openpgp: ECDSA key and signature support

Add support for creating and signing with ECDSA OpenPGP keys

Change-Id: I6d530325ab801ba800187b88e8cfea079cfa41ed
Reviewed-on: https://go-review.googlesource.com/20608
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jacob H. Haven <jacob@jhaven.me>
Reviewed-by: Adam Langley <agl@golang.org>
diff --git a/openpgp/packet/private_key.go b/openpgp/packet/private_key.go
index 740a27d..545846b 100644
--- a/openpgp/packet/private_key.go
+++ b/openpgp/packet/private_key.go
@@ -8,16 +8,18 @@
 	"bytes"
 	"crypto/cipher"
 	"crypto/dsa"
+	"crypto/ecdsa"
 	"crypto/rsa"
 	"crypto/sha1"
-	"golang.org/x/crypto/openpgp/elgamal"
-	"golang.org/x/crypto/openpgp/errors"
-	"golang.org/x/crypto/openpgp/s2k"
 	"io"
 	"io/ioutil"
 	"math/big"
 	"strconv"
 	"time"
+
+	"golang.org/x/crypto/openpgp/elgamal"
+	"golang.org/x/crypto/openpgp/errors"
+	"golang.org/x/crypto/openpgp/s2k"
 )
 
 // PrivateKey represents a possibly encrypted private key. See RFC 4880,
@@ -54,6 +56,13 @@
 	return pk
 }
 
+func NewECDSAPrivateKey(currentTime time.Time, priv *ecdsa.PrivateKey) *PrivateKey {
+	pk := new(PrivateKey)
+	pk.PublicKey = *NewECDSAPublicKey(currentTime, &priv.PublicKey)
+	pk.PrivateKey = priv
+	return pk
+}
+
 func (pk *PrivateKey) parse(r io.Reader) (err error) {
 	err = (&pk.PublicKey).parse(r)
 	if err != nil {
@@ -139,6 +148,8 @@
 		err = serializeDSAPrivateKey(privateKeyBuf, priv)
 	case *elgamal.PrivateKey:
 		err = serializeElGamalPrivateKey(privateKeyBuf, priv)
+	case *ecdsa.PrivateKey:
+		err = serializeECDSAPrivateKey(privateKeyBuf, priv)
 	default:
 		err = errors.InvalidArgumentError("unknown private key type")
 	}
@@ -198,6 +209,10 @@
 	return writeBig(w, priv.X)
 }
 
+func serializeECDSAPrivateKey(w io.Writer, priv *ecdsa.PrivateKey) error {
+	return writeBig(w, priv.D)
+}
+
 // Decrypt decrypts an encrypted private key using a passphrase.
 func (pk *PrivateKey) Decrypt(passphrase []byte) error {
 	if !pk.Encrypted {
@@ -249,6 +264,8 @@
 		return pk.parseDSAPrivateKey(data)
 	case PubKeyAlgoElGamal:
 		return pk.parseElGamalPrivateKey(data)
+	case PubKeyAlgoECDSA:
+		return pk.parseECDSAPrivateKey(data)
 	}
 	panic("impossible")
 }
@@ -324,3 +341,22 @@
 
 	return nil
 }
+
+func (pk *PrivateKey) parseECDSAPrivateKey(data []byte) (err error) {
+	ecdsaPub := pk.PublicKey.PublicKey.(*ecdsa.PublicKey)
+
+	buf := bytes.NewBuffer(data)
+	d, _, err := readMPI(buf)
+	if err != nil {
+		return
+	}
+
+	pk.PrivateKey = &ecdsa.PrivateKey{
+		PublicKey: *ecdsaPub,
+		D:         new(big.Int).SetBytes(d),
+	}
+	pk.Encrypted = false
+	pk.encryptedData = nil
+
+	return nil
+}
diff --git a/openpgp/packet/private_key_test.go b/openpgp/packet/private_key_test.go
index 25c8931..81d3961 100644
--- a/openpgp/packet/private_key_test.go
+++ b/openpgp/packet/private_key_test.go
@@ -5,6 +5,12 @@
 package packet
 
 import (
+	"bytes"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"hash"
 	"testing"
 	"time"
 )
@@ -56,6 +62,57 @@
 	}
 }
 
