// SignIdentity adds a signature to e, from signer, attesting that identity is
// associated with e. The provided identity must already be an element of
// e.Identities and the private key of signer must have been decrypted if
// necessary.
func (e *Entity) SignIdentity(identity string, signer *Entity) os.Error {
	if signer.PrivateKey == nil {
		return error.InvalidArgumentError("signing Entity must have a private key")
	}
	if signer.PrivateKey.Encrypted {
		return error.InvalidArgumentError("signing Entity's private key must be decrypted")
	}
	ident, ok := e.Identities[identity]
	if !ok {
		return error.InvalidArgumentError("given identity string not found in Entity")
	}

	sig := &packet.Signature{
		SigType:      packet.SigTypeGenericCert,
		PubKeyAlgo:   signer.PrivateKey.PubKeyAlgo,
		Hash:         crypto.SHA256,
		CreationTime: uint32(time.Seconds()),
		IssuerKeyId:  &signer.PrivateKey.KeyId,
	}
	if err := sig.SignKey(e.PrimaryKey, signer.PrivateKey); err != nil {
		return err
	}
	ident.Signatures = append(ident.Signatures, sig)
	return nil
}

// VerifySignature 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 *PublicKey) VerifySignature(signed hash.Hash, sig *Signature) (err os.Error) {
	if !pk.CanSign() {
		return error.InvalidArgumentError("public key cannot generate signatures")
	}

	signed.Write(sig.HashSuffix)
	hashBytes := signed.Sum()

	if hashBytes[0] != sig.HashTag[0] || hashBytes[1] != sig.HashTag[1] {
		return error.SignatureError("hash tag doesn't match")
	}

	if pk.PubKeyAlgo != sig.PubKeyAlgo {
		return error.InvalidArgumentError("public key and signature use different algorithms")
	}

	switch pk.PubKeyAlgo {
	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
		rsaPublicKey, _ := pk.PublicKey.(*rsa.PublicKey)
		err = rsa.VerifyPKCS1v15(rsaPublicKey, sig.Hash, hashBytes, sig.RSASignature)
		if err != nil {
			return error.SignatureError("RSA verification failure")
		}
		return nil
	case PubKeyAlgoDSA:
		dsaPublicKey, _ := pk.PublicKey.(*dsa.PublicKey)
		if !dsa.Verify(dsaPublicKey, hashBytes, sig.DSASigR, sig.DSASigS) {
			return error.SignatureError("DSA verification failure")
		}
		return nil
	default:
		panic("shouldn't happen")
	}
	panic("unreachable")
}

func detachSign(w io.Writer, signer *Entity, message io.Reader, sigType packet.SignatureType) (err error) {
	if signer.PrivateKey == nil {
		return error_.InvalidArgumentError("signing key doesn't have a private key")
	}
	if signer.PrivateKey.Encrypted {
		return error_.InvalidArgumentError("signing key is encrypted")
	}

	sig := new(packet.Signature)
	sig.SigType = sigType
	sig.PubKeyAlgo = signer.PrivateKey.PubKeyAlgo
	sig.Hash = crypto.SHA256
	sig.CreationTime = uint32(time.Seconds())
	sig.IssuerKeyId = &signer.PrivateKey.KeyId

	h, wrappedHash, err := hashForSignature(sig.Hash, sig.SigType)
	if err != nil {
		return
	}
	io.Copy(wrappedHash, message)

	err = sig.Sign(h, signer.PrivateKey)
	if err != nil {
		return
	}

	return sig.Serialize(w)
}

// ReadArmoredKeyRing reads one or more public/private keys from an armor keyring file.
func ReadArmoredKeyRing(r io.Reader) (EntityList, os.Error) {
	block, err := armor.Decode(r)
	if err == os.EOF {
		return nil, error.InvalidArgumentError("no armored data found")
	}
	if err != nil {
		return nil, err
	}
	if block.Type != PublicKeyType && block.Type != PrivateKeyType {
		return nil, error.InvalidArgumentError("expected public or private key block, got: " + block.Type)
	}

