vendor/golang.org/x/crypto/openpgp/packet/encrypted_key.go

   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
   5 package packet
   6
   7 import (
   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
  18 const encryptedKeyVersion = 3
  19
  20 // EncryptedKey represents a public-key encrypted session key. See RFC 4880,
  21 // section 5.1.
  22 type 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
  31 func (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
  56 func 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.
  67 func (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.
 100 func (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.
 132 func 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
 157 func 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
 176 func 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 }