From 28a2369414eacb9ebc08bd8f0df0ef274df5e368 Mon Sep 17 00:00:00 2001
From: Adam Langley <agl@golang.org>
Date: Thu, 10 Feb 2011 19:59:12 -0500
Subject: [PATCH] crypto/openpgp/packet: add remainder of packet types.

(The unittest for Signature may seem a little small, but it's tested by
the higher level code.)

R=bradfitzgo
CC=golang-dev
https://golang.org/cl/4173043
---
 .../crypto/openpgp/packet/encrypted_key.go    |  66 +++
 .../openpgp/packet/encrypted_key_test.go      |  67 +++
 src/pkg/crypto/openpgp/packet/reader.go       |  63 +++
 src/pkg/crypto/openpgp/packet/signature.go    | 468 ++++++++++++++++++
 .../crypto/openpgp/packet/signature_test.go   |  28 ++
 5 files changed, 692 insertions(+)
 create mode 100644 src/pkg/crypto/openpgp/packet/encrypted_key.go
 create mode 100644 src/pkg/crypto/openpgp/packet/encrypted_key_test.go
 create mode 100644 src/pkg/crypto/openpgp/packet/reader.go
 create mode 100644 src/pkg/crypto/openpgp/packet/signature.go
 create mode 100644 src/pkg/crypto/openpgp/packet/signature_test.go

diff --git a/src/pkg/crypto/openpgp/packet/encrypted_key.go b/src/pkg/crypto/openpgp/packet/encrypted_key.go
new file mode 100644
index 00000000000..4a926cdb110
--- /dev/null
+++ b/src/pkg/crypto/openpgp/packet/encrypted_key.go
@@ -0,0 +1,66 @@
+// 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 (
+	"crypto/openpgp/error"
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/binary"
+	"io"
+	"os"
+	"strconv"
+)
+
+// EncryptedKey represents a public-key encrypted session key. See RFC 4880,
+// section 5.1.
+type EncryptedKey struct {
+	KeyId      uint64
+	Algo       PublicKeyAlgorithm
+	Encrypted  []byte
+	CipherFunc CipherFunction // only valid after a sucessful Decrypt
+	Key        []byte         // only valid after a sucessful Decrypt
+}
+
+func (e *EncryptedKey) parse(r io.Reader) (err os.Error) {
+	var buf [10]byte
+	_, err = readFull(r, buf[:])
+	if err != nil {
+		return
+	}
+	if buf[0] != 3 {
+		return error.UnsupportedError("unknown EncryptedKey version " + strconv.Itoa(int(buf[0])))
+	}
+	e.KeyId = binary.BigEndian.Uint64(buf[1:9])
+	e.Algo = PublicKeyAlgorithm(buf[9])
+	if e.Algo == PubKeyAlgoRSA || e.Algo == PubKeyAlgoRSAEncryptOnly {
+		e.Encrypted, _, err = readMPI(r)
+	}
+	_, err = consumeAll(r)
+	return
+}
+
+// DecryptRSA decrypts an RSA encrypted session key with the given private key.