+func populateHash(hashFunc crypto.Hash, msg []byte) (hash.Hash, error) {
+	h := hashFunc.New()
+	if _, err := h.Write(msg); err != nil {
+		return nil, err
+	}
+	return h, nil
+}
+
+func TestECDSAPrivateKey(t *testing.T) {
+	ecdsaPriv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf bytes.Buffer
+	if err := NewECDSAPrivateKey(time.Now(), ecdsaPriv).Serialize(&buf); err != nil {
+		t.Fatal(err)
+	}
+
+	p, err := Read(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	priv, ok := p.(*PrivateKey)
+	if !ok {
+		t.Fatal("didn't parse private key")
+	}
+
+	sig := &Signature{
+		PubKeyAlgo: PubKeyAlgoECDSA,
+		Hash:       crypto.SHA256,
+	}
+	msg := []byte("Hello World!")
+
+	h, err := populateHash(sig.Hash, msg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := sig.Sign(h, priv, nil); err != nil {
+		t.Fatal(err)
+	}
+
+	if h, err = populateHash(sig.Hash, msg); err != nil {
+		t.Fatal(err)
+	}
+	if err := priv.VerifySignature(h, sig); err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestIssue11505(t *testing.T) {
 	// parsing a rsa private key with p or q == 1 used to panic due to a divide by zero
 	_, _ = Read(readerFromHex("9c3004303030300100000011303030000000000000010130303030303030303030303030303030303030303030303030303030303030303030303030303030303030"))
diff --git a/openpgp/packet/public_key.go b/openpgp/packet/public_key.go
index 37a6472..c769933 100644
--- a/openpgp/packet/public_key.go
+++ b/openpgp/packet/public_key.go
@@ -224,6 +224,32 @@
 	return pk
 }
 
+func NewECDSAPublicKey(creationTime time.Time, pub *ecdsa.PublicKey) *PublicKey {
+	pk := &PublicKey{
+		CreationTime: creationTime,
+		PubKeyAlgo:   PubKeyAlgoECDSA,
+		PublicKey:    pub,
+		ec:           new(ecdsaKey),
+	}
+
+	switch pub.Curve {
+	case elliptic.P256():
+		pk.ec.oid = oidCurveP256
+	case elliptic.P384():
+		pk.ec.oid = oidCurveP384
+	case elliptic.P521():
+		pk.ec.oid = oidCurveP521
+	default:
+		panic("unknown elliptic curve")
+	}
+
+	pk.ec.p.bytes = elliptic.Marshal(pub.Curve, pub.X, pub.Y)
+	pk.ec.p.bitLength = uint16(8 * len(pk.ec.p.bytes))
+
+	pk.setFingerPrintAndKeyId()
+	return pk
+}
+
 func (pk *PublicKey) parse(r io.Reader) (err error) {
 	// RFC 4880, section 5.5.2
 	var buf [6]byte
diff --git a/openpgp/packet/signature.go b/openpgp/packet/signature.go
index 1f29d3d..4368f6b 100644
--- a/openpgp/packet/signature.go
+++ b/openpgp/packet/signature.go
@@ -8,6 +8,7 @@
 	"bytes"
 	"crypto"
 	"crypto/dsa"
+	"crypto/ecdsa"
 	"crypto/rsa"
 	"encoding/binary"
 	"hash"
@@ -532,6 +533,12 @@
 			sig.DSASigS.bytes = s.Bytes()
 			sig.DSASigS.bitLength = uint16(8 * len(sig.DSASigS.bytes))
 		}
+	case PubKeyAlgoECDSA:
+		r, s, err := ecdsa.Sign(config.Random(), priv.PrivateKey.(*ecdsa.PrivateKey), digest)
+		if err == nil {
+			sig.ECDSASigR = fromBig(r)
+			sig.ECDSASigS = fromBig(s)
+		}
 	default:
 		err = errors.UnsupportedError("public key algorithm: " + strconv.Itoa(int(sig.PubKeyAlgo)))
 	}
diff --git a/openpgp/read_test.go b/openpgp/read_test.go
index 7524a02..b8867d0 100644
--- a/openpgp/read_test.go
+++ b/openpgp/read_test.go
@@ -80,6 +80,17 @@
 	}
 }
 
