Official Go implementation of the Ethereum protocol
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go-ethereum/p2p/rlpx/rlpx.go

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// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
// Package rlpx implements the RLPx transport protocol.
package rlpx
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/hmac"
"crypto/rand"
"encoding/binary"
"errors"
"fmt"
"hash"
"io"
mrand "math/rand"
"net"
"time"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/crypto/ecies"
"github.com/ethereum/go-ethereum/rlp"
"github.com/golang/snappy"
"golang.org/x/crypto/sha3"
)
// Conn is an RLPx network connection. It wraps a low-level network connection. The
// underlying connection should not be used for other activity when it is wrapped by Conn.
//
// Before sending messages, a handshake must be performed by calling the Handshake method.
// This type is not generally safe for concurrent use, but reading and writing of messages
// may happen concurrently after the handshake.
type Conn struct {
dialDest *ecdsa.PublicKey
conn net.Conn
session *sessionState
// These are the buffers for snappy compression.
// Compression is enabled if they are non-nil.
snappyReadBuffer []byte
snappyWriteBuffer []byte
}
// sessionState contains the session keys.
type sessionState struct {
enc cipher.Stream
dec cipher.Stream
egressMAC hashMAC
ingressMAC hashMAC
rbuf readBuffer
wbuf writeBuffer
}
// hashMAC holds the state of the RLPx v4 MAC contraption.
type hashMAC struct {
cipher cipher.Block
hash hash.Hash
aesBuffer [16]byte
hashBuffer [32]byte
seedBuffer [32]byte
}
func newHashMAC(cipher cipher.Block, h hash.Hash) hashMAC {
m := hashMAC{cipher: cipher, hash: h}
if cipher.BlockSize() != len(m.aesBuffer) {
panic(fmt.Errorf("invalid MAC cipher block size %d", cipher.BlockSize()))
}
if h.Size() != len(m.hashBuffer) {
panic(fmt.Errorf("invalid MAC digest size %d", h.Size()))
}
return m
}
// NewConn wraps the given network connection. If dialDest is non-nil, the connection
// behaves as the initiator during the handshake.
func NewConn(conn net.Conn, dialDest *ecdsa.PublicKey) *Conn {
return &Conn{
dialDest: dialDest,
conn: conn,
}
}
// SetSnappy enables or disables snappy compression of messages. This is usually called
// after the devp2p Hello message exchange when the negotiated version indicates that
// compression is available on both ends of the connection.
func (c *Conn) SetSnappy(snappy bool) {
if snappy {
c.snappyReadBuffer = []byte{}
c.snappyWriteBuffer = []byte{}
} else {
c.snappyReadBuffer = nil
c.snappyWriteBuffer = nil
}
}
// SetReadDeadline sets the deadline for all future read operations.
func (c *Conn) SetReadDeadline(time time.Time) error {
return c.conn.SetReadDeadline(time)
}
// SetWriteDeadline sets the deadline for all future write operations.
func (c *Conn) SetWriteDeadline(time time.Time) error {
return c.conn.SetWriteDeadline(time)
}
// SetDeadline sets the deadline for all future read and write operations.
func (c *Conn) SetDeadline(time time.Time) error {
return c.conn.SetDeadline(time)
}
// Read reads a message from the connection.
// The returned data buffer is valid until the next call to Read.
func (c *Conn) Read() (code uint64, data []byte, wireSize int, err error) {
if c.session == nil {
panic("can't ReadMsg before handshake")
}
frame, err := c.session.readFrame(c.conn)
if err != nil {
return 0, nil, 0, err
}
code, data, err = rlp.SplitUint64(frame)
if err != nil {
return 0, nil, 0, fmt.Errorf("invalid message code: %v", err)
}
wireSize = len(data)
// If snappy is enabled, verify and decompress message.
