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.
// If atcap is true, the connection will be disconnected with DiscTooManyPeers
// after the key exchange.
func setupConn(fd net.Conn, prv *ecdsa.PrivateKey, our *protoHandshake, dial *discover.Node, atcap bool) (*conn, error) {
if dial == nil {
return setupInboundConn(fd, prv, our, atcap)
} else {
return setupOutboundConn(fd, prv, our, dial, atcap)
}
}
func setupInboundConn(fd net.Conn, prv *ecdsa.PrivateKey, our *protoHandshake, atcap bool) (*conn, error) {
secrets, err := receiverEncHandshake(fd, prv, nil)
if err != nil {
return nil, fmt.Errorf("encryption handshake failed: %v", err)
}
rw := newRlpxFrameRW(fd, secrets)
if atcap {
SendItems(rw, discMsg, DiscTooManyPeers)
return nil, errors.New("we have too many peers")
}
// Run the protocol handshake using authenticated messages.
rhs, err := readProtocolHandshake(rw, secrets.RemoteID, our)
if err != nil {
return nil, err
}
if err := Send(rw, handshakeMsg, our); err != nil {
return nil, fmt.Errorf("protocol handshake write error: %v", err)
}
return &conn{rw, rhs}, nil
}
func setupOutboundConn(fd net.Conn, prv *ecdsa.PrivateKey, our *protoHandshake, dial *discover.Node, atcap bool) (*conn, error) {
secrets, err := initiatorEncHandshake(fd, prv, dial.ID, nil)
if err != nil {
return nil, fmt.Errorf("encryption handshake failed: %v", err)
}
rw := newRlpxFrameRW(fd, secrets)
if atcap {
SendItems(rw, discMsg, DiscTooManyPeers)
return nil, errors.New("we have too many peers")
}
// Run the protocol handshake using authenticated messages.
//
// Note that even though writing the handshake is first, we prefer
// returning the handshake read error. If the remote side
// disconnects us early with a valid reason, we should return it
// as the error so it can be tracked elsewhere.
werr := make(chan error, 1)
go func() { werr <- Send(rw, handshakeMsg, our) }()
rhs, err := readProtocolHandshake(rw, secrets.RemoteID, our)
if err != nil {
return nil, err
}
if err := <-werr; err != nil {
return nil, fmt.Errorf("protocol handshake write 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(rw MsgReadWriter, wantID discover.NodeID, our *protoHandshake) (*protoHandshake, error) {
msg, err := rw.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 [1]DiscReason
rlp.Decode(msg.Payload, &reason)
return nil, reason[0]
}
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 {
SendItems(rw, discMsg, DiscIncompatibleVersion)
return nil, fmt.Errorf("required version %d, received %d\n", baseProtocolVersion, hs.Version)
}
if (hs.ID == discover.NodeID{}) {
SendItems(rw, discMsg, DiscInvalidIdentity)
return nil, errors.New("invalid public key in handshake")
}
if hs.ID != wantID {
SendItems(rw, discMsg, DiscUnexpectedIdentity)
return nil, errors.New("handshake node ID does not match encryption handshake")
}
return &hs, nil
}