+func (e *EncryptedKey) DecryptRSA(priv *rsa.PrivateKey) (err os.Error) {
+	if e.Algo != PubKeyAlgoRSA && e.Algo != PubKeyAlgoRSAEncryptOnly {
+		return error.InvalidArgumentError("EncryptedKey not RSA encrypted")
+	}
+	b, err := rsa.DecryptPKCS1v15(rand.Reader, priv, e.Encrypted)
+	if err != nil {
+		return
+	}
+	e.CipherFunc = CipherFunction(b[0])
+	e.Key = b[1 : len(b)-2]
+	expectedChecksum := uint16(b[len(b)-2])<<8 | uint16(b[len(b)-1])
+	var checksum uint16
+	for _, v := range e.Key {
+		checksum += uint16(v)
+	}
+	if checksum != expectedChecksum {
+		return error.StructuralError("EncryptedKey checksum incorrect")
+	}
+
+	return
+}
diff --git a/src/pkg/crypto/openpgp/packet/encrypted_key_test.go b/src/pkg/crypto/openpgp/packet/encrypted_key_test.go
new file mode 100644
index 00000000000..755ae7a3074
--- /dev/null
+++ b/src/pkg/crypto/openpgp/packet/encrypted_key_test.go
@@ -0,0 +1,67 @@
+// 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/rsa"
+	"fmt"
+	"testing"
+)
+
+func bigFromBase10(s string) *big.Int {
+	b, ok := new(big.Int).SetString(s, 10)
+	if !ok {
+		panic("bigFromBase10 failed")
+	}
+	return b
+}
+
+func TestEncryptedKey(t *testing.T) {
+	p, err := Read(readerFromHex(encryptedKeyHex))
+	if err != nil {
+		t.Errorf("error from Read: %s", err)
+		return
+	}
+	ek, ok := p.(*EncryptedKey)
+	if !ok {
+		t.Errorf("didn't parse an EncryptedKey, got %#v", p)
+		return
+	}
+
+	if ek.KeyId != 0x2a67d68660df41c7 || ek.Algo != PubKeyAlgoRSA {
+		t.Errorf("unexpected EncryptedKey contents: %#v", ek)
+		return
+	}
+
+	pub := rsa.PublicKey{
+		E: 65537,
+		N: bigFromBase10("115804063926007623305902631768113868327816898845124614648849934718568541074358183759250136204762053879858102352159854352727097033322663029387610959884180306668628526686121021235757016368038585212410610742029286439607686208110250133174279811431933746643015923132833417396844716207301518956640020862630546868823"),
+	}
+
+	priv := &rsa.PrivateKey{
+		PublicKey: pub,
+		D:         bigFromBase10("32355588668219869544751561565313228297765464314098552250409557267371233892496951383426602439009993875125222579159850054973310859166139474359774543943714622292329487391199285040721944491839695981199720170366763547754915493640685849961780092241140181198779299712578774460837139360803883139311171713302987058393"),
+	}
+
+	err = ek.DecryptRSA(priv)
+	if err != nil {
+		t.Errorf("error from DecryptRSA: %s", err)
+		return
+	}
+
+	if ek.CipherFunc != CipherAES256 {
+		t.Errorf("unexpected EncryptedKey contents: %#v", ek)
+		return
+	}
+
+	keyHex := fmt.Sprintf("%x", ek.Key)
+	if keyHex != expectedKeyHex {
+		t.Errorf("bad key, got %s want %x", keyHex, expectedKeyHex)
+	}
+}
+
+const encryptedKeyHex = "c18c032a67d68660df41c70104005789d0de26b6a50c985a02a13131ca829c413a35d0e6fa8d6842599252162808ac7439c72151c8c6183e76923fe3299301414d0c25a2f06a2257db3839e7df0ec964773f6e4c4ac7ff3b48c444237166dd46ba8ff443a5410dc670cb486672fdbe7c9dfafb75b4fea83af3a204fe2a7dfa86bd20122b4f3d2646cbeecb8f7be8"
+const expectedKeyHex = "d930363f7e0308c333b9618617ea728963d8df993665ae7be1092d4926fd864b"
diff --git a/src/pkg/crypto/openpgp/packet/reader.go b/src/pkg/crypto/openpgp/packet/reader.go
new file mode 100644
index 00000000000..5febc3bc8dc
--- /dev/null
+++ b/src/pkg/crypto/openpgp/packet/reader.go
@@ -0,0 +1,63 @@
+// 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 (
+	"crypto/openpgp/error"
+	"io"
+	"os"
+)
+
+// Reader reads packets from an io.Reader and allows packets to be 'unread' so
+// that they result from the next call to Next.
+type Reader struct {
+	q       []Packet
+	readers []io.Reader
+}
+
+// Next returns the most recently unread Packet, or reads another packet from
+// the top-most io.Reader. Unknown packet types are skipped.
