1// Copyright 2011 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5package packet 6 7import ( 8 "crypto/rsa" 9 "encoding/binary" 10 "io" 11 "math/big" 12 "strconv" 13 14 "golang.org/x/crypto/openpgp/elgamal" 15 "golang.org/x/crypto/openpgp/errors" 16) 17 18const encryptedKeyVersion = 3 19 20// EncryptedKey represents a public-key encrypted session key. See RFC 4880, 21// section 5.1. 22type EncryptedKey struct { 23 KeyId uint64 24 Algo PublicKeyAlgorithm 25 CipherFunc CipherFunction // only valid after a successful Decrypt 26 Key []byte // only valid after a successful Decrypt 27 28 encryptedMPI1, encryptedMPI2 parsedMPI 29} 30 31func (e *EncryptedKey) parse(r io.Reader) (err error) { 32 var buf [10]byte 33 _, err = readFull(r, buf[:]) 34 if err != nil { 35 return 36 } 37 if buf[0] != encryptedKeyVersion { 38 return errors.UnsupportedError("unknown EncryptedKey version " + strconv.Itoa(int(buf[0]))) 39 } 40 e.KeyId = binary.BigEndian.Uint64(buf[1:9]) 41 e.Algo = PublicKeyAlgorithm(buf[9]) 42 switch e.Algo { 43 case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly: 44 e.encryptedMPI1.bytes, e.encryptedMPI1.bitLength, err = readMPI(r) 45 case PubKeyAlgoElGamal: 46 e.encryptedMPI1.bytes, e.encryptedMPI1.bitLength, err = readMPI(r) 47 if err != nil { 48 return 49 } 50 e.encryptedMPI2.bytes, e.encryptedMPI2.bitLength, err = readMPI(r) 51 } 52 _, err = consumeAll(r) 53 return 54} 55 56func checksumKeyMaterial(key []byte) uint16 { 57 var checksum uint16 58 for _, v := range key { 59 checksum += uint16(v) 60 } 61 return checksum 62} 63 64// Decrypt decrypts an encrypted session key with the given private key. The 65// private key must have been decrypted first. 66// If config is nil, sensible defaults will be used. 67func (e *EncryptedKey) Decrypt(priv *PrivateKey, config *Config) error { 68 var err error 69 var b []byte 70 71 // TODO(agl): use session key decryption routines here to avoid 72 // padding oracle attacks. 73 switch priv.PubKeyAlgo { 74 case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly: 75 b, err = rsa.DecryptPKCS1v15(config.Random(), priv.PrivateKey.(*rsa.PrivateKey), e.encryptedMPI1.bytes) 76 case PubKeyAlgoElGamal: 77 c1 := new(big.Int).SetBytes(e.encryptedMPI1.bytes) 78 c2 := new(big.Int).SetBytes(e.encryptedMPI2.bytes) 79 b, err = elgamal.Decrypt(priv.PrivateKey.(*elgamal.PrivateKey), c1, c2) 80 default: 81 err = errors.InvalidArgumentError("cannot decrypted encrypted session key with private key of type " + strconv.Itoa(int(priv.PubKeyAlgo))) 82 } 83 84 if err != nil { 85 return err 86 } 87 88 e.CipherFunc = CipherFunction(b[0]) 89 e.Key = b[1 : len(b)-2] 90 expectedChecksum := uint16(b[len(b)-2])<<8 | uint16(b[len(b)-1]) 91 checksum := checksumKeyMaterial(e.Key) 92 if checksum != expectedChecksum { 93 return errors.StructuralError("EncryptedKey checksum incorrect") 94 } 95 96 return nil 97} 98 99// Serialize writes the encrypted key packet, e, to w. 100func (e *EncryptedKey) Serialize(w io.Writer) error { 101 var mpiLen int 102 switch e.Algo { 103 case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly: 104 mpiLen = 2 + len(e.encryptedMPI1.bytes) 105 case PubKeyAlgoElGamal: 106 mpiLen = 2 + len(e.encryptedMPI1.bytes) + 2 + len(e.encryptedMPI2.bytes) 107 default: 108 return errors.InvalidArgumentError("don't