src/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         "golang.org/x/crypto/curve25519"
  31         "golang.org/x/crypto/salsa20"
  32         "golang.org/x/crypto/salsa20/salsa"
  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 // Apply HSalsa20 function for data. Used to hash public keys.
  65 func HApply(data *[32]byte) {
  66         salsa.HSalsa20(data, new([16]byte), data, &salsa.Sigma)
  67 }
  68
  69 // Zero handshake's memory state
  70 func (h *Handshake) Zero() {
  71         if h.rNonce != nil {
  72                 SliceZero(h.rNonce[:])
  73         }
  74         if h.dhPriv != nil {
  75                 SliceZero(h.dhPriv[:])
  76         }
  77         if h.key != nil {
  78                 SliceZero(h.key[:])
  79         }
  80         if h.dsaPubH != nil {
  81                 SliceZero(h.dsaPubH[:])
  82         }
  83         if h.rServer != nil {
  84                 SliceZero(h.rServer[:])
  85         }
  86         if h.rClient != nil {
  87                 SliceZero(h.rClient[:])
  88         }
  89         if h.sServer != nil {
  90                 SliceZero(h.sServer[:])
  91         }
  92         if h.sClient != nil {
  93                 SliceZero(h.sClient[:])
  94         }
  95 }
  96
  97 func (h *Handshake) rNonceNext(count uint64) []byte {
  98         nonce := make([]byte, RSize)
  99         nonceCurrent, _ := binary.Uvarint(h.rNonce[:])
 100         binary.PutUvarint(nonce, nonceCurrent+count)
 101         return nonce
 102 }
 103
 104 func dhKeypairGen() (*[32]byte, *[32]byte) {
 105         priv := new([32]byte)
 106         pub := new([32]byte)
 107         repr := new([32]byte)
 108         reprFound := false
 109         for !reprFound {
 110                 if _, err := Rand.Read(priv[:]); err != nil {
 111                         log.Fatalln("Error reading random for DH private key:", err)
 112                 }
 113                 reprFound = extra25519.ScalarBaseMult(pub, repr, priv)
 114         }
 115         return priv, repr
 116 }
 117
 118 func dhKeyGen(priv, pub *[32]byte) *[32]byte {
 119         key := new([32]byte)
 120         curve25519.ScalarMult(key, priv, pub)
 121         HApply(key)
 122         return key
 123 }
 124
 125 // Create new handshake state.
 126 func NewHandshake(addr string, conn io.Writer, conf *PeerConf) *Handshake {
 127         state := Handshake{
 128                 addr:     addr,
 129                 conn:     conn,
 130                 LastPing: time.Now(),
 131                 Conf:     conf,
 132         }
 133         state.dsaPubH = new([ed25519.PublicKeySize]byte)
 134         copy(state.dsaPubH[:], state.Conf.Verifier.Pub[:])
 135         HApply(state.dsaPubH)
 136         return &state
 137 }
 138
 139 // Generate ID tag from client identification and data.
 140 func idTag(id *PeerId, data []byte) []byte {
 141         ciph, err := xtea.NewCipher(id[:])
 142         if err != nil {
 143                 panic(err)
 144         }
 145         enc := make([]byte, xtea.BlockSize)
 146         ciph.Encrypt(enc, data[:xtea.BlockSize])
 147         return enc
 148 }
 149
 150 // Start handshake's procedure from the client. It is the entry point
 151 // for starting the handshake procedure. // First handshake packet
 152 // will be sent immediately.
 153 func HandshakeStart(addr string, conn io.Writer, conf *PeerConf) *Handshake {
 154         state := NewHandshake(addr, conn, conf)
 155         var dhPubRepr *[32]byte
 156         state.dhPriv, dhPubRepr = dhKeypairGen()
 157
 158         state.rNonce = new([RSize]byte)
 159         if _, err := Rand.Read(state.rNonce[:]); err != nil {
 160                 log.Fatalln("Error reading random for nonce:", err)
 161         }
 162         var enc []byte
 163         if conf.Noise {
 164                 enc = make([]byte, conf.MTU-xtea.BlockSize-RSize)
 165         } else {
 166                 enc = make([]byte, 32)
 167         }
 168         copy(enc, dhPubRepr[:])
 169         if conf.EncLess {
 170                 var err error
 171                 enc, err = EncLessEncode(state.dsaPubH, state.rNonce[:], enc)
 172                 if err != err {
 173                         panic(err)
 174                 }
 175         } else {
 176                 salsa20.XORKeyStream(enc, enc, state.rNonce[:], state.dsaPubH)
 177         }
 178         data := append(state.rNonce[:], enc...)