	return ReadKeyRing(block.Body)
}

// SerializeSymmetricallyEncrypted serializes a symmetrically encrypted packet
// to w and returns a WriteCloser to which the to-be-encrypted packets can be
// written.
func SerializeSymmetricallyEncrypted(w io.Writer, c CipherFunction, key []byte) (contents io.WriteCloser, err os.Error) {
	if c.KeySize() != len(key) {
		return nil, error.InvalidArgumentError("SymmetricallyEncrypted.Serialize: bad key length")
	}
	writeCloser := noOpCloser{w}
	ciphertext, err := serializeStreamHeader(writeCloser, packetTypeSymmetricallyEncryptedMDC)
	if err != nil {
		return
	}

	_, err = ciphertext.Write([]byte{symmetricallyEncryptedVersion})
	if err != nil {
		return
	}

	block := c.new(key)
	blockSize := block.BlockSize()
	iv := make([]byte, blockSize)
	_, err = rand.Reader.Read(iv)
	if err != nil {
		return
	}
	s, prefix := cipher.NewOCFBEncrypter(block, iv, cipher.OCFBNoResync)
	_, err = ciphertext.Write(prefix)
	if err != nil {
		return
	}
	plaintext := cipher.StreamWriter{S: s, W: ciphertext}

	h := sha1.New()
	h.Write(iv)
	h.Write(iv[blockSize-2:])
	contents = &seMDCWriter{w: plaintext, h: h}
	return
}

// Decrypt decrypts an encrypted session key with the given private key. The
// private key must have been decrypted first.
func (e *EncryptedKey) Decrypt(priv *PrivateKey) 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(rand.Reader, priv.PrivateKey.(*rsa.PrivateKey), e.encryptedMPI1)
	case PubKeyAlgoElGamal:
		c1 := new(big.Int).SetBytes(e.encryptedMPI1)
		c2 := new(big.Int).SetBytes(e.encryptedMPI2)
		b, err = elgamal.Decrypt(priv.PrivateKey.(*elgamal.PrivateKey), c1, c2)
	default:
		err = error_.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 error_.StructuralError("EncryptedKey checksum incorrect")
	}

	return nil
}

// buildHashSuffix constructs the HashSuffix member of sig in preparation for signing.
func (sig *Signature) buildHashSuffix() (err os.Error) {
	hashedSubpacketsLen := subpacketsLength(sig.outSubpackets, true)

	var ok bool
	l := 6 + hashedSubpacketsLen
	sig.HashSuffix = make([]byte, l+6)
	sig.HashSuffix[0] = 4
	sig.HashSuffix[1] = uint8(sig.SigType)
	sig.HashSuffix[2] = uint8(sig.PubKeyAlgo)
	sig.HashSuffix[3], ok = s2k.HashToHashId(sig.Hash)
	if !ok {
		sig.HashSuffix = nil
		return error.InvalidArgumentError("hash cannot be represented in OpenPGP: " + strconv.Itoa(int(sig.Hash)))
	}
	sig.HashSuffix[4] = byte(hashedSubpacketsLen >> 8)
	sig.HashSuffix[5] = byte(hashedSubpacketsLen)
	serializeSubpackets(sig.HashSuffix[6:l], sig.outSubpackets, true)
	trailer := sig.HashSuffix[l:]
	trailer[0] = 4
	trailer[1] = 0xff
	trailer[2] = byte(l >> 24)
	trailer[3] = byte(l >> 16)
	trailer[4] = byte(l >> 8)
	trailer[5] = byte(l)
	return
}

