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// 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/rsa"
"encoding/binary"
"io"
"math/big"
"strconv"
"golang.org/x/crypto/openpgp/elgamal"
"golang.org/x/crypto/openpgp/errors"
)
const encryptedKeyVersion = 3
// EncryptedKey represents a public-key encrypted session key. See RFC 4880,
// section 5.1.
type EncryptedKey struct {
KeyId uint64
Algo PublicKeyAlgorithm
CipherFunc CipherFunction // only valid after a successful Decrypt
Key []byte // only valid after a successful Decrypt
encryptedMPI1, encryptedMPI2 parsedMPI
}
func (e *EncryptedKey) parse(r io.Reader) (err error) {
var buf [10]byte
_, err = readFull(r, buf[:])
if err != nil {
return
}
if buf[0] != encryptedKeyVersion {
return errors.UnsupportedError("unknown EncryptedKey version " + strconv.Itoa(int(buf[0])))
}
e.KeyId = binary.BigEndian.Uint64(buf[1:9])
e.Algo = PublicKeyAlgorithm(buf[9])
switch e.Algo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
e.encryptedMPI1.bytes, e.encryptedMPI1.bitLength, err = readMPI(r)
case PubKeyAlgoElGamal:
e.encryptedMPI1.bytes, e.encryptedMPI1.bitLength, err = readMPI(r)
if err != nil {
return
}
e.encryptedMPI2.bytes, e.encryptedMPI2.bitLength, err = readMPI(r)
}
_, err = consumeAll(r)
return
}
func checksumKeyMaterial(key []byte) uint16 {
var checksum uint16
for _, v := range key {
checksum += uint16(v)
}
return checksum
}
// Decrypt decrypts an encrypted session key with the given private key. The
// private key must have been decrypted first.
// If config is nil, sensible defaults will be used.
func (e *EncryptedKey) Decrypt(priv *PrivateKey, config *Config) error {
var err error
var b []byte
// TODO(agl): use session key decryption routines here to avoid
// padding oracle attacks.
switch priv.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
b, err = rsa.DecryptPKCS1v15(config.Random(), priv.PrivateKey.(*rsa.PrivateKey), e.encryptedMPI1.bytes)
case PubKeyAlgoElGamal:
c1 := new(big.Int).SetBytes(e.encryptedMPI1.bytes)
c2 := new(big.Int).SetBytes(e.encryptedMPI2.bytes)
b, err = elgamal.Decrypt(priv.PrivateKey.(*elgamal.PrivateKey), c1, c2)
default:
err = errors.InvalidArgumentError("cannot decrypted encrypted session key with private key of type " + strconv.Itoa(int(priv.PubKeyAlgo)))
}
if err != nil {
return err
}
e.CipherFunc = CipherFunction(b[0])
e.Key = b[1 : len(b)-2]
expectedChecksum := uint16(b[len(b)-2])<<8 | uint16(b[len(b)-1])
checksum := checksumKeyMaterial(e.Key)
if checksum != expectedChecksum {
return errors.StructuralError("EncryptedKey checksum incorrect")
}
return nil
}
// Serialize writes the encrypted key packet, e, to w.
func (e *EncryptedKey) Serialize(w io.Writer) error {
var mpiLen int
switch e.Algo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
mpiLen = 2 + len(e.encryptedMPI1.bytes)
case PubKeyAlgoElGamal:
mpiLen = 2 + len(e.encryptedMPI1.bytes) + 2 + len(e.encryptedMPI2.bytes)
default:
return errors.InvalidArgumentError("don't know how to serialize encrypted key type " + strconv.Itoa(int(e.Algo)))
}
serializeHeader(w, packetTypeEncryptedKey, 1 /* version */ +8 /* key id */ +1 /* algo */ +mpiLen)
w.Write([]byte{encryptedKeyVersion})
binary.Write(w, binary.BigEndian, e.KeyId)
w.Write([]byte{byte(e.Algo)})
switch e.Algo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
writeMPIs(w, e.encryptedMPI1)
case PubKeyAlgoElGamal:
writeMPIs(w, e.encryptedMPI1, e.encryptedMPI2)
default:
panic("internal error")
}
return nil
}
// SerializeEncryptedKey serializes an encrypted key packet to w that contains
// key, encrypted to pub.
// If config is nil, sensible defaults will be used.
func SerializeEncryptedKey(w io.Writer, pub *PublicKey, cipherFunc CipherFunction, key []byte, config *Config) error {
var buf [10]byte
buf[0] = encryptedKeyVersion
binary.BigEndian.PutUint64(buf[1:9], pub.KeyId)
buf[9] = byte(pub.PubKeyAlgo)
keyBlock := make([]byte, 1 /* cipher type */ +len(key)+2 /* checksum */)
keyBlock[0] = byte(cipherFunc)
copy(keyBlock[1:], key)
checksum := checksumKeyMaterial(key)
keyBlock[1+len(key)] = byte(checksum >> 8)
keyBlock[1+len(key)+1] = byte(checksum)
switch pub.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
return serializeEncryptedKeyRSA(w, config.Random(), buf, pub.PublicKey.(*rsa.PublicKey), keyBlock)
case PubKeyAlgoElGamal:
return serializeEncryptedKeyElGamal(w, config.Random(), buf, pub.PublicKey.(*elgamal.PublicKey), keyBlock)
case PubKeyAlgoDSA, PubKeyAlgoRSASignOnly:
return errors.InvalidArgumentError("cannot encrypt to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo)))
}
return errors.UnsupportedError("encrypting a key to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo)))
}
func serializeEncryptedKeyRSA(w io.Writer, rand io.Reader, header [10]byte, pub *rsa.PublicKey, keyBlock []byte) error {
cipherText, err := rsa.EncryptPKCS1v15(rand, pub, keyBlock)
if err != nil {
return errors.InvalidArgumentError("RSA encryption failed: " + err.Error())
}
packetLen := 10 /* header length */ + 2 /* mpi size */ + len(cipherText)
err = serializeHeader(w, packetTypeEncryptedKey, packetLen)
if err != nil {
return err
}
_, err = w.Write(header[:])
if err != nil {
return err
}
return writeMPI(w, 8*uint16(len(cipherText)), cipherText)
}
func serializeEncryptedKeyElGamal(w io.Writer, rand io.Reader, header [10]byte, pub *elgamal.PublicKey, keyBlock []byte) error {
c1, c2, err := elgamal.Encrypt(rand, pub, keyBlock)
if err != nil {
return errors.InvalidArgumentError("ElGamal encryption failed: " + err.Error())
}
packetLen := 10 /* header length */
packetLen += 2 /* mpi size */ + (c1.BitLen()+7)/8
packetLen += 2 /* mpi size */ + (c2.BitLen()+7)/8
err = serializeHeader(w, packetTypeEncryptedKey, packetLen)
if err != nil {
return err
}
_, err = w.Write(header[:])
if err != nil {
return err
}
err = writeBig(w, c1)
if err != nil {
return err
}
return writeBig(w, c2)
}
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