Merge pull request #249 from zcash/241-spendingkey-ct_eq

Replace `PartialEq, PartialOrd` with `ConstantTimeEq` on `{Extended}SpendingKey`

src/keys.rs

@@ -32,9 +32,15 @@ const ZIP32_PURPOSE: u32 = 32;
 /// Defined in [Zcash Protocol Spec § 4.2.3: Orchard Key Components][orchardkeycomponents].
 ///
 /// [orchardkeycomponents]: https://zips.z.cash/protocol/nu5.pdf#orchardkeycomponents
-#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Debug, Copy, Clone)]
 pub struct SpendingKey([u8; 32]);
 
+impl ConstantTimeEq for SpendingKey {
+    fn ct_eq(&self, other: &Self) -> Choice {
+        self.to_bytes().ct_eq(other.to_bytes())
+    }
+}
+
 impl SpendingKey {
     /// Generates a random spending key.
     ///

src/zip32.rs

@@ -6,6 +6,7 @@ use std::{
 };
 
 use blake2b_simd::Params as Blake2bParams;
+use subtle::{Choice, ConstantTimeEq};
 
 use crate::{
     keys::{FullViewingKey, SpendingKey},
@@ -101,13 +102,13 @@ pub(crate) struct ExtendedSpendingKey {
     sk: SpendingKey,
 }
 
-impl std::cmp::PartialEq for ExtendedSpendingKey {
-    fn eq(&self, rhs: &ExtendedSpendingKey) -> bool {
-        self.depth == rhs.depth
-            && self.parent_fvk_tag == rhs.parent_fvk_tag
-            && self.child_index == rhs.child_index
-            && self.chain_code == rhs.chain_code
-            && self.sk == rhs.sk
+impl ConstantTimeEq for ExtendedSpendingKey {
+    fn ct_eq(&self, rhs: &Self) -> Choice {
+        self.depth.ct_eq(&rhs.depth)
+            & self.parent_fvk_tag.0.ct_eq(&rhs.parent_fvk_tag.0)
+            & self.child_index.0.ct_eq(&rhs.child_index.0)
+            & self.chain_code.0.ct_eq(&rhs.chain_code.0)
+            & self.sk.ct_eq(&rhs.sk)
     }
 }
 
@@ -229,16 +230,17 @@ mod tests {
         let xsk_m = ExtendedSpendingKey::master(&seed).unwrap();
 
         let xsk_5h = xsk_m.derive_child(5.try_into().unwrap()).unwrap();
-        assert_eq!(
-            ExtendedSpendingKey::from_path(&seed, &[5.try_into().unwrap()]).unwrap(),
-            xsk_5h
-        );
+        assert!(bool::from(
+            ExtendedSpendingKey::from_path(&seed, &[5.try_into().unwrap()])
+                .unwrap()
+                .ct_eq(&xsk_5h)
+        ));
 
         let xsk_5h_7 = xsk_5h.derive_child(7.try_into().unwrap()).unwrap();
-        assert_eq!(
+        assert!(bool::from(
             ExtendedSpendingKey::from_path(&seed, &[5.try_into().unwrap(), 7.try_into().unwrap()])
-                .unwrap(),
-            xsk_5h_7
-        );
+                .unwrap()
+                .ct_eq(&xsk_5h_7)
+        ));
     }
 }