crypto/openpgp: return error from userIdSignatureHash

Signature#SignUserId was ignoring the error returned by userIdSignatureHash.
This error can happen, for example, when the Signature's Hash property is
uninitialized. Not returning the error makes it hard for the user to detect
the problem.

Change-Id: I0ae0033e77bfb1ea1c06b0769f949e48c713adc6
Reviewed-on: https://go-review.googlesource.com/27997
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

openpgp/packet/signature.go

@@ -553,7 +553,7 @@ func (sig *Signature) Sign(h hash.Hash, priv *PrivateKey, config *Config) (err e
 func (sig *Signature) SignUserId(id string, pub *PublicKey, priv *PrivateKey, config *Config) error {
 	h, err := userIdSignatureHash(id, pub, sig.Hash)
 	if err != nil {
-		return nil
+		return err
 	}
 	return sig.Sign(h, priv, config)
 }

openpgp/packet/signature_test.go

@@ -39,4 +39,40 @@ func TestSignatureReserialize(t *testing.T) {
 	}
 }
 
+func TestSignUserId(t *testing.T) {
+	sig := &Signature{
+		SigType:    SigTypeGenericCert,
+		PubKeyAlgo: PubKeyAlgoRSA,
+		Hash:       0, // invalid hash function
+	}
+
+	packet, err := Read(readerFromHex(rsaPkDataHex))
+	if err != nil {
+		t.Fatalf("failed to deserialize public key: %v", err)
+	}
+	pubKey := packet.(*PublicKey)
+
+	packet, err = Read(readerFromHex(privKeyRSAHex))
+	if err != nil {
+		t.Fatalf("failed to deserialize private key: %v", err)
+	}
+	privKey := packet.(*PrivateKey)
+
+	err = sig.SignUserId("", pubKey, privKey, nil)
+	if err == nil {
+		t.Errorf("did not receive an error when expected")
+	}
+
+	sig.Hash = crypto.SHA256
+	err = privKey.Decrypt([]byte("testing"))
+	if err != nil {
+		t.Fatalf("failed to decrypt private key: %v", err)
+	}
+
+	err = sig.SignUserId("", pubKey, privKey, nil)
+	if err != nil {
+		t.Errorf("failed to sign user id: %v", err)
+	}
+}
+
 const signatureDataHex = "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"