/
mse.go
501 lines (461 loc) · 9.71 KB
/
mse.go
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
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
// https://wiki.vuze.com/w/Message_Stream_Encryption
package mse
import (
"bytes"
"crypto/rand"
"crypto/rc4"
"crypto/sha1"
"encoding/binary"
"errors"
"expvar"
"fmt"
"io"
"io/ioutil"
"math/big"
"strconv"
"sync"
"github.com/anacrolix/missinggo"
"github.com/bradfitz/iter"
)
const (
maxPadLen = 512
cryptoMethodPlaintext = 1
cryptoMethodRC4 = 2
)
var (
// Prime P according to the spec, and G, the generator.
p, g big.Int
// The rand.Int max arg for use in newPadLen()
newPadLenMax big.Int
// For use in initer's hashes
req1 = []byte("req1")
req2 = []byte("req2")
req3 = []byte("req3")
// Verification constant "VC" which is all zeroes in the bittorrent
// implementation.
vc [8]byte
// Zero padding
zeroPad [512]byte
// Tracks counts of received crypto_provides
cryptoProvidesCount = expvar.NewMap("mseCryptoProvides")
)
func init() {
p.SetString("0xFFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A63A36210000000000090563", 0)
g.SetInt64(2)
newPadLenMax.SetInt64(maxPadLen + 1)
}
func hash(parts ...[]byte) []byte {
h := sha1.New()
for _, p := range parts {
n, err := h.Write(p)
if err != nil {
panic(err)
}
if n != len(p) {
panic(n)
}
}
return h.Sum(nil)
}
func newEncrypt(initer bool, s []byte, skey []byte) (c *rc4.Cipher) {
c, err := rc4.NewCipher(hash([]byte(func() string {
if initer {
return "keyA"
} else {
return "keyB"
}
}()), s, skey))
if err != nil {
panic(err)
}
var burnSrc, burnDst [1024]byte
c.XORKeyStream(burnDst[:], burnSrc[:])
return
}
type cipherReader struct {
c *rc4.Cipher
r io.Reader
}
func (me *cipherReader) Read(b []byte) (n int, err error) {
be := make([]byte, len(b))
n, err = me.r.Read(be)
me.c.XORKeyStream(b[:n], be[:n])
return
}
func newCipherReader(c *rc4.Cipher, r io.Reader) io.Reader {
return &cipherReader{c, r}
}
type cipherWriter struct {
c *rc4.Cipher
w io.Writer
}
func (me *cipherWriter) Write(b []byte) (n int, err error) {
be := make([]byte, len(b))
me.c.XORKeyStream(be, b)
n, err = me.w.Write(be)
if n != len(be) {
// The cipher will have advanced beyond the callers stream position.
// We can't use the cipher anymore.
me.c = nil
}
return
}
func readY(r io.Reader) (y big.Int, err error) {
var b [96]byte
_, err = io.ReadFull(r, b[:])
if err != nil {
return
}
y.SetBytes(b[:])
return
}
func newX() big.Int {
var X big.Int
X.SetBytes(func() []byte {
var b [20]byte
_, err := rand.Read(b[:])
if err != nil {
panic(err)
}
return b[:]
}())
return X
}
func paddedLeft(b []byte, _len int) []byte {
if len(b) == _len {
return b
}
ret := make([]byte, _len)
if n := copy(ret[_len-len(b):], b); n != len(b) {
panic(n)
}
return ret
}
// Calculate, and send Y, our public key.
func (h *handshake) postY(x *big.Int) error {
var y big.Int
y.Exp(&g, x, &p)
return h.postWrite(paddedLeft(y.Bytes(), 96))
}
func (h *handshake) establishS() (err error) {
x := newX()
h.postY(&x)
var b [96]byte
_, err = io.ReadFull(h.conn, b[:])
if err != nil {
return
}
var Y, S big.Int
Y.SetBytes(b[:])
S.Exp(&Y, &x, &p)
missinggo.CopyExact(&h.s, paddedLeft(S.Bytes(), 96))
return
}
func newPadLen() int64 {
i, err := rand.Int(rand.Reader, &newPadLenMax)
if err != nil {
panic(err)
}
ret := i.Int64()
if ret < 0 || ret > maxPadLen {
panic(ret)
}
return ret
}
type handshake struct {
conn io.ReadWriter
s [96]byte
initer bool
skeys [][]byte
skey []byte
ia []byte // Initial payload. Only used by the initiator.
