1 // https://wiki.vuze.com/w/Message_Stream_Encryption
19 "github.com/bradfitz/iter"
25 cryptoMethodPlaintext = 1
30 // Prime P according to the spec, and G, the generator.
32 // The rand.Int max arg for use in newPadLen()
34 // For use in initer's hashes
41 p.SetString("0xFFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A63A36210000000000090563", 0)
43 newPadLenMax.SetInt64(maxPadLen + 1)
46 func hash(parts ...[]byte) []byte {
48 for _, p := range parts {
60 func newEncrypt(initer bool, s []byte, skey []byte) (c *rc4.Cipher) {
61 c, err := rc4.NewCipher(hash([]byte(func() string {
71 var burnSrc, burnDst [1024]byte
72 c.XORKeyStream(burnDst[:], burnSrc[:])
76 type cipherReader struct {
81 func (me *cipherReader) Read(b []byte) (n int, err error) {
82 be := make([]byte, len(b))
83 n, err = me.r.Read(be)
84 me.c.XORKeyStream(b[:n], be[:n])
88 func newCipherReader(c *rc4.Cipher, r io.Reader) io.Reader {
89 return &cipherReader{c, r}
92 type cipherWriter struct {
97 func (me *cipherWriter) Write(b []byte) (n int, err error) {
98 be := make([]byte, len(b))
99 me.c.XORKeyStream(be, b)
100 n, err = me.w.Write(be)
102 // The cipher will have advanced beyond the callers stream position.
103 // We can't use the cipher anymore.
109 func readY(r io.Reader) (y big.Int, err error) {
111 _, err = io.ReadFull(r, b[:])
119 func newX() big.Int {
121 X.SetBytes(func() []byte {
123 _, err := rand.Read(b[:])
132 // Calculate, and send Y, our public key.
133 func (h *handshake) postY(x *big.Int) error {
138 b1 := make([]byte, 96)
139 if n := copy(b1[96-len(b):], b); n != len(b) {
144 return h.postWrite(b)
147 func (h *handshake) establishS() (err error) {
151 _, err = io.ReadFull(h.conn, b[:])
161 func newPadLen() int64 {
162 i, err := rand.Int(rand.Reader, &newPadLenMax)
167 if ret < 0 || ret > maxPadLen {
173 type handshake struct {
174 conn io.ReadWriteCloser
191 func (h *handshake) finishWriting() (err error) {
194 h.writeCond.Broadcast()
207 func (h *handshake) writer() {
211 h.writerCond.Broadcast()
217 if len(h.writes) != 0 {
227 h.writes = h.writes[1:]
229 _, err := h.conn.Write(b)
239 func (h *handshake) postWrite(b []byte) error {
241 defer h.writeMu.Unlock()
242 if h.writeErr != nil {
245 h.writes = append(h.writes, b)
250 func xor(dst, src []byte) (ret []byte) {
255 ret = make([]byte, 0, max)
256 for i := range iter.N(max) {
257 ret = append(ret, dst[i]^src[i])
262 func marshal(w io.Writer, data ...interface{}) (err error) {
263 for _, data := range data {
264 err = binary.Write(w, binary.BigEndian, data)
272 func unmarshal(r io.Reader, data ...interface{}) (err error) {
273 for _, data := range data {
274 err = binary.Read(r, binary.BigEndian, data)
282 type cryptoNegotiation struct {
289 func (me *cryptoNegotiation) UnmarshalReader(r io.Reader) (err error) {
290 err = binary.Read(r, binary.BigEndian, me.VC[:])
291 // _, err = io.ReadFull(r, me.VC[:])
295 err = binary.Read(r, binary.BigEndian, &me.Method)
299 err = binary.Read(r, binary.BigEndian, &me.PadLen)
304 _, err = io.CopyN(ioutil.Discard, r, int64(me.PadLen))
308 func (me *cryptoNegotiation) MarshalWriter(w io.Writer) (err error) {
309 // _, err = w.Write(me.VC[:])
310 err = binary.Write(w, binary.BigEndian, me.VC[:])
314 err = binary.Write(w, binary.BigEndian, me.Method)
318 err = binary.Write(w, binary.BigEndian, me.PadLen)
322 _, err = w.Write(make([]byte, me.PadLen))
326 // Looking for b at the end of a.
