Merge pull request #53 from tendermint/constant-time-equals

Constant time equals

priv_key.go

@@ -1,7 +1,7 @@
 package crypto
 
 import (
-	"bytes"
+	"crypto/subtle"
 
 	secp256k1 "github.com/btcsuite/btcd/btcec"
 	"github.com/tendermint/ed25519"
@@ -69,9 +69,11 @@ func (privKey PrivKeyEd25519) PubKey() PubKey {
 	return PubKeyEd25519(pubBytes).Wrap()
 }
 
+// Equals - you probably don't need to use this.
+// Runs in constant time based on length of the keys.
 func (privKey PrivKeyEd25519) Equals(other PrivKey) bool {
 	if otherEd, ok := other.Unwrap().(PrivKeyEd25519); ok {
-		return bytes.Equal(privKey[:], otherEd[:])
+		return subtle.ConstantTimeCompare(privKey[:], otherEd[:]) == 1
 	} else {
 		return false
 	}
@@ -156,9 +158,11 @@ func (privKey PrivKeySecp256k1) PubKey() PubKey {
 	return pub.Wrap()
 }
 
+// Equals - you probably don't need to use this.
+// Runs in constant time based on length of the keys.
 func (privKey PrivKeySecp256k1) Equals(other PrivKey) bool {
 	if otherSecp, ok := other.Unwrap().(PrivKeySecp256k1); ok {
-		return bytes.Equal(privKey[:], otherSecp[:])
+		return subtle.ConstantTimeCompare(privKey[:], otherSecp[:]) == 1
 	} else {
 		return false
 	}

signature.go

@@ -87,8 +87,8 @@ func (sig SignatureSecp256k1) IsZero() bool { return len(sig) == 0 }
 func (sig SignatureSecp256k1) String() string { return fmt.Sprintf("/%X.../", Fingerprint(sig[:])) }
 
 func (sig SignatureSecp256k1) Equals(other Signature) bool {
-	if otherEd, ok := other.Unwrap().(SignatureSecp256k1); ok {
-		return bytes.Equal(sig[:], otherEd[:])
+	if otherSecp, ok := other.Unwrap().(SignatureSecp256k1); ok {
+		return bytes.Equal(sig[:], otherSecp[:])
 	} else {
 		return false
 	}

signature_test.go

@@ -141,3 +141,27 @@ func TestWrapping(t *testing.T) {
 	}
 
 }
+
+func TestPrivKeyEquality(t *testing.T) {
+	{
+		privKey := GenPrivKeySecp256k1().Wrap()
+		privKey2 := GenPrivKeySecp256k1().Wrap()
+		assert.False(t, privKey.Equals(privKey2))
+		assert.False(t, privKey2.Equals(privKey))
+
+		privKeyCopy := privKey // copy
+		assert.True(t, privKey.Equals(privKeyCopy))
+		assert.True(t, privKeyCopy.Equals(privKey))
+	}
+
+	{
+		privKey := GenPrivKeyEd25519().Wrap()
+		privKey2 := GenPrivKeyEd25519().Wrap()
+		assert.False(t, privKey.Equals(privKey2))
+		assert.False(t, privKey2.Equals(privKey))
+
+		privKeyCopy := privKey // copy
+		assert.True(t, privKey.Equals(privKeyCopy))
+		assert.True(t, privKeyCopy.Equals(privKey))
+	}
+}