know how to serialize encrypted key type " + strconv.Itoa(int(e.Algo))) 109 } 110 111 serializeHeader(w, packetTypeEncryptedKey, 1 /* version */ +8 /* key id */ +1 /* algo */ +mpiLen) 112 113 w.Write([]byte{encryptedKeyVersion}) 114 binary.Write(w, binary.BigEndian, e.KeyId) 115 w.Write([]byte{byte(e.Algo)}) 116 117 switch e.Algo { 118 case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly: 119 writeMPIs(w, e.encryptedMPI1) 120 case PubKeyAlgoElGamal: 121 writeMPIs(w, e.encryptedMPI1, e.encryptedMPI2) 122 default: 123 panic("internal error") 124 } 125 126 return nil 127} 128 129// SerializeEncryptedKey serializes an encrypted key packet to w that contains 130// key, encrypted to pub. 131// If config is nil, sensible defaults will be used. 132func SerializeEncryptedKey(w io.Writer, pub *PublicKey, cipherFunc CipherFunction, key []byte, config *Config) error { 133 var buf [10]byte 134 buf[0] = encryptedKeyVersion 135 binary.BigEndian.PutUint64(buf[1:9], pub.KeyId) 136 buf[9] = byte(pub.PubKeyAlgo) 137 138 keyBlock := make([]byte, 1 /* cipher type */ +len(key)+2 /* checksum */) 139 keyBlock[0] = byte(cipherFunc) 140 copy(keyBlock[1:], key) 141 checksum := checksumKeyMaterial(key) 142 keyBlock[1+len(key)] = byte(checksum >> 8) 143 keyBlock[1+len(key)+1] = byte(checksum) 144 145 switch pub.PubKeyAlgo { 146 case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly: 147 return serializeEncryptedKeyRSA(w, config.Random(), buf, pub.PublicKey.(*rsa.PublicKey), keyBlock) 148 case PubKeyAlgoElGamal: 149 return serializeEncryptedKeyElGamal(w, config.Random(), buf, pub.PublicKey.(*elgamal.PublicKey), keyBlock) 150 case PubKeyAlgoDSA, PubKeyAlgoRSASignOnly: 151 return errors.InvalidArgumentError("cannot encrypt to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo))) 152 } 153 154 return errors.UnsupportedError("encrypting a key to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo))) 155} 156 157func serializeEncryptedKeyRSA(w io.Writer, rand io.Reader, header [10]byte, pub *rsa.PublicKey, keyBlock []byte) error { 158 cipherText, err := rsa.EncryptPKCS1v15(rand, pub, keyBlock) 159 if err != nil { 160 return errors.InvalidArgumentError("RSA encryption failed: " + err.Error()) 161 } 162 163 packetLen := 10 /* header length */ + 2 /* mpi size */ + len(cipherText) 164 165 err = serializeHeader(w, packetTypeEncryptedKey, packetLen) 166 if err != nil { 167 return err 168 } 169 _, err = w.Write(header[:]) 170 if err != nil { 171 return err 172 } 173 return writeMPI(w, 8*uint16(len(cipherText)), cipherText) 174} 175 176func serializeEncryptedKeyElGamal(w io.Writer, rand io.Reader, header [10]byte, pub *elgamal.PublicKey, keyBlock []byte) error { 177 c1, c2, err := elgamal.Encrypt(rand, pub, keyBlock) 178 if err != nil { 179 return errors.InvalidArgumentError("ElGamal encryption failed: " + err.Error()) 180 } 181 182 packetLen := 10 /* header length */ 183 packetLen += 2 /* mpi size */ + (c1.BitLen()+7)/8 184 packetLen += 2 /* mpi size */ + (c2.BitLen()+7)/8 185 186 err = serializeHeader(w, packetTypeEncryptedKey, packetLen) 187 if err != nil { 188 return err 189 } 190 _, err = w.Write(header[:]) 191 if err != nil { 192 return err 193 } 194 err = writeBig(w, c1) 195 if err != nil { 196 return err 197 } 198 return writeBig(w, c2) 199} 200