if c.snappyReadBuffer != nil {
var actualSize int
actualSize, err = snappy.DecodedLen(data)
if err != nil {
return code, nil, 0, err
}
if actualSize > maxUint24 {
return code, nil, 0, errPlainMessageTooLarge
}
c.snappyReadBuffer = growslice(c.snappyReadBuffer, actualSize)
data, err = snappy.Decode(c.snappyReadBuffer, data)
}
return code, data, wireSize, err
}
func (h *sessionState) readFrame(conn io.Reader) ([]byte, error) {
h.rbuf.reset()
// Read the frame header.
header, err := h.rbuf.read(conn, 32)
if err != nil {
return nil, err
}
// Verify header MAC.
wantHeaderMAC := h.ingressMAC.computeHeader(header[:16])
if !hmac.Equal(wantHeaderMAC, header[16:]) {
return nil, errors.New("bad header MAC")
}
// Decrypt the frame header to get the frame size.
h.dec.XORKeyStream(header[:16], header[:16])
fsize := readUint24(header[:16])
// Frame size rounded up to 16 byte boundary for padding.
rsize := fsize
if padding := fsize % 16; padding > 0 {
rsize += 16 - padding
}
// Read the frame content.
frame, err := h.rbuf.read(conn, int(rsize))
if err != nil {
return nil, err
}
// Validate frame MAC.
frameMAC, err := h.rbuf.read(conn, 16)
if err != nil {
return nil, err
}
wantFrameMAC := h.ingressMAC.computeFrame(frame)
if !hmac.Equal(wantFrameMAC, frameMAC) {
return nil, errors.New("bad frame MAC")
}
// Decrypt the frame data.
h.dec.XORKeyStream(frame, frame)
return frame[:fsize], nil
}
// Write writes a message to the connection.
//
// Write returns the written size of the message data. This may be less than or equal to
// len(data) depending on whether snappy compression is enabled.
func (c *Conn) Write(code uint64, data []byte) (uint32, error) {
if c.session == nil {
panic("can't WriteMsg before handshake")
}
if len(data) > maxUint24 {
return 0, errPlainMessageTooLarge
}
if c.snappyWriteBuffer != nil {
// Ensure the buffer has sufficient size.
// Package snappy will allocate its own buffer if the provided
// one is smaller than MaxEncodedLen.
c.snappyWriteBuffer = growslice(c.snappyWriteBuffer, snappy.MaxEncodedLen(len(data)))
data = snappy.Encode(c.snappyWriteBuffer, data)
}
wireSize := uint32(len(data))
err := c.session.writeFrame(c.conn, code, data)
return wireSize, err
}
func (h *sessionState) writeFrame(conn io.Writer, code uint64, data []byte) error {
h.wbuf.reset()
// Write header.
fsize := rlp.IntSize(code) + len(data)
if fsize > maxUint24 {
return errPlainMessageTooLarge
}
header := h.wbuf.appendZero(16)
putUint24(uint32(fsize), header)
copy(header[3:], zeroHeader)
h.enc.XORKeyStream(header, header)
// Write header MAC.
h.wbuf.Write(h.egressMAC.computeHeader(header))
// Encode and encrypt the frame data.
offset := len(h.wbuf.data)
h.wbuf.data = rlp.AppendUint64(h.wbuf.data, code)
h.wbuf.Write(data)
if padding := fsize % 16; padding > 0 {
h.wbuf.appendZero(16 - padding)
}
framedata := h.wbuf.data[offset:]
h.enc.XORKeyStream(framedata, framedata)
// Write frame MAC.
h.wbuf.Write(h.egressMAC.computeFrame(framedata))
_, err := conn.Write(h.wbuf.data)
return err
}
// computeHeader computes the MAC of a frame header.
func (m *hashMAC) computeHeader(header []byte) []byte {
sum1 := m.hash.Sum(m.hashBuffer[:0])
return m.compute(sum1, header)
}
// computeFrame computes the MAC of framedata.
func (m *hashMAC) computeFrame(framedata []byte) []byte {
m.hash.Write(framedata)
seed := m.hash.Sum(m.seedBuffer[:0])
return m.compute(seed, seed[:16])
}
// compute computes the MAC of a 16-byte 'seed'.