 179         data = append(data, idTag(state.Conf.Id, state.rNonce[:])...)
 180         state.conn.Write(data)
 181         return state
 182 }
 183
 184 // Process handshake message on the server side.
 185 // This function is intended to be called on server's side.
 186 // If this is the final handshake message, then new Peer object
 187 // will be created and used as a transport. If no mutually
 188 // authenticated Peer is ready, then return nil.
 189 func (h *Handshake) Server(data []byte) *Peer {
 190         // R + ENC(H(DSAPub), R, El(CDHPub)) + IDtag
 191         if h.rNonce == nil && ((!h.Conf.EncLess && len(data) >= 48) ||
 192                 (h.Conf.EncLess && len(data) == EncLessEnlargeSize+h.Conf.MTU)) {
 193                 h.rNonce = new([RSize]byte)
 194                 copy(h.rNonce[:], data[:RSize])
 195
 196                 // Decrypt remote public key
 197                 cDHRepr := new([32]byte)
 198                 if h.Conf.EncLess {
 199                         out, err := EncLessDecode(
 200                                 h.dsaPubH,
 201                                 h.rNonce[:],
 202                                 data[RSize:len(data)-xtea.BlockSize],
 203                         )
 204                         if err != nil {
 205                                 log.Println("Unable to decode packet from", h.addr, err)
 206                                 return nil
 207                         }
 208                         copy(cDHRepr[:], out)
 209                 } else {
 210                         salsa20.XORKeyStream(
 211                                 cDHRepr[:],
 212                                 data[RSize:RSize+32],
 213                                 h.rNonce[:],
 214                                 h.dsaPubH,
 215                         )
 216                 }
 217
 218                 // Generate DH keypair
 219                 var dhPubRepr *[32]byte
 220                 h.dhPriv, dhPubRepr = dhKeypairGen()
 221
 222                 // Compute shared key
 223                 cDH := new([32]byte)
 224                 extra25519.RepresentativeToPublicKey(cDH, cDHRepr)
 225                 h.key = dhKeyGen(h.dhPriv, cDH)
 226
 227                 var encPub []byte
 228                 var err error
 229                 if h.Conf.EncLess {
 230                         encPub = make([]byte, h.Conf.MTU)
 231                         copy(encPub, dhPubRepr[:])
 232                         encPub, err = EncLessEncode(h.dsaPubH, h.rNonceNext(1), encPub)
 233                         if err != nil {
 234                                 panic(err)
 235                         }
 236                 } else {
 237                         encPub = make([]byte, 32)
 238                         salsa20.XORKeyStream(encPub, dhPubRepr[:], h.rNonceNext(1), h.dsaPubH)
 239                 }
 240
 241                 // Generate R* and encrypt them
 242                 h.rServer = new([RSize]byte)
 243                 if _, err = Rand.Read(h.rServer[:]); err != nil {
 244                         log.Fatalln("Error reading random for R:", err)
 245                 }
 246                 h.sServer = new([SSize]byte)
 247                 if _, err = Rand.Read(h.sServer[:]); err != nil {
 248                         log.Fatalln("Error reading random for S:", err)
 249                 }
 250                 var encRs []byte
 251                 if h.Conf.Noise && !h.Conf.EncLess {
 252                         encRs = make([]byte, h.Conf.MTU-len(encPub)-xtea.BlockSize)
 253                 } else if h.Conf.EncLess {
 254                         encRs = make([]byte, h.Conf.MTU-xtea.BlockSize)
 255                 } else {
 256                         encRs = make([]byte, RSize+SSize)
 257                 }
 258                 copy(encRs, append(h.rServer[:], h.sServer[:]...))
 259                 if h.Conf.EncLess {
 260                         encRs, err = EncLessEncode(h.key, h.rNonce[:], encRs)
 261                         if err != nil {
 262                                 panic(err)
 263                         }
 264                 } else {
 265                         salsa20.XORKeyStream(encRs, encRs, h.rNonce[:], h.key)
 266                 }
 267
 268                 // Send that to client
 269                 h.conn.Write(append(encPub, append(encRs, idTag(h.Conf.Id, encPub)...)...))
