kex.c revision 98675 
1/*
2 * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23 */
24
25#include "includes.h"
26RCSID("$OpenBSD: kex.c,v 1.50 2002/05/15 15:47:49 mouring Exp $");
27
28#include <openssl/crypto.h>
29
30#include "ssh2.h"
31#include "xmalloc.h"
32#include "buffer.h"
33#include "bufaux.h"
34#include "packet.h"
35#include "compat.h"
36#include "cipher.h"
37#include "kex.h"
38#include "key.h"
39#include "log.h"
40#include "mac.h"
41#include "match.h"
42#include "dispatch.h"
43#include "monitor.h"
44
45#define KEX_COOKIE_LEN	16
46
47/* Use privilege separation for sshd */
48int use_privsep;
49struct monitor *pmonitor;
50
51
52/* prototype */
53static void kex_kexinit_finish(Kex *);
54static void kex_choose_conf(Kex *);
55
56/* put algorithm proposal into buffer */
57static void
58kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
59{
60	int i;
61
62	buffer_clear(b);
63	/*
64	 * add a dummy cookie, the cookie will be overwritten by
65	 * kex_send_kexinit(), each time a kexinit is set
66	 */
67	for (i = 0; i < KEX_COOKIE_LEN; i++)
68		buffer_put_char(b, 0);
69	for (i = 0; i < PROPOSAL_MAX; i++)
70		buffer_put_cstring(b, proposal[i]);
71	buffer_put_char(b, 0);			/* first_kex_packet_follows */
72	buffer_put_int(b, 0);			/* uint32 reserved */
73}
74
75/* parse buffer and return algorithm proposal */
76static char **
77kex_buf2prop(Buffer *raw)
78{
79	Buffer b;
80	int i;
81	char **proposal;
82
83	proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
84
85	buffer_init(&b);
86	buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
87	/* skip cookie */
88	for (i = 0; i < KEX_COOKIE_LEN; i++)
89		buffer_get_char(&b);
90	/* extract kex init proposal strings */
91	for (i = 0; i < PROPOSAL_MAX; i++) {
92		proposal[i] = buffer_get_string(&b,NULL);
93		debug2("kex_parse_kexinit: %s", proposal[i]);
94	}
95	/* first kex follows / reserved */
96	i = buffer_get_char(&b);
97	debug2("kex_parse_kexinit: first_kex_follows %d ", i);
98	i = buffer_get_int(&b);
99	debug2("kex_parse_kexinit: reserved %d ", i);
100	buffer_free(&b);
101	return proposal;
102}
103
104static void
105kex_prop_free(char **proposal)
106{
107	int i;
108
109	for (i = 0; i < PROPOSAL_MAX; i++)
110		xfree(proposal[i]);
111	xfree(proposal);
112}
113
114static void
115kex_protocol_error(int type, u_int32_t seq, void *ctxt)
116{
117	error("Hm, kex protocol error: type %d seq %u", type, seq);
118}
119
120static void
121kex_reset_dispatch(void)
122{
123	dispatch_range(SSH2_MSG_TRANSPORT_MIN,
124	    SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
125	dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
126}
127
128void
129kex_finish(Kex *kex)
130{
131	kex_reset_dispatch();
132
133	packet_start(SSH2_MSG_NEWKEYS);
134	packet_send();
135	/* packet_write_wait(); */
136	debug("SSH2_MSG_NEWKEYS sent");
137
138	debug("waiting for SSH2_MSG_NEWKEYS");
139	packet_read_expect(SSH2_MSG_NEWKEYS);
140	packet_check_eom();
141	debug("SSH2_MSG_NEWKEYS received");
142
143	kex->done = 1;
144	buffer_clear(&kex->peer);
145	/* buffer_clear(&kex->my); */
146	kex->flags &= ~KEX_INIT_SENT;
147	xfree(kex->name);
148	kex->name = NULL;
149}
150
151void
152kex_send_kexinit(Kex *kex)
153{
154	u_int32_t rand = 0;
155	u_char *cookie;
156	int i;
157
158	if (kex == NULL) {
159		error("kex_send_kexinit: no kex, cannot rekey");
160		return;
161	}
162	if (kex->flags & KEX_INIT_SENT) {
163		debug("KEX_INIT_SENT");
164		return;
165	}
166	kex->done = 0;
167
168	/* generate a random cookie */
169	if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
170		fatal("kex_send_kexinit: kex proposal too short");
171	cookie = buffer_ptr(&kex->my);
172	for (i = 0; i < KEX_COOKIE_LEN; i++) {
173		if (i % 4 == 0)
174			rand = arc4random();
175		cookie[i] = rand;
176		rand >>= 8;
177	}
178	packet_start(SSH2_MSG_KEXINIT);
179	packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
180	packet_send();
181	debug("SSH2_MSG_KEXINIT sent");
182	kex->flags |= KEX_INIT_SENT;
