crypto/rsa,crypto/ecdsa,crypto/ed25519: implement PrivateKey.Equal

Fixes #38190

Change-Id: I10766068ee18974e81b3bd78ee0b4d83cc9d1a8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/231417
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/crypto/ecdsa/ecdsa.go b/src/crypto/ecdsa/ecdsa.go
index 786b8a9884..ccce873859 100644
--- a/src/crypto/ecdsa/ecdsa.go
+++ b/src/crypto/ecdsa/ecdsa.go
@@ -62,6 +62,9 @@ type PublicKey struct {
 	X, Y *big.Int
 }
 
+// Any methods implemented on PublicKey might need to also be implemented on
+// PrivateKey, as the latter embeds the former and will expose its methods.
+
 // Equal reports whether pub and x have the same value.
 //
 // Two keys are only considered to have the same value if they have the same Curve value.
@@ -91,6 +94,17 @@ func (priv *PrivateKey) Public() crypto.PublicKey {
 	return &priv.PublicKey
 }
 
+// Equal reports whether priv and x have the same value.
+//
+// See PublicKey.Equal for details on how Curve is compared.
+func (priv *PrivateKey) Equal(x crypto.PrivateKey) bool {
+	xx, ok := x.(*PrivateKey)
+	if !ok {
+		return false
+	}
+	return priv.PublicKey.Equal(&xx.PublicKey) && priv.D.Cmp(xx.D) == 0
+}
+
 // Sign signs digest with priv, reading randomness from rand. The opts argument
 // is not currently used but, in keeping with the crypto.Signer interface,
 // should be the hash function used to digest the message.