// Serialize marshals sig to w. SignRSA or SignDSA must have been called first.
func (sig *Signature) Serialize(w io.Writer) (err os.Error) {
	if sig.RSASignature == nil && sig.DSASigR == nil {
		return error.InvalidArgumentError("Signature: need to call SignRSA or SignDSA before Serialize")
	}

	sigLength := 0
	switch sig.PubKeyAlgo {
	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
		sigLength = len(sig.RSASignature)
	case PubKeyAlgoDSA:
		sigLength = 2 /* MPI length */
		sigLength += (sig.DSASigR.BitLen() + 7) / 8
		sigLength += 2 /* MPI length */
		sigLength += (sig.DSASigS.BitLen() + 7) / 8
	default:
		panic("impossible")
	}

	unhashedSubpacketsLen := subpacketsLength(sig.outSubpackets, false)
	length := len(sig.HashSuffix) - 6 /* trailer not included */ +
		2 /* length of unhashed subpackets */ + unhashedSubpacketsLen +
		2 /* hash tag */ + 2 /* length of signature MPI */ + sigLength
	err = serializeHeader(w, packetTypeSignature, length)
	if err != nil {
		return
	}

	_, err = w.Write(sig.HashSuffix[:len(sig.HashSuffix)-6])
	if err != nil {
		return
	}

	unhashedSubpackets := make([]byte, 2+unhashedSubpacketsLen)
	unhashedSubpackets[0] = byte(unhashedSubpacketsLen >> 8)
	unhashedSubpackets[1] = byte(unhashedSubpacketsLen)
	serializeSubpackets(unhashedSubpackets[2:], sig.outSubpackets, false)

	_, err = w.Write(unhashedSubpackets)
	if err != nil {
		return
	}
	_, err = w.Write(sig.HashTag[:])
	if err != nil {
		return
	}

	switch sig.PubKeyAlgo {
	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
		err = writeMPI(w, 8*uint16(len(sig.RSASignature)), sig.RSASignature)
	case PubKeyAlgoDSA:
		err = writeBig(w, sig.DSASigR)
		if err == nil {
			err = writeBig(w, sig.DSASigS)
		}
	default:
		panic("impossible")
	}
	return
}

// Serialize marshals sig to w. SignRSA or SignDSA must have been called first.
func (sig *Signature) Serialize(w io.Writer) (err error) {
	if len(sig.outSubpackets) == 0 {
		sig.outSubpackets = sig.rawSubpackets
	}
	if sig.RSASignature.bytes == nil && sig.DSASigR.bytes == nil {
		return error_.InvalidArgumentError("Signature: need to call SignRSA or SignDSA before Serialize")
	}

	sigLength := 0
	switch sig.PubKeyAlgo {
	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
		sigLength = 2 + len(sig.RSASignature.bytes)
	case PubKeyAlgoDSA:
		sigLength = 2 + len(sig.DSASigR.bytes)
		sigLength += 2 + len(sig.DSASigS.bytes)
	default:
		panic("impossible")
	}

	unhashedSubpacketsLen := subpacketsLength(sig.outSubpackets, false)
	length := len(sig.HashSuffix) - 6 /* trailer not included */ +
		2 /* length of unhashed subpackets */ + unhashedSubpacketsLen +
		2 /* hash tag */ + sigLength
	err = serializeHeader(w, packetTypeSignature, length)
	if err != nil {
		return
	}

	_, err = w.Write(sig.HashSuffix[:len(sig.HashSuffix)-6])
	if err != nil {
		return
	}

	unhashedSubpackets := make([]byte, 2+unhashedSubpacketsLen)
	unhashedSubpackets[0] = byte(unhashedSubpacketsLen >> 8)
	unhashedSubpackets[1] = byte(unhashedSubpacketsLen)
	serializeSubpackets(unhashedSubpackets[2:], sig.outSubpackets, false)

	_, err = w.Write(unhashedSubpackets)
	if err != nil {
		return
	}
	_, err = w.Write(sig.HashTag[:])
	if err != nil {
		return
	}

	switch sig.PubKeyAlgo {
	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
		err = writeMPIs(w, sig.RSASignature)
	case PubKeyAlgoDSA:
		err = writeMPIs(w, sig.DSASigR, sig.DSASigS)
	default:
		panic("impossible")
	}
	return
}

