kex.c revision 1.37 
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 1.37 2001/12/05 10:06:12 deraadt 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
44#define KEX_COOKIE_LEN	16
45
46/* prototype */
47static void kex_kexinit_finish(Kex *);
48static void kex_choose_conf(Kex *);
49
50/* put algorithm proposal into buffer */
51static void
52kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
53{
54	u_int32_t rand = 0;
55	int i;
56
57	buffer_clear(b);
58	for (i = 0; i < KEX_COOKIE_LEN; i++) {
59		if (i % 4 == 0)
60			rand = arc4random();
61		buffer_put_char(b, rand & 0xff);
62		rand >>= 8;
63	}
64	for (i = 0; i < PROPOSAL_MAX; i++)
65		buffer_put_cstring(b, proposal[i]);
66	buffer_put_char(b, 0);			/* first_kex_packet_follows */
67	buffer_put_int(b, 0);			/* uint32 reserved */
68}
69
70/* parse buffer and return algorithm proposal */
71static char **
72kex_buf2prop(Buffer *raw)
73{
74	Buffer b;
75	int i;
76	char **proposal;
77
78	proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
79
80	buffer_init(&b);
81	buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
82	/* skip cookie */
83	for (i = 0; i < KEX_COOKIE_LEN; i++)
84		buffer_get_char(&b);
85	/* extract kex init proposal strings */
86	for (i = 0; i < PROPOSAL_MAX; i++) {
87		proposal[i] = buffer_get_string(&b,NULL);
88		debug2("kex_parse_kexinit: %s", proposal[i]);
89	}
90	/* first kex follows / reserved */
91	i = buffer_get_char(&b);
92	debug2("kex_parse_kexinit: first_kex_follows %d ", i);
93	i = buffer_get_int(&b);
94	debug2("kex_parse_kexinit: reserved %d ", i);
95	buffer_free(&b);
96	return proposal;
97}
98
99static void
100kex_prop_free(char **proposal)
101{
102	int i;
103
104	for (i = 0; i < PROPOSAL_MAX; i++)
105		xfree(proposal[i]);
106	xfree(proposal);
107}
108
109static void
110kex_protocol_error(int type, int plen, void *ctxt)
111{
112	error("Hm, kex protocol error: type %d plen %d", type, plen);
113}
114
115static void
116kex_clear_dispatch(void)
117{
118	int i;
119
120	/* Numbers 30-49 are used for kex packets */
121	for (i = 30; i <= 49; i++)
122		dispatch_set(i, &kex_protocol_error);
123}
124
125void
126kex_finish(Kex *kex)
127{
128	int plen;
129
130	kex_clear_dispatch();
131
132	packet_start(SSH2_MSG_NEWKEYS);
133	packet_send();
134	/* packet_write_wait(); */
135	debug("SSH2_MSG_NEWKEYS sent");
136
137	debug("waiting for SSH2_MSG_NEWKEYS");
138	packet_read_expect(&plen, SSH2_MSG_NEWKEYS);
139	debug("SSH2_MSG_NEWKEYS received");
140
141	kex->done = 1;
142	buffer_clear(&kex->peer);
143	/* buffer_clear(&kex->my); */
144	kex->flags &= ~KEX_INIT_SENT;
145	xfree(kex->name);
146	kex->name = NULL;
147}
148
149void
150kex_send_kexinit(Kex *kex)
151{
152	if (kex == NULL) {
153		error("kex_send_kexinit: no kex, cannot rekey");
154		return;
155	}
156	if (kex->flags & KEX_INIT_SENT) {
157		debug("KEX_INIT_SENT");
158		return;
159	}
160	kex->done = 0;
161	packet_start(SSH2_MSG_KEXINIT);
162	packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
163	packet_send();
164	debug("SSH2_MSG_KEXINIT sent");
165	kex->flags |= KEX_INIT_SENT;
166}
167
168void
169kex_input_kexinit(int type, int plen, void *ctxt)
170{
171	char *ptr;
172	int dlen;
173	int i;
174	Kex *kex = (Kex *)ctxt;
175
176	debug("SSH2_MSG_KEXINIT received");
177	if (kex == NULL)
178		fatal("kex_input_kexinit: no kex, cannot rekey");
179
180	ptr = packet_get_raw(&dlen);
181	buffer_append(&kex->peer, ptr, dlen);
182
183	/* discard packet */
184	for (i = 0; i < KEX_COOKIE_LEN; i++)
185		packet_get_char();
186	for (i = 0; i < PROPOSAL_MAX; i++)
187		xfree(packet_get_string(NULL));
188	packet_get_char();
189	packet_get_int();
190	packet_done();
191
