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