crypto/openpgp/packet: add public key support

Note that DSA public key support is nascent and the verification
functions clearly don't support it yet. I'm intending to get RSA keys
working first.

R=bradfitzgo
CC=golang-dev
https://golang.org/cl/3973054

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

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packet
+
+import (
+	"big"
+	"crypto/dsa"
+	"crypto/openpgp/error"
+	"crypto/rsa"
+	"crypto/sha1"
+	"encoding/binary"
+	"hash"
+	"io"
+	"os"
+)
+
+// PublicKey represents an OpenPGP public key. See RFC 4880, section 5.5.2.
+type PublicKey struct {
+	CreationTime uint32 // seconds since the epoch
+	PubKeyAlgo   PublicKeyAlgorithm
+	PublicKey    interface{} // Either a *rsa.PublicKey or *dsa.PublicKey
+	Fingerprint  [20]byte
+	KeyId        uint64
+	IsSubKey     bool
+
+	n, e, p, q, g, y parsedMPI
+}
+
+func (pk *PublicKey) parse(r io.Reader) (err os.Error) {
+	// RFC 4880, section 5.5.2
+	var buf [6]byte
+	_, err = readFull(r, buf[:])
+	if err != nil {
+		return
+	}
+	if buf[0] != 4 {
+		return error.UnsupportedError("public key version")
+	}
+	pk.CreationTime = uint32(buf[1])<<24 | uint32(buf[2])<<16 | uint32(buf[3])<<8 | uint32(buf[4])
+	pk.PubKeyAlgo = PublicKeyAlgorithm(buf[5])
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
+		err = pk.parseRSA(r)
+	case PubKeyAlgoDSA:
+		err = pk.parseDSA(r)
+	default:
+		err = error.UnsupportedError("public key type")
+	}
+	if err != nil {
+		return
+	}
+
+	// RFC 4880, section 12.2
+	fingerPrint := sha1.New()
+	pk.SerializeSignaturePrefix(fingerPrint)
+	pk.Serialize(fingerPrint)
+	copy(pk.Fingerprint[:], fingerPrint.Sum())
+	pk.KeyId = binary.BigEndian.Uint64(pk.Fingerprint[12:20])
+
+	return
+}
+
+// parseRSA parses RSA public key material from the given Reader. See RFC 4880,
+// section 5.5.2.
+func (pk *PublicKey) parseRSA(r io.Reader) (err os.Error) {
+	pk.n.bytes, pk.n.bitLength, err = readMPI(r)
+	if err != nil {
+		return
+	}
+	pk.e.bytes, pk.e.bitLength, err = readMPI(r)
+	if err != nil {
+		return
+	}
+
+	if len(pk.e.bytes) > 3 {
+		err = error.UnsupportedError("large public exponent")
+		return
+	}
+	rsa := &rsa.PublicKey{
+		N: new(big.Int).SetBytes(pk.n.bytes),
+		E: 0,
+	}
+	for i := 0; i < len(pk.e.bytes); i++ {
+		rsa.E <<= 8
+		rsa.E |= int(pk.e.bytes[i])
+	}
+	pk.PublicKey = rsa
+	return
+}
+
+// parseRSA parses DSA public key material from the given Reader. See RFC 4880,
+// section 5.5.2.
+func (pk *PublicKey) parseDSA(r io.Reader) (err os.Error) {
+	pk.p.bytes, pk.p.bitLength, err = readMPI(r)
+	if err != nil {
+		return
+	}
+	pk.q.bytes, pk.q.bitLength, err = readMPI(r)
+	if err != nil {
+		return
+	}
+	pk.g.bytes, pk.g.bitLength, err = readMPI(r)
+	if err != nil {
+		return
+	}
+	pk.y.bytes, pk.y.bitLength, err = readMPI(r)
+	if err != nil {
+		return
+	}
+
+	dsa := new(dsa.PublicKey)
+	dsa.P = new(big.Int).SetBytes(pk.p.bytes)
+	dsa.Q = new(big.Int).SetBytes(pk.q.bytes)
+	dsa.G = new(big.Int).SetBytes(pk.g.bytes)
+	dsa.Y = new(big.Int).SetBytes(pk.y.bytes)
+	pk.PublicKey = dsa
+	return
+}
+
+// SerializeSignaturePrefix writes the prefix for this public key to the given Writer.
+// The prefix is used when calculating a signature over this public key. See
+// RFC 4880, section 5.2.4.
+func (pk *PublicKey) SerializeSignaturePrefix(h hash.Hash) {
+	var pLength uint16
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
+		pLength += 2 + uint16(len(pk.n.bytes))
+		pLength += 2 + uint16(len(pk.e.bytes))
+	case PubKeyAlgoDSA:
+		pLength += 2 + uint16(len(pk.p.bytes))
+		pLength += 2 + uint16(len(pk.q.bytes))