 270                 h.LastPing = time.Now()
 271         } else
 272         // ENC(K, R+1, RS + RC + SC + Sign(DSAPriv, K)) + IDtag
 273         if h.rClient == nil && ((!h.Conf.EncLess && len(data) >= 120) ||
 274                 (h.Conf.EncLess && len(data) == EncLessEnlargeSize+h.Conf.MTU)) {
 275                 var dec []byte
 276                 var err error
 277                 if h.Conf.EncLess {
 278                         dec, err = EncLessDecode(
 279                                 h.key,
 280                                 h.rNonceNext(1),
 281                                 data[:len(data)-xtea.BlockSize],
 282                         )
 283                         if err != nil {
 284                                 log.Println("Unable to decode packet from", h.addr, err)
 285                                 return nil
 286                         }
 287                         dec = dec[:RSize+RSize+SSize+ed25519.SignatureSize]
 288                 } else {
 289                         dec = make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
 290                         salsa20.XORKeyStream(
 291                                 dec,
 292                                 data[:RSize+RSize+SSize+ed25519.SignatureSize],
 293                                 h.rNonceNext(1),
 294                                 h.key,
 295                         )
 296                 }
 297                 if subtle.ConstantTimeCompare(dec[:RSize], h.rServer[:]) != 1 {
 298                         log.Println("Invalid server's random number with", h.addr)
 299                         return nil
 300                 }
 301                 sign := new([ed25519.SignatureSize]byte)
 302                 copy(sign[:], dec[RSize+RSize+SSize:])
 303                 if !ed25519.Verify(h.Conf.Verifier.Pub, h.key[:], sign) {
 304                         log.Println("Invalid signature from", h.addr)
 305                         return nil
 306                 }
 307
 308                 // Send final answer to client
 309                 var enc []byte
 310                 if h.Conf.Noise {
 311                         enc = make([]byte, h.Conf.MTU-xtea.BlockSize)
 312                 } else {
 313                         enc = make([]byte, RSize)
 314                 }
 315                 copy(enc, dec[RSize:RSize+RSize])
 316                 if h.Conf.EncLess {
 317                         enc, err = EncLessEncode(h.key, h.rNonceNext(2), enc)
 318                         if err != nil {
 319                                 panic(err)
 320                         }
 321                 } else {
 322                         salsa20.XORKeyStream(enc, enc, h.rNonceNext(2), h.key)
 323                 }
 324                 h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
 325
 326                 // Switch peer
 327                 peer := newPeer(
 328                         false,
 329                         h.addr,
 330                         h.conn,
 331                         h.Conf,
 332                         keyFromSecrets(h.sServer[:], dec[RSize+RSize:RSize+RSize+SSize]))
 333                 h.LastPing = time.Now()
 334                 return peer
 335         } else {
 336                 log.Println("Invalid handshake message from", h.addr)
 337         }
 338         return nil
 339 }
 340
 341 // Process handshake message on the client side.
 342 // This function is intended to be called on client's side.
 343 // If this is the final handshake message, then new Peer object
 344 // will be created and used as a transport. If no mutually
 345 // authenticated Peer is ready, then return nil.
