src/cypherpunks.ru/govpn/handshake.go

   1 /*
   2 GoVPN -- simple secure free software virtual private network daemon
   3 Copyright (C) 2014-2016 Sergey Matveev <stargrave@stargrave.org>
   4
   5 This program is free software: you can redistribute it and/or modify
   6 it under the terms of the GNU General Public License as published by
   7 the Free Software Foundation, either version 3 of the License, or
   8 (at your option) any later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18
  19 package govpn
  20
  21 import (
  22         "crypto/subtle"
  23         "encoding/binary"
  24         "io"
  25         "log"
  26         "time"
  27
  28         "github.com/agl/ed25519"
  29         "github.com/agl/ed25519/extra25519"
  30         "github.com/dchest/blake2b"
  31         "golang.org/x/crypto/curve25519"
  32         "golang.org/x/crypto/salsa20"
  33         "golang.org/x/crypto/xtea"
  34 )
  35
  36 const (
  37         RSize = 8
  38         SSize = 32
  39 )
  40
  41 type Handshake struct {
  42         addr     string
  43         conn     io.Writer
  44         LastPing time.Time
  45         Conf     *PeerConf
  46         dsaPubH  *[ed25519.PublicKeySize]byte
  47         key      *[32]byte
  48         rNonce   *[RSize]byte
  49         dhPriv   *[32]byte    // own private DH key
  50         rServer  *[RSize]byte // random string for authentication
  51         rClient  *[RSize]byte
  52         sServer  *[SSize]byte // secret string for main key calculation
  53         sClient  *[SSize]byte
  54 }
  55
  56 func keyFromSecrets(server, client []byte) *[SSize]byte {
  57         k := new([SSize]byte)
  58         for i := 0; i < SSize; i++ {
  59                 k[i] = server[i] ^ client[i]
  60         }
  61         return k
  62 }
  63
  64 // Zero handshake's memory state
  65 func (h *Handshake) Zero() {
  66         if h.rNonce != nil {
  67                 SliceZero(h.rNonce[:])
  68         }
  69         if h.dhPriv != nil {
  70                 SliceZero(h.dhPriv[:])
  71         }
  72         if h.key != nil {
  73                 SliceZero(h.key[:])
  74         }
  75         if h.dsaPubH != nil {
  76                 SliceZero(h.dsaPubH[:])
  77         }
  78         if h.rServer != nil {
  79                 SliceZero(h.rServer[:])
  80         }
  81         if h.rClient != nil {
  82                 SliceZero(h.rClient[:])
  83         }
  84         if h.sServer != nil {
  85                 SliceZero(h.sServer[:])
  86         }
  87         if h.sClient != nil {
  88                 SliceZero(h.sClient[:])
  89         }
  90 }
  91
  92 func (h *Handshake) rNonceNext(count uint64) []byte {
  93         nonce := make([]byte, RSize)
  94         nonceCurrent, _ := binary.Uvarint(h.rNonce[:])
  95         binary.PutUvarint(nonce, nonceCurrent+count)
  96         return nonce
  97 }
  98
  99 func dhKeypairGen() (*[32]byte, *[32]byte) {
 100         priv := new([32]byte)
 101         pub := new([32]byte)
 102         repr := new([32]byte)
 103         reprFound := false
 104         for !reprFound {
 105                 if _, err := Rand.Read(priv[:]); err != nil {
 106                         log.Fatalln("Error reading random for DH private key:", err)
 107                 }
 108                 reprFound = extra25519.ScalarBaseMult(pub, repr, priv)
 109         }
 110         return priv, repr
 111 }
 112
 113 func dhKeyGen(priv, pub *[32]byte) *[32]byte {
 114         key := new([32]byte)
 115         curve25519.ScalarMult(key, priv, pub)
 116         hashed := blake2b.Sum256(key[:])
 117         return &hashed
 118 }
 119
 120 // Create new handshake state.
 121 func NewHandshake(addr string, conn io.Writer, conf *PeerConf) *Handshake {
 122         state := Handshake{
 123                 addr:     addr,
 124                 conn:     conn,
 125                 LastPing: time.Now(),
 126                 Conf:     conf,
 127         }
 128         state.dsaPubH = new([ed25519.PublicKeySize]byte)
 129         copy(state.dsaPubH[:], state.Conf.Verifier.Pub[:])
 130         hashed := blake2b.Sum256(state.dsaPubH[:])
 131         state.dsaPubH = &hashed
 132         return &state
 133 }
 134
 135 // Generate ID tag from client identification and data.