183}
184
185void
186kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
187{
188	char *ptr;
189	int dlen;
190	int i;
191	Kex *kex = (Kex *)ctxt;
192
193	debug("SSH2_MSG_KEXINIT received");
194	if (kex == NULL)
195		fatal("kex_input_kexinit: no kex, cannot rekey");
196
197	ptr = packet_get_raw(&dlen);
198	buffer_append(&kex->peer, ptr, dlen);
199
200	/* discard packet */
201	for (i = 0; i < KEX_COOKIE_LEN; i++)
202		packet_get_char();
203	for (i = 0; i < PROPOSAL_MAX; i++)
204		xfree(packet_get_string(NULL));
205	packet_get_char();
206	packet_get_int();
207	packet_check_eom();
208
209	kex_kexinit_finish(kex);
210}
211
212Kex *
213kex_setup(char *proposal[PROPOSAL_MAX])
214{
215	Kex *kex;
216
217	kex = xmalloc(sizeof(*kex));
218	memset(kex, 0, sizeof(*kex));
219	buffer_init(&kex->peer);
220	buffer_init(&kex->my);
221	kex_prop2buf(&kex->my, proposal);
222	kex->done = 0;
223
224	kex_send_kexinit(kex);					/* we start */
225	kex_reset_dispatch();
226
227	return kex;
228}
229
230static void
231kex_kexinit_finish(Kex *kex)
232{
233	if (!(kex->flags & KEX_INIT_SENT))
234		kex_send_kexinit(kex);
235
236	kex_choose_conf(kex);
237
238	switch (kex->kex_type) {
239	case DH_GRP1_SHA1:
240		kexdh(kex);
241		break;
242	case DH_GEX_SHA1:
243		kexgex(kex);
244		break;
245	default:
246		fatal("Unsupported key exchange %d", kex->kex_type);
247	}
248}
249
250static void
251choose_enc(Enc *enc, char *client, char *server)
252{
253	char *name = match_list(client, server, NULL);
254	if (name == NULL)
255		fatal("no matching cipher found: client %s server %s", client, server);
256	if ((enc->cipher = cipher_by_name(name)) == NULL)
257		fatal("matching cipher is not supported: %s", name);
258	enc->name = name;
259	enc->enabled = 0;
260	enc->iv = NULL;
261	enc->key = NULL;
262	enc->key_len = cipher_keylen(enc->cipher);
263	enc->block_size = cipher_blocksize(enc->cipher);
264}
265static void
266choose_mac(Mac *mac, char *client, char *server)
267{
268	char *name = match_list(client, server, NULL);
269	if (name == NULL)
270		fatal("no matching mac found: client %s server %s", client, server);
271	if (mac_init(mac, name) < 0)
272		fatal("unsupported mac %s", name);
273	/* truncate the key */
274	if (datafellows & SSH_BUG_HMAC)
275		mac->key_len = 16;
276	mac->name = name;
277	mac->key = NULL;
278	mac->enabled = 0;
279}
280static void
281choose_comp(Comp *comp, char *client, char *server)
282{
283	char *name = match_list(client, server, NULL);
284	if (name == NULL)
285		fatal("no matching comp found: client %s server %s", client, server);
286	if (strcmp(name, "zlib") == 0) {
287		comp->type = 1;
288	} else if (strcmp(name, "none") == 0) {
289		comp->type = 0;
290	} else {
291		fatal("unsupported comp %s", name);
292	}
293	comp->name = name;
294}
295static void
296choose_kex(Kex *k, char *client, char *server)
297{
298	k->name = match_list(client, server, NULL);
299	if (k->name == NULL)
300		fatal("no kex alg");
301	if (strcmp(k->name, KEX_DH1) == 0) {
302		k->kex_type = DH_GRP1_SHA1;
303	} else if (strcmp(k->name, KEX_DHGEX) == 0) {
304		k->kex_type = DH_GEX_SHA1;
305	} else
306		fatal("bad kex alg %s", k->name);
307}
308static void
309choose_hostkeyalg(Kex *k, char *client, char *server)
310{
311	char *hostkeyalg = match_list(client, server, NULL);
312	if (hostkeyalg == NULL)
313		fatal("no hostkey alg");
314	k->hostkey_type = key_type_from_name(hostkeyalg);
315	if (k->hostkey_type == KEY_UNSPEC)
316		fatal("bad hostkey alg '%s'", hostkeyalg);
317	xfree(hostkeyalg);
318}
319
320static void
321kex_choose_conf(Kex *kex)
322{
323	Newkeys *newkeys;
324	char **my, **peer;
325	char **cprop, **sprop;
326	int nenc, nmac, ncomp;
327	int mode;
328	int ctos;				/* direction: if true client-to-server */
329	int need;
330
331	my   = kex_buf2prop(&kex->my);
332	peer = kex_buf2prop(&kex->peer);
333
334	if (kex->server) {
335		cprop=peer;
336		sprop=my;
337	} else {
338		cprop=my;
339		sprop=peer;
340	}
341
342	/* Algorithm Negotiation */