+		pLength += 2 + uint16(len(pk.g.bytes))
+		pLength += 2 + uint16(len(pk.y.bytes))
+	default:
+		panic("unknown public key algorithm")
+	}
+	pLength += 6
+	h.Write([]byte{0x99, byte(pLength >> 8), byte(pLength)})
+	return
+}
+
+// Serialize marshals the PublicKey to w in the form of an OpenPGP public key
+// packet, not including the packet header.
+func (pk *PublicKey) Serialize(w io.Writer) (err os.Error) {
+	var buf [6]byte
+	buf[0] = 4
+	buf[1] = byte(pk.CreationTime >> 24)
+	buf[2] = byte(pk.CreationTime >> 16)
+	buf[3] = byte(pk.CreationTime >> 8)
+	buf[4] = byte(pk.CreationTime)
+	buf[5] = byte(pk.PubKeyAlgo)
+
+	_, err = w.Write(buf[:])
+	if err != nil {
+		return
+	}
+
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
+		return writeMPIs(w, pk.n, pk.e)
+	case PubKeyAlgoDSA:
+		return writeMPIs(w, pk.p, pk.q, pk.g, pk.y)
+	}
+	return error.InvalidArgumentError("bad public-key algorithm")
+}
+
+// CanSign returns true iff this public key can generate signatures
+func (pk *PublicKey) CanSign() bool {
+	return pk.PubKeyAlgo != PubKeyAlgoRSAEncryptOnly && pk.PubKeyAlgo != PubKeyAlgoElgamal
+}
+
+// VerifySignature returns nil iff sig is a valid signature, made by this
+// public key, of the data hashed into signed. signed is mutated by this call.
+func (pk *PublicKey) VerifySignature(signed hash.Hash, sig *Signature) (err os.Error) {
+	if !pk.CanSign() {
+		return error.InvalidArgumentError("public key cannot generate signatures")
+	}
+
+	rsaPublicKey, ok := pk.PublicKey.(*rsa.PublicKey)
+	if !ok {
+		// TODO(agl): support DSA and ECDSA keys.
+		return error.UnsupportedError("non-RSA public key")
+	}
+
+	signed.Write(sig.HashSuffix)
+	hashBytes := signed.Sum()
+
+	if hashBytes[0] != sig.HashTag[0] || hashBytes[1] != sig.HashTag[1] {
+		return error.SignatureError("hash tag doesn't match")
+	}
+
+	err = rsa.VerifyPKCS1v15(rsaPublicKey, sig.Hash, hashBytes, sig.Signature)
+	if err != nil {
+		return error.SignatureError("RSA verification failure")
+	}
+	return nil
+}
+
+// VerifyKeySignature returns nil iff sig is a valid signature, make by this
+// public key, of the public key in signed.
+func (pk *PublicKey) VerifyKeySignature(signed *PublicKey, sig *Signature) (err os.Error) {
+	h := sig.Hash.New()
+	if h == nil {
+		return error.UnsupportedError("hash function")
+	}
+
+	// RFC 4880, section 5.2.4
+	pk.SerializeSignaturePrefix(h)
+	pk.Serialize(h)
+	signed.SerializeSignaturePrefix(h)
+	signed.Serialize(h)
+
+	return pk.VerifySignature(h, sig)
+}
+
+// VerifyUserIdSignature returns nil iff sig is a valid signature, make by this
+// public key, of the given user id.
+func (pk *PublicKey) VerifyUserIdSignature(id string, sig *Signature) (err os.Error) {
+	h := sig.Hash.New()
+	if h == nil {
+		return error.UnsupportedError("hash function")
+	}
+
+	// RFC 4880, section 5.2.4
+	pk.SerializeSignaturePrefix(h)
+	pk.Serialize(h)
+
+	var buf [5]byte
+	buf[0] = 0xb4
+	buf[1] = byte(len(id) >> 24)
+	buf[2] = byte(len(id) >> 16)
+	buf[3] = byte(len(id) >> 8)
+	buf[4] = byte(len(id))
+	h.Write(buf[:])
+	h.Write([]byte(id))
+
+	return pk.VerifySignature(h, sig)
+}
+
+// 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 reserialised exactly.
+type parsedMPI struct {
+	bytes     []byte
+	bitLength uint16
+}
+
+// writeMPIs is a utility function for serialising several big integers to the
+// given Writer.
+func writeMPIs(w io.Writer, mpis ...parsedMPI) (err os.Error) {
+	for _, mpi := range mpis {
+		err = writeMPI(w, mpi.bitLength, mpi.bytes)
+		if err != nil {
+			return
+		}
+	}
+	return
+}