+func (r *Reader) Next() (p Packet, err os.Error) {
+	if len(r.q) > 0 {
+		p = r.q[len(r.q)-1]
+		r.q = r.q[:len(r.q)-1]
+		return
+	}
+
+	for len(r.readers) > 0 {
+		p, err = Read(r.readers[len(r.readers)-1])
+		if err == nil {
+			return
+		}
+		if err == os.EOF {
+			r.readers = r.readers[:len(r.readers)-1]
+			continue
+		}
+		if _, ok := err.(error.UnknownPacketTypeError); !ok {
+			return nil, err
+		}
+	}
+
+	return nil, os.EOF
+}
+
+// Push causes the Reader to start reading from a new io.Reader. When an EOF
+// error is seen from the new io.Reader, it is popped and the Reader continues
+// to read from the next most recent io.Reader.
+func (r *Reader) Push(reader io.Reader) {
+	r.readers = append(r.readers, reader)
+}
+
+// Unread causes the given Packet to be returned from the next call to Next.
+func (r *Reader) Unread(p Packet) {
+	r.q = append(r.q, p)
+}
+
+func NewReader(r io.Reader) *Reader {
+	return &Reader{
+		q:       nil,
+		readers: []io.Reader{r},
+	}
+}
diff --git a/src/pkg/crypto/openpgp/packet/signature.go b/src/pkg/crypto/openpgp/packet/signature.go
new file mode 100644
index 00000000000..fd2518ab41e
--- /dev/null
+++ b/src/pkg/crypto/openpgp/packet/signature.go
@@ -0,0 +1,468 @@
+// 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 (
+	"crypto"
+	"crypto/openpgp/error"
+	"crypto/openpgp/s2k"
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/binary"
+	"hash"
+	"io"
+	"os"
+	"strconv"
+)
+
+// Signature represents a signature. See RFC 4880, section 5.2.
+type Signature struct {
+	SigType    SignatureType
+	PubKeyAlgo PublicKeyAlgorithm
+	Hash       crypto.Hash
+
+	// HashSuffix is extra data that is hashed in after the signed data.
+	HashSuffix []byte
+	// HashTag contains the first two bytes of the hash for fast rejection
+	// of bad signed data.
+	HashTag      [2]byte
+	CreationTime uint32 // Unix epoch time
+	Signature    []byte
+
+	// The following are optional so are nil when not included in the
+	// signature.
+
+	SigLifetimeSecs, KeyLifetimeSecs                        *uint32
+	PreferredSymmetric, PreferredHash, PreferredCompression []uint8
+	IssuerKeyId                                             *uint64
+	IsPrimaryId                                             *bool
+
+	// FlagsValid is set if any flags were given. See RFC 4880, section
+	// 5.2.3.21 for details.
