openpgp: don't generate PubKeyAlgoRSASignOnly keys

These are deprecated according to RFC4880 and should no longer be
generated: https://tools.ietf.org/html/rfc4880#section-13.5
With that, the notion of a "sign-only" private key doesn't make sense
(as that is a signature property, not a private key property), so remove
it from the comment.

Fixes golang/go#27888

Change-Id: I7d41acd0793b2caf3c0897e580f42375c72d82a8
Reviewed-on: https://go-review.googlesource.com/c/137896
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

openpgp/packet/packet.go

@@ -404,14 +404,16 @@ const (
 type PublicKeyAlgorithm uint8
 
 const (
-	PubKeyAlgoRSA            PublicKeyAlgorithm = 1
-	PubKeyAlgoRSAEncryptOnly PublicKeyAlgorithm = 2
-	PubKeyAlgoRSASignOnly    PublicKeyAlgorithm = 3
-	PubKeyAlgoElGamal        PublicKeyAlgorithm = 16
-	PubKeyAlgoDSA            PublicKeyAlgorithm = 17
+	PubKeyAlgoRSA     PublicKeyAlgorithm = 1
+	PubKeyAlgoElGamal PublicKeyAlgorithm = 16
+	PubKeyAlgoDSA     PublicKeyAlgorithm = 17
 	// RFC 6637, Section 5.
 	PubKeyAlgoECDH  PublicKeyAlgorithm = 18
 	PubKeyAlgoECDSA PublicKeyAlgorithm = 19
+
+	// Deprecated in RFC 4880, Section 13.5. Use key flags instead.
+	PubKeyAlgoRSAEncryptOnly PublicKeyAlgorithm = 2
+	PubKeyAlgoRSASignOnly    PublicKeyAlgorithm = 3
 )
 
 // CanEncrypt returns true if it's possible to encrypt a message to a public

openpgp/packet/private_key.go

@@ -64,7 +64,7 @@ func NewECDSAPrivateKey(currentTime time.Time, priv *ecdsa.PrivateKey) *PrivateK
 	return pk
 }
 
-// NewSignerPrivateKey creates a sign-only PrivateKey from a crypto.Signer that
+// NewSignerPrivateKey creates a PrivateKey from a crypto.Signer that
 // implements RSA or ECDSA.
 func NewSignerPrivateKey(currentTime time.Time, signer crypto.Signer) *PrivateKey {
 	pk := new(PrivateKey)
@@ -73,10 +73,8 @@ func NewSignerPrivateKey(currentTime time.Time, signer crypto.Signer) *PrivateKe
 	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:

openpgp/packet/private_key_test.go

@@ -172,12 +172,8 @@ func TestRSASignerPrivateKey(t *testing.T) {
 
 	priv := NewSignerPrivateKey(time.Now(), &rsaSigner{rsaPriv})
 
-	if priv.PubKeyAlgo != PubKeyAlgoRSASignOnly {
-		t.Fatal("NewSignerPrivateKey should have made a sign-only RSA private key")
-	}
-
 	sig := &Signature{
-		PubKeyAlgo: PubKeyAlgoRSASignOnly,
+		PubKeyAlgo: PubKeyAlgoRSA,
 		Hash:       crypto.SHA256,
 	}
 	msg := []byte("Hello World!")