// Copyright 2013 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/md5"
"crypto/rsa"
"encoding/binary"
"fmt"
"hash"
"io"
"math/big"
"strconv"
"time"
"golang.org/x/crypto/openpgp/errors"
)
// PublicKeyV3 represents older, version 3 public keys. These keys are less secure and
// should not be used for signing or encrypting. They are supported here only for
// parsing version 3 key material and validating signatures.
// See RFC 4880, section 5.5.2.
type PublicKeyV3 struct {
CreationTime time.Time
DaysToExpire uint16
PubKeyAlgo PublicKeyAlgorithm
PublicKey *rsa.PublicKey
Fingerprint [16]byte
KeyId uint64
IsSubkey bool
n, e parsedMPI
}
// newRSAPublicKeyV3 returns a PublicKey that wraps the given rsa.PublicKey.
// Included here for testing purposes only. RFC 4880, section 5.5.2:
// "an implementation MUST NOT generate a V3 key, but MAY accept it."
func newRSAPublicKeyV3(creationTime time.Time, pub *rsa.PublicKey) *PublicKeyV3 {
pk := &PublicKeyV3{
CreationTime: creationTime,
PublicKey: pub,
n: fromBig(pub.N),
e: fromBig(big.NewInt(int64(pub.E))),
}
pk.setFingerPrintAndKeyId()
return pk
}
func (pk *PublicKeyV3) parse(r io.Reader) (err error) {
// RFC 4880, section 5.5.2
var buf [8]byte
if _, err = readFull(r, buf[:]); err != nil {
return
}
if buf[0] < 2 || buf[0] > 3 {
return errors.UnsupportedError("public key version")
}
pk.CreationTime = time.Unix(int64(uint32(buf[1])<<24|uint32(buf[2])<<16|uint32(buf[3])<<8|uint32(buf[4])), 0)
pk.DaysToExpire = binary.BigEndian.Uint16(buf[5:7])
pk.PubKeyAlgo = PublicKeyAlgorithm(buf[7])
switch pk.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
err = pk.parseRSA(r)
default:
err = errors.UnsupportedError("public key type: " + strconv.Itoa(int(pk.PubKeyAlgo)))
}
if err != nil {
return
}
pk.setFingerPrintAndKeyId()
return
}
func (pk *PublicKeyV3) setFingerPrintAndKeyId() {
// RFC 4880, section 12.2
fingerPrint := md5.New()
fingerPrint.Write(pk.n.bytes)
fingerPrint.Write(pk.e.bytes)
fingerPrint.Sum(pk.Fingerprint[:0])
pk.KeyId = binary.BigEndian.Uint64(pk.n.bytes[len(pk.n.bytes)-8:])
}
// parseRSA parses RSA public key material from the given Reader. See RFC 4880,
// section 5.5.2.
func (pk *PublicKeyV3) parseRSA(r io.Reader) (err error) {
if pk.n.bytes, pk.n.bitLength, err = readMPI(r); err != nil {
return
}
if pk.e.bytes, pk.e.bitLength, err = readMPI(r); err != nil {
return
}
// RFC 4880 Section 12.2 requires the low 8 bytes of the
// modulus to form the key id.
if len(pk.n.bytes) < 8 {
return errors.StructuralError("v3 public key modulus is too short")
}
if len(pk.e.bytes) > 3 {
err = errors.UnsupportedError("large public exponent")
return
}
rsa := &rsa.PublicKey{N: new(big.Int).SetBytes(pk.n.bytes)}
for i := 0; i < len(pk.e.bytes); i++ {
rsa.E <<= 8
rsa.E |= int(pk.e.bytes[i])
}
pk.PublicKey = rsa
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 *PublicKeyV3) SerializeSignaturePrefix(w io.Writer) {
var pLength uint16
switch pk.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
pLength += 2 + uint16(len(pk.n.bytes))
pLength += 2 + uint16(len(pk.e.bytes))
default:
panic("unknown public key algorithm")
}
pLength += 6
w.Write([]byte{0x99, byte(pLength >> 8), byte(pLength)})
return
}
func (pk *PublicKeyV3) Serialize(w io.Writer) (err error) {
length := 8 // 8 byte header
switch pk.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
length += 2 + len(pk.n.bytes)
length += 2 + len(pk.e.bytes)
default:
panic("unknown public key algorithm")
}
packetType := packetTypePublicKey
if pk.IsSubkey {
packetType = packetTypePublicSubkey
}
if err = serializeHeader(w, packetType, length); err != nil {
return
}
return pk.serializeWithoutHeaders(w)
}
// serializeWithoutHeaders marshals the PublicKey to w in the form of an
// OpenPGP public key packet, not including the packet header.