//
// To do this, it encrypts the current value of the hash state, then XORs the ciphertext
// with seed. The obtained value is written back into the hash state and hash output is
// taken again. The first 16 bytes of the resulting sum are the MAC value.
//
// This MAC construction is a horrible, legacy thing.
func (m *hashMAC) compute(sum1, seed []byte) []byte {
if len(seed) != len(m.aesBuffer) {
panic("invalid MAC seed")
}
m.cipher.Encrypt(m.aesBuffer[:], sum1)
for i := range m.aesBuffer {
m.aesBuffer[i] ^= seed[i]
}
m.hash.Write(m.aesBuffer[:])
sum2 := m.hash.Sum(m.hashBuffer[:0])
return sum2[:16]
}
// Handshake performs the handshake. This must be called before any data is written
// or read from the connection.
func (c *Conn) Handshake(prv *ecdsa.PrivateKey) (*ecdsa.PublicKey, error) {
var (
sec Secrets
err error
h handshakeState
)
if c.dialDest != nil {
sec, err = h.runInitiator(c.conn, prv, c.dialDest)
} else {
sec, err = h.runRecipient(c.conn, prv)
}
if err != nil {
return nil, err
}
c.InitWithSecrets(sec)
c.session.rbuf = h.rbuf
c.session.wbuf = h.wbuf
return sec.remote, err
}
// InitWithSecrets injects connection secrets as if a handshake had
// been performed. This cannot be called after the handshake.
func (c *Conn) InitWithSecrets(sec Secrets) {
if c.session != nil {
panic("can't handshake twice")
}
macc, err := aes.NewCipher(sec.MAC)
if err != nil {
panic("invalid MAC secret: " + err.Error())
}
encc, err := aes.NewCipher(sec.AES)
if err != nil {
panic("invalid AES secret: " + err.Error())
}
// we use an all-zeroes IV for AES because the key used
// for encryption is ephemeral.
iv := make([]byte, encc.BlockSize())
c.session = &sessionState{
enc: cipher.NewCTR(encc, iv),
dec: cipher.NewCTR(encc, iv),
egressMAC: newHashMAC(macc, sec.EgressMAC),
ingressMAC: newHashMAC(macc, sec.IngressMAC),
}
}
// Close closes the underlying network connection.
func (c *Conn) Close() error {
return c.conn.Close()
}
// Constants for the handshake.
const (
sskLen = 16 // ecies.MaxSharedKeyLength(pubKey) / 2
sigLen = crypto.SignatureLength // elliptic S256
pubLen = 64 // 512 bit pubkey in uncompressed representation without format byte
shaLen = 32 // hash length (for nonce etc)
eciesOverhead = 65 /* pubkey */ + 16 /* IV */ + 32 /* MAC */
)
var (
// this is used in place of actual frame header data.
// TODO: replace this when Msg contains the protocol type code.
zeroHeader = []byte{0xC2, 0x80, 0x80}
// errPlainMessageTooLarge is returned if a decompressed message length exceeds
// the allowed 24 bits (i.e. length >= 16MB).
errPlainMessageTooLarge = errors.New("message length >= 16MB")
)
// Secrets represents the connection secrets which are negotiated during the handshake.
type Secrets struct {
AES, MAC []byte
EgressMAC, IngressMAC hash.Hash
remote *ecdsa.PublicKey
}
// handshakeState contains the state of the encryption handshake.
type handshakeState struct {
initiator bool
remote *ecies.PublicKey // remote-pubk
initNonce, respNonce []byte // nonce
randomPrivKey *ecies.PrivateKey // ecdhe-random
remoteRandomPub *ecies.PublicKey // ecdhe-random-pubk
rbuf readBuffer
wbuf writeBuffer
}
// RLPx v4 handshake auth (defined in EIP-8).