// NewEntity returns an Entity that contains a fresh RSA/RSA keypair with a
// single identity composed of the given full name, comment and email, any of
// which may be empty but must not contain any of "()<>\x00".
func NewEntity(rand io.Reader, currentTimeSecs int64, name, comment, email string) (*Entity, os.Error) {
	uid := packet.NewUserId(name, comment, email)
	if uid == nil {
		return nil, error.InvalidArgumentError("user id field contained invalid characters")
	}
	signingPriv, err := rsa.GenerateKey(rand, defaultRSAKeyBits)
	if err != nil {
		return nil, err
	}
	encryptingPriv, err := rsa.GenerateKey(rand, defaultRSAKeyBits)
	if err != nil {
		return nil, err
	}

	t := uint32(currentTimeSecs)

	e := &Entity{
		PrimaryKey: packet.NewRSAPublicKey(t, &signingPriv.PublicKey, false /* not a subkey */),
		PrivateKey: packet.NewRSAPrivateKey(t, signingPriv, false /* not a subkey */),
		Identities: make(map[string]*Identity),
	}
	isPrimaryId := true
	e.Identities[uid.Id] = &Identity{
		Name:   uid.Name,
		UserId: uid,
		SelfSignature: &packet.Signature{
			CreationTime: t,
			SigType:      packet.SigTypePositiveCert,
			PubKeyAlgo:   packet.PubKeyAlgoRSA,
			Hash:         crypto.SHA256,
			IsPrimaryId:  &isPrimaryId,
			FlagsValid:   true,
			FlagSign:     true,
			FlagCertify:  true,
			IssuerKeyId:  &e.PrimaryKey.KeyId,
		},
	}

	e.Subkeys = make([]Subkey, 1)
	e.Subkeys[0] = Subkey{
		PublicKey:  packet.NewRSAPublicKey(t, &encryptingPriv.PublicKey, true /* is a subkey */),
		PrivateKey: packet.NewRSAPrivateKey(t, encryptingPriv, true /* is a subkey */),
		Sig: &packet.Signature{
			CreationTime:              t,
			SigType:                   packet.SigTypeSubkeyBinding,
			PubKeyAlgo:                packet.PubKeyAlgoRSA,
			Hash:                      crypto.SHA256,
			FlagsValid:                true,
			FlagEncryptStorage:        true,
			FlagEncryptCommunications: true,
			IssuerKeyId:               &e.PrimaryKey.KeyId,
		},
	}

	return e, nil
}

// Decrypt returns a ReadCloser, from which the decrypted contents of the
// packet can be read. An incorrect key can, with high probability, be detected
// immediately and this will result in a KeyIncorrect error being returned.
func (se *SymmetricallyEncrypted) Decrypt(c CipherFunction, key []byte) (io.ReadCloser, os.Error) {
	keySize := c.KeySize()
	if keySize == 0 {
		return nil, error.UnsupportedError("unknown cipher: " + strconv.Itoa(int(c)))
	}
	if len(key) != keySize {
		return nil, error.InvalidArgumentError("SymmetricallyEncrypted: incorrect key length")
	}

	if se.prefix == nil {
		se.prefix = make([]byte, c.blockSize()+2)
		_, err := readFull(se.contents, se.prefix)
		if err != nil {
			return nil, err
		}
	} else if len(se.prefix) != c.blockSize()+2 {
		return nil, error.InvalidArgumentError("can't try ciphers with different block lengths")
	}

	ocfbResync := cipher.OCFBResync
	if se.MDC {
		// MDC packets use a different form of OCFB mode.
		ocfbResync = cipher.OCFBNoResync
	}

	s := cipher.NewOCFBDecrypter(c.new(key), se.prefix, ocfbResync)
	if s == nil {
		return nil, error.KeyIncorrectError
	}

	plaintext := cipher.StreamReader{S: s, R: se.contents}

	if se.MDC {
		// MDC packets have an embedded hash that we need to check.
		h := sha1.New()
		h.Write(se.prefix)
		return &seMDCReader{in: plaintext, h: h}, nil
	}

	// Otherwise, we just need to wrap plaintext so that it's a valid ReadCloser.
	return seReader{plaintext}, nil
}