func (pk *PublicKeyV3) serializeWithoutHeaders(w io.Writer) (err error) {
var buf [8]byte
// Version 3
buf[0] = 3
// Creation time
t := uint32(pk.CreationTime.Unix())
buf[1] = byte(t >> 24)
buf[2] = byte(t >> 16)
buf[3] = byte(t >> 8)
buf[4] = byte(t)
// Days to expire
buf[5] = byte(pk.DaysToExpire >> 8)
buf[6] = byte(pk.DaysToExpire)
// Public key algorithm
buf[7] = byte(pk.PubKeyAlgo)
if _, err = w.Write(buf[:]); err != nil {
return
}
switch pk.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
return writeMPIs(w, pk.n, pk.e)
}
return errors.InvalidArgumentError("bad public-key algorithm")
}
// CanSign returns true iff this public key can generate signatures
func (pk *PublicKeyV3) CanSign() bool {
return pk.PubKeyAlgo != PubKeyAlgoRSAEncryptOnly
}
// VerifySignatureV3 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 *PublicKeyV3) VerifySignatureV3(signed hash.Hash, sig *SignatureV3) (err error) {
if !pk.CanSign() {
return errors.InvalidArgumentError("public key cannot generate signatures")
}
suffix := make([]byte, 5)
suffix[0] = byte(sig.SigType)
binary.BigEndian.PutUint32(suffix[1:], uint32(sig.CreationTime.Unix()))
signed.Write(suffix)
hashBytes := signed.Sum(nil)
if hashBytes[0] != sig.HashTag[0] || hashBytes[1] != sig.HashTag[1] {
return errors.SignatureError("hash tag doesn't match")
}
if pk.PubKeyAlgo != sig.PubKeyAlgo {
return errors.InvalidArgumentError("public key and signature use different algorithms")
}
switch pk.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
if err = rsa.VerifyPKCS1v15(pk.PublicKey, sig.Hash, hashBytes, sig.RSASignature.bytes); err != nil {
return errors.SignatureError("RSA verification failure")
}
return
default:
// V3 public keys only support RSA.
panic("shouldn't happen")
}
}
// VerifyUserIdSignatureV3 returns nil iff sig is a valid signature, made by this
// public key, that id is the identity of pub.
func (pk *PublicKeyV3) VerifyUserIdSignatureV3(id string, pub *PublicKeyV3, sig *SignatureV3) (err error) {
h, err := userIdSignatureV3Hash(id, pk, sig.Hash)
if err != nil {
return err
}
return pk.VerifySignatureV3(h, sig)
}
// VerifyKeySignatureV3 returns nil iff sig is a valid signature, made by this
// public key, of signed.
func (pk *PublicKeyV3) VerifyKeySignatureV3(signed *PublicKeyV3, sig *SignatureV3) (err error) {
h, err := keySignatureHash(pk, signed, sig.Hash)
if err != nil {
return err
}
return pk.VerifySignatureV3(h, sig)
}
// userIdSignatureV3Hash returns a Hash of the message that needs to be signed
// to assert that pk is a valid key for id.
func userIdSignatureV3Hash(id string, pk signingKey, hfn crypto.Hash) (h hash.Hash, err error) {
if !hfn.Available() {
return nil, errors.UnsupportedError("hash function")
}
h = hfn.New()
// RFC 4880, section 5.2.4
pk.SerializeSignaturePrefix(h)
pk.serializeWithoutHeaders(h)
h.Write([]byte(id))
return
}
// KeyIdString returns the public key's fingerprint in capital hex
// (e.g. "6C7EE1B8621CC013").
func (pk *PublicKeyV3) KeyIdString() string {
return fmt.Sprintf("%X", pk.KeyId)
}
// KeyIdShortString returns the short form of public key's fingerprint
// in capital hex, as shown by gpg --list-keys (e.g. "621CC013").
func (pk *PublicKeyV3) KeyIdShortString() string {
return fmt.Sprintf("%X", pk.KeyId&0xFFFFFFFF)
}
// BitLength returns the bit length for the given public key.
func (pk *PublicKeyV3) BitLength() (bitLength uint16, err error) {
switch pk.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
bitLength = pk.n.bitLength
default:
err = errors.InvalidArgumentError("bad public-key algorithm")
}
return
}
