// decrypt decrypts an encrypted payload with a private key.
func (self *Message) decrypt(key *ecdsa.PrivateKey) error {
cleartext, err := crypto.Decrypt(key, self.Payload)
if err == nil {
self.Payload = cleartext
}
return err
}
func decodeAuthMsg(prv *ecdsa.PrivateKey, token []byte, auth []byte) (*encHandshake, error) {
var err error
h := new(encHandshake)
// generate random keypair for session
h.randomPrivKey, err = ecies.GenerateKey(rand.Reader, secp256k1.S256(), nil)
if err != nil {
return nil, err
}
// generate random nonce
h.respNonce = make([]byte, shaLen)
if _, err = rand.Read(h.respNonce); err != nil {
return nil, err
}
msg, err := crypto.Decrypt(prv, auth)
if err != nil {
return nil, fmt.Errorf("could not decrypt auth message (%v)", err)
}
// decode message parameters
// signature || sha3(ecdhe-random-pubk) || pubk || nonce || token-flag
h.initNonce = msg[authMsgLen-shaLen-1 : authMsgLen-1]
copy(h.remoteID[:], msg[sigLen+shaLen:sigLen+shaLen+pubLen])
rpub, err := h.remoteID.Pubkey()
if err != nil {
return nil, fmt.Errorf("bad remoteID: %#v", err)
}
h.remotePub = ecies.ImportECDSAPublic(rpub)
// recover remote random pubkey from signed message.
if token == nil {
// TODO: it is an error if the initiator has a token and we don't. check that.
// no session token means we need to generate shared secret.
// ecies shared secret is used as initial session token for new peers.
// generate shared key from prv and remote pubkey.
if token, err = h.ecdhShared(prv); err != nil {
return nil, err
}
}
signedMsg := xor(token, h.initNonce)
remoteRandomPub, err := secp256k1.RecoverPubkey(signedMsg, msg[:sigLen])
if err != nil {
return nil, err
}
// validate the sha3 of recovered pubkey
remoteRandomPubMAC := msg[sigLen : sigLen+shaLen]
shaRemoteRandomPub := crypto.Sha3(remoteRandomPub[1:])
if !bytes.Equal(remoteRandomPubMAC, shaRemoteRandomPub) {
return nil, fmt.Errorf("sha3 of recovered ephemeral pubkey does not match checksum in auth message")
}
h.remoteRandomPub, _ = importPublicKey(remoteRandomPub)
return h, nil
}
// decodeAuthResp decode an encrypted authentication response message.
func (h *encHandshake) decodeAuthResp(auth []byte, prv *ecdsa.PrivateKey) error {
msg, err := crypto.Decrypt(prv, auth)
if err != nil {
return fmt.Errorf("could not decrypt auth response (%v)", err)
}
h.respNonce = msg[pubLen : pubLen+shaLen]
h.remoteRandomPub, err = importPublicKey(msg[:pubLen])
if err != nil {
return err
}
// ignore token flag for now
return nil
}