192	kex_kexinit_finish(kex);
193}
194
195Kex *
196kex_setup(char *proposal[PROPOSAL_MAX])
197{
198	Kex *kex;
199
200	kex = xmalloc(sizeof(*kex));
201	memset(kex, 0, sizeof(*kex));
202	buffer_init(&kex->peer);
203	buffer_init(&kex->my);
204	kex_prop2buf(&kex->my, proposal);
205	kex->done = 0;
206
207	kex_send_kexinit(kex);					/* we start */
208	kex_clear_dispatch();
209	dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
210
211	return kex;
212}
213
214static void
215kex_kexinit_finish(Kex *kex)
216{
217	if (!(kex->flags & KEX_INIT_SENT))
218		kex_send_kexinit(kex);
219
220	kex_choose_conf(kex);
221
222	switch (kex->kex_type) {
223	case DH_GRP1_SHA1:
224		kexdh(kex);
225		break;
226	case DH_GEX_SHA1:
227		kexgex(kex);
228		break;
229	default:
230		fatal("Unsupported key exchange %d", kex->kex_type);
231	}
232}
233
234static void
235choose_enc(Enc *enc, char *client, char *server)
236{
237	char *name = match_list(client, server, NULL);
238	if (name == NULL)
239		fatal("no matching cipher found: client %s server %s", client, server);
240	enc->cipher = cipher_by_name(name);
241	if (enc->cipher == NULL)
242		fatal("matching cipher is not supported: %s", name);
243	enc->name = name;
244	enc->enabled = 0;
245	enc->iv = NULL;
246	enc->key = NULL;
247}
248static void
249choose_mac(Mac *mac, char *client, char *server)
250{
251	char *name = match_list(client, server, NULL);
252	if (name == NULL)
253		fatal("no matching mac found: client %s server %s", client, server);
254	if (mac_init(mac, name) < 0)
255		fatal("unsupported mac %s", name);
256	/* truncate the key */
257	if (datafellows & SSH_BUG_HMAC)
258		mac->key_len = 16;
259	mac->name = name;
260	mac->key = NULL;
261	mac->enabled = 0;
262}
263static void
264choose_comp(Comp *comp, char *client, char *server)
265{
266	char *name = match_list(client, server, NULL);
267	if (name == NULL)
268		fatal("no matching comp found: client %s server %s", client, server);
269	if (strcmp(name, "zlib") == 0) {
270		comp->type = 1;
271	} else if (strcmp(name, "none") == 0) {
272		comp->type = 0;
273	} else {
274		fatal("unsupported comp %s", name);
275	}
276	comp->name = name;
277}
278static void
279choose_kex(Kex *k, char *client, char *server)
280{
281	k->name = match_list(client, server, NULL);
282	if (k->name == NULL)
283		fatal("no kex alg");
284	if (strcmp(k->name, KEX_DH1) == 0) {
285		k->kex_type = DH_GRP1_SHA1;
286	} else if (strcmp(k->name, KEX_DHGEX) == 0) {
287		k->kex_type = DH_GEX_SHA1;
288	} else
289		fatal("bad kex alg %s", k->name);
290}
291static void
292choose_hostkeyalg(Kex *k, char *client, char *server)
293{
294	char *hostkeyalg = match_list(client, server, NULL);
295	if (hostkeyalg == NULL)
296		fatal("no hostkey alg");
297	k->hostkey_type = key_type_from_name(hostkeyalg);
298	if (k->hostkey_type == KEY_UNSPEC)
299		fatal("bad hostkey alg '%s'", hostkeyalg);
300	xfree(hostkeyalg);
301}
302
303static void
304kex_choose_conf(Kex *kex)
305{
306	Newkeys *newkeys;
307	char **my, **peer;
308	char **cprop, **sprop;
309	int nenc, nmac, ncomp;
310	int mode;
311	int ctos;				/* direction: if true client-to-server */
312	int need;
313
314	my   = kex_buf2prop(&kex->my);
315	peer = kex_buf2prop(&kex->peer);
316
317	if (kex->server) {
318		cprop=peer;
319		sprop=my;
320	} else {
321		cprop=my;
322		sprop=peer;
323	}
324
325	/* Algorithm Negotiation */
326	for (mode = 0; mode < MODE_MAX; mode++) {
327		newkeys = xmalloc(sizeof(*newkeys));
328		memset(newkeys, 0, sizeof(*newkeys));
329		kex->newkeys[mode] = newkeys;
330		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
331		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
