release/src/router/tinc/src/sptps.c

   1 /*
   2     sptps.c -- Simple Peer-to-Peer Security
   3     Copyright (C) 2011-2014 Guus Sliepen <guus@tinc-vpn.org>,
   4                   2010      Brandon L. Black <blblack@gmail.com>
   5
   6     This program is free software; you can redistribute it and/or modify
   7     it under the terms of the GNU General Public License as published by
   8     the Free Software Foundation; either version 2 of the License, or
   9     (at your option) any later version.
  10
  11     This program is distributed in the hope that it will be useful,
  12     but WITHOUT ANY WARRANTY; without even the implied warranty of
  13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14     GNU General Public License for more details.
  15
  16     You should have received a copy of the GNU General Public License along
  17     with this program; if not, write to the Free Software Foundation, Inc.,
  18     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  19 */
  20
  21 #include "system.h"
  22
  23 #include "chacha-poly1305/chacha-poly1305.h"
  24 #include "crypto.h"
  25 #include "ecdh.h"
  26 #include "ecdsa.h"
  27 #include "logger.h"
  28 #include "prf.h"
  29 #include "sptps.h"
  30
  31 unsigned int sptps_replaywin = 16;
  32
  33 /*
  34    Nonce MUST be exchanged first (done)
  35    Signatures MUST be done over both nonces, to guarantee the signature is fresh
  36    Otherwise: if ECDHE key of one side is compromised, it can be reused!
  37
  38    Add explicit tag to beginning of structure to distinguish the client and server when signing. (done)
  39
  40    Sign all handshake messages up to ECDHE kex with long-term public keys. (done)
  41
  42    HMACed KEX finished message to prevent downgrade attacks and prove you have the right key material (done by virtue of Ed25519 over the whole ECDHE exchange?)
  43
  44    Explicit close message needs to be added.
  45
  46    Maybe do add some alert messages to give helpful error messages? Not more than TLS sends.
  47
  48    Use counter mode instead of OFB. (done)
  49
  50    Make sure ECC operations are fixed time (aka prevent side-channel attacks).
  51 */
  52
  53 void sptps_log_quiet(sptps_t *s, int s_errno, const char *format, va_list ap) {
  54 }
  55
  56 void sptps_log_stderr(sptps_t *s, int s_errno, const char *format, va_list ap) {
  57         vfprintf(stderr, format, ap);
  58         fputc('\n', stderr);
  59 }
  60
  61 void (*sptps_log)(sptps_t *s, int s_errno, const char *format, va_list ap) = sptps_log_stderr;
  62
  63 // Log an error message.
  64 static bool error(sptps_t *s, int s_errno, const char *format, ...) {
  65         if(format) {
  66                 va_list ap;
  67                 va_start(ap, format);
  68                 sptps_log(s, s_errno, format, ap);
  69                 va_end(ap);
  70         }
  71
  72         errno = s_errno;
  73         return false;
  74 }
  75
  76 static void warning(sptps_t *s, const char *format, ...) {
  77         va_list ap;
  78         va_start(ap, format);
  79         sptps_log(s, 0, format, ap);
  80         va_end(ap);
  81 }
  82
  83 // Send a record (datagram version, accepts all record types, handles encryption and authentication).
  84 static bool send_record_priv_datagram(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
  85         char buffer[len + 21UL];
  86
  87         // Create header with sequence number, length and record type
  88         uint32_t seqno = s->outseqno++;
  89         uint32_t netseqno = ntohl(seqno);
  90
  91         memcpy(buffer, &netseqno, 4);
  92         buffer[4] = type;
  93         memcpy(buffer + 5, data, len);
  94
  95         if(s->outstate) {
  96                 // If first handshake has finished, encrypt and HMAC
  97                 chacha_poly1305_encrypt(s->outcipher, seqno, buffer + 4, len + 1, buffer + 4, NULL);
  98                 return s->send_data(s->handle, type, buffer, len + 21UL);
  99         } else {
 100                 // Otherwise send as plaintext
 101                 return s->send_data(s->handle, type, buffer, len + 5UL);
 102         }
 103 }
 104 // Send a record (private version, accepts all record types, handles encryption and authentication).
 105 static bool send_record_priv(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
 106         if(s->datagram)
 107                 return send_record_priv_datagram(s, type, data, len);
 108
 109         char buffer[len + 19UL];
 110
 111         // Create header with sequence number, length and record type
 112         uint32_t seqno = s->outseqno++;
 113         uint16_t netlen = htons(len);
 114
 115         memcpy(buffer, &netlen, 2);
 116         buffer[2] = type;
 117         memcpy(buffer + 3, data, len);
 118
 119         if(s->outstate) {
 120                 // If first handshake has finished, encrypt and HMAC
 121                 chacha_poly1305_encrypt(s->outcipher, seqno, buffer + 2, len + 1, buffer + 2, NULL);
 122                 return s->send_data(s->handle, type, buffer, len + 19UL);
 123         } else {
 124                 // Otherwise send as plaintext
 125                 return s->send_data(s->handle, type, buffer, len + 3UL);
 126         }
 127 }
 128
 129 // Send an application record.
 130 bool sptps_send_record(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
 131         // Sanity checks: application cannot send data before handshake is finished,
 132         // and only record types 0..127 are allowed.
 133         if(!s->outstate)
 134                 return error(s, EINVAL, "Handshake phase not finished yet");
 135
 136         if(type >= SPTPS_HANDSHAKE)
 137                 return error(s, EINVAL, "Invalid application record type");
 138
 139         return send_record_priv(s, type, data, len);
 140 }
 141
 142 // Send a Key EXchange record, containing a random nonce and an ECDHE public key.
 143 static bool send_kex(sptps_t *s) {
 144         size_t keylen = ECDH_SIZE;
 145
 146         // Make room for our KEX message, which we will keep around since send_sig() needs it.
 147         if(s->mykex)
 148                 return false;
 149         s->mykex = realloc(s->mykex, 1 + 32 + keylen);
 150         if(!s->mykex)
 151                 return error(s, errno, strerror(errno));
 152
 153         // Set version byte to zero.
 154         s->mykex[0] = SPTPS_VERSION;
 155
 156         // Create a random nonce.
 157         randomize(s->mykex + 1, 32);
 158
 159         // Create a new ECDH public key.
 160         if(!(s->ecdh = ecdh_generate_public(s->mykex + 1 + 32)))
 161                 return error(s, EINVAL, "Failed to generate ECDH public key");
 162
 163         return send_record_priv(s, SPTPS_HANDSHAKE, s->mykex, 1 + 32 + keylen);
 164 }
 165
 166 // Send a SIGnature record, containing an Ed25519 signature over both KEX records.
 167 static bool send_sig(sptps_t *s) {
 168         size_t keylen = ECDH_SIZE;
 169         size_t siglen = ecdsa_size(s->mykey);
 170
 171         // Concatenate both KEX messages, plus tag indicating if it is from the connection originator, plus label
 172         char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
 173         char sig[siglen];
 174
 175         msg[0] = s->initiator;
 176         memcpy(msg + 1, s->mykex, 1 + 32 + keylen);
 177         memcpy(msg + 1 + 33 + keylen, s->hiskex, 1 + 32 + keylen);
 178         memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
 179
 180         // Sign the result.
 181         if(!ecdsa_sign(s->mykey, msg, sizeof msg, sig))
 182                 return error(s, EINVAL, "Failed to sign SIG record");
 183
 184         // Send the SIG exchange record.
 185         return send_record_priv(s, SPTPS_HANDSHAKE, sig, sizeof sig);
 186 }
 187
 188 // Generate key material from the shared secret created from the ECDHE key exchange.
 189 static bool generate_key_material(sptps_t *s, const char *shared, size_t len) {
 190         // Initialise cipher and digest structures if necessary
 191         if(!s->outstate) {
 192                 s->incipher = chacha_poly1305_init();
 193                 s->outcipher = chacha_poly1305_init();
 194                 if(!s->incipher || !s->outcipher)
 195                         return error(s, EINVAL, "Failed to open cipher");
 196         }
 197
 198         // Allocate memory for key material
 199         size_t keylen = 2 * CHACHA_POLY1305_KEYLEN;
 200
 201         s->key = realloc(s->key, keylen);
 202         if(!s->key)
 203                 return error(s, errno, strerror(errno));
 204
 205         // Create the HMAC seed, which is "key expansion" + session label + server nonce + client nonce
 206         char seed[s->labellen + 64 + 13];
 207         strcpy(seed, "key expansion");
 208         if(s->initiator) {
 209                 memcpy(seed + 13, s->mykex + 1, 32);
 210                 memcpy(seed + 45, s->hiskex + 1, 32);
 211         } else {
 212                 memcpy(seed + 13, s->hiskex + 1, 32);
 213                 memcpy(seed + 45, s->mykex + 1, 32);
 214         }
 215         memcpy(seed + 77, s->label, s->labellen);
 216
 217         // Use PRF to generate the key material
 218         if(!prf(shared, len, seed, s->labellen + 64 + 13, s->key, keylen))
 219                 return error(s, EINVAL, "Failed to generate key material");
 220
 221         return true;
 222 }
 223
 224 // Send an ACKnowledgement record.
 225 static bool send_ack(sptps_t *s) {
 226         return send_record_priv(s, SPTPS_HANDSHAKE, "", 0);
 227 }
 228
 229 // Receive an ACKnowledgement record.
 230 static bool receive_ack(sptps_t *s, const char *data, uint16_t len) {
 231         if(len)
 232                 return error(s, EIO, "Invalid ACK record length");
 233
 234         if(s->initiator) {
 235                 if(!chacha_poly1305_set_key(s->incipher, s->key))
 236                         return error(s, EINVAL, "Failed to set counter");
 237         } else {
 238                 if(!chacha_poly1305_set_key(s->incipher, s->key + CHACHA_POLY1305_KEYLEN))
 239                         return error(s, EINVAL, "Failed to set counter");
 240         }
 241
 242         free(s->key);
 243         s->key = NULL;
 244         s->instate = true;
 245
 246         return true;
 247 }
 248
 249 // Receive a Key EXchange record, respond by sending a SIG record.
 250 static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
 251         // Verify length of the HELLO record
 252         if(len != 1 + 32 + ECDH_SIZE)
 253                 return error(s, EIO, "Invalid KEX record length");
 254
 255         // Ignore version number for now.
 256
 257         // Make a copy of the KEX message, send_sig() and receive_sig() need it
 258         if(s->hiskex)
 259                 return error(s, EINVAL, "Received a second KEX message before first has been processed");
 260         s->hiskex = realloc(s->hiskex, len);
 261         if(!s->hiskex)
 262                 return error(s, errno, strerror(errno));
 263
 264         memcpy(s->hiskex, data, len);
 265
 266         return send_sig(s);
 267 }
 268
 269 // Receive a SIGnature record, verify it, if it passed, compute the shared secret and calculate the session keys.
 270 static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
 271         size_t keylen = ECDH_SIZE;
 272         size_t siglen = ecdsa_size(s->hiskey);
 273
 274         // Verify length of KEX record.
 275         if(len != siglen)
 276                 return error(s, EIO, "Invalid KEX record length");
 277
 278         // Concatenate both KEX messages, plus tag indicating if it is from the connection originator
 279         char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
 280
 281         msg[0] = !s->initiator;
 282         memcpy(msg + 1, s->hiskex, 1 + 32 + keylen);
 283         memcpy(msg + 1 + 33 + keylen, s->mykex, 1 + 32 + keylen);
 284         memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
 285
 286         // Verify signature.
 287         if(!ecdsa_verify(s->hiskey, msg, sizeof msg, data))
 288                 return error(s, EIO, "Failed to verify SIG record");
 289
 290         // Compute shared secret.
 291         char shared[ECDH_SHARED_SIZE];
 292         if(!ecdh_compute_shared(s->ecdh, s->hiskex + 1 + 32, shared))
 293                 return error(s, EINVAL, "Failed to compute ECDH shared secret");
 294         s->ecdh = NULL;
 295
 296         // Generate key material from shared secret.
 297         if(!generate_key_material(s, shared, sizeof shared))
 298                 return false;
 299
 300         free(s->mykex);
 301         free(s->hiskex);
 302
 303         s->mykex = NULL;
 304         s->hiskex = NULL;
 305
 306         // Send cipher change record
 307         if(s->outstate && !send_ack(s))
 308                 return false;
 309
 310         // TODO: only set new keys after ACK has been set/received
 311         if(s->initiator) {
 312                 if(!chacha_poly1305_set_key(s->outcipher, s->key + CHACHA_POLY1305_KEYLEN))
 313                         return error(s, EINVAL, "Failed to set key");
 314         } else {
 315                 if(!chacha_poly1305_set_key(s->outcipher, s->key))
 316                         return error(s, EINVAL, "Failed to set key");
 317         }
 318
 319         return true;
 320 }
 321
 322 // Force another Key EXchange (for testing purposes).
 323 bool sptps_force_kex(sptps_t *s) {
 324         if(!s->outstate || s->state != SPTPS_SECONDARY_KEX)
 325                 return error(s, EINVAL, "Cannot force KEX in current state");
 326
 327         s->state = SPTPS_KEX;
 328         return send_kex(s);
 329 }
 330
 331 // Receive a handshake record.
 332 static bool receive_handshake(sptps_t *s, const char *data, uint16_t len) {
 333         // Only a few states to deal with handshaking.
 334         switch(s->state) {
 335                 case SPTPS_SECONDARY_KEX:
 336                         // We receive a secondary KEX request, first respond by sending our own.
 337                         if(!send_kex(s))
 338                                 return false;
 339                 case SPTPS_KEX:
 340                         // We have sent our KEX request, we expect our peer to sent one as well.
 341                         if(!receive_kex(s, data, len))
 342                                 return false;
 343                         s->state = SPTPS_SIG;
 344                         return true;
 345                 case SPTPS_SIG:
 346                         // If we already sent our secondary public ECDH key, we expect the peer to send his.
 347                         if(!receive_sig(s, data, len))
 348                                 return false;
 349                         if(s->outstate)
 350                                 s->state = SPTPS_ACK;
 351                         else {
 352                                 s->outstate = true;
 353                                 if(!receive_ack(s, NULL, 0))
 354                                         return false;
 355                                 s->receive_record(s->handle, SPTPS_HANDSHAKE, NULL, 0);
 356                                 s->state = SPTPS_SECONDARY_KEX;
 357                         }
 358
 359                         return true;
 360                 case SPTPS_ACK:
 361                         // We expect a handshake message to indicate transition to the new keys.
 362                         if(!receive_ack(s, data, len))
 363                                 return false;
 364                         s->receive_record(s->handle, SPTPS_HANDSHAKE, NULL, 0);
 365                         s->state = SPTPS_SECONDARY_KEX;
 366                         return true;
 367                 // TODO: split ACK into a VERify and ACK?
 368                 default:
 369                         return error(s, EIO, "Invalid session state %d", s->state);
 370         }
 371 }
 372
 373 static bool sptps_check_seqno(sptps_t *s, uint32_t seqno, bool update_state) {
 374         // Replay protection using a sliding window of configurable size.
 375         // s->inseqno is expected sequence number
 376         // seqno is received sequence number
 377         // s->late[] is a circular buffer, a 1 bit means a packet has not been received yet
 378         // The circular buffer contains bits for sequence numbers from s->inseqno - s->replaywin * 8 to (but excluding) s->inseqno.
 379         if(s->replaywin) {
 380                 if(seqno != s->inseqno) {
 381                         if(seqno >= s->inseqno + s->replaywin * 8) {
 382                                 // Prevent packets that jump far ahead of the queue from causing many others to be dropped.
 383                                 bool farfuture = s->farfuture < s->replaywin >> 2;
 384                                 if (update_state)
 385                                         s->farfuture++;
 386                                 if(farfuture)
 387                                         return error(s, EIO, "Packet is %d seqs in the future, dropped (%u)\n", seqno - s->inseqno, s->farfuture);
 388
 389                                 // Unless we have seen lots of them, in which case we consider the others lost.
 390                                 warning(s, "Lost %d packets\n", seqno - s->inseqno);
 391                                 if (update_state) {
 392                                         // Mark all packets in the replay window as being late.
 393                                         memset(s->late, 255, s->replaywin);
 394                                 }
 395                         } else if (seqno < s->inseqno) {
 396                                 // If the sequence number is farther in the past than the bitmap goes, or if the packet was already received, drop it.
 397                                 if((s->inseqno >= s->replaywin * 8 && seqno < s->inseqno - s->replaywin * 8) || !(s->late[(seqno / 8) % s->replaywin] & (1 << seqno % 8)))
 398                                         return error(s, EIO, "Received late or replayed packet, seqno %d, last received %d\n", seqno, s->inseqno);
 399                         } else if (update_state) {
 400                                 // We missed some packets. Mark them in the bitmap as being late.
 401                                 for(int i = s->inseqno; i < seqno; i++)
 402                                         s->late[(i / 8) % s->replaywin] |= 1 << i % 8;
 403                         }
 404                 }
 405
 406                 if (update_state) {
 407                         // Mark the current packet as not being late.
 408                         s->late[(seqno / 8) % s->replaywin] &= ~(1 << seqno % 8);
 409                         s->farfuture = 0;
 410                 }
 411         }
 412
 413         if (update_state) {
 414                 if(seqno >= s->inseqno)
 415                         s->inseqno = seqno + 1;
 416
 417                 if(!s->inseqno)
 418                         s->received = 0;
 419                 else
 420                         s->received++;
 421         }
 422
 423         return true;
 424 }
 425
 426 // Check datagram for valid HMAC
 427 bool sptps_verify_datagram(sptps_t *s, const void *data, size_t len) {
 428         if(!s->instate || len < 21)
 429                 return error(s, EIO, "Received short packet");
 430
 431         uint32_t seqno;
 432         memcpy(&seqno, data, 4);
 433         seqno = ntohl(seqno);
 434         if (!sptps_check_seqno(s, seqno, false))
 435                 return false;
 436
 437         char buffer[len];
 438         size_t outlen;
 439         return chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, buffer, &outlen);
 440 }
 441
 442 // Receive incoming data, datagram version.
 443 static bool sptps_receive_data_datagram(sptps_t *s, const char *data, size_t len) {
 444         if(len < (s->instate ? 21 : 5))
 445                 return error(s, EIO, "Received short packet");
 446
 447         uint32_t seqno;
 448         memcpy(&seqno, data, 4);
 449         seqno = ntohl(seqno);
 450
 451         if(!s->instate) {
 452                 if(seqno != s->inseqno)
 453                         return error(s, EIO, "Invalid packet seqno: %d != %d", seqno, s->inseqno);
 454
 455                 s->inseqno = seqno + 1;
 456
 457                 uint8_t type = data[4];
 458
 459                 if(type != SPTPS_HANDSHAKE)
 460                         return error(s, EIO, "Application record received before handshake finished");
 461
 462                 return receive_handshake(s, data + 5, len - 5);
 463         }
 464
 465         // Decrypt
 466
 467         char buffer[len];
 468
 469         size_t outlen;
 470
 471         if(!chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, buffer, &outlen))
 472                 return error(s, EIO, "Failed to decrypt and verify packet");
 473
 474         if(!sptps_check_seqno(s, seqno, true))
 475                 return false;
 476
 477         // Append a NULL byte for safety.
 478         buffer[len - 20] = 0;
 479
 480         uint8_t type = buffer[0];
 481
 482         if(type < SPTPS_HANDSHAKE) {
 483                 if(!s->instate)
 484                         return error(s, EIO, "Application record received before handshake finished");
 485                 if(!s->receive_record(s->handle, type, buffer + 1, len - 21))
 486                         abort();
 487         } else if(type == SPTPS_HANDSHAKE) {
 488                 if(!receive_handshake(s, buffer + 1, len - 21))
 489                         abort();
 490         } else {
 491                 return error(s, EIO, "Invalid record type %d", type);
 492         }
 493
 494         return true;
 495 }
 496
 497 // Receive incoming data. Check if it contains a complete record, if so, handle it.
 498 bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
 499         if(!s->state)
 500                 return error(s, EIO, "Invalid session state zero");
 501
 502         if(s->datagram)
 503                 return sptps_receive_data_datagram(s, data, len);
 504
 505         while(len) {
 506                 // First read the 2 length bytes.
 507                 if(s->buflen < 2) {
 508                         size_t toread = 2 - s->buflen;
 509                         if(toread > len)
 510                                 toread = len;
 511
 512                         memcpy(s->inbuf + s->buflen, data, toread);
 513
 514                         s->buflen += toread;
 515                         len -= toread;
 516                         data += toread;
 517
 518                         // Exit early if we don't have the full length.
 519                         if(s->buflen < 2)
 520                                 return true;
 521
 522                         // Get the length bytes
 523
 524                         memcpy(&s->reclen, s->inbuf, 2);
 525                         s->reclen = ntohs(s->reclen);
 526
 527                         // If we have the length bytes, ensure our buffer can hold the whole request.
 528                         s->inbuf = realloc(s->inbuf, s->reclen + 19UL);
 529                         if(!s->inbuf)
 530                                 return error(s, errno, strerror(errno));
 531
 532                         // Exit early if we have no more data to process.
 533                         if(!len)
 534                                 return true;
 535                 }
 536
 537                 // Read up to the end of the record.
 538                 size_t toread = s->reclen + (s->instate ? 19UL : 3UL) - s->buflen;
 539                 if(toread > len)
 540                         toread = len;
 541
 542                 memcpy(s->inbuf + s->buflen, data, toread);
 543                 s->buflen += toread;
 544                 len -= toread;
 545                 data += toread;
 546
 547                 // If we don't have a whole record, exit.
 548                 if(s->buflen < s->reclen + (s->instate ? 19UL : 3UL))
 549                         return true;
 550
 551                 // Update sequence number.
 552
 553                 uint32_t seqno = s->inseqno++;
 554
 555                 // Check HMAC and decrypt.
 556                 if(s->instate) {
 557                         if(!chacha_poly1305_decrypt(s->incipher, seqno, s->inbuf + 2UL, s->reclen + 17UL, s->inbuf + 2UL, NULL))
 558                                 return error(s, EINVAL, "Failed to decrypt and verify record");
 559                 }
 560
 561                 // Append a NULL byte for safety.
 562                 s->inbuf[s->reclen + 3UL] = 0;
 563
 564                 uint8_t type = s->inbuf[2];
 565
 566                 if(type < SPTPS_HANDSHAKE) {
 567                         if(!s->instate)
 568                                 return error(s, EIO, "Application record received before handshake finished");
 569                         if(!s->receive_record(s->handle, type, s->inbuf + 3, s->reclen))
 570                                 return false;
 571                 } else if(type == SPTPS_HANDSHAKE) {
 572                         if(!receive_handshake(s, s->inbuf + 3, s->reclen))
 573                                 return false;
 574                 } else {
 575                         return error(s, EIO, "Invalid record type %d", type);
 576                 }
 577
 578                 s->buflen = 0;
 579         }
 580
 581         return true;
 582 }
 583
 584 // Start a SPTPS session.
 585 bool sptps_start(sptps_t *s, void *handle, bool initiator, bool datagram, ecdsa_t *mykey, ecdsa_t *hiskey, const void *label, size_t labellen, send_data_t send_data, receive_record_t receive_record) {
 586         // Initialise struct sptps
 587         memset(s, 0, sizeof *s);
 588
 589         s->handle = handle;
 590         s->initiator = initiator;
 591         s->datagram = datagram;
 592         s->mykey = mykey;
 593         s->hiskey = hiskey;
 594         s->replaywin = sptps_replaywin;
 595         if(s->replaywin) {
 596                 s->late = malloc(s->replaywin);
 597                 if(!s->late)
 598                         return error(s, errno, strerror(errno));
 599                 memset(s->late, 0, s->replaywin);
 600         }
 601
 602         s->label = malloc(labellen);
 603         if(!s->label)
 604                 return error(s, errno, strerror(errno));
 605
 606         if(!datagram) {
 607                 s->inbuf = malloc(7);
 608                 if(!s->inbuf)
 609                         return error(s, errno, strerror(errno));
 610                 s->buflen = 0;
 611         }
 612
 613         memcpy(s->label, label, labellen);
 614         s->labellen = labellen;
 615
 616         s->send_data = send_data;
 617         s->receive_record = receive_record;
 618
 619         // Do first KEX immediately
 620         s->state = SPTPS_KEX;
 621         return send_kex(s);
 622 }
 623
 624 // Stop a SPTPS session.
 625 bool sptps_stop(sptps_t *s) {
 626         // Clean up any resources.
 627         chacha_poly1305_exit(s->incipher);
 628         chacha_poly1305_exit(s->outcipher);
 629         ecdh_free(s->ecdh);
 630         free(s->inbuf);
 631         free(s->mykex);
 632         free(s->hiskex);
 633         free(s->key);
 634         free(s->label);
 635         free(s->late);
 636         memset(s, 0, sizeof *s);
 637         return true;
 638 }