package p2p import ( "crypto/ecdsa" "crypto/elliptic" "crypto/rand" "errors" "fmt" "hash" "io" "net" "github.com/ethereum/go-ethereum/crypto" "github.com/ethereum/go-ethereum/crypto/ecies" "github.com/ethereum/go-ethereum/crypto/secp256k1" "github.com/ethereum/go-ethereum/crypto/sha3" "github.com/ethereum/go-ethereum/p2p/discover" "github.com/ethereum/go-ethereum/rlp" ) const ( sskLen = 16 // ecies.MaxSharedKeyLength(pubKey) / 2 sigLen = 65 // elliptic S256 pubLen = 64 // 512 bit pubkey in uncompressed representation without format byte shaLen = 32 // hash length (for nonce etc) authMsgLen = sigLen + shaLen + pubLen + shaLen + 1 authRespLen = pubLen + shaLen + 1 eciesBytes = 65 + 16 + 32 encAuthMsgLen = authMsgLen + eciesBytes // size of the final ECIES payload sent as initiator's handshake encAuthRespLen = authRespLen + eciesBytes // size of the final ECIES payload sent as receiver's handshake ) // conn represents a remote connection after encryption handshake // and protocol handshake have completed. // // The MsgReadWriter is usually layered as follows: // // netWrapper (I/O timeouts, thread-safe ReadMsg, WriteMsg) // rlpxFrameRW (message encoding, encryption, authentication) // bufio.ReadWriter (buffering) // net.Conn (network I/O) // type conn struct { MsgReadWriter *protoHandshake } // secrets represents the connection secrets // which are negotiated during the encryption handshake. type secrets struct { RemoteID discover.NodeID AES, MAC []byte EgressMAC, IngressMAC hash.Hash Token []byte } // protoHandshake is the RLP structure of the protocol handshake. type protoHandshake struct { Version uint64 Name string Caps []Cap ListenPort uint64 ID discover.NodeID } // setupConn starts a protocol session on the given connection. // It runs the encryption handshake and the protocol handshake. // If dial is non-nil, the connection the local node is the initiator. func setupConn(fd net.Conn, prv *ecdsa.PrivateKey, our *protoHandshake, dial *discover.Node) (*conn, error) { if dial == nil { return setupInboundConn(fd, prv, our) } else { return setupOutboundConn(fd, prv, our, dial) } } func setupInboundConn(fd net.Conn, prv *ecdsa.PrivateKey, our *protoHandshake) (*conn, error) { secrets, err := receiverEncHandshake(fd, prv, nil) if err != nil { return nil, fmt.Errorf("encryption handshake failed: %v", err) } // Run the protocol handshake using authenticated messages. rw := newRlpxFrameRW(fd, secrets) rhs, err := readProtocolHandshake(rw, our) if err != nil { return nil, err } if rhs.ID != secrets.RemoteID { return nil, errors.New("node ID in protocol handshake does not match encryption handshake") } // TODO: validate that handshake node ID matches if err := Send(rw, handshakeMsg, our); err != nil { return nil, fmt.Errorf("protocol write error: %v", err) } return &conn{rw, rhs}, nil } func setupOutboundConn(fd net.Conn, prv *ecdsa.PrivateKey, our *protoHandshake, dial *discover.Node) (*conn, error) { secrets, err := initiatorEncHandshake(fd, prv, dial.ID, nil) if err != nil { return nil, fmt.Errorf("encryption handshake failed: %v", err) } // Run the protocol handshake using authenticated messages. rw := newRlpxFrameRW(fd, secrets) if err := Send(rw, handshakeMsg, our); err != nil { return nil, fmt.Errorf("protocol write error: %v", err) } rhs, err := readProtocolHandshake(rw, our) if err != nil { return nil, fmt.Errorf("protocol handshake read error: %v", err) } if rhs.ID != dial.ID { return nil, errors.New("dialed node id mismatch") } return &conn{rw, rhs}, nil } // encHandshake contains the