 136 func idTag(id *PeerId, data []byte) []byte {
 137         ciph, err := xtea.NewCipher(id[:])
 138         if err != nil {
 139                 panic(err)
 140         }
 141         enc := make([]byte, xtea.BlockSize)
 142         ciph.Encrypt(enc, data[:xtea.BlockSize])
 143         return enc
 144 }
 145
 146 // Start handshake's procedure from the client. It is the entry point
 147 // for starting the handshake procedure. // First handshake packet
 148 // will be sent immediately.
 149 func HandshakeStart(addr string, conn io.Writer, conf *PeerConf) *Handshake {
 150         state := NewHandshake(addr, conn, conf)
 151         var dhPubRepr *[32]byte
 152         state.dhPriv, dhPubRepr = dhKeypairGen()
 153
 154         state.rNonce = new([RSize]byte)
 155         if _, err := Rand.Read(state.rNonce[:]); err != nil {
 156                 log.Fatalln("Error reading random for nonce:", err)
 157         }
 158         var enc []byte
 159         if conf.Noise {
 160                 enc = make([]byte, conf.MTU-xtea.BlockSize-RSize)
 161         } else {
 162                 enc = make([]byte, 32)
 163         }
 164         copy(enc, dhPubRepr[:])
 165         if conf.Encless {
 166                 var err error
 167                 enc, err = EnclessEncode(state.dsaPubH, state.rNonce[:], enc)
 168                 if err != err {
 169                         panic(err)
 170                 }
 171         } else {
 172                 salsa20.XORKeyStream(enc, enc, state.rNonce[:], state.dsaPubH)
 173         }
 174         data := append(state.rNonce[:], enc...)
 175         data = append(data, idTag(state.Conf.Id, state.rNonce[:])...)
 176         state.conn.Write(data)
 177         return state
 178 }
 179
 180 // Process handshake message on the server side.
 181 // This function is intended to be called on server's side.
 182 // If this is the final handshake message, then new Peer object
 183 // will be created and used as a transport. If no mutually
 184 // authenticated Peer is ready, then return nil.
 185 func (h *Handshake) Server(data []byte) *Peer {
 186         // R + ENC(H(DSAPub), R, El(CDHPub)) + IDtag
 187         if h.rNonce == nil && ((!h.Conf.Encless && len(data) >= 48) ||
 188                 (h.Conf.Encless && len(data) == EnclessEnlargeSize+h.Conf.MTU)) {
 189                 h.rNonce = new([RSize]byte)
 190                 copy(h.rNonce[:], data[:RSize])
 191
 192                 // Decrypt remote public key
 193                 cDHRepr := new([32]byte)
 194                 if h.Conf.Encless {
 195                         out, err := EnclessDecode(
 196                                 h.dsaPubH,
 197                                 h.rNonce[:],
 198                                 data[RSize:len(data)-xtea.BlockSize],
 199                         )
 200                         if err != nil {
 201                                 log.Println("Unable to decode packet from", h.addr, err)
 202                                 return nil
 203                         }
 204                         copy(cDHRepr[:], out)
 205                 } else {
 206                         salsa20.XORKeyStream(
 207                                 cDHRepr[:],
 208                                 data[RSize:RSize+32],
 209                                 h.rNonce[:],
 210                                 h.dsaPubH,
 211                         )
 212                 }
 213
 214                 // Generate DH keypair
 215                 var dhPubRepr *[32]byte
 216                 h.dhPriv, dhPubRepr = dhKeypairGen()
 217
 218                 // Compute shared key
 219                 cDH := new([32]byte)
 220                 extra25519.RepresentativeToPublicKey(cDH, cDHRepr)
 221                 h.key = dhKeyGen(h.dhPriv, cDH)
 222
 223                 var encPub []byte
 224                 var err error
 225                 if h.Conf.Encless {
 226                         encPub = make([]byte, h.Conf.MTU)
 227                         copy(encPub, dhPubRepr[:])
 228                         encPub, err = EnclessEncode(h.dsaPubH, h.rNonceNext(1), encPub)
 229                         if err != nil {
 230                                 panic(err)
 231                         }
 232                 } else {
 233                         encPub = make([]byte, 32)
 234                         salsa20.XORKeyStream(encPub, dhPubRepr[:], h.rNonceNext(1), h.dsaPubH)
 235                 }
 236
 237                 // Generate R* and encrypt them
 238                 h.rServer = new([RSize]byte)
 239                 if _, err = Rand.Read(h.rServer[:]); err != nil {
 240                         log.Fatalln("Error reading random for R:", err)
 241                 }
 242                 h.sServer = new([SSize]byte)
 243                 if _, err = Rand.Read(h.sServer[:]); err != nil {
 244                         log.Fatalln("Error reading random for S:", err)
 245                 }
 246                 var encRs []byte
 247                 if h.Conf.Noise && !h.Conf.Encless {
 248                         encRs = make([]byte, h.Conf.MTU-len(encPub)-xtea.BlockSize)
 249                 } else if h.Conf.Encless {
 250                         encRs = make([]byte, h.Conf.MTU-xtea.BlockSize)
 251                 } else {
 252                         encRs = make([]byte, RSize+SSize)
 253                 }
 254                 copy(encRs, append(h.rServer[:], h.sServer[:]...))
