232 lines
7.0 KiB
Go
232 lines
7.0 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package packet
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import (
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"encoding/binary"
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"io"
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"math/big"
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"strconv"
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"github.com/keybase/go-crypto/openpgp/ecdh"
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"github.com/keybase/go-crypto/openpgp/elgamal"
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"github.com/keybase/go-crypto/openpgp/errors"
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"github.com/keybase/go-crypto/rsa"
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)
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const encryptedKeyVersion = 3
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// EncryptedKey represents a public-key encrypted session key. See RFC 4880,
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// section 5.1.
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type EncryptedKey struct {
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KeyId uint64
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Algo PublicKeyAlgorithm
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CipherFunc CipherFunction // only valid after a successful Decrypt
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Key []byte // only valid after a successful Decrypt
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encryptedMPI1, encryptedMPI2 parsedMPI
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ecdh_C []byte
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}
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func (e *EncryptedKey) parse(r io.Reader) (err error) {
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var buf [10]byte
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_, err = readFull(r, buf[:])
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if err != nil {
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return
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}
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if buf[0] != encryptedKeyVersion {
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return errors.UnsupportedError("unknown EncryptedKey version " + strconv.Itoa(int(buf[0])))
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}
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e.KeyId = binary.BigEndian.Uint64(buf[1:9])
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e.Algo = PublicKeyAlgorithm(buf[9])
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switch e.Algo {
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case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
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e.encryptedMPI1.bytes, e.encryptedMPI1.bitLength, err = readMPI(r)
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case PubKeyAlgoElGamal:
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e.encryptedMPI1.bytes, e.encryptedMPI1.bitLength, err = readMPI(r)
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if err != nil {
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return
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}
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e.encryptedMPI2.bytes, e.encryptedMPI2.bitLength, err = readMPI(r)
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case PubKeyAlgoECDH:
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e.encryptedMPI1.bytes, e.encryptedMPI1.bitLength, err = readMPI(r)
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if err != nil {
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return err
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}
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_, err = readFull(r, buf[:1]) // read C len (1 byte)
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if err != nil {
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return err
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}
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e.ecdh_C = make([]byte, int(buf[0]))
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_, err = readFull(r, e.ecdh_C)
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}
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if err != nil {
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return err
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}
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_, err = consumeAll(r)
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return err
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}
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func checksumKeyMaterial(key []byte) uint16 {
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var checksum uint16
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for _, v := range key {
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checksum += uint16(v)
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}
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return checksum
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}
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// Decrypt decrypts an encrypted session key with the given private key. The
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// private key must have been decrypted first.
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// If config is nil, sensible defaults will be used.
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func (e *EncryptedKey) Decrypt(priv *PrivateKey, config *Config) error {
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if priv == nil || priv.PrivateKey == nil {
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return errors.InvalidArgumentError("attempting to decrypt with nil PrivateKey")
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}
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var err error
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var b []byte
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// TODO(agl): use session key decryption routines here to avoid
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// padding oracle attacks.
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switch priv.PubKeyAlgo {
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case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
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k := priv.PrivateKey.(*rsa.PrivateKey)
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b, err = rsa.DecryptPKCS1v15(config.Random(), k, padToKeySize(&k.PublicKey, e.encryptedMPI1.bytes))
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case PubKeyAlgoElGamal:
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c1 := new(big.Int).SetBytes(e.encryptedMPI1.bytes)
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c2 := new(big.Int).SetBytes(e.encryptedMPI2.bytes)
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b, err = elgamal.Decrypt(priv.PrivateKey.(*elgamal.PrivateKey), c1, c2)
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case PubKeyAlgoECDH:
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// Note: Unmarshal checks if point is on the curve.
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c1, c2 := ecdh.Unmarshal(priv.PrivateKey.(*ecdh.PrivateKey).Curve, e.encryptedMPI1.bytes)
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if c1 == nil {
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return errors.InvalidArgumentError("failed to parse EC point for encryption key")
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}
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b, err = decryptKeyECDH(priv, c1, c2, e.ecdh_C)
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default:
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err = errors.InvalidArgumentError("cannot decrypted encrypted session key with private key of type " + strconv.Itoa(int(priv.PubKeyAlgo)))
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}
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if err != nil {
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return err
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}
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e.CipherFunc = CipherFunction(b[0])
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e.Key = b[1 : len(b)-2]
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expectedChecksum := uint16(b[len(b)-2])<<8 | uint16(b[len(b)-1])
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checksum := checksumKeyMaterial(e.Key)
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if checksum != expectedChecksum {
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return errors.StructuralError("EncryptedKey checksum incorrect")
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}
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return nil
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}
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// Serialize writes the encrypted key packet, e, to w.
