openpgp: add PublicKey KeyId string accessors

R=agl, agl1
CC=golang-dev
https://golang.org/cl/4297041

src/pkg/crypto/openpgp/packet/public_key.go

@@ -11,6 +11,7 @@ import (
 	"crypto/rsa"
 	"crypto/sha1"
 	"encoding/binary"
+	"fmt"
 	"hash"
 	"io"
 	"os"
@@ -239,6 +240,18 @@ func (pk *PublicKey) VerifyUserIdSignature(id string, sig *Signature) (err os.Er
 	return pk.VerifySignature(h, sig)
 }
 
+// KeyIdString returns the public key's fingerprint in capital hex
+// (e.g. "6C7EE1B8621CC013").
+func (pk *PublicKey) KeyIdString() string {
+	return fmt.Sprintf("%X", pk.Fingerprint[12:20])
+}
+
+// KeyIdShortString returns the short form of public key's fingerprint
+// in capital hex, as shown by gpg --list-keys (e.g. "621CC013").
+func (pk *PublicKey) KeyIdShortString() string {
+	return fmt.Sprintf("%X", pk.Fingerprint[16:20])
+}
+
 // A parsedMPI is used to store the contents of a big integer, along with the
 // bit length that was specified in the original input. This allows the MPI to
 // be reserialized exactly.

src/pkg/crypto/openpgp/packet/public_key_test.go

@@ -16,9 +16,11 @@ var pubKeyTests = []struct {
 	creationTime   uint32
 	pubKeyAlgo     PublicKeyAlgorithm
 	keyId          uint64
+	keyIdString    string
+	keyIdShort     string
 }{
-	{rsaPkDataHex, rsaFingerprintHex, 0x4d3c5c10, PubKeyAlgoRSA, 0xa34d7e18c20c31bb},
-	{dsaPkDataHex, dsaFingerprintHex, 0x4d432f89, PubKeyAlgoDSA, 0x8e8fbe54062f19ed},
+	{rsaPkDataHex, rsaFingerprintHex, 0x4d3c5c10, PubKeyAlgoRSA, 0xa34d7e18c20c31bb, "A34D7E18C20C31BB", "C20C31BB"},
+	{dsaPkDataHex, dsaFingerprintHex, 0x4d432f89, PubKeyAlgoDSA, 0x8e8fbe54062f19ed, "8E8FBE54062F19ED", "062F19ED"},
 }
 
 func TestPublicKeyRead(t *testing.T) {
@@ -46,6 +48,12 @@ func TestPublicKeyRead(t *testing.T) {
 		if pk.KeyId != test.keyId {
 			t.Errorf("#%d: bad keyid got:%x want:%x", i, pk.KeyId, test.keyId)
 		}
+		if g, e := pk.KeyIdString(), test.keyIdString; g != e {
+			t.Errorf("#%d: bad KeyIdString got:%q want:%q", i, g, e)
+		}
+		if g, e := pk.KeyIdShortString(), test.keyIdShort; g != e {
+			t.Errorf("#%d: bad KeyIdShortString got:%q want:%q", i, g, e)
+		}
 	}
 }