type authMsgV4 struct {
Signature [sigLen]byte
InitiatorPubkey [pubLen]byte
Nonce [shaLen]byte
Version uint
// Ignore additional fields (forward-compatibility)
Rest []rlp.RawValue `rlp:"tail"`
}
// RLPx v4 handshake response (defined in EIP-8).
type authRespV4 struct {
RandomPubkey [pubLen]byte
Nonce [shaLen]byte
Version uint
// Ignore additional fields (forward-compatibility)
Rest []rlp.RawValue `rlp:"tail"`
}
// runRecipient 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.
func (h *handshakeState) runRecipient(conn io.ReadWriter, prv *ecdsa.PrivateKey) (s Secrets, err error) {
authMsg := new(authMsgV4)
authPacket, err := h.readMsg(authMsg, prv, conn)
if err != nil {
return s, err
}
if err := h.handleAuthMsg(authMsg, prv); err != nil {
return s, err
}
authRespMsg, err := h.makeAuthResp()
if err != nil {
return s, err
}
authRespPacket, err := h.sealEIP8(authRespMsg)
if err != nil {
return s, err
}
if _, err = conn.Write(authRespPacket); err != nil {
return s, err
}
return h.secrets(authPacket, authRespPacket)
}
func (h *handshakeState) handleAuthMsg(msg *authMsgV4, prv *ecdsa.PrivateKey) error {
// Import the remote identity.
rpub, err := importPublicKey(msg.InitiatorPubkey[:])
if err != nil {
return err
}
h.initNonce = msg.Nonce[:]
h.remote = rpub
// Generate random keypair for ECDH.
// If a private key is already set, use it instead of generating one (for testing).
if h.randomPrivKey == nil {
h.randomPrivKey, err = ecies.GenerateKey(rand.Reader, crypto.S256(), nil)
if err != nil {
return err
}
}
// Check the signature.
token, err := h.staticSharedSecret(prv)
if err != nil {
return err
}
signedMsg := xor(token, h.initNonce)
remoteRandomPub, err := crypto.Ecrecover(signedMsg, msg.Signature[:])
if err != nil {
return err
}
h.remoteRandomPub, _ = importPublicKey(remoteRandomPub)
return nil
}
// secrets is called after the handshake is completed.
// It extracts the connection secrets from the handshake values.
func (h *handshakeState) 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.Keccak256(ecdheSecret, crypto.Keccak256(h.respNonce, h.initNonce))
aesSecret := crypto.Keccak256(ecdheSecret, sharedSecret)
s := Secrets{
remote: h.remote.ExportECDSA(),
AES: aesSecret,
MAC: crypto.Keccak256(ecdheSecret, aesSecret),
}
// setup sha3 instances for the MACs
mac1 := sha3.NewLegacyKeccak256()
mac1.Write(xor(s.MAC, h.respNonce))
mac1.Write(auth)
mac2 := sha3.NewLegacyKeccak256()
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
}
// staticSharedSecret returns the static shared secret, the result
// of key agreement between the local and remote static node key.
func (h *handshakeState) staticSharedSecret(prv *ecdsa.PrivateKey) ([]byte, error) {
return ecies.ImportECDSA(prv).GenerateShared(h.remote, sskLen, sskLen)
}
// runInitiator 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.
func (h *handshakeState) runInitiator(conn io.ReadWriter, prv *ecdsa.PrivateKey, remote *ecdsa.PublicKey) (s Secrets, err error) {
h.initiator = true
h.remote = ecies.ImportECDSAPublic(remote)
authMsg, err := h.makeAuthMsg(prv)
if err != nil {
return s, err
}
authPacket, err := h.sealEIP8(authMsg)
if err != nil {
return s, err
}
if _, err = conn.Write(authPacket); err != nil {
return s, err
}
authRespMsg := new(authRespV4)
authRespPacket, err := h.readMsg(authRespMsg, prv, conn)
if err != nil {
return s, err
}
if err := h.handleAuthResp(authRespMsg); err != nil {
return s, err
}
return h.secrets(authPacket, authRespPacket)
}
// makeAuthMsg creates the initiator handshake message.