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func (e *EncryptedKey) Serialize(w io.Writer) error {
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var mpiLen int
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switch e.Algo {
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case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
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mpiLen = 2 + len(e.encryptedMPI1.bytes)
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case PubKeyAlgoElGamal:
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mpiLen = 2 + len(e.encryptedMPI1.bytes) + 2 + len(e.encryptedMPI2.bytes)
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default:
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return errors.InvalidArgumentError("don't know how to serialize encrypted key type " + strconv.Itoa(int(e.Algo)))
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}
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serializeHeader(w, packetTypeEncryptedKey, 1 /* version */ +8 /* key id */ +1 /* algo */ +mpiLen)
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w.Write([]byte{encryptedKeyVersion})
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binary.Write(w, binary.BigEndian, e.KeyId)
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w.Write([]byte{byte(e.Algo)})
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switch e.Algo {
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case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
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writeMPIs(w, e.encryptedMPI1)
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case PubKeyAlgoElGamal:
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writeMPIs(w, e.encryptedMPI1, e.encryptedMPI2)
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default:
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panic("internal error")
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}
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return nil
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}
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// SerializeEncryptedKey serializes an encrypted key packet to w that contains
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// key, encrypted to pub.
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// If config is nil, sensible defaults will be used.
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func SerializeEncryptedKey(w io.Writer, pub *PublicKey, cipherFunc CipherFunction, key []byte, config *Config) error {
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var buf [10]byte
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buf[0] = encryptedKeyVersion
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binary.BigEndian.PutUint64(buf[1:9], pub.KeyId)
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buf[9] = byte(pub.PubKeyAlgo)
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keyBlock := make([]byte, 1 /* cipher type */ +len(key)+2 /* checksum */)
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keyBlock[0] = byte(cipherFunc)
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copy(keyBlock[1:], key)
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checksum := checksumKeyMaterial(key)
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keyBlock[1+len(key)] = byte(checksum >> 8)
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keyBlock[1+len(key)+1] = byte(checksum)
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switch pub.PubKeyAlgo {
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case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly:
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return serializeEncryptedKeyRSA(w, config.Random(), buf, pub.PublicKey.(*rsa.PublicKey), keyBlock)
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case PubKeyAlgoElGamal:
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return serializeEncryptedKeyElGamal(w, config.Random(), buf, pub.PublicKey.(*elgamal.PublicKey), keyBlock)
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case PubKeyAlgoECDH:
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return serializeEncryptedKeyECDH(w, config.Random(), buf, pub, keyBlock)
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case PubKeyAlgoDSA, PubKeyAlgoRSASignOnly:
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return errors.InvalidArgumentError("cannot encrypt to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo)))
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}
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return errors.UnsupportedError("encrypting a key to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo)))
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}
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func serializeEncryptedKeyRSA(w io.Writer, rand io.Reader, header [10]byte, pub *rsa.PublicKey, keyBlock []byte) error {
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cipherText, err := rsa.EncryptPKCS1v15(rand, pub, keyBlock)
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if err != nil {
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return errors.InvalidArgumentError("RSA encryption failed: " + err.Error())
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}
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packetLen := 10 /* header length */ + 2 /* mpi size */ + len(cipherText)
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err = serializeHeader(w, packetTypeEncryptedKey, packetLen)
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if err != nil {
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return err
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}
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_, err = w.Write(header[:])
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if err != nil {
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return err
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}
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return writeMPI(w, 8*uint16(len(cipherText)), cipherText)
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}
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func serializeEncryptedKeyElGamal(w io.Writer, rand io.Reader, header [10]byte, pub *elgamal.PublicKey, keyBlock []byte) error {
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c1, c2, err := elgamal.Encrypt(rand, pub, keyBlock)
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if err != nil {
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return errors.InvalidArgumentError("ElGamal encryption failed: " + err.Error())
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}
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packetLen := 10 /* header length */
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packetLen += 2 /* mpi size */ + (c1.BitLen()+7)/8
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packetLen += 2 /* mpi size */ + (c2.BitLen()+7)/8
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err = serializeHeader(w, packetTypeEncryptedKey, packetLen)
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if err != nil {
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return err
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}
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_, err = w.Write(header[:])
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if err != nil {
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return err
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}
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err = writeBig(w, c1)
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if err != nil {
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return err
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}
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return writeBig(w, c2)
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}
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