Annotation of src/usr.bin/ssh/kex.c, Revision 1.52
1.1 markus 1: /*
1.36 markus 2: * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
1.1 markus 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"
1.52 ! markus 26: RCSID("$OpenBSD: kex.c,v 1.51 2002/06/24 14:55:38 markus Exp $");
1.18 markus 27:
28: #include <openssl/crypto.h>
1.1 markus 29:
30: #include "ssh2.h"
31: #include "xmalloc.h"
32: #include "buffer.h"
33: #include "bufaux.h"
1.7 markus 34: #include "packet.h"
1.1 markus 35: #include "compat.h"
1.18 markus 36: #include "cipher.h"
1.1 markus 37: #include "kex.h"
1.13 markus 38: #include "key.h"
1.18 markus 39: #include "log.h"
1.21 markus 40: #include "mac.h"
1.23 markus 41: #include "match.h"
1.26 markus 42: #include "dispatch.h"
1.48 provos 43: #include "monitor.h"
1.1 markus 44:
1.7 markus 45: #define KEX_COOKIE_LEN 16
1.48 provos 46:
47: /* Use privilege separation for sshd */
48: int use_privsep;
1.50 mouring 49: struct monitor *pmonitor;
1.48 provos 50:
1.7 markus 51:
1.35 itojun 52: /* prototype */
53: static void kex_kexinit_finish(Kex *);
54: static void kex_choose_conf(Kex *);
1.26 markus 55:
56: /* put algorithm proposal into buffer */
1.35 itojun 57: static void
1.26 markus 58: kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
1.1 markus 59: {
60: int i;
1.26 markus 61:
62: buffer_clear(b);
1.49 markus 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);
1.1 markus 69: for (i = 0; i < PROPOSAL_MAX; i++)
1.26 markus 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 */
1.1 markus 73: }
74:
1.26 markus 75: /* parse buffer and return algorithm proposal */
1.35 itojun 76: static char **
1.26 markus 77: kex_buf2prop(Buffer *raw)
1.7 markus 78: {
1.26 markus 79: Buffer b;
1.7 markus 80: int i;
1.26 markus 81: char **proposal;
1.7 markus 82:
1.26 markus 83: proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
1.7 markus 84:
1.26 markus 85: buffer_init(&b);
86: buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
1.7 markus 87: /* skip cookie */
88: for (i = 0; i < KEX_COOKIE_LEN; i++)
1.26 markus 89: buffer_get_char(&b);
1.7 markus 90: /* extract kex init proposal strings */
91: for (i = 0; i < PROPOSAL_MAX; i++) {
1.26 markus 92: proposal[i] = buffer_get_string(&b,NULL);
93: debug2("kex_parse_kexinit: %s", proposal[i]);
1.7 markus 94: }
1.26 markus 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;
1.1 markus 102: }
103:
1.35 itojun 104: static void
1.26 markus 105: kex_prop_free(char **proposal)
1.1 markus 106: {
107: int i;
1.26 markus 108:
109: for (i = 0; i < PROPOSAL_MAX; i++)
110: xfree(proposal[i]);
111: xfree(proposal);
1.1 markus 112: }
113:
1.35 itojun 114: static void
1.41 markus 115: kex_protocol_error(int type, u_int32_t seq, void *ctxt)
1.1 markus 116: {
1.41 markus 117: error("Hm, kex protocol error: type %d seq %u", type, seq);
1.26 markus 118: }
1.1 markus 119:
1.35 itojun 120: static void
1.44 markus 121: kex_reset_dispatch(void)
1.29 markus 122: {
1.42 markus 123: dispatch_range(SSH2_MSG_TRANSPORT_MIN,
124: SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
1.44 markus 125: dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
1.29 markus 126: }
127:
128: void
1.28 markus 129: kex_finish(Kex *kex)
1.26 markus 130: {
1.44 markus 131: kex_reset_dispatch();
1.28 markus 132:
1.26 markus 133: packet_start(SSH2_MSG_NEWKEYS);
134: packet_send();
135: /* packet_write_wait(); */
136: debug("SSH2_MSG_NEWKEYS sent");
1.19 stevesk 137:
1.52 ! markus 138: debug("expecting SSH2_MSG_NEWKEYS");
1.40 markus 139: packet_read_expect(SSH2_MSG_NEWKEYS);
1.46 markus 140: packet_check_eom();
1.26 markus 141: debug("SSH2_MSG_NEWKEYS received");
1.32 markus 142:
1.30 markus 143: kex->done = 1;
1.26 markus 144: buffer_clear(&kex->peer);
1.27 markus 145: /* buffer_clear(&kex->my); */
1.26 markus 146: kex->flags &= ~KEX_INIT_SENT;
1.32 markus 147: xfree(kex->name);
148: kex->name = NULL;
1.26 markus 149: }
1.1 markus 150:
1.26 markus 151: void
152: kex_send_kexinit(Kex *kex)
153: {
1.49 markus 154: u_int32_t rand = 0;
155: u_char *cookie;
156: int i;
157:
1.29 markus 158: if (kex == NULL) {
159: error("kex_send_kexinit: no kex, cannot rekey");
160: return;
161: }
1.28 markus 162: if (kex->flags & KEX_INIT_SENT) {
163: debug("KEX_INIT_SENT");
164: return;