+func TestReadP256Key(t *testing.T) {
+	kring, err := ReadKeyRing(readerFromHex(p256TestKeyHex))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if len(kring) != 1 || uint32(kring[0].PrimaryKey.KeyId) != 0x5918513E {
+		t.Errorf("bad parse: %#v", kring)
+	}
+}
+
 func TestDSAHashTruncatation(t *testing.T) {
 	// dsaKeyWithSHA512 was generated with GnuPG and --cert-digest-algo
 	// SHA512 in order to require DSA hash truncation to verify correctly.
@@ -326,6 +337,11 @@
 	testDetachedSignature(t, kring, readerFromHex(missingHashFunctionHex+detachedSignatureDSAHex), signedInput, "binary", testKey3KeyId)
 }
 
+func TestDetachedSignatureP256(t *testing.T) {
+	kring, _ := ReadKeyRing(readerFromHex(p256TestKeyHex))
+	testDetachedSignature(t, kring, readerFromHex(detachedSignatureP256Hex), signedInput, "binary", testKeyP256KeyId)
+}
+
 func testHashFunctionError(t *testing.T, signatureHex string) {
 	kring, _ := ReadKeyRing(readerFromHex(testKeys1And2Hex))
 	_, err := CheckDetachedSignature(kring, nil, readerFromHex(signatureHex))
@@ -419,6 +435,7 @@
 
 const testKey1KeyId = 0xA34D7E18C20C31BB
 const testKey3KeyId = 0x338934250CCC0360
+const testKeyP256KeyId = 0xd44a2c495918513e
 
 const signedInput = "Signed message\nline 2\nline 3\n"
 const signedTextInput = "Signed message\r\nline 2\r\nline 3\r\n"
@@ -433,6 +450,8 @@
 
 const detachedSignatureDSAHex = "884604001102000605024d6c4eac000a0910338934250ccc0360f18d00a087d743d6405ed7b87755476629600b8b694a39e900a0abff8126f46faf1547c1743c37b21b4ea15b8f83"
 
+const detachedSignatureP256Hex = "885e0400130a0006050256e5bb00000a0910d44a2c495918513edef001009841a4f792beb0befccb35c8838a6a87d9b936beaa86db6745ddc7b045eee0cf00fd1ac1f78306b17e965935dd3f8bae4587a76587e4af231efe19cc4011a8434817"
+
 const testKeys1And2Hex = "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"
 
 const testKeys1And2PrivateHex = "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"
@@ -453,6 +472,10 @@
 
 const dsaTestKeyPrivateHex = "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"
 
+const p256TestKeyHex = "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"
+
+const p256TestKeyPrivateHex = "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"
+
 const armoredPrivateKeyBlock = `-----BEGIN PGP PRIVATE KEY BLOCK-----
 Version: GnuPG v1.4.10 (GNU/Linux)
 
diff --git a/openpgp/write_test.go b/openpgp/write_test.go
index 8e9a335..2161ebc 100644
--- a/openpgp/write_test.go
+++ b/openpgp/write_test.go
@@ -50,6 +50,20 @@
 	testDetachedSignature(t, kring, out, signedInput, "check", testKey3KeyId)
 }
 
+func TestSignDetachedP256(t *testing.T) {
+	kring, _ := ReadKeyRing(readerFromHex(p256TestKeyPrivateHex))
+	kring[0].PrivateKey.Decrypt([]byte("passphrase"))
+
+	out := bytes.NewBuffer(nil)
+	message := bytes.NewBufferString(signedInput)
+	err := DetachSign(out, kring[0], message, nil)
+	if err != nil {
+		t.Error(err)
+	}
+
+	testDetachedSignature(t, kring, out, signedInput, "check", testKeyP256KeyId)
+}
+
 func TestNewEntity(t *testing.T) {
 	if testing.Short() {
 		return