+	FlagsValid                                                           bool
+	FlagCertify, FlagSign, FlagEncryptCommunications, FlagEncryptStorage bool
+
+	outSubpackets []outputSubpacket
+}
+
+func (sig *Signature) parse(r io.Reader) (err os.Error) {
+	// RFC 4880, section 5.2.3
+	var buf [5]byte
+	_, err = readFull(r, buf[:1])
+	if err != nil {
+		return
+	}
+	if buf[0] != 4 {
+		err = error.UnsupportedError("signature packet version " + strconv.Itoa(int(buf[0])))
+		return
+	}
+
+	_, err = readFull(r, buf[:5])
+	if err != nil {
+		return
+	}
+	sig.SigType = SignatureType(buf[0])
+	sig.PubKeyAlgo = PublicKeyAlgorithm(buf[1])
+	switch sig.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
+	default:
+		err = error.UnsupportedError("public key algorithm " + strconv.Itoa(int(sig.PubKeyAlgo)))
+		return
+	}
+
+	var ok bool
+	sig.Hash, ok = s2k.HashIdToHash(buf[2])
+	if !ok {
+		return error.UnsupportedError("hash function " + strconv.Itoa(int(buf[2])))
+	}
+
+	hashedSubpacketsLength := int(buf[3])<<8 | int(buf[4])
+	l := 6 + hashedSubpacketsLength
+	sig.HashSuffix = make([]byte, l+6)
+	sig.HashSuffix[0] = 4
+	copy(sig.HashSuffix[1:], buf[:5])
+	hashedSubpackets := sig.HashSuffix[6:l]
+	_, err = readFull(r, hashedSubpackets)
+	if err != nil {
+		return
+	}
+	// See RFC 4880, section 5.2.4
+	trailer := sig.HashSuffix[l:]
+	trailer[0] = 4
+	trailer[1] = 0xff
+	trailer[2] = uint8(l >> 24)
+	trailer[3] = uint8(l >> 16)
+	trailer[4] = uint8(l >> 8)
+	trailer[5] = uint8(l)
+
+	err = parseSignatureSubpackets(sig, hashedSubpackets, true)
+	if err != nil {
+		return
+	}
+
+	_, err = readFull(r, buf[:2])
+	if err != nil {
+		return
+	}
+	unhashedSubpacketsLength := int(buf[0])<<8 | int(buf[1])
+	unhashedSubpackets := make([]byte, unhashedSubpacketsLength)
+	_, err = readFull(r, unhashedSubpackets)
+	if err != nil {
+		return
+	}
+	err = parseSignatureSubpackets(sig, unhashedSubpackets, false)
+	if err != nil {
+		return
+	}
+
+	_, err = readFull(r, sig.HashTag[:2])
+	if err != nil {
+		return
+	}
+
+	// We have already checked that the public key algorithm is RSA.
+	sig.Signature, _, err = readMPI(r)
+	return
+}
+
+// parseSignatureSubpackets parses subpackets of the main signature packet. See
+// RFC 4880, section 5.2.3.1.
+func parseSignatureSubpackets(sig *Signature, subpackets []byte, isHashed bool) (err os.Error) {
+	for len(subpackets) > 0 {
+		subpackets, err = parseSignatureSubpacket(sig, subpackets, isHashed)
+		if err != nil {
+			return
+		}
+	}
+
+	if sig.CreationTime == 0 {
+		err = error.StructuralError("no creation time in signature")
+	}
+
+	return
+}
+
+type signatureSubpacketType uint8
+
+const (
+	creationTimeSubpacket        signatureSubpacketType = 2
+	signatureExpirationSubpacket signatureSubpacketType = 3
+	keyExpirySubpacket           signatureSubpacketType = 9
+	prefSymmetricAlgosSubpacket  signatureSubpacketType = 11
+	issuerSubpacket              signatureSubpacketType = 16
+	prefHashAlgosSubpacket       signatureSubpacketType = 21
+	prefCompressionSubpacket     signatureSubpacketType = 22
+	primaryUserIdSubpacket       signatureSubpacketType = 25
+	keyFlagsSubpacket            signatureSubpacketType = 27
+)
+
+// parseSignatureSubpacket parses a single subpacket. len(subpacket) is >= 1.
