", branch = "release/4.0" }

src/x25519.rs

@@ -14,14 +14,14 @@
 //! This implements x25519 key exchange as specified by Mike Hamburg
 //! and Adam Langley in [RFC7748](https://tools.ietf.org/html/rfc7748).
 
-use curve25519_dalek::constants::ED25519_BASEPOINT_TABLE;
+use curve25519_dalek::{
-use curve25519_dalek::montgomery::MontgomeryPoint;
+    edwards::EdwardsPoint, montgomery::MontgomeryPoint, scalar::Scalar, traits::IsIdentity,
-use curve25519_dalek::scalar::Scalar;
+};
-use curve25519_dalek::traits::IsIdentity;
 
 use rand_core::CryptoRng;
 use rand_core::RngCore;
 
+#[cfg(feature = "zeroize")]
 use zeroize::Zeroize;
 
 /// A Diffie-Hellman public key, corresponding to an [`EphemeralSecret`] or
@@ -32,7 +32,8 @@ use zeroize::Zeroize;
 /// (in this crate) does *not* automatically happen, but either must be derived
 /// for Drop or explicitly called.
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug, Zeroize)]
+#[cfg_attr(feature = "zeroize", derive(Zeroize))]
+#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
 pub struct PublicKey(pub(crate) MontgomeryPoint);
 
 impl From<[u8; 32]> for PublicKey {
@@ -64,8 +65,8 @@ impl PublicKey {
 /// are no serialization methods defined.  This means that [`EphemeralSecret`]s can only be
 /// generated from fresh randomness by [`EphemeralSecret::new`] and the compiler statically checks
 /// that the resulting secret is used at most once.
-#[derive(Zeroize)]
+#[cfg_attr(feature = "zeroize", derive(Zeroize))]
-#[zeroize(drop)]
+#[cfg_attr(feature = "zeroize", zeroize(drop))]
 pub struct EphemeralSecret(pub(crate) Scalar);
 
 impl EphemeralSecret {
@@ -81,14 +82,14 @@ impl EphemeralSecret {
 
         csprng.fill_bytes(&mut bytes);
 
-        EphemeralSecret(clamp_scalar(bytes))
+        EphemeralSecret(Scalar::from_bits_clamped(bytes))
     }
 }
 
 impl<'a> From<&'a EphemeralSecret> for PublicKey {
     /// Given an x25519 [`EphemeralSecret`] key, compute its corresponding [`PublicKey`].
     fn from(secret: &'a EphemeralSecret) -> PublicKey {
-        PublicKey((&ED25519_BASEPOINT_TABLE * &secret.0).to_montgomery())
+        PublicKey(EdwardsPoint::mul_base(&secret.0).to_montgomery())
     }
 }
 
@@ -111,8 +112,9 @@ impl<'a> From<&'a EphemeralSecret> for PublicKey {
 /// secret keys are never reused, which can have very serious security
 /// implications for many protocols.
 #[cfg(feature = "reusable_secrets")]
-#[derive(Clone, Zeroize)]
+#[cfg_attr(feature = "zeroize", derive(Zeroize))]
-#[zeroize(drop)]
+#[cfg_attr(feature = "zeroize", zeroize(drop))]
+#[derive(Clone)]
 pub struct ReusableSecret(pub(crate) Scalar);
 
 #[cfg(feature = "reusable_secrets")]
@@ -129,7 +131,7 @@ impl ReusableSecret {
 
         csprng.fill_bytes(&mut bytes);
 
-        ReusableSecret(clamp_scalar(bytes))
+        ReusableSecret(Scalar::from_bits_clamped(bytes))
     }
 }
 
@@ -137,7 +139,7 @@ impl ReusableSecret {
 impl<'a> From<&'a ReusableSecret> for PublicKey {
     /// Given an x25519 [`ReusableSecret`] key, compute its corresponding [`PublicKey`].
     fn from(secret: &'a ReusableSecret) -> PublicKey {
-        PublicKey((&ED25519_BASEPOINT_TABLE * &secret.0).to_montgomery())
+        PublicKey(EdwardsPoint::mul_base(&secret.0).to_montgomery())
     }
 }
 
@@ -156,8 +158,9 @@ impl<'a> From<&'a ReusableSecret> for PublicKey {
 /// secret keys are never reused, which can have very serious security
 /// implications for many protocols.
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-#[derive(Clone, Zeroize)]
+#[cfg_attr(feature = "zeroize", derive(Zeroize))]
-#[zeroize(drop)]
+#[cfg_attr(feature = "zeroize", zeroize(drop))]
+#[derive(Clone)]
 pub struct StaticSecret(
     #[cfg_attr(feature = "serde", serde(with = "AllowUnreducedScalarBytes"))] pub(crate) Scalar,
 );
@@ -175,7 +178,7 @@ impl StaticSecret {
 
         csprng.fill_bytes(&mut bytes);
 
-        StaticSecret(clamp_scalar(bytes))
+        StaticSecret(Scalar::from_bits_clamped(bytes))
     }
 