165: }
1.30 markus 166: kex->done = 0;
1.49 markus 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: }
1.26 markus 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;
1.1 markus 183: }
184:
1.26 markus 185: void
1.41 markus 186: kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
1.11 provos 187: {
1.26 markus 188: char *ptr;
189: int dlen;
1.31 markus 190: int i;
1.26 markus 191: Kex *kex = (Kex *)ctxt;
1.11 provos 192:
1.26 markus 193: debug("SSH2_MSG_KEXINIT received");
1.29 markus 194: if (kex == NULL)
195: fatal("kex_input_kexinit: no kex, cannot rekey");
1.11 provos 196:
1.26 markus 197: ptr = packet_get_raw(&dlen);
198: buffer_append(&kex->peer, ptr, dlen);
1.31 markus 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));
1.51 markus 205: (void) packet_get_char();
206: (void) packet_get_int();
1.39 markus 207: packet_check_eom();
1.19 stevesk 208:
1.26 markus 209: kex_kexinit_finish(kex);
210: }
1.11 provos 211:
1.26 markus 212: Kex *
1.28 markus 213: kex_setup(char *proposal[PROPOSAL_MAX])
1.26 markus 214: {
215: Kex *kex;
1.11 provos 216:
1.26 markus 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);
1.30 markus 222: kex->done = 0;
1.26 markus 223:
224: kex_send_kexinit(kex); /* we start */
1.44 markus 225: kex_reset_dispatch();
1.26 markus 226:
227: return kex;
1.11 provos 228: }
229:
1.35 itojun 230: static void
1.26 markus 231: kex_kexinit_finish(Kex *kex)
1.1 markus 232: {
1.26 markus 233: if (!(kex->flags & KEX_INIT_SENT))
234: kex_send_kexinit(kex);
1.1 markus 235:
1.26 markus 236: kex_choose_conf(kex);
1.1 markus 237:
1.37 deraadt 238: switch (kex->kex_type) {
1.26 markus 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);
1.1 markus 247: }
248: }
249:
1.35 itojun 250: static void
1.1 markus 251: choose_enc(Enc *enc, char *client, char *server)
252: {
1.23 markus 253: char *name = match_list(client, server, NULL);
1.1 markus 254: if (name == NULL)
255: fatal("no matching cipher found: client %s server %s", client, server);
1.45 markus 256: if ((enc->cipher = cipher_by_name(name)) == NULL)
1.12 markus 257: fatal("matching cipher is not supported: %s", name);
1.1 markus 258: enc->name = name;
259: enc->enabled = 0;
260: enc->iv = NULL;
261: enc->key = NULL;
1.45 markus 262: enc->key_len = cipher_keylen(enc->cipher);
263: enc->block_size = cipher_blocksize(enc->cipher);
1.1 markus 264: }
1.35 itojun 265: static void
1.1 markus 266: choose_mac(Mac *mac, char *client, char *server)
267: {
1.23 markus 268: char *name = match_list(client, server, NULL);
1.1 markus 269: if (name == NULL)
270: fatal("no matching mac found: client %s server %s", client, server);
1.21 markus 271: if (mac_init(mac, name) < 0)
1.1 markus 272: fatal("unsupported mac %s", name);
1.21 markus 273: /* truncate the key */
274: if (datafellows & SSH_BUG_HMAC)
275: mac->key_len = 16;
1.1 markus 276: mac->name = name;
277: mac->key = NULL;
278: mac->enabled = 0;
279: }
1.35 itojun 280: static void
1.1 markus 281: choose_comp(Comp *comp, char *client, char *server)
282: {
1.23 markus 283: char *name = match_list(client, server, NULL);
1.1 markus 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: }
1.35 itojun 295: static void
1.1 markus 296: choose_kex(Kex *k, char *client, char *server)
297: {
1.23 markus 298: k->name = match_list(client, server, NULL);
1.1 markus 299: if (k->name == NULL)
300: fatal("no kex alg");
1.11 provos 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
1.1 markus 306: fatal("bad kex alg %s", k->name);
307: }
1.35 itojun 308: static void
1.1 markus 309: choose_hostkeyalg(Kex *k, char *client, char *server)
310: {
1.23 markus 311: char *hostkeyalg = match_list(client, server, NULL);
1.13 markus 312: if (hostkeyalg == NULL)
1.1 markus 313: fatal("no hostkey alg");
1.13 markus 314: k->hostkey_type = key_type_from_name(hostkeyalg);
315: if (k->hostkey_type == KEY_UNSPEC)
316: fatal("bad hostkey alg '%s'", hostkeyalg);
1.17 markus 317: xfree(hostkeyalg);
1.1 markus 318: }
319:
1.35 itojun 320: static void
1.27 markus 321: kex_choose_conf(Kex *kex)
1.1 markus 322: {
1.27 markus 323: Newkeys *newkeys;
1.26 markus 324: char **my, **peer;
325: char **cprop, **sprop;
1.27 markus 326: int nenc, nmac, ncomp;
1.1 markus 327: int mode;
328: int ctos; /* direction: if true client-to-server */