+func parseSignatureSubpacket(sig *Signature, subpacket []byte, isHashed bool) (rest []byte, err os.Error) {
+	// RFC 4880, section 5.2.3.1
+	var length uint32
+	switch {
+	case subpacket[0] < 192:
+		length = uint32(subpacket[0])
+		subpacket = subpacket[1:]
+	case subpacket[0] < 255:
+		if len(subpacket) < 2 {
+			goto Truncated
+		}
+		length = uint32(subpacket[0]-192)<<8 + uint32(subpacket[1]) + 192
+		subpacket = subpacket[2:]
+	default:
+		if len(subpacket) < 5 {
+			goto Truncated
+		}
+		length = uint32(subpacket[1])<<24 |
+			uint32(subpacket[2])<<16 |
+			uint32(subpacket[3])<<8 |
+			uint32(subpacket[4])
+		subpacket = subpacket[5:]
+	}
+	if length > uint32(len(subpacket)) {
+		goto Truncated
+	}
+	rest = subpacket[length:]
+	subpacket = subpacket[:length]
+	if len(subpacket) == 0 {
+		err = error.StructuralError("zero length signature subpacket")
+		return
+	}
+	packetType := subpacket[0] & 0x7f
+	isCritial := subpacket[0]&0x80 == 0x80
+	subpacket = subpacket[1:]
+	switch signatureSubpacketType(packetType) {
+	case creationTimeSubpacket:
+		if !isHashed {
+			err = error.StructuralError("signature creation time in non-hashed area")
+			return
+		}
+		if len(subpacket) != 4 {
+			err = error.StructuralError("signature creation time not four bytes")
+			return
+		}
+		sig.CreationTime = binary.BigEndian.Uint32(subpacket)
+	case signatureExpirationSubpacket:
+		// Signature expiration time, section 5.2.3.10
+		if !isHashed {
+			return
+		}
+		if len(subpacket) != 4 {
+			err = error.StructuralError("expiration subpacket with bad length")
+			return
+		}
+		sig.SigLifetimeSecs = new(uint32)
+		*sig.SigLifetimeSecs = binary.BigEndian.Uint32(subpacket)
+	case keyExpirySubpacket:
+		// Key expiration time, section 5.2.3.6
+		if !isHashed {
+			return
+		}
+		if len(subpacket) != 4 {
+			err = error.StructuralError("key expiration subpacket with bad length")
+			return
+		}
+		sig.KeyLifetimeSecs = new(uint32)
+		*sig.KeyLifetimeSecs = binary.BigEndian.Uint32(subpacket)
+	case prefSymmetricAlgosSubpacket:
+		// Preferred symmetric algorithms, section 5.2.3.7
+		if !isHashed {
+			return
+		}
+		sig.PreferredSymmetric = make([]byte, len(subpacket))
+		copy(sig.PreferredSymmetric, subpacket)
+	case issuerSubpacket:
+		// Issuer, section 5.2.3.5
+		if len(subpacket) != 8 {
+			err = error.StructuralError("issuer subpacket with bad length")
+			return
+		}
+		sig.IssuerKeyId = new(uint64)
+		*sig.IssuerKeyId = binary.BigEndian.Uint64(subpacket)
+	case prefHashAlgosSubpacket:
+		// Preferred hash algorithms, section 5.2.3.8
+		if !isHashed {
+			return
+		}
+		sig.PreferredHash = make([]byte, len(subpacket))
+		copy(sig.PreferredHash, subpacket)
+	case prefCompressionSubpacket:
+		// Preferred compression algorithms, section 5.2.3.9
+		if !isHashed {
+			return
+		}
+		sig.PreferredCompression = make([]byte, len(subpacket))
+		copy(sig.PreferredCompression, subpacket)
+	case primaryUserIdSubpacket:
+		// Primary User ID, section 5.2.3.19
+		if !isHashed {
+			return
+		}
+		if len(subpacket) != 1 {
+			err = error.StructuralError("primary user id subpacket with bad length")
+			return
+		}
+		sig.IsPrimaryId = new(bool)
+		if subpacket[0] > 0 {
+			*sig.IsPrimaryId = true
+		}
+	case keyFlagsSubpacket:
+		// Key flags, section 5.2.3.21
+		if !isHashed {
+			return
+		}
+		if len(subpacket) == 0 {
+			err = error.StructuralError("empty key flags subpacket")
+			return
+		}
+		sig.FlagsValid = true
+		if subpacket[0]&1 != 0 {
+			sig.FlagCertify = true
+		}
+		if subpacket[0]&2 != 0 {
+			sig.FlagSign = true
+		}
+		if subpacket[0]&4 != 0 {
+			sig.FlagEncryptCommunications = true
+		}
+		if subpacket[0]&8 != 0 {
+			sig.FlagEncryptStorage = true
+		}
+
+	default:
+		if isCritial {
+			err = error.UnsupportedError("unknown critical signature subpacket type " + strconv.Itoa(int(packetType)))
+			return
+		}
+	}
+	return
+
+Truncated:
+	err = error.StructuralError("signature subpacket truncated")
+	return
+}
+
+// subpacketLengthLength returns the length, in bytes, of an encoded length value.