writeMu sync.Mutex
writes [][]byte
writeErr error
writeCond sync.Cond
writeClose bool
writerMu sync.Mutex
writerCond sync.Cond
writerDone bool
}
func (h *handshake) finishWriting() {
h.writeMu.Lock()
h.writeClose = true
h.writeCond.Broadcast()
h.writeMu.Unlock()
h.writerMu.Lock()
for !h.writerDone {
h.writerCond.Wait()
}
h.writerMu.Unlock()
return
}
func (h *handshake) writer() {
defer func() {
h.writerMu.Lock()
h.writerDone = true
h.writerCond.Broadcast()
h.writerMu.Unlock()
}()
for {
h.writeMu.Lock()
for {
if len(h.writes) != 0 {
break
}
if h.writeClose {
h.writeMu.Unlock()
return
}
h.writeCond.Wait()
}
b := h.writes[0]
h.writes = h.writes[1:]
h.writeMu.Unlock()
_, err := h.conn.Write(b)
if err != nil {
h.writeMu.Lock()
h.writeErr = err
h.writeMu.Unlock()
return
}
}
}
func (h *handshake) postWrite(b []byte) error {
h.writeMu.Lock()
defer h.writeMu.Unlock()
if h.writeErr != nil {
return h.writeErr
}
h.writes = append(h.writes, b)
h.writeCond.Signal()
return nil
}
func xor(dst, src []byte) (ret []byte) {
max := len(dst)
if max > len(src) {
max = len(src)
}
ret = make([]byte, 0, max)
for i := range iter.N(max) {
ret = append(ret, dst[i]^src[i])
}
return
}
func marshal(w io.Writer, data ...interface{}) (err error) {
for _, data := range data {
err = binary.Write(w, binary.BigEndian, data)
if err != nil {
break
}
}
return
}
func unmarshal(r io.Reader, data ...interface{}) (err error) {
for _, data := range data {
err = binary.Read(r, binary.BigEndian, data)
if err != nil {
break
}
}
return
}
// Looking for b at the end of a.
func suffixMatchLen(a, b []byte) int {
if len(b) > len(a) {
b = b[:len(a)]
}
// i is how much of b to try to match
for i := len(b); i > 0; i-- {
// j is how many chars we've compared
j := 0
for ; j < i; j++ {
if b[i-1-j] != a[len(a)-1-j] {
goto shorter
}
}
return j
shorter:
}
return 0
}
func readUntil(r io.Reader, b []byte) error {
b1 := make([]byte, len(b))
i := 0
for {
_, err := io.ReadFull(r, b1[i:])
if err != nil {
return err
}
i = suffixMatchLen(b1, b)
if i == len(b) {
break
}
if copy(b1, b1[len(b1)-i:]) != i {
panic("wat")
}
}
return nil
}
type readWriter struct {
io.Reader
io.Writer
}
func (h *handshake) newEncrypt(initer bool) *rc4.Cipher {
return newEncrypt(initer, h.s[:], h.skey)
}
func (h *handshake) initerSteps() (ret io.ReadWriter, err error) {
h.postWrite(hash(req1, h.s[:]))
h.postWrite(xor(hash(req2, h.skey), hash(req3, h.s[:])))
buf := &bytes.Buffer{}
padLen := uint16(newPadLen())
err = marshal(buf, vc[:], uint32(cryptoMethodRC4), padLen, zeroPad[:padLen], uint16(len(h.ia)), h.ia)
if err != nil {
return
}
e := h.newEncrypt(true)
be := make([]byte, buf.Len())
e.XORKeyStream(be, buf.Bytes())
h.postWrite(be)
bC := h.newEncrypt(false)
var eVC [8]byte
bC.XORKeyStream(eVC[:], vc[:])
// Read until the all zero VC. At this point we've only read the 96 byte
// public key, Y. There is potentially 512 byte padding, between us and
// the 8 byte verification constant.