func (h *handshakeState) makeAuthMsg(prv *ecdsa.PrivateKey) (*authMsgV4, error) {
// Generate random initiator nonce.
h.initNonce = make([]byte, shaLen)
_, err := rand.Read(h.initNonce)
if err != nil {
return nil, err
}
// Generate random keypair to for ECDH.
h.randomPrivKey, err = ecies.GenerateKey(rand.Reader, crypto.S256(), nil)
if err != nil {
return nil, err
}
// Sign known message: static-shared-secret ^ nonce
token, err := h.staticSharedSecret(prv)
if err != nil {
return nil, err
}
signed := xor(token, h.initNonce)
signature, err := crypto.Sign(signed, h.randomPrivKey.ExportECDSA())
if err != nil {
return nil, err
}
msg := new(authMsgV4)
copy(msg.Signature[:], signature)
copy(msg.InitiatorPubkey[:], crypto.FromECDSAPub(&prv.PublicKey)[1:])
copy(msg.Nonce[:], h.initNonce)
msg.Version = 4
return msg, nil
}
func (h *handshakeState) handleAuthResp(msg *authRespV4) (err error) {
h.respNonce = msg.Nonce[:]
h.remoteRandomPub, err = importPublicKey(msg.RandomPubkey[:])
return err
}
func (h *handshakeState) makeAuthResp() (msg *authRespV4, err error) {
// Generate random nonce.
h.respNonce = make([]byte, shaLen)
if _, err = rand.Read(h.respNonce); err != nil {
return nil, err
}
msg = new(authRespV4)
copy(msg.Nonce[:], h.respNonce)
copy(msg.RandomPubkey[:], exportPubkey(&h.randomPrivKey.PublicKey))
msg.Version = 4
return msg, nil
}
// readMsg reads an encrypted handshake message, decoding it into msg.
func (h *handshakeState) readMsg(msg interface{}, prv *ecdsa.PrivateKey, r io.Reader) ([]byte, error) {
h.rbuf.reset()
h.rbuf.grow(512)
// Read the size prefix.
prefix, err := h.rbuf.read(r, 2)
if err != nil {
return nil, err
}
size := binary.BigEndian.Uint16(prefix)
// Read the handshake packet.
packet, err := h.rbuf.read(r, int(size))
if err != nil {
return nil, err
}
dec, err := ecies.ImportECDSA(prv).Decrypt(packet, nil, prefix)
if err != nil {
return nil, err
}
// Can't use rlp.DecodeBytes here because it rejects
// trailing data (forward-compatibility).
s := rlp.NewStream(bytes.NewReader(dec), 0)
err = s.Decode(msg)
return h.rbuf.data[:len(prefix)+len(packet)], err
}
// sealEIP8 encrypts a handshake message.
func (h *handshakeState) sealEIP8(msg interface{}) ([]byte, error) {
h.wbuf.reset()
// Write the message plaintext.
if err := rlp.Encode(&h.wbuf, msg); err != nil {
return nil, err
}
// Pad with random amount of data. the amount needs to be at least 100 bytes to make
// the message distinguishable from pre-EIP-8 handshakes.
h.wbuf.appendZero(mrand.Intn(100) + 100)
prefix := make([]byte, 2)
binary.BigEndian.PutUint16(prefix, uint16(len(h.wbuf.data)+eciesOverhead))
enc, err := ecies.Encrypt(rand.Reader, h.remote, h.wbuf.data, nil, prefix)
return append(prefix, enc...), err
}
// 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
pub, err := crypto.UnmarshalPubkey(pubKey65)
if err != nil {
return nil, err
}
return ecies.ImportECDSAPublic(pub), 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
}