+func subpacketLengthLength(length int) int {
+	if length < 192 {
+		return 1
+	}
+	if length < 16320 {
+		return 2
+	}
+	return 5
+}
+
+// serialiseSubpacketLength marshals the given length into to.
+func serialiseSubpacketLength(to []byte, length int) int {
+	if length < 192 {
+		to[0] = byte(length)
+		return 1
+	}
+	if length < 16320 {
+		length -= 192
+		to[0] = byte(length >> 8)
+		to[1] = byte(length)
+		return 2
+	}
+	to[0] = 255
+	to[1] = byte(length >> 24)
+	to[2] = byte(length >> 16)
+	to[3] = byte(length >> 8)
+	to[4] = byte(length)
+	return 5
+}
+
+// subpacketsLength returns the serialised length, in bytes, of the given
+// subpackets.
+func subpacketsLength(subpackets []outputSubpacket, hashed bool) (length int) {
+	for _, subpacket := range subpackets {
+		if subpacket.hashed == hashed {
+			length += subpacketLengthLength(len(subpacket.contents) + 1)
+			length += 1 // type byte
+			length += len(subpacket.contents)
+		}
+	}
+	return
+}
+
+// serialiseSubpackets marshals the given subpackets into to.
+func serialiseSubpackets(to []byte, subpackets []outputSubpacket, hashed bool) {
+	for _, subpacket := range subpackets {
+		if subpacket.hashed == hashed {
+			n := serialiseSubpacketLength(to, len(subpacket.contents)+1)
+			to[n] = byte(subpacket.subpacketType)
+			to = to[1+n:]
+			n = copy(to, subpacket.contents)
+			to = to[n:]
+		}
+	}
+	return
+}
+
+// buildHashSuffix constructs the HashSuffix member of sig in preparation for signing.
+func (sig *Signature) buildHashSuffix() (err os.Error) {
+	sig.outSubpackets = sig.buildSubpackets()
+	hashedSubpacketsLen := subpacketsLength(sig.outSubpackets, true)
+
+	var ok bool
+	l := 6 + hashedSubpacketsLen
+	sig.HashSuffix = make([]byte, l+6)
+	sig.HashSuffix[0] = 4
+	sig.HashSuffix[1] = uint8(sig.SigType)
+	sig.HashSuffix[2] = uint8(sig.PubKeyAlgo)
+	sig.HashSuffix[3], ok = s2k.HashToHashId(sig.Hash)
+	if !ok {
+		sig.HashSuffix = nil
+		return error.InvalidArgumentError("hash cannot be repesented in OpenPGP: " + strconv.Itoa(int(sig.Hash)))
+	}
+	sig.HashSuffix[4] = byte(hashedSubpacketsLen >> 8)
+	sig.HashSuffix[5] = byte(hashedSubpacketsLen)
+	serialiseSubpackets(sig.HashSuffix[6:l], sig.outSubpackets, true)
+	trailer := sig.HashSuffix[l:]
+	trailer[0] = 4
+	trailer[1] = 0xff
+	trailer[2] = byte(l >> 24)
+	trailer[3] = byte(l >> 16)
+	trailer[4] = byte(l >> 8)
+	trailer[5] = byte(l)
+	return
+}
+
+// SignRSA signs a message with an RSA private key. The hash, h, must contain
+// the hash of message to be signed and will be mutated by this function.