// readArmored reads an armored block with the given type.
func readArmored(r io.Reader, expectedType string) (body io.Reader, err os.Error) {
	block, err := armor.Decode(r)
	if err != nil {
		return
	}

	if block.Type != expectedType {
		return nil, error.InvalidArgumentError("expected '" + expectedType + "', got: " + block.Type)
	}

	return block.Body, nil
}

func (pk *PrivateKey) Serialize(w io.Writer) (err os.Error) {
	// TODO(agl): support encrypted private keys
	buf := bytes.NewBuffer(nil)
	err = pk.PublicKey.serializeWithoutHeaders(buf)
	if err != nil {
		return
	}
	buf.WriteByte(0 /* no encryption */)

	privateKeyBuf := bytes.NewBuffer(nil)

	switch priv := pk.PrivateKey.(type) {
	case *rsa.PrivateKey:
		err = serializeRSAPrivateKey(privateKeyBuf, priv)
	default:
		err = error.InvalidArgumentError("non-RSA private key")
	}
	if err != nil {
		return
	}

	ptype := packetTypePrivateKey
	contents := buf.Bytes()
	privateKeyBytes := privateKeyBuf.Bytes()
	if pk.IsSubkey {
		ptype = packetTypePrivateSubkey
	}
	err = serializeHeader(w, ptype, len(contents)+len(privateKeyBytes)+2)
	if err != nil {
		return
	}
	_, err = w.Write(contents)
	if err != nil {
		return
	}
	_, err = w.Write(privateKeyBytes)
	if err != nil {
		return
	}

	checksum := mod64kHash(privateKeyBytes)
	var checksumBytes [2]byte
	checksumBytes[0] = byte(checksum >> 8)
	checksumBytes[1] = byte(checksum)
	_, err = w.Write(checksumBytes[:])

	return
}

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 error_.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)
}

// DecryptRSA decrypts an RSA encrypted session key with the given private key.
func (e *EncryptedKey) DecryptRSA(priv *rsa.PrivateKey) (err os.Error) {
	if e.Algo != PubKeyAlgoRSA && e.Algo != PubKeyAlgoRSAEncryptOnly {
		return error.InvalidArgumentError("EncryptedKey not RSA encrypted")
	}
	b, err := rsa.DecryptPKCS1v15(rand.Reader, priv, e.Encrypted)
	if err != nil {
		return
	}
	e.CipherFunc = CipherFunction(b[0])
	e.Key = b[1 : len(b)-2]
	expectedChecksum := uint16(b[len(b)-2])<<8 | uint16(b[len(b)-1])
	var checksum uint16
	for _, v := range e.Key {
		checksum += uint16(v)
	}
	if checksum != expectedChecksum {
		return error.StructuralError("EncryptedKey checksum incorrect")
	}

	return
}

// serializeWithoutHeaders marshals the PublicKey to w in the form of an
// OpenPGP public key packet, not including the packet header.
func (pk *PublicKey) serializeWithoutHeaders(w io.Writer) (err os.Error) {
	var buf [6]byte
	buf[0] = 4
	buf[1] = byte(pk.CreationTime >> 24)
	buf[2] = byte(pk.CreationTime >> 16)
	buf[3] = byte(pk.CreationTime >> 8)
	buf[4] = byte(pk.CreationTime)
	buf[5] = byte(pk.PubKeyAlgo)

	_, err = w.Write(buf[:])
	if err != nil {
		return
	}

	switch pk.PubKeyAlgo {
	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
		return writeMPIs(w, pk.n, pk.e)
	case PubKeyAlgoDSA:
		return writeMPIs(w, pk.p, pk.q, pk.g, pk.y)
	}
	return error.InvalidArgumentError("bad public-key algorithm")
}

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 error_.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)
}

// SerializeEncryptedKey serializes an encrypted key packet to w that contains
// key, encrypted to pub.
func SerializeEncryptedKey(w io.Writer, rand io.Reader, pub *PublicKey, cipherFunc CipherFunction, key []byte) 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, rand, buf, pub.PublicKey.(*rsa.PublicKey), keyBlock)
	case PubKeyAlgoElGamal:
		return serializeEncryptedKeyElGamal(w, rand, buf, pub.PublicKey.(*elgamal.PublicKey), keyBlock)
	case PubKeyAlgoDSA, PubKeyAlgoRSASignOnly:
		return error_.InvalidArgumentError("cannot encrypt to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo)))
	}

	return error_.UnsupportedError("encrypting a key to public key of type " + strconv.Itoa(int(pub.PubKeyAlgo)))
}

