Implement partial equality for key types (#102)

* Implement parital equality for key types

Signed-off-by: Justin Abrahms <justin@abrah.ms>

* use subtle for PartialEq impl for SigningKey

* fix no_std

---------

Signed-off-by: Justin Abrahms <justin@abrah.ms>
Co-authored-by: Justin Abrahms <justin@abrah.ms>

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 Entries are listed in reverse chronological order.
 
+# 4.0.4 (Unreleased)
+
+* Implement `PartialEq` and `Eq` in `SigningKey` and `VerificationKey`.
+
 # 4.0.3
 
 * Update `curve25519-dalek` to `4.1.0`

Cargo.toml

@@ -27,6 +27,7 @@ pkcs8 = { version = "0.10.1", optional = true, features = ["alloc", "pem"] }
 rand_core = "0.6"
 serde = { version = "1", default-features = false, optional = true, features = ["derive"] }
 sha2 = { version = "0.10", default-features = false }
+subtle = { version = "2.5.0", default-features = false }
 zeroize = { version = "1.5", features = [ "zeroize_derive" ] }
 
 [dev-dependencies]
@@ -43,7 +44,7 @@ default = ["serde", "std"]
 pem = ["der", "ed25519/pem"]
 pkcs8 = ["dep:pkcs8"]
 serde = ["dep:serde", "ed25519/serde"]
-std = ["ed25519/std"]
+std = ["ed25519/std", "subtle/std"]
 
 [[test]]
 name = "rfc8032"

src/signing_key.rs

@@ -13,6 +13,7 @@ use core::convert::TryInto;
 use curve25519_dalek::{constants, digest::Update, scalar::Scalar};
 use rand_core::{CryptoRng, RngCore};
 use sha2::{Digest, Sha512};
+use subtle::ConstantTimeEq;
 use zeroize::Zeroize;
 
 pub use ed25519::{
@@ -137,6 +138,20 @@ impl From<[u8; 32]> for SigningKey {
     }
 }
 
+impl ConstantTimeEq for SigningKey {
+    fn ct_eq(&self, other: &Self) -> subtle::Choice {
+        self.seed.ct_eq(&other.seed)
+    }
+}
+
+impl PartialEq for SigningKey {
+    fn eq(&self, other: &Self) -> bool {
+        self.ct_eq(other).into()
+    }
+}
+
+impl Eq for SigningKey {}
+
 #[cfg(feature = "pkcs8")]
 impl<'a> TryFrom<PrivateKeyInfo<'a>> for SigningKey {
     type Error = Error;

src/verification_key.rs

@@ -113,7 +113,7 @@ impl<'a> TryFrom<SubjectPublicKeyInfoRef<'a>> for VerificationKeyBytes {
 ///   Curve25519, and non-canonical encodings MUST be accepted;
 ///
 /// [ps]: https://zips.z.cash/protocol/protocol.pdf#concreteed25519
-#[derive(Copy, Clone, Debug)]
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(feature = "serde", serde(try_from = "VerificationKeyBytes"))]
 #[cfg_attr(feature = "serde", serde(into = "VerificationKeyBytes"))]

tests/unit_tests.rs

@@ -11,31 +11,28 @@ fn parsing() {
     let pkb = VerificationKeyBytes::from(&sk);
     let sig = sk.sign(b"test");
 
-    // Most of these types don't implement Eq, so we check a round trip
-    // conversion to bytes, using these as the reference points:
-
     let sk_array: [u8; 32] = sk.into();
     let pk_array: [u8; 32] = pk.into();
     let pkb_array: [u8; 32] = pkb.into();
     let sig_array: [u8; 64] = sig.into();
 
-    let sk2 = SigningKey::try_from(sk.as_ref()).unwrap();
-    let pk2 = VerificationKey::try_from(pk.as_ref()).unwrap();
-    let pkb2 = VerificationKeyBytes::try_from(pkb.as_ref()).unwrap();
-    let sig2 = Signature::try_from(<[u8; 64]>::from(sig).as_ref()).unwrap();
+    let sk2 = SigningKey::try_from(sk_array).unwrap();
+    let pk2 = VerificationKey::try_from(pk_array).unwrap();
+    let pkb2 = VerificationKeyBytes::try_from(pkb_array).unwrap();
+    let sig2 = Signature::try_from(sig_array).unwrap();
 
-    assert_eq!(&sk_array[..], sk2.as_ref());
-    assert_eq!(&pk_array[..], pk2.as_ref());
-    assert_eq!(&pkb_array[..], pkb2.as_ref());
-    assert_eq!(&sig_array[..], <[u8; 64]>::from(sig2).as_ref());
+    assert_eq!(sk, sk2);
+    assert_eq!(pk, pk2);
+    assert_eq!(pkb, pkb2);
+    assert_eq!(sig, sig2);
 
     let sk3: SigningKey = bincode::deserialize(sk.as_ref()).unwrap();
     let pk3: VerificationKey = bincode::deserialize(pk.as_ref()).unwrap();
     let pkb3: VerificationKeyBytes = bincode::deserialize(pkb.as_ref()).unwrap();
 
-    assert_eq!(&sk_array[..], sk3.as_ref());
-    assert_eq!(&pk_array[..], pk3.as_ref());
-    assert_eq!(&pkb_array[..], pkb3.as_ref());
+    assert_eq!(sk, sk3);
+    assert_eq!(pk, pk3);
+    assert_eq!(pkb, pkb3);
 }
 
 #[test]