+func (sig *Signature) SignRSA(h hash.Hash, priv *rsa.PrivateKey) (err os.Error) {
+	err = sig.buildHashSuffix()
+	if err != nil {
+		return
+	}
+
+	h.Write(sig.HashSuffix)
+	digest := h.Sum()
+	copy(sig.HashTag[:], digest)
+	sig.Signature, err = rsa.SignPKCS1v15(rand.Reader, priv, sig.Hash, digest)
+	return
+}
+
+// Serialize marshals sig to w. SignRSA must have been called first.
+func (sig *Signature) Serialize(w io.Writer) (err os.Error) {
+	if sig.Signature == nil {
+		return error.InvalidArgumentError("Signature: need to call SignRSA before Serialize")
+	}
+
+	unhashedSubpacketsLen := subpacketsLength(sig.outSubpackets, false)
+	length := len(sig.HashSuffix) - 6 /* trailer not included */ +
+		2 /* length of unhashed subpackets */ + unhashedSubpacketsLen +
+		2 /* hash tag */ + 2 /* length of signature MPI */ + len(sig.Signature)
+	err = serialiseHeader(w, packetTypeSignature, length)
+	if err != nil {
+		return
+	}
+
+	_, err = w.Write(sig.HashSuffix[:len(sig.HashSuffix)-6])
+	if err != nil {
+		return
+	}
+
+	unhashedSubpackets := make([]byte, 2+unhashedSubpacketsLen)
+	unhashedSubpackets[0] = byte(unhashedSubpacketsLen >> 8)
+	unhashedSubpackets[1] = byte(unhashedSubpacketsLen)
+	serialiseSubpackets(unhashedSubpackets[2:], sig.outSubpackets, false)
+
+	_, err = w.Write(unhashedSubpackets)
+	if err != nil {
+		return
+	}
+	_, err = w.Write(sig.HashTag[:])
+	if err != nil {
+		return
+	}
+	return writeMPI(w, 8*uint16(len(sig.Signature)), sig.Signature)
+}
+
+// outputSubpacket represents a subpacket to be marshaled.
+type outputSubpacket struct {
+	hashed        bool // true if this subpacket is in the hashed area.
+	subpacketType signatureSubpacketType
+	contents      []byte
+}
+
+func (sig *Signature) buildSubpackets() (subpackets []outputSubpacket) {
+	creationTime := make([]byte, 4)
+	creationTime[0] = byte(sig.CreationTime >> 24)
+	creationTime[1] = byte(sig.CreationTime >> 16)
+	creationTime[2] = byte(sig.CreationTime >> 8)
+	creationTime[3] = byte(sig.CreationTime)
+	subpackets = append(subpackets, outputSubpacket{true, creationTimeSubpacket, creationTime})
+
+	if sig.IssuerKeyId != nil {
+		keyId := make([]byte, 8)
+		binary.BigEndian.PutUint64(keyId, *sig.IssuerKeyId)
+		subpackets = append(subpackets, outputSubpacket{true, issuerSubpacket, keyId})
+	}
+
+	return
+}
diff --git a/src/pkg/crypto/openpgp/packet/signature_test.go b/src/pkg/crypto/openpgp/packet/signature_test.go
new file mode 100644
index 00000000000..1305548b2ae
--- /dev/null
+++ b/src/pkg/crypto/openpgp/packet/signature_test.go
@@ -0,0 +1,28 @@
+// 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"
+	"crypto"
+	"encoding/hex"
+	"testing"
+)
+
+func TestSignatureRead(t *testing.T) {
+	signatureData, _ := hex.DecodeString(signatureDataHex)
+	buf := bytes.NewBuffer(signatureData)
+	packet, err := Read(buf)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	sig, ok := packet.(*Signature)
+	if !ok || sig.SigType != SigTypeBinary || sig.PubKeyAlgo != PubKeyAlgoRSA || sig.Hash != crypto.SHA1 {
+		t.Errorf("failed to parse, got: %#v", packet)
+	}
+}
+
+const signatureDataHex = "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"