332		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
333		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
334		choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
335		choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
336		choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
337		debug("kex: %s %s %s %s",
338		    ctos ? "client->server" : "server->client",
339		    newkeys->enc.name,
340		    newkeys->mac.name,
341		    newkeys->comp.name);
342	}
343	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
344	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
345	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
346	need = 0;
347	for (mode = 0; mode < MODE_MAX; mode++) {
348		newkeys = kex->newkeys[mode];
349		if (need < newkeys->enc.cipher->key_len)
350			need = newkeys->enc.cipher->key_len;
351		if (need < newkeys->enc.cipher->block_size)
352			need = newkeys->enc.cipher->block_size;
353		if (need < newkeys->mac.key_len)
354			need = newkeys->mac.key_len;
355	}
356	/* XXX need runden? */
357	kex->we_need = need;
358
359	kex_prop_free(my);
360	kex_prop_free(peer);
361}
362
363static u_char *
364derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
365{
366	Buffer b;
367	EVP_MD *evp_md = EVP_sha1();
368	EVP_MD_CTX md;
369	char c = id;
370	int have;
371	int mdsz = evp_md->md_size;
372	u_char *digest = xmalloc(roundup(need, mdsz));
373
374	buffer_init(&b);
375	buffer_put_bignum2(&b, shared_secret);
376
377	/* K1 = HASH(K || H || "A" || session_id) */
378	EVP_DigestInit(&md, evp_md);
379	if (!(datafellows & SSH_BUG_DERIVEKEY))
380		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
381	EVP_DigestUpdate(&md, hash, mdsz);
382	EVP_DigestUpdate(&md, &c, 1);
383	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
384	EVP_DigestFinal(&md, digest, NULL);
385
386	/*
387	 * expand key:
388	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
389	 * Key = K1 || K2 || ... || Kn
390	 */
391	for (have = mdsz; need > have; have += mdsz) {
392		EVP_DigestInit(&md, evp_md);
393		if (!(datafellows & SSH_BUG_DERIVEKEY))
394			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
395		EVP_DigestUpdate(&md, hash, mdsz);
396		EVP_DigestUpdate(&md, digest, have);
397		EVP_DigestFinal(&md, digest + have, NULL);
398	}
399	buffer_free(&b);
400#ifdef DEBUG_KEX
401	fprintf(stderr, "key '%c'== ", c);
402	dump_digest("key", digest, need);
403#endif
404	return digest;
405}
406
407Newkeys *current_keys[MODE_MAX];
408
409#define NKEYS	6
410void
411kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
412{
413	u_char *keys[NKEYS];
414	int i, mode, ctos;
415
416	for (i = 0; i < NKEYS; i++)
417		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
418
419	debug("kex_derive_keys");
420	for (mode = 0; mode < MODE_MAX; mode++) {
421		current_keys[mode] = kex->newkeys[mode];
422		kex->newkeys[mode] = NULL;
423		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
424		current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
425		current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
426		current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
427	}
428}
429
430Newkeys *
431kex_get_newkeys(int mode)
432{
433	Newkeys *ret;
434
435	ret = current_keys[mode];
436	current_keys[mode] = NULL;
437	return ret;
438}
439
440#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
441void
442dump_digest(char *msg, u_char *digest, int len)
443{
444	int i;
445
446	fprintf(stderr, "%s\n", msg);
447	for (i = 0; i< len; i++) {
448		fprintf(stderr, "%02x", digest[i]);
449		if (i%32 == 31)
450			fprintf(stderr, "\n");
451		else if (i%8 == 7)
452			fprintf(stderr, " ");
453	}
454	fprintf(stderr, "\n");
455}
456#endif
457