openpgp: allow RSA/ECDSA signers to return a pointer

Fixes golang/go#27606

Change-Id: I88b2f7c7796b43449a17a6be963c05f741dbf904
Reviewed-on: https://go-review.googlesource.com/137895
Reviewed-by: Filippo Valsorda <filippo@golang.org>

openpgp/packet/private_key.go

@@ -68,10 +68,17 @@ func NewECDSAPrivateKey(currentTime time.Time, priv *ecdsa.PrivateKey) *PrivateK
 // implements RSA or ECDSA.
 func NewSignerPrivateKey(currentTime time.Time, signer crypto.Signer) *PrivateKey {
 	pk := new(PrivateKey)
+	// In general, the public Keys should be used as pointers. We still
+	// type-switch on the values, for backwards-compatibility.
 	switch pubkey := signer.Public().(type) {
+	case *rsa.PublicKey:
+		pk.PublicKey = *NewRSAPublicKey(currentTime, pubkey)
+		pk.PubKeyAlgo = PubKeyAlgoRSASignOnly
 	case rsa.PublicKey:
 		pk.PublicKey = *NewRSAPublicKey(currentTime, &pubkey)
 		pk.PubKeyAlgo = PubKeyAlgoRSASignOnly
+	case *ecdsa.PublicKey:
+		pk.PublicKey = *NewECDSAPublicKey(currentTime, pubkey)
 	case ecdsa.PublicKey:
 		pk.PublicKey = *NewECDSAPublicKey(currentTime, &pubkey)
 	default:

openpgp/packet/private_key_test.go

@@ -14,7 +14,6 @@ import (
 	"crypto/x509"
 	"encoding/hex"
 	"hash"
-	"io"
 	"testing"
 	"time"
 )
@@ -162,15 +161,7 @@ func TestECDSAPrivateKey(t *testing.T) {
 }
 
 type rsaSigner struct {
-	priv *rsa.PrivateKey
-}
-
-func (s *rsaSigner) Public() crypto.PublicKey {
-	return s.priv.PublicKey
-}
-
-func (s *rsaSigner) Sign(rand io.Reader, msg []byte, opts crypto.SignerOpts) ([]byte, error) {
-	return s.priv.Sign(rand, msg, opts)
+	*rsa.PrivateKey
 }
 
 func TestRSASignerPrivateKey(t *testing.T) {
@@ -208,15 +199,7 @@ func TestRSASignerPrivateKey(t *testing.T) {
 }
 
 type ecdsaSigner struct {
-	priv *ecdsa.PrivateKey
-}
-
-func (s *ecdsaSigner) Public() crypto.PublicKey {
-	return s.priv.PublicKey
-}
-
-func (s *ecdsaSigner) Sign(rand io.Reader, msg []byte, opts crypto.SignerOpts) ([]byte, error) {
-	return s.priv.Sign(rand, msg, opts)
+	*ecdsa.PrivateKey
 }
 
 func TestECDSASignerPrivateKey(t *testing.T) {