329: int need;
330:
1.27 markus 331: my = kex_buf2prop(&kex->my);
332: peer = kex_buf2prop(&kex->peer);
1.26 markus 333:
1.27 markus 334: if (kex->server) {
1.26 markus 335: cprop=peer;
336: sprop=my;
337: } else {
338: cprop=my;
339: sprop=peer;
340: }
1.1 markus 341:
1.30 markus 342: /* Algorithm Negotiation */
1.1 markus 343: for (mode = 0; mode < MODE_MAX; mode++) {
1.27 markus 344: newkeys = xmalloc(sizeof(*newkeys));
345: memset(newkeys, 0, sizeof(*newkeys));
1.30 markus 346: kex->newkeys[mode] = newkeys;
1.27 markus 347: ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
1.1 markus 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;
1.27 markus 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]);
1.2 markus 354: debug("kex: %s %s %s %s",
1.1 markus 355: ctos ? "client->server" : "server->client",
1.27 markus 356: newkeys->enc.name,
357: newkeys->mac.name,
358: newkeys->comp.name);
1.1 markus 359: }
1.27 markus 360: choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
361: choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
1.1 markus 362: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
363: need = 0;
364: for (mode = 0; mode < MODE_MAX; mode++) {
1.30 markus 365: newkeys = kex->newkeys[mode];
1.45 markus 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;
1.27 markus 370: if (need < newkeys->mac.key_len)
371: need = newkeys->mac.key_len;
1.1 markus 372: }
1.7 markus 373: /* XXX need runden? */
1.27 markus 374: kex->we_need = need;
1.26 markus 375:
376: kex_prop_free(my);
377: kex_prop_free(peer);
378: }
379:
1.35 itojun 380: static u_char *
1.27 markus 381: derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
1.26 markus 382: {
383: Buffer b;
1.47 markus 384: const EVP_MD *evp_md = EVP_sha1();
1.26 markus 385: EVP_MD_CTX md;
386: char c = id;
387: int have;
1.43 markus 388: int mdsz = EVP_MD_size(evp_md);
1.30 markus 389: u_char *digest = xmalloc(roundup(need, mdsz));
1.26 markus 390:
391: buffer_init(&b);
392: buffer_put_bignum2(&b, shared_secret);
393:
1.30 markus 394: /* K1 = HASH(K || H || "A" || session_id) */
1.26 markus 395: EVP_DigestInit(&md, evp_md);
1.34 markus 396: if (!(datafellows & SSH_BUG_DERIVEKEY))
397: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
1.30 markus 398: EVP_DigestUpdate(&md, hash, mdsz);
399: EVP_DigestUpdate(&md, &c, 1);
1.27 markus 400: EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
1.26 markus 401: EVP_DigestFinal(&md, digest, NULL);
402:
1.30 markus 403: /*
404: * expand key:
405: * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
406: * Key = K1 || K2 || ... || Kn
407: */
1.26 markus 408: for (have = mdsz; need > have; have += mdsz) {
409: EVP_DigestInit(&md, evp_md);
1.34 markus 410: if (!(datafellows & SSH_BUG_DERIVEKEY))
411: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
1.26 markus 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;
1.1 markus 422: }
423:
1.30 markus 424: Newkeys *current_keys[MODE_MAX];
1.27 markus 425:
1.23 markus 426: #define NKEYS 6
1.26 markus 427: void
1.27 markus 428: kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
1.1 markus 429: {
1.15 markus 430: u_char *keys[NKEYS];
1.27 markus 431: int i, mode, ctos;
1.1 markus 432:
433: for (i = 0; i < NKEYS; i++)
1.27 markus 434: keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
1.1 markus 435:
1.52 ! markus 436: debug2("kex_derive_keys");
1.1 markus 437: for (mode = 0; mode < MODE_MAX; mode++) {
1.30 markus 438: current_keys[mode] = kex->newkeys[mode];
439: kex->newkeys[mode] = NULL;
1.27 markus 440: ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
1.30 markus 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];
1.1 markus 444: }
1.27 markus 445: }
446:
447: Newkeys *
448: kex_get_newkeys(int mode)
449: {
1.30 markus 450: Newkeys *ret;
451:
452: ret = current_keys[mode];
453: current_keys[mode] = NULL;
454: return ret;
1.1 markus 455: }
1.26 markus 456:
457: #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
458: void
459: dump_digest(char *msg, u_char *digest, int len)
460: {
461: int i;
462:
463: fprintf(stderr, "%s\n", msg);
1.37 deraadt 464: for (i = 0; i< len; i++) {
1.26 markus 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
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