// Encrypt encrypts a message to a number of recipients and, optionally, signs
// it. hints contains optional information, that is also encrypted, that aids
// the recipients in processing the message. The resulting WriteCloser must
// be closed after the contents of the file have been written.
func Encrypt(ciphertext io.Writer, to []*Entity, signed *Entity, hints *FileHints) (plaintext io.WriteCloser, err error) {
	var signer *packet.PrivateKey
	if signed != nil {
		signer = signed.signingKey().PrivateKey
		if signer == nil || signer.Encrypted {
			return nil, error_.InvalidArgumentError("signing key must be decrypted")
		}
	}

	// These are the possible ciphers that we'll use for the message.
	candidateCiphers := []uint8{
		uint8(packet.CipherAES128),
		uint8(packet.CipherAES256),
		uint8(packet.CipherCAST5),
	}
	// These are the possible hash functions that we'll use for the signature.
	candidateHashes := []uint8{
		hashToHashId(crypto.SHA256),
		hashToHashId(crypto.SHA512),
		hashToHashId(crypto.SHA1),
		hashToHashId(crypto.RIPEMD160),
	}
	// In the event that a recipient doesn't specify any supported ciphers
	// or hash functions, these are the ones that we assume that every
	// implementation supports.
	defaultCiphers := candidateCiphers[len(candidateCiphers)-1:]
	defaultHashes := candidateHashes[len(candidateHashes)-1:]

	encryptKeys := make([]Key, len(to))
	for i := range to {
		encryptKeys[i] = to[i].encryptionKey()
		if encryptKeys[i].PublicKey == nil {
			return nil, error_.InvalidArgumentError("cannot encrypt a message to key id " + strconv.Uitob64(to[i].PrimaryKey.KeyId, 16) + " because it has no encryption keys")
		}

		sig := to[i].primaryIdentity().SelfSignature

		preferredSymmetric := sig.PreferredSymmetric
		if len(preferredSymmetric) == 0 {
			preferredSymmetric = defaultCiphers
		}
		preferredHashes := sig.PreferredHash
		if len(preferredHashes) == 0 {
			preferredHashes = defaultHashes
		}
		candidateCiphers = intersectPreferences(candidateCiphers, preferredSymmetric)
		candidateHashes = intersectPreferences(candidateHashes, preferredHashes)
	}

	if len(candidateCiphers) == 0 || len(candidateHashes) == 0 {
		return nil, error_.InvalidArgumentError("cannot encrypt because recipient set shares no common algorithms")
	}

	cipher := packet.CipherFunction(candidateCiphers[0])
	hash, _ := s2k.HashIdToHash(candidateHashes[0])
	symKey := make([]byte, cipher.KeySize())
	if _, err := io.ReadFull(rand.Reader, symKey); err != nil {
		return nil, err
	}

	for _, key := range encryptKeys {
		if err := packet.SerializeEncryptedKey(ciphertext, rand.Reader, key.PublicKey, cipher, symKey); err != nil {
			return nil, err
		}
	}

	encryptedData, err := packet.SerializeSymmetricallyEncrypted(ciphertext, cipher, symKey)
	if err != nil {
		return
	}

	if signer != nil {
		ops := &packet.OnePassSignature{
			SigType:    packet.SigTypeBinary,
			Hash:       hash,
			PubKeyAlgo: signer.PubKeyAlgo,
			KeyId:      signer.KeyId,
			IsLast:     true,
		}
		if err := ops.Serialize(encryptedData); err != nil {
			return nil, err
		}
	}

	if hints == nil {
		hints = &FileHints{}
	}

	w := encryptedData
	if signer != nil {
		// If we need to write a signature packet after the literal
		// data then we need to stop literalData from closing
		// encryptedData.
		w = noOpCloser{encryptedData}

	}
//.........这里部分代码省略.........