 346 func (h *Handshake) Client(data []byte) *Peer {
 347         // ENC(H(DSAPub), R+1, El(SDHPub)) + ENC(K, R, RS + SS) + IDtag
 348         if h.rServer == nil && h.key == nil &&
 349                 ((!h.Conf.EncLess && len(data) >= 80) ||
 350                         (h.Conf.EncLess && len(data) == 2*(EncLessEnlargeSize+h.Conf.MTU))) {
 351                 // Decrypt remote public key
 352                 sDHRepr := new([32]byte)
 353                 var tmp []byte
 354                 var err error
 355                 if h.Conf.EncLess {
 356                         tmp, err = EncLessDecode(
 357                                 h.dsaPubH,
 358                                 h.rNonceNext(1),
 359                                 data[:len(data)/2],
 360                         )
 361                         if err != nil {
 362                                 log.Println("Unable to decode packet from", h.addr, err)
 363                                 return nil
 364                         }
 365                         copy(sDHRepr[:], tmp[:32])
 366                 } else {
 367                         salsa20.XORKeyStream(
 368                                 sDHRepr[:],
 369                                 data[:32],
 370                                 h.rNonceNext(1),
 371                                 h.dsaPubH,
 372                         )
 373                 }
 374
 375                 // Compute shared key
 376                 sDH := new([32]byte)
 377                 extra25519.RepresentativeToPublicKey(sDH, sDHRepr)
 378                 h.key = dhKeyGen(h.dhPriv, sDH)
 379
 380                 // Decrypt Rs
 381                 h.rServer = new([RSize]byte)
 382                 h.sServer = new([SSize]byte)
 383                 if h.Conf.EncLess {
 384                         tmp, err = EncLessDecode(
 385                                 h.key,
 386                                 h.rNonce[:],
 387                                 data[len(data)/2:len(data)-xtea.BlockSize],
 388                         )
 389                         if err != nil {
 390                                 log.Println("Unable to decode packet from", h.addr, err)
 391                                 return nil
 392                         }
 393                         copy(h.rServer[:], tmp[:RSize])
 394                         copy(h.sServer[:], tmp[RSize:RSize+SSize])
 395                 } else {
 396                         decRs := make([]byte, RSize+SSize)
 397                         salsa20.XORKeyStream(
 398                                 decRs,
 399                                 data[SSize:SSize+RSize+SSize],
 400                                 h.rNonce[:],
 401                                 h.key,
 402                         )
 403                         copy(h.rServer[:], decRs[:RSize])
 404                         copy(h.sServer[:], decRs[RSize:])
 405                 }
 406
 407                 // Generate R* and signature and encrypt them
 408                 h.rClient = new([RSize]byte)
 409                 if _, err = Rand.Read(h.rClient[:]); err != nil {
 410                         log.Fatalln("Error reading random for R:", err)
 411                 }
 412                 h.sClient = new([SSize]byte)
 413                 if _, err = Rand.Read(h.sClient[:]); err != nil {
 414                         log.Fatalln("Error reading random for S:", err)
 415                 }
 416                 sign := ed25519.Sign(h.Conf.DSAPriv, h.key[:])
 417
 418                 var enc []byte
 419                 if h.Conf.Noise {
 420                         enc = make([]byte, h.Conf.MTU-xtea.BlockSize)
 421                 } else {
 422                         enc = make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
 423                 }
 424                 copy(enc, h.rServer[:])
 425                 copy(enc[RSize:], h.rClient[:])
 426                 copy(enc[RSize+RSize:], h.sClient[:])
 427                 copy(enc[RSize+RSize+SSize:], sign[:])
 428                 if h.Conf.EncLess {
 429                         enc, err = EncLessEncode(h.key, h.rNonceNext(1), enc)
 430                         if err != nil {
 431                                 panic(err)
 432                         }
 433                 } else {
 434                         salsa20.XORKeyStream(enc, enc, h.rNonceNext(1), h.key)
 435                 }
 436
 437                 // Send that to server
 438                 h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
 439                 h.LastPing = time.Now()
 440         } else
 441         // ENC(K, R+2, RC) + IDtag
 442         if h.key != nil && ((!h.Conf.EncLess && len(data) >= 16) ||
 443                 (h.Conf.EncLess && len(data) == EncLessEnlargeSize+h.Conf.MTU)) {
 444                 var err error
 445                 // Decrypt rClient
 446                 var dec []byte
 447                 if h.Conf.EncLess {
 448                         dec, err = EncLessDecode(
 449                                 h.key,
 450                                 h.rNonceNext(2),
 451                                 data[:len(data)-xtea.BlockSize],
 452                         )
 453                         if err != nil {
 454                                 log.Println("Unable to decode packet from", h.addr, err)
 455                                 return nil
 456                         }
 457                         dec = dec[:RSize]
 458                 } else {
 459                         dec = make([]byte, RSize)
 460                         salsa20.XORKeyStream(dec, data[:RSize], h.rNonceNext(2), h.key)
 461                 }
 462                 if subtle.ConstantTimeCompare(dec, h.rClient[:]) != 1 {
 463                         log.Println("Invalid client's random number with", h.addr)
 464                         return nil
 465                 }
 466
 467                 // Switch peer
 468                 peer := newPeer(
 469                         true,
 470                         h.addr,
 471                         h.conn,
 472                         h.Conf,
 473                         keyFromSecrets(h.sServer[:], h.sClient[:]),
 474                 )
 475                 h.LastPing = time.Now()
 476                 return peer
 477         } else {
 478                 log.Println("Invalid handshake stage from", h.addr)
 479         }
 480         return nil
 481 }