err = readUntil(io.LimitReader(h.conn, 520), eVC[:])
if err != nil {
if err == io.EOF {
err = errors.New("failed to synchronize on VC")
} else {
err = fmt.Errorf("error reading until VC: %s", err)
}
return
}
r := &cipherReader{bC, h.conn}
var method uint32
err = unmarshal(r, &method, &padLen)
if err != nil {
return
}
if method != cryptoMethodRC4 {
err = fmt.Errorf("receiver chose unsupported method: %x", method)
return
}
_, err = io.CopyN(ioutil.Discard, r, int64(padLen))
if err != nil {
return
}
ret = readWriter{r, &cipherWriter{e, h.conn}}
return
}
var ErrNoSecretKeyMatch = errors.New("no skey matched")
func (h *handshake) receiverSteps() (ret io.ReadWriter, err error) {
// There is up to 512 bytes of padding, then the 20 byte hash.
err = readUntil(io.LimitReader(h.conn, 532), hash(req1, h.s[:]))
if err != nil {
if err == io.EOF {
err = errors.New("failed to synchronize on S hash")
}
return
}
var b [20]byte
_, err = io.ReadFull(h.conn, b[:])
if err != nil {
return
}
err = ErrNoSecretKeyMatch
for _, skey := range h.skeys {
if bytes.Equal(xor(hash(req2, skey), hash(req3, h.s[:])), b[:]) {
h.skey = skey
err = nil
break
}
}
if err != nil {
return
}
r := newCipherReader(newEncrypt(true, h.s[:], h.skey), h.conn)
var (
vc [8]byte
method uint32
padLen uint16
)
err = unmarshal(r, vc[:], &method, &padLen)
if err != nil {
return
}
cryptoProvidesCount.Add(strconv.FormatUint(uint64(method), 16), 1)
if method&cryptoMethodRC4 == 0 {
err = errors.New("no supported crypto methods were provided")
return
}
_, err = io.CopyN(ioutil.Discard, r, int64(padLen))
if err != nil {
return
}
var lenIA uint16
unmarshal(r, &lenIA)
if lenIA != 0 {
h.ia = make([]byte, lenIA)
unmarshal(r, h.ia)
}
buf := &bytes.Buffer{}
w := cipherWriter{h.newEncrypt(false), buf}
padLen = uint16(newPadLen())
err = marshal(&w, &vc, uint32(cryptoMethodRC4), padLen, zeroPad[:padLen])
if err != nil {
return
}
err = h.postWrite(buf.Bytes())
if err != nil {
return
}
ret = readWriter{io.MultiReader(bytes.NewReader(h.ia), r), &cipherWriter{w.c, h.conn}}
return
}
func (h *handshake) Do() (ret io.ReadWriter, err error) {
h.writeCond.L = &h.writeMu
h.writerCond.L = &h.writerMu
go h.writer()
defer func() {
h.finishWriting()
if err == nil {
err = h.writeErr
}
}()
err = h.establishS()
if err != nil {
err = fmt.Errorf("error while establishing secret: %s", err)
return
}
pad := make([]byte, newPadLen())
io.ReadFull(rand.Reader, pad)
err = h.postWrite(pad)
if err != nil {
return
}
if h.initer {
ret, err = h.initerSteps()
} else {
ret, err = h.receiverSteps()
}
return
}
func InitiateHandshake(rw io.ReadWriter, skey []byte, initialPayload []byte) (ret io.ReadWriter, err error) {
h := handshake{
conn: rw,
initer: true,
skey: skey,
ia: initialPayload,
}
return h.Do()
}
func ReceiveHandshake(rw io.ReadWriter, skeys [][]byte) (ret io.ReadWriter, err error) {
h := handshake{
conn: rw,
initer: false,
skeys: skeys,
}
return h.Do()
}