state of the encryption handshake. type encHandshake struct { initiator bool remoteID discover.NodeID remotePub *ecies.PublicKey // remote-pubk initNonce, respNonce []byte // nonce randomPrivKey *ecies.PrivateKey // ecdhe-random remoteRandomPub *ecies.PublicKey // ecdhe-random-pubk } // secrets is called after the handshake is completed. // It extracts the connection secrets from the handshake values. func (h *encHandshake) secrets(auth, authResp []byte) (secrets, error) { ecdheSecret, err := h.randomPrivKey.GenerateShared(h.remoteRandomPub, sskLen, sskLen) if err != nil { return secrets{}, err } // derive base secrets from ephemeral key agreement sharedSecret := crypto.Sha3(ecdheSecret, crypto.Sha3(h.respNonce, h.initNonce)) aesSecret := crypto.Sha3(ecdheSecret, sharedSecret) s := secrets{ RemoteID: h.remoteID, AES: aesSecret, MAC: crypto.Sha3(ecdheSecret, aesSecret), Token: crypto.Sha3(sharedSecret), } // setup sha3 instances for the MACs mac1 := sha3.NewKeccak256() mac1.Write(xor(s.MAC, h.respNonce)) mac1.Write(auth) mac2 := sha3.NewKeccak256() mac2.Write(xor(s.MAC, h.initNonce)) mac2.Write(authResp) if h.initiator { s.EgressMAC, s.IngressMAC = mac1, mac2 } else { s.EgressMAC, s.IngressMAC = mac2, mac1 } return s, nil } func (h *encHandshake) ecdhShared(prv *ecdsa.PrivateKey) ([]byte, error) { return ecies.ImportECDSA(prv).GenerateShared(h.remotePub, sskLen, sskLen) } // initiatorEncHandshake negotiates a session token on conn. // it should be called on the dialing side of the connection. // // prv is the local client's private key. // token is the token from a previous session with this node. func initiatorEncHandshake(conn io.ReadWriter, prv *ecdsa.PrivateKey, remoteID discover.NodeID, token []byte) (s secrets, err error) { h, err := newInitiatorHandshake(remoteID) if err != nil { return s, err } auth, err := h.authMsg(prv, token) if err != nil { return s, err } if _, err = conn.Write(auth); err != nil { return s, err } response := make([]byte, encAuthRespLen) if _, err = io.ReadFull(conn, response); err != nil { return s, err } if err := h.decodeAuthResp(response, prv); err != nil { return s, err } return h.secrets(auth, response) } func newInitiatorHandshake(remoteID discover.NodeID) (*encHandshake, error) { // generate random initiator nonce n := make([]byte, shaLen) if _, err := rand.Read(n); err != nil { return nil, err } // generate random keypair to use for signing randpriv, err := ecies.GenerateKey(rand.Reader, crypto.S256(), nil) if err != nil { return nil, err } rpub, err := remoteID.Pubkey() if err != nil { return nil, fmt.Errorf("bad remoteID: %v", err) } h := &encHandshake{ initiator: true, remoteID: remoteID, remotePub: ecies.ImportECDSAPublic(rpub), initNonce: n, randomPrivKey: randpriv, } return h, nil } // authMsg creates an encrypted initiator handshake message. func (h *encHandshake) authMsg(prv *ecdsa.PrivateKey, token []byte) ([]byte, error) { var tokenFlag byte if token == nil { // no session token found 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 var err error if token, err = h.ecdhShared(prv); err != nil { return nil, err } } else { // for known peers, we use stored token from the previous session tokenFlag = 0x01 } // sign known message: // ecdh-shared-secret^nonce for new peers // token^nonce for old peers signed := xor(token, h.initNonce) signature, err := crypto.Sign(signed, h.randomPrivKey.ExportECDSA()) if err != nil { return nil, err } // encode auth message // signature || sha3(ecdhe-random-pubk) || pubk || nonce || token-flag msg := make([]byte, authMsgLen) n := copy(msg, signature) n += copy(msg[n:], crypto.Sha3(exportPubkey(&h.randomPrivKey.PublicKey))) n += copy(msg[n:], crypto.FromECDSAPub(&prv.PublicKey)[1:]) n += copy(msg[n:], h.initNonce) msg[n] = tokenFlag // encrypt auth message using remote-pubk return ecies.Encrypt(rand.Reader, h.remotePub, msg, nil, 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 } // receiverEncHandshake negotiates a session token on conn. // it should be called on the listening side of the connection. // // prv is the local client's private key. // token is the token from a previous session with this node. func receiverEncHandshake(conn io.ReadWriter, prv *ecdsa.PrivateKey, token []byte) (s secrets, err error) { // read remote auth sent by initiator. auth := make([]byte, encAuthMsgLen) if _, err := io.ReadFull(conn, auth); err != nil { return s, err } h, err := decodeAuthMsg(prv, token, auth) if err != nil { return s, err } // send auth response resp, err := h.authResp(prv, token) if err != nil { return s, err } if _, err = conn.Write(resp); err != nil { return s, err } return h.secrets(auth, resp) } 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, crypto.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 } h.remoteRandomPub, _ = importPublicKey(remoteRandomPub) return h, nil } // authResp generates the encrypted authentication response message. func (h *encHandshake) authResp(prv *ecdsa.PrivateKey, token []byte) ([]byte, error) { // responder auth message // E(remote-pubk, ecdhe-random-pubk || nonce || 0x0) resp := make([]byte, authRespLen) n := copy(resp, exportPubkey(&h.randomPrivKey.PublicKey)) n += copy(resp[n:], h.respNonce) if token == nil { resp[n] = 0 } else { resp[n] = 1 } // encrypt using remote-pubk return ecies.Encrypt(rand.Reader, h.remotePub, resp, nil, nil) } // importPublicKey unmarshals 512 bit public keys. func importPublicKey(pubKey []byte) (*ecies.PublicKey, error) { var pubKey65 []byte switch len(pubKey) { case 64: // add 'uncompressed key' flag pubKey65 = append([]byte{0x04}, pubKey...) case 65: pubKey65 = pubKey default: return nil, fmt.Errorf("invalid public key length %v (expect 64/65)", len(pubKey)) } // TODO: fewer pointless conversions return ecies.ImportECDSAPublic(crypto.ToECDSAPub(pubKey65)), nil } func exportPubkey(pub *ecies.PublicKey) []byte { if pub == nil { panic("nil pubkey") } return elliptic.Marshal(pub.Curve, pub.X, pub.Y)[1:] } func xor(one, other []byte) (xor []byte) { xor = make([]byte, len(one)) for i := 0; i < len(one); i++ { xor[i] = one[i] ^ other[i] } return xor } func readProtocolHandshake(r MsgReader, our *protoHandshake) (*protoHandshake, error) { // read and handle remote handshake msg, err := r.ReadMsg() if err != nil { return nil, err } if msg.Code == discMsg { // disconnect before protocol handshake is valid according to the // spec and we send it ourself if Server.addPeer fails. var reason DiscReason rlp.Decode(msg.Payload, &reason) return nil, reason } if msg.Code != handshakeMsg { return nil, fmt.Errorf("expected handshake, got %x", msg.Code) } if msg.Size > baseProtocolMaxMsgSize { return nil, fmt.Errorf("message too big (%d > %d)", msg.Size, baseProtocolMaxMsgSize) } var hs protoHandshake if err := msg.Decode(&hs); err != nil { return nil, err } // validate handshake info if hs.Version != our.Version { return nil, newPeerError(errP2PVersionMismatch, "required version %d, received %d\n", baseProtocolVersion, hs.Version) } if (hs.ID == discover.NodeID{}) { return nil, newPeerError(errPubkeyInvalid, "missing") } return &hs, nil }