Annotation of src/usr.bin/ssh/kex.c, Revision 1.53
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"
1.53 ! markus 26: RCSID("$OpenBSD: kex.c,v 1.52 2002/11/21 22:45:31 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 **
1.53 ! markus 77: kex_buf2prop(Buffer *raw, int *first_kex_follows)
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);
1.53 ! markus 97: if (first_kex_follows != NULL)
! 98: *first_kex_follows = i;
1.26 markus 99: debug2("kex_parse_kexinit: first_kex_follows %d ", i);
100: i = buffer_get_int(&b);
101: debug2("kex_parse_kexinit: reserved %d ", i);
102: buffer_free(&b);
103: return proposal;
1.1 markus 104: }
105:
1.35 itojun 106: static void
1.26 markus 107: kex_prop_free(char **proposal)
1.1 markus 108: {
109: int i;
1.26 markus 110:
111: for (i = 0; i < PROPOSAL_MAX; i++)
112: xfree(proposal[i]);
113: xfree(proposal);
1.1 markus 114: }
115:
1.35 itojun 116: static void
1.41 markus 117: kex_protocol_error(int type, u_int32_t seq, void *ctxt)
1.1 markus 118: {
1.41 markus 119: error("Hm, kex protocol error: type %d seq %u", type, seq);
1.26 markus 120: }
1.1 markus 121:
1.35 itojun 122: static void
1.44 markus 123: kex_reset_dispatch(void)
1.29 markus 124: {
1.42 markus 125: dispatch_range(SSH2_MSG_TRANSPORT_MIN,
126: SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
1.44 markus 127: dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
1.29 markus 128: }
129:
130: void
1.28 markus 131: kex_finish(Kex *kex)
1.26 markus 132: {
1.44 markus 133: kex_reset_dispatch();
1.28 markus 134:
1.26 markus 135: packet_start(SSH2_MSG_NEWKEYS);
136: packet_send();
137: /* packet_write_wait(); */
138: debug("SSH2_MSG_NEWKEYS sent");
1.19 stevesk 139:
1.52 markus 140: debug("expecting SSH2_MSG_NEWKEYS");
1.40 markus 141: packet_read_expect(SSH2_MSG_NEWKEYS);
1.46 markus 142: