2 sptps.c -- Simple Peer-to-Peer Security
3 Copyright (C) 2014-2017 Guus Sliepen <guus@meshlink.io>
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 2 of the License, or
8 (at your option) any later version.
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.
15 You should have received a copy of the GNU General Public License along
16 with this program; if not, write to the Free Software Foundation, Inc.,
17 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
22 #include "chacha-poly1305/chacha-poly1305.h"
30 unsigned int sptps_replaywin = 32;
33 Nonce MUST be exchanged first (done)
34 Signatures MUST be done over both nonces, to guarantee the signature is fresh
35 Otherwise: if ECDHE key of one side is compromised, it can be reused!
37 Add explicit tag to beginning of structure to distinguish the client and server when signing. (done)
39 Sign all handshake messages up to ECDHE kex with long-term public keys. (done)
41 HMACed KEX finished message to prevent downgrade attacks and prove you have the right key material (done by virtue of ECDSA over the whole ECDHE exchange?)
43 Explicit close message needs to be added.
45 Maybe do add some alert messages to give helpful error messages? Not more than TLS sends.
47 Use counter mode instead of OFB. (done)
49 Make sure ECC operations are fixed time (aka prevent side-channel attacks).
52 void sptps_log_quiet(sptps_t *s, int s_errno, const char *format, va_list ap) {
59 void sptps_log_stderr(sptps_t *s, int s_errno, const char *format, va_list ap) {
62 vfprintf(stderr, format, ap);
66 void (*sptps_log)(sptps_t *s, int s_errno, const char *format, va_list ap) = sptps_log_stderr;
68 // Log an error message.
69 static bool error(sptps_t *s, int s_errno, const char *format, ...) {
73 sptps_log(s, s_errno, format, ap);
81 static void warning(sptps_t *s, const char *format, ...) {
84 sptps_log(s, 0, format, ap);
88 // Send a record (datagram version, accepts all record types, handles encryption and authentication).
89 static bool send_record_priv_datagram(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
90 char buffer[len + 21UL];
92 // Create header with sequence number, length and record type
93 uint32_t seqno = s->outseqno++;
94 uint32_t netseqno = ntohl(seqno);
96 memcpy(buffer, &netseqno, 4);
98 memcpy(buffer + 5, data, len);
101 // If first handshake has finished, encrypt and HMAC
102 chacha_poly1305_encrypt(s->outcipher, seqno, buffer + 4, len + 1, buffer + 4, NULL);
103 return s->send_data(s->handle, type, buffer, len + 21UL);
105 // Otherwise send as plaintext
106 return s->send_data(s->handle, type, buffer, len + 5UL);
109 // Send a record (private version, accepts all record types, handles encryption and authentication).
110 static bool send_record_priv(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
112 return send_record_priv_datagram(s, type, data, len);
114 char buffer[len + 19UL];
116 // Create header with sequence number, length and record type
117 uint32_t seqno = s->outseqno++;
118 uint16_t netlen = htons(len);
120 memcpy(buffer, &netlen, 2);
122 memcpy(buffer + 3, data, len);
125 // If first handshake has finished, encrypt and HMAC
126 chacha_poly1305_encrypt(s->outcipher, seqno, buffer + 2, len + 1, buffer + 2, NULL);
127 return s->send_data(s->handle, type, buffer, len + 19UL);
129 // Otherwise send as plaintext
130 return s->send_data(s->handle, type, buffer, len + 3UL);
134 // Send an application record.
135 bool sptps_send_record(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
136 // Sanity checks: application cannot send data before handshake is finished,
137 // and only record types 0..127 are allowed.
139 return error(s, EINVAL, "Handshake phase not finished yet");
141 if(type >= SPTPS_HANDSHAKE)
142 return error(s, EINVAL, "Invalid application record type");
144 return send_record_priv(s, type, data, len);
147 // Send a Key EXchange record, containing a random nonce and an ECDHE public key.
148 static bool send_kex(sptps_t *s) {
149 size_t keylen = ECDH_SIZE;
151 // Make room for our KEX message, which we will keep around since send_sig() needs it.
154 s->mykex = realloc(s->mykex, 1 + 32 + keylen);
156 return error(s, errno, strerror(errno));
158 // Set version byte to zero.
159 s->mykex[0] = SPTPS_VERSION;
161 // Create a random nonce.
162 randomize(s->mykex + 1, 32);
164 // Create a new ECDH public key.
165 if(!(s->ecdh = ecdh_generate_public(s->mykex + 1 + 32)))
166 return error(s, EINVAL, "Failed to generate ECDH public key");
168 return send_record_priv(s, SPTPS_HANDSHAKE, s->mykex, 1 + 32 + keylen);
171 // Send a SIGnature record, containing an ECDSA signature over both KEX records.
172 static bool send_sig(sptps_t *s) {
173 size_t keylen = ECDH_SIZE;
174 size_t siglen = ecdsa_size(s->mykey);
176 // Concatenate both KEX messages, plus tag indicating if it is from the connection originator, plus label
177 char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
180 msg[0] = s->initiator;
181 memcpy(msg + 1, s->mykex, 1 + 32 + keylen);
182 memcpy(msg + 1 + 33 + keylen, s->hiskex, 1 + 32 + keylen);
183 memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
186 if(!ecdsa_sign(s->mykey, msg, sizeof(msg), sig))
187 return error(s, EINVAL, "Failed to sign SIG record");
189 // Send the SIG exchange record.
190 return send_record_priv(s, SPTPS_HANDSHAKE, sig, sizeof(sig));
193 // Generate key material from the shared secret created from the ECDHE key exchange.
194 static bool generate_key_material(sptps_t *s, const char *shared, size_t len) {
195 // Initialise cipher and digest structures if necessary
197 s->incipher = chacha_poly1305_init();
198 s->outcipher = chacha_poly1305_init();
199 if(!s->incipher || !s->outcipher)
200 return error(s, EINVAL, "Failed to open cipher");
203 // Allocate memory for key material
204 size_t keylen = 2 * CHACHA_POLY1305_KEYLEN;
206 s->key = realloc(s->key, keylen);
208 return error(s, errno, strerror(errno));
210 // Create the HMAC seed, which is "key expansion" + session label + server nonce + client nonce
211 char seed[s->labellen + 64 + 13];
212 strcpy(seed, "key expansion");
214 memcpy(seed + 13, s->mykex + 1, 32);
215 memcpy(seed + 45, s->hiskex + 1, 32);
217 memcpy(seed + 13, s->hiskex + 1, 32);
218 memcpy(seed + 45, s->mykex + 1, 32);
220 memcpy(seed + 77, s->label, s->labellen);
222 // Use PRF to generate the key material
223 if(!prf(shared, len, seed, s->labellen + 64 + 13, s->key, keylen))
224 return error(s, EINVAL, "Failed to generate key material");
229 // Send an ACKnowledgement record.
230 static bool send_ack(sptps_t *s) {
231 return send_record_priv(s, SPTPS_HANDSHAKE, "", 0);
234 // Receive an ACKnowledgement record.
235 static bool receive_ack(sptps_t *s, const char *data, uint16_t len) {
238 return error(s, EIO, "Invalid ACK record length");
241 if(!chacha_poly1305_set_key(s->incipher, s->key))
242 return error(s, EINVAL, "Failed to set counter");
244 if(!chacha_poly1305_set_key(s->incipher, s->key + CHACHA_POLY1305_KEYLEN))
245 return error(s, EINVAL, "Failed to set counter");
255 // Receive a Key EXchange record, respond by sending a SIG record.
256 static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
257 // Verify length of the HELLO record
258 if(len != 1 + 32 + ECDH_SIZE)
259 return error(s, EIO, "Invalid KEX record length");
261 // Ignore version number for now.
263 // Make a copy of the KEX message, send_sig() and receive_sig() need it
265 return error(s, EINVAL, "Received a second KEX message before first has been processed");
266 s->hiskex = realloc(s->hiskex, len);
268 return error(s, errno, strerror(errno));
270 memcpy(s->hiskex, data, len);
275 // Receive a SIGnature record, verify it, if it passed, compute the shared secret and calculate the session keys.
276 static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
277 size_t keylen = ECDH_SIZE;
278 size_t siglen = ecdsa_size(s->hiskey);
280 // Verify length of KEX record.
282 return error(s, EIO, "Invalid KEX record length");
284 // Concatenate both KEX messages, plus tag indicating if it is from the connection originator
285 char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
287 msg[0] = !s->initiator;
288 memcpy(msg + 1, s->hiskex, 1 + 32 + keylen);
289 memcpy(msg + 1 + 33 + keylen, s->mykex, 1 + 32 + keylen);
290 memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
293 if(!ecdsa_verify(s->hiskey, msg, sizeof(msg), data))
294 return error(s, EIO, "Failed to verify SIG record");
296 // Compute shared secret.
297 char shared[ECDH_SHARED_SIZE];
298 if(!ecdh_compute_shared(s->ecdh, s->hiskex + 1 + 32, shared))
299 return error(s, EINVAL, "Failed to compute ECDH shared secret");
302 // Generate key material from shared secret.
303 if(!generate_key_material(s, shared, sizeof(shared)))
312 // Send cipher change record
313 if(s->outstate && !send_ack(s))
316 // TODO: only set new keys after ACK has been set/received
318 if(!chacha_poly1305_set_key(s->outcipher, s->key + CHACHA_POLY1305_KEYLEN))
319 return error(s, EINVAL, "Failed to set key");
321 if(!chacha_poly1305_set_key(s->outcipher, s->key))
322 return error(s, EINVAL, "Failed to set key");
328 // Force another Key EXchange (for testing purposes).
329 bool sptps_force_kex(sptps_t *s) {
330 if(!s->outstate || s->state != SPTPS_SECONDARY_KEX)
331 return error(s, EINVAL, "Cannot force KEX in current state");
333 s->state = SPTPS_KEX;
337 // Receive a handshake record.
338 static bool receive_handshake(sptps_t *s, const char *data, uint16_t len) {
339 // Only a few states to deal with handshaking.
341 case SPTPS_SECONDARY_KEX:
342 // We receive a secondary KEX request, first respond by sending our own.
347 // We have sent our KEX request, we expect our peer to sent one as well.
348 if(!receive_kex(s, data, len))
350 s->state = SPTPS_SIG;
353 // If we already sent our secondary public ECDH key, we expect the peer to send his.
354 if(!receive_sig(s, data, len))
357 s->state = SPTPS_ACK;
360 if(!receive_ack(s, NULL, 0))
362 s->receive_record(s->handle, SPTPS_HANDSHAKE, NULL, 0);
363 s->state = SPTPS_SECONDARY_KEX;
368 // We expect a handshake message to indicate transition to the new keys.
369 if(!receive_ack(s, data, len))
371 s->receive_record(s->handle, SPTPS_HANDSHAKE, NULL, 0);
372 s->state = SPTPS_SECONDARY_KEX;
374 // TODO: split ACK into a VERify and ACK?
376 return error(s, EIO, "Invalid session state %d", s->state);
380 // Check datagram for valid HMAC
381 bool sptps_verify_datagram(sptps_t *s, const void *data, size_t len) {
383 return error(s, EIO, "SPTPS state not ready to verify this datagram");
386 return error(s, EIO, "Received short packet in sptps_verify_datagram");
389 memcpy(&seqno, data, 4);
390 seqno = ntohl(seqno);
391 // TODO: check whether seqno makes sense, to avoid CPU intensive decrypt
395 return chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, buffer, &outlen);
398 // Receive incoming data, datagram version.
399 static bool sptps_receive_data_datagram(sptps_t *s, const void *vdata, size_t len) {
400 const char *data = vdata;
402 if(len < (s->instate ? 21 : 5))
403 return error(s, EIO, "Received short packet in sptps_receive_data_datagram");
406 memcpy(&seqno, data, 4);
407 seqno = ntohl(seqno);
410 if(seqno != s->inseqno)
411 return error(s, EIO, "Invalid packet seqno: %d != %d", seqno, s->inseqno);
413 s->inseqno = seqno + 1;
415 uint8_t type = data[4];
417 if(type != SPTPS_HANDSHAKE)
418 return error(s, EIO, "Application record received before handshake finished");
420 return receive_handshake(s, data + 5, len - 5);
429 if(!chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, buffer, &outlen))
430 return error(s, EIO, "Failed to decrypt and verify packet");
432 // Replay protection using a sliding window of configurable size.
433 // s->inseqno is expected sequence number
434 // seqno is received sequence number
435 // s->late[] is a circular buffer, a 1 bit means a packet has not been received yet
436 // The circular buffer contains bits for sequence numbers from s->inseqno - s->replaywin * 8 to (but excluding) s->inseqno.
438 if(seqno != s->inseqno) {
439 if(seqno >= s->inseqno + s->replaywin * 8) {
440 // TODO: Prevent packets that jump far ahead of the queue from causing many others to be dropped.
441 warning(s, "Lost %d packets\n", seqno - s->inseqno);
442 // Mark all packets in the replay window as being late.
443 memset(s->late, 255, s->replaywin);
444 } else if(seqno < s->inseqno) {
445 // If the sequence number is farther in the past than the bitmap goes, or if the packet was already received, drop it.
446 if((s->inseqno >= s->replaywin * 8 && seqno < s->inseqno - s->replaywin * 8) || !(s->late[(seqno / 8) % s->replaywin] & (1 << seqno % 8)))
447 return error(s, EIO, "Received late or replayed packet, seqno %d, last received %d\n", seqno, s->inseqno);
449 // We missed some packets. Mark them in the bitmap as being late.
450 for(uint32_t i = s->inseqno; i < seqno; i++)
451 s->late[(i / 8) % s->replaywin] |= 1 << i % 8;
455 // Mark the current packet as not being late.
456 s->late[(seqno / 8) % s->replaywin] &= ~(1 << seqno % 8);
459 if(seqno >= s->inseqno)
460 s->inseqno = seqno + 1;
467 // Append a NULL byte for safety.
468 buffer[len - 20] = 0;
470 uint8_t type = buffer[0];
472 if(type < SPTPS_HANDSHAKE) {
474 return error(s, EIO, "Application record received before handshake finished");
475 if(!s->receive_record(s->handle, type, buffer + 1, len - 21))
477 } else if(type == SPTPS_HANDSHAKE) {
478 if(!receive_handshake(s, buffer + 1, len - 21))
481 return error(s, EIO, "Invalid record type %d", type);
486 // Receive incoming data. Check if it contains a complete record, if so, handle it.
487 bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
489 return error(s, EIO, "Invalid session state zero");
492 return sptps_receive_data_datagram(s, data, len);
495 // First read the 2 length bytes.
497 size_t toread = 2 - s->buflen;
501 memcpy(s->inbuf + s->buflen, data, toread);
507 // Exit early if we don't have the full length.
511 // Get the length bytes
513 memcpy(&s->reclen, s->inbuf, 2);
514 s->reclen = ntohs(s->reclen);
516 // If we have the length bytes, ensure our buffer can hold the whole request.
517 s->inbuf = realloc(s->inbuf, s->reclen + 19UL);
519 return error(s, errno, strerror(errno));
521 // Exit early if we have no more data to process.
526 // Read up to the end of the record.
527 size_t toread = s->reclen + (s->instate ? 19UL : 3UL) - s->buflen;
531 memcpy(s->inbuf + s->buflen, data, toread);
536 // If we don't have a whole record, exit.
537 if(s->buflen < s->reclen + (s->instate ? 19UL : 3UL))
540 // Update sequence number.
542 uint32_t seqno = s->inseqno++;
544 // Check HMAC and decrypt.
546 if(!chacha_poly1305_decrypt(s->incipher, seqno, s->inbuf + 2UL, s->reclen + 17UL, s->inbuf + 2UL, NULL))
547 return error(s, EINVAL, "Failed to decrypt and verify record");
550 // Append a NULL byte for safety.
551 s->inbuf[s->reclen + 3UL] = 0;
553 uint8_t type = s->inbuf[2];
555 if(type < SPTPS_HANDSHAKE) {
557 return error(s, EIO, "Application record received before handshake finished");
558 if(!s->receive_record(s->handle, type, s->inbuf + 3, s->reclen))
560 } else if(type == SPTPS_HANDSHAKE) {
561 if(!receive_handshake(s, s->inbuf + 3, s->reclen))
564 return error(s, EIO, "Invalid record type %d", type);
572 // Start a SPTPS session.
573 bool sptps_start(sptps_t *s, void *handle, bool initiator, bool datagram, ecdsa_t *mykey, ecdsa_t *hiskey, const char *label, size_t labellen, send_data_t send_data, receive_record_t receive_record) {
574 if(!s || !mykey || !hiskey || !label || !labellen || !send_data || !receive_record)
575 return error(s, EINVAL, "Invalid argument to sptps_start()");
577 // Initialise struct sptps
578 memset(s, 0, sizeof(*s));
581 s->initiator = initiator;
582 s->datagram = datagram;
585 s->replaywin = sptps_replaywin;
587 s->late = malloc(s->replaywin);
589 return error(s, errno, strerror(errno));
590 memset(s->late, 0, s->replaywin);
593 s->label = malloc(labellen);
595 return error(s, errno, strerror(errno));
598 s->inbuf = malloc(7);
600 return error(s, errno, strerror(errno));
604 memcpy(s->label, label, labellen);
605 s->labellen = labellen;
607 s->send_data = send_data;
608 s->receive_record = receive_record;
610 // Do first KEX immediately
611 s->state = SPTPS_KEX;
615 // Stop a SPTPS session.
616 bool sptps_stop(sptps_t *s) {
617 // Clean up any resources.
618 chacha_poly1305_exit(s->incipher);
619 chacha_poly1305_exit(s->outcipher);
627 memset(s, 0, sizeof(*s));