327 func suffixMatchLen(a, b []byte) int {
331 // i is how much of b to try to match
332 for i := len(b); i > 0; i-- {
333 // j is how many chars we've compared
336 if b[i-1-j] != a[len(a)-1-j] {
346 func readUntil(r io.Reader, b []byte) error {
347 log.Println("read until", b)
348 b1 := make([]byte, len(b))
351 _, err := io.ReadFull(r, b1[i:])
355 i = suffixMatchLen(b1, b)
359 if copy(b1, b1[len(b1)-i:]) != i {
366 type readWriter struct {
371 func (h *handshake) initerSteps() (ret io.ReadWriter, err error) {
372 h.postWrite(hash(req1, h.s.Bytes()))
373 h.postWrite(xor(hash(req2, h.skey), hash(req3, h.s.Bytes())))
374 buf := &bytes.Buffer{}
375 err = (&cryptoNegotiation{
376 Method: cryptoMethodRC4,
377 PadLen: uint16(newPadLen()),
378 }).MarshalWriter(buf)
382 err = marshal(buf, uint16(0))
386 e := newEncrypt(true, h.s.Bytes(), h.skey)
387 be := make([]byte, buf.Len())
388 e.XORKeyStream(be, buf.Bytes())
390 bC := newEncrypt(false, h.s.Bytes(), h.skey)
392 bC.XORKeyStream(eVC[:], make([]byte, 8))
394 // Read until the all zero VC.
395 err = readUntil(h.conn, eVC[:])
397 err = fmt.Errorf("error reading until VC: %s", err)
400 var cn cryptoNegotiation
401 r := &cipherReader{bC, h.conn}
402 err = cn.UnmarshalReader(io.MultiReader(bytes.NewReader(make([]byte, 8)), r))
403 log.Printf("initer got %v", cn)
405 err = fmt.Errorf("error reading crypto negotiation: %s", err)
408 ret = readWriter{r, &cipherWriter{e, h.conn}}
412 func (h *handshake) receiverSteps() (ret io.ReadWriter, err error) {
413 err = readUntil(h.conn, hash(req1, h.s.Bytes()))
418 _, err = io.ReadFull(h.conn, b[:])
422 err = errors.New("skey doesn't match")
423 for _, skey := range h.skeys {
424 if bytes.Equal(xor(hash(req2, skey), hash(req3, h.s.Bytes())), b[:]) {
433 var cn cryptoNegotiation
434 r := newCipherReader(newEncrypt(true, h.s.Bytes(), h.skey), h.conn)
435 err = cn.UnmarshalReader(r)
439 log.Printf("receiver got %v", cn)
440 if cn.Method&cryptoMethodRC4 == 0 {
441 err = errors.New("no supported crypto methods were provided")
444 unmarshal(r, new(uint16))
445 buf := &bytes.Buffer{}
446 w := cipherWriter{newEncrypt(false, h.s.Bytes(), h.skey), buf}
447 err = (&cryptoNegotiation{
448 Method: cryptoMethodRC4,
449 PadLen: uint16(newPadLen()),
454 err = h.postWrite(buf.Bytes())
458 ret = readWriter{r, &cipherWriter{w.c, h.conn}}
462 func (h *handshake) Do() (ret io.ReadWriter, err error) {
465 err = fmt.Errorf("error while establishing secret: %s", err)
468 pad := make([]byte, newPadLen())
469 io.ReadFull(rand.Reader, pad)
470 err = h.postWrite(pad)
475 ret, err = h.initerSteps()
477 ret, err = h.receiverSteps()
482 err = h.finishWriting()
486 log.Print("ermahgerd, finished MSE handshake")
490 func InitiateHandshake(rw io.ReadWriteCloser, skey []byte) (ret io.ReadWriter, err error) {
496 h.writeCond.L = &h.writeMu
497 h.writerCond.L = &h.writerMu
501 func ReceiveHandshake(rw io.ReadWriteCloser, skeys [][]byte) (ret io.ReadWriter, err error) {
507 h.writeCond.L = &h.writeMu
508 h.writerCond.L = &h.writerMu