 255                 if h.Conf.Encless {
 256                         encRs, err = EnclessEncode(h.key, h.rNonce[:], encRs)
 257                         if err != nil {
 258                                 panic(err)
 259                         }
 260                 } else {
 261                         salsa20.XORKeyStream(encRs, encRs, h.rNonce[:], h.key)
 262                 }
 263
 264                 // Send that to client
 265                 h.conn.Write(append(encPub, append(encRs, idTag(h.Conf.Id, encPub)...)...))
 266                 h.LastPing = time.Now()
 267         } else
 268         // ENC(K, R+1, RS + RC + SC + Sign(DSAPriv, K)) + IDtag
 269         if h.rClient == nil && ((!h.Conf.Encless && len(data) >= 120) ||
 270                 (h.Conf.Encless && len(data) == EnclessEnlargeSize+h.Conf.MTU)) {
 271                 var dec []byte
 272                 var err error
 273                 if h.Conf.Encless {
 274                         dec, err = EnclessDecode(
 275                                 h.key,
 276                                 h.rNonceNext(1),
 277                                 data[:len(data)-xtea.BlockSize],
 278                         )
 279                         if err != nil {
 280                                 log.Println("Unable to decode packet from", h.addr, err)
 281                                 return nil
 282                         }
 283                         dec = dec[:RSize+RSize+SSize+ed25519.SignatureSize]
 284                 } else {
 285                         dec = make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
 286                         salsa20.XORKeyStream(
 287                                 dec,
 288                                 data[:RSize+RSize+SSize+ed25519.SignatureSize],
 289                                 h.rNonceNext(1),
 290                                 h.key,
 291                         )
 292                 }
 293                 if subtle.ConstantTimeCompare(dec[:RSize], h.rServer[:]) != 1 {
 294                         log.Println("Invalid server's random number with", h.addr)
 295                         return nil
 296                 }
 297                 sign := new([ed25519.SignatureSize]byte)
 298                 copy(sign[:], dec[RSize+RSize+SSize:])
 299                 if !ed25519.Verify(h.Conf.Verifier.Pub, h.key[:], sign) {
 300                         log.Println("Invalid signature from", h.addr)
 301                         return nil
 302                 }
 303
 304                 // Send final answer to client
 305                 var enc []byte
 306                 if h.Conf.Noise {
 307                         enc = make([]byte, h.Conf.MTU-xtea.BlockSize)
 308                 } else {
 309                         enc = make([]byte, RSize)
 310                 }
 311                 copy(enc, dec[RSize:RSize+RSize])
 312                 if h.Conf.Encless {
 313                         enc, err = EnclessEncode(h.key, h.rNonceNext(2), enc)
 314                         if err != nil {
 315                                 panic(err)
 316                         }
 317                 } else {
 318                         salsa20.XORKeyStream(enc, enc, h.rNonceNext(2), h.key)
 319                 }
 320                 h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
 321
 322                 // Switch peer
 323                 peer := newPeer(
 324                         false,
 325                         h.addr,
 326                         h.conn,
 327                         h.Conf,
 328                         keyFromSecrets(h.sServer[:], dec[RSize+RSize:RSize+RSize+SSize]))
 329                 h.LastPing = time.Now()
 330                 return peer
 331         } else {
 332                 log.Println("Invalid handshake message from", h.addr)
 333         }
 334         return nil
 335 }
 336
 337 // Process handshake message on the client side.
 338 // This function is intended to be called on client's side.
 339 // If this is the final handshake message, then new Peer object
 340 // will be created and used as a transport. If no mutually
 341 // authenticated Peer is ready, then return nil.