343	for (mode = 0; mode < MODE_MAX; mode++) {
344		newkeys = xmalloc(sizeof(*newkeys));
345		memset(newkeys, 0, sizeof(*newkeys));
346		kex->newkeys[mode] = newkeys;
347		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
348		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
349		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
350		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
351		choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
352		choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
353		choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
354		debug("kex: %s %s %s %s",
355		    ctos ? "client->server" : "server->client",
356		    newkeys->enc.name,
357		    newkeys->mac.name,
358		    newkeys->comp.name);
359	}
360	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
361	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
362	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
363	need = 0;
364	for (mode = 0; mode < MODE_MAX; mode++) {
365		newkeys = kex->newkeys[mode];
366		if (need < newkeys->enc.key_len)
367			need = newkeys->enc.key_len;
368		if (need < newkeys->enc.block_size)
369			need = newkeys->enc.block_size;
370		if (need < newkeys->mac.key_len)
371			need = newkeys->mac.key_len;
372	}
373	/* XXX need runden? */
374	kex->we_need = need;
375
376	kex_prop_free(my);
377	kex_prop_free(peer);
378}
379
380static u_char *
381derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
382{
383	Buffer b;
384	const EVP_MD *evp_md = EVP_sha1();
385	EVP_MD_CTX md;
386	char c = id;
387	int have;
388	int mdsz = EVP_MD_size(evp_md);
389	u_char *digest = xmalloc(roundup(need, mdsz));
390
391	buffer_init(&b);
392	buffer_put_bignum2(&b, shared_secret);
393
394	/* K1 = HASH(K || H || "A" || session_id) */
395	EVP_DigestInit(&md, evp_md);
396	if (!(datafellows & SSH_BUG_DERIVEKEY))
397		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
398	EVP_DigestUpdate(&md, hash, mdsz);
399	EVP_DigestUpdate(&md, &c, 1);
400	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
401	EVP_DigestFinal(&md, digest, NULL);
402
403	/*
404	 * expand key:
405	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
406	 * Key = K1 || K2 || ... || Kn
407	 */
408	for (have = mdsz; need > have; have += mdsz) {
409		EVP_DigestInit(&md, evp_md);
410		if (!(datafellows & SSH_BUG_DERIVEKEY))
411			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
412		EVP_DigestUpdate(&md, hash, mdsz);
413		EVP_DigestUpdate(&md, digest, have);
414		EVP_DigestFinal(&md, digest + have, NULL);
415	}
416	buffer_free(&b);
417#ifdef DEBUG_KEX
418	fprintf(stderr, "key '%c'== ", c);
419	dump_digest("key", digest, need);
420#endif
421	return digest;
422}
423
424Newkeys *current_keys[MODE_MAX];
425
426#define NKEYS	6
427void
428kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
429{
430	u_char *keys[NKEYS];
431	int i, mode, ctos;
432
433	for (i = 0; i < NKEYS; i++)
434		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
435
436	debug("kex_derive_keys");
437	for (mode = 0; mode < MODE_MAX; mode++) {
438		current_keys[mode] = kex->newkeys[mode];
439		kex->newkeys[mode] = NULL;
440		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
441		current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
442		current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
443		current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
444	}
445}
446
447Newkeys *
448kex_get_newkeys(int mode)
449{
450	Newkeys *ret;
451
452	ret = current_keys[mode];
453	current_keys[mode] = NULL;
454	return ret;
455}
456
457#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
458void
459dump_digest(char *msg, u_char *digest, int len)
460{
461	int i;
462
463	fprintf(stderr, "%s\n", msg);
464	for (i = 0; i< len; i++) {
465		fprintf(stderr, "%02x", digest[i]);
466		if (i%32 == 31)
467			fprintf(stderr, "\n");
468		else if (i%8 == 7)
469			fprintf(stderr, " ");
470	}
471	fprintf(stderr, "\n");
472}
473#endif
474