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

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packet
+
+import (
+	"bytes"
+	"encoding/hex"
+	"testing"
+)
+
+var pubKeyTests = []struct {
+	hexData        string
+	hexFingerprint string
+	creationTime   uint32
+	pubKeyAlgo     PublicKeyAlgorithm
+	keyId          uint64
+}{
+	{rsaPkDataHex, rsaFingerprintHex, 0x4d3c5c10, PubKeyAlgoRSA, 0xa34d7e18c20c31bb},
+	{dsaPkDataHex, dsaFingerprintHex, 0x4d432f89, PubKeyAlgoDSA, 0x8e8fbe54062f19ed},
+}
+
+func TestPublicKeyRead(t *testing.T) {
+	for i, test := range pubKeyTests {
+		packet, err := Read(readerFromHex(test.hexData))
+		if err != nil {
+			t.Errorf("#%d: Read error: %s", i, err)
+			return
+		}
+		pk, ok := packet.(*PublicKey)
+		if !ok {
+			t.Errorf("#%d: failed to parse, got: %#v", i, packet)
+			return
+		}
+		if pk.PubKeyAlgo != test.pubKeyAlgo {
+			t.Errorf("#%d: bad public key algorithm got:%x want:%x", i, pk.PubKeyAlgo, test.pubKeyAlgo)
+		}
+		if pk.CreationTime != test.creationTime {
+			t.Errorf("#%d: bad creation time got:%x want:%x", i, pk.CreationTime, test.creationTime)
+		}
+		expectedFingerprint, _ := hex.DecodeString(test.hexFingerprint)
+		if !bytes.Equal(expectedFingerprint, pk.Fingerprint[:]) {
+			t.Errorf("#%d: bad fingerprint got:%x want:%x", i, pk.Fingerprint[:], expectedFingerprint)
+		}
+		if pk.KeyId != test.keyId {
+			t.Errorf("#%d: bad keyid got:%x want:%x", i, pk.KeyId, test.keyId)
+		}
+	}
+}
+
+const rsaFingerprintHex = "5fb74b1d03b1e3cb31bc2f8aa34d7e18c20c31bb"
+
+const rsaPkDataHex = "988d044d3c5c10010400b1d13382944bd5aba23a4312968b5095d14f947f600eb478e14a6fcb16b0e0cac764884909c020bc495cfcc39a935387c661507bdb236a0612fb582cac3af9b29cc2c8c70090616c41b662f4da4c1201e195472eb7f4ae1ccbcbf9940fe21d985e379a5563dde5b9a23d35f1cfaa5790da3b79db26f23695107bfaca8e7b5bcd0011010001"
+
+const dsaFingerprintHex = "eece4c094db002103714c63c8e8fbe54062f19ed"
+
+const dsaPkDataHex = "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"