 342 func (h *Handshake) Client(data []byte) *Peer {
 343         // ENC(H(DSAPub), R+1, El(SDHPub)) + ENC(K, R, RS + SS) + IDtag
 344         if h.rServer == nil && h.key == nil &&
 345                 ((!h.Conf.Encless && len(data) >= 80) ||
 346                         (h.Conf.Encless && len(data) == 2*(EnclessEnlargeSize+h.Conf.MTU))) {
 347                 // Decrypt remote public key
 348                 sDHRepr := new([32]byte)
 349                 var tmp []byte
 350                 var err error
 351                 if h.Conf.Encless {
 352                         tmp, err = EnclessDecode(
 353                                 h.dsaPubH,
 354                                 h.rNonceNext(1),
 355                                 data[:len(data)/2],
 356                         )
 357                         if err != nil {
 358                                 log.Println("Unable to decode packet from", h.addr, err)
 359                                 return nil
 360                         }
 361                         copy(sDHRepr[:], tmp[:32])
 362                 } else {
 363                         salsa20.XORKeyStream(
 364                                 sDHRepr[:],
 365                                 data[:32],
 366                                 h.rNonceNext(1),
 367                                 h.dsaPubH,
 368                         )
 369                 }
 370
 371                 // Compute shared key
 372                 sDH := new([32]byte)
 373                 extra25519.RepresentativeToPublicKey(sDH, sDHRepr)
 374                 h.key = dhKeyGen(h.dhPriv, sDH)
 375
 376                 // Decrypt Rs
 377                 h.rServer = new([RSize]byte)
 378                 h.sServer = new([SSize]byte)
 379                 if h.Conf.Encless {
 380                         tmp, err = EnclessDecode(
 381                                 h.key,
 382                                 h.rNonce[:],
 383                                 data[len(data)/2:len(data)-xtea.BlockSize],
 384                         )
 385                         if err != nil {
 386                                 log.Println("Unable to decode packet from", h.addr, err)
 387                                 return nil
 388                         }
 389                         copy(h.rServer[:], tmp[:RSize])
 390                         copy(h.sServer[:], tmp[RSize:RSize+SSize])
 391                 } else {
 392                         decRs := make([]byte, RSize+SSize)
 393                         salsa20.XORKeyStream(
 394                                 decRs,
 395                                 data[SSize:SSize+RSize+SSize],
 396                                 h.rNonce[:],
 397                                 h.key,
 398                         )
 399                         copy(h.rServer[:], decRs[:RSize])
 400                         copy(h.sServer[:], decRs[RSize:])
 401                 }
 402
 403                 // Generate R* and signature and encrypt them
 404                 h.rClient = new([RSize]byte)
 405                 if _, err = Rand.Read(h.rClient[:]); err != nil {
 406                         log.Fatalln("Error reading random for R:", err)
 407                 }
 408                 h.sClient = new([SSize]byte)
 409                 if _, err = Rand.Read(h.sClient[:]); err != nil {
 410                         log.Fatalln("Error reading random for S:", err)
 411                 }
 412                 sign := ed25519.Sign(h.Conf.DSAPriv, h.key[:])
 413
 414                 var enc []byte
 415                 if h.Conf.Noise {
 416                         enc = make([]byte, h.Conf.MTU-xtea.BlockSize)
 417                 } else {
 418                         enc = make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
 419                 }
 420                 copy(enc, h.rServer[:])
 421                 copy(enc[RSize:], h.rClient[:])
 422                 copy(enc[RSize+RSize:], h.sClient[:])
 423                 copy(enc[RSize+RSize+SSize:], sign[:])
 424                 if h.Conf.Encless {
 425                         enc, err = EnclessEncode(h.key, h.rNonceNext(1), enc)
 426                         if err != nil {
 427                                 panic(err)
 428                         }
 429                 } else {
 430                         salsa20.XORKeyStream(enc, enc, h.rNonceNext(1), h.key)
 431                 }
 432
 433                 // Send that to server
 434                 h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
 435                 h.LastPing = time.Now()
 436         } else
 437         // ENC(K, R+2, RC) + IDtag
 438         if h.key != nil && ((!h.Conf.Encless && len(data) >= 16) ||
 439                 (h.Conf.Encless && len(data) == EnclessEnlargeSize+h.Conf.MTU)) {
 440                 var err error
 441                 // Decrypt rClient
 442                 var dec []byte
 443                 if h.Conf.Encless {
 444                         dec, err = EnclessDecode(
 445                                 h.key,
 446                                 h.rNonceNext(2),
 447                                 data[:len(data)-xtea.BlockSize],
 448                         )
 449                         if err != nil {
 450                                 log.Println("Unable to decode packet from", h.addr, err)
 451                                 return nil
 452                         }
 453                         dec = dec[:RSize]
 454                 } else {
 455                         dec = make([]byte, RSize)
 456                         salsa20.XORKeyStream(dec, data[:RSize], h.rNonceNext(2), h.key)
 457                 }
 458                 if subtle.ConstantTimeCompare(dec, h.rClient[:]) != 1 {
 459                         log.Println("Invalid client's random number with", h.addr)
 460                         return nil
 461                 }
 462
 463                 // Switch peer
 464                 peer := newPeer(
 465                         true,
 466                         h.addr,
 467                         h.conn,
 468                         h.Conf,
 469                         keyFromSecrets(h.sServer[:], h.sClient[:]),
 470                 )
 471                 h.LastPing = time.Now()
 472                 return peer
 473         } else {
 474                 log.Println("Invalid handshake stage from", h.addr)
 475         }
 476         return nil
 477 }