     /// Extract this key's bytes for serialization.
@@ -187,14 +190,14 @@ impl StaticSecret {
 impl From<[u8; 32]> for StaticSecret {
     /// Load a secret key from a byte array.
     fn from(bytes: [u8; 32]) -> StaticSecret {
-        StaticSecret(clamp_scalar(bytes))
+        StaticSecret(Scalar::from_bits_clamped(bytes))
     }
 }
 
 impl<'a> From<&'a StaticSecret> for PublicKey {
     /// Given an x25519 [`StaticSecret`] key, compute its corresponding [`PublicKey`].
     fn from(secret: &'a StaticSecret) -> PublicKey {
-        PublicKey((&ED25519_BASEPOINT_TABLE * &secret.0).to_montgomery())
+        PublicKey(EdwardsPoint::mul_base(&secret.0).to_montgomery())
     }
 }
 
@@ -202,8 +205,8 @@ impl<'a> From<&'a StaticSecret> for PublicKey {
 ///
 /// Each party computes this using their [`EphemeralSecret`] or [`StaticSecret`] and their
 /// counterparty's [`PublicKey`].
-#[derive(Zeroize)]
+#[cfg_attr(feature = "zeroize", derive(Zeroize))]
-#[zeroize(drop)]
+#[cfg_attr(feature = "zeroize", zeroize(drop))]
 pub struct SharedSecret(pub(crate) MontgomeryPoint);
 
 impl SharedSecret {
@@ -258,22 +261,6 @@ impl SharedSecret {
     }
 }
 
-/// "Decode" a scalar from a 32-byte array.
-///
-/// By "decode" here, what is really meant is applying key clamping by twiddling
-/// some bits.
-///
-/// # Returns
-///
-/// A `Scalar`.
-fn clamp_scalar(mut scalar: [u8; 32]) -> Scalar {
-    scalar[0] &= 248;
-    scalar[31] &= 127;
-    scalar[31] |= 64;
-
-    Scalar::from_bits(scalar)
-}
-
 /// The bare, byte-oriented x25519 function, exactly as specified in RFC7748.
 ///
 /// This can be used with [`X25519_BASEPOINT_BYTES`] for people who
@@ -305,7 +292,7 @@ fn clamp_scalar(mut scalar: [u8; 32]) -> Scalar {
 /// assert_eq!(alice_shared, bob_shared);
 /// ```
 pub fn x25519(k: [u8; 32], u: [u8; 32]) -> [u8; 32] {
-    (clamp_scalar(k) * MontgomeryPoint(u)).to_bytes()
+    (Scalar::from_bits_clamped(k) * MontgomeryPoint(u)).to_bytes()
 }
 
 /// The X25519 basepoint, for use with the bare, byte-oriented x25519
@@ -325,6 +312,6 @@ struct AllowUnreducedScalarBytes(
 );
 impl From<AllowUnreducedScalarBytes> for Scalar {
     fn from(bytes: AllowUnreducedScalarBytes) -> Scalar {
-        clamp_scalar(bytes.0)
+        Scalar::from_bits_clamped(bytes.0)
     }
 }

tests/x25519_tests.rs

@@ -1,16 +1,7 @@
-use curve25519_dalek::constants::ED25519_BASEPOINT_TABLE;
+use curve25519_dalek::{edwards::EdwardsPoint, scalar::Scalar};
-use curve25519_dalek::scalar::Scalar;
 
 use x25519_dalek::*;
 
-fn clamp_scalar(mut scalar: [u8; 32]) -> Scalar {
-    scalar[0] &= 248;
-    scalar[31] &= 127;
-    scalar[31] |= 64;
-
-    Scalar::from_bits(scalar)
-}
-
 #[test]
 fn byte_basepoint_matches_edwards_scalar_mul() {
     let mut scalar_bytes = [0x37; 32];
@@ -20,9 +11,10 @@ fn byte_basepoint_matches_edwards_scalar_mul() {
 
         let result = x25519(scalar_bytes, X25519_BASEPOINT_BYTES);
 
-        let expected = (&ED25519_BASEPOINT_TABLE * &clamp_scalar(scalar_bytes))
+        let expected = {
-            .to_montgomery()
+            let scalar = Scalar::from_bits_clamped(scalar_bytes);
-            .to_bytes();
+            EdwardsPoint::mul_base(&scalar).to_montgomery().to_bytes()
+        };
 
         assert_eq!(result, expected);
     }
@@ -72,7 +64,7 @@ fn serde_bincode_static_secret_matches_from_bytes() {
     use bincode;
 
     let expected = StaticSecret::from([0x24; 32]);
-    let clamped_bytes = clamp_scalar([0x24; 32]).to_bytes();
+    let clamped_bytes = Scalar::from_bits_clamped([0x24; 32]).to_bytes();
     let decoded: StaticSecret = bincode::deserialize(&clamped_bytes).unwrap();
 
     assert_eq!(decoded.to_bytes(), expected.to_bytes());