// SymmetricallyEncrypt acts like gpg -c: it encrypts a file with a passphrase.
// The resulting WriteCloser must be closed after the contents of the file have
// been written.
func SymmetricallyEncrypt(ciphertext io.Writer, passphrase []byte, hints *FileHints) (plaintext io.WriteCloser, err error) {
if hints == nil {
hints = &FileHints{}
}
key, err := packet.SerializeSymmetricKeyEncrypted(ciphertext, rand.Reader, passphrase, packet.CipherAES128)
if err != nil {
return
}
w, err := packet.SerializeSymmetricallyEncrypted(ciphertext, packet.CipherAES128, key)
if err != nil {
return
}
return packet.SerializeLiteral(w, hints.IsBinary, hints.FileName, hints.EpochSeconds)
}
// 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}
}
literalData, err := packet.SerializeLiteral(w, hints.IsBinary, hints.FileName, hints.EpochSeconds)
if err != nil {
return nil, err
}
if signer != nil {
return signatureWriter{encryptedData, literalData, hash, hash.New(), signer}, nil
}
return literalData, nil
}