aboutsummaryrefslogtreecommitdiffstats
path: root/p2p/handshake.go
blob: 3ad25bae4928888801e140894c28c46ef8646ede (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
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:
//
//     lockedRW         (thread-safety for 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.
    // TODO: move buffering setup here (out of newFrameRW)
    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 := writeProtocolHandshake(rw, our); err != nil {
        return nil, fmt.Errorf("protocol write error: %v", err)
    }
    return &conn{&lockedRW{wrapped: 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.
    // TODO: move buffering setup here (out of newFrameRW)
    rw := newRlpxFrameRW(fd, secrets)
    if err := writeProtocolHandshake(rw, 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{&lockedRW{wrapped: 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 writeProtocolHandshake(w MsgWriter, our *protoHandshake) error {
    return EncodeMsg(w, handshakeMsg, our.Version, our.Name, our.Caps, our.ListenPort, our.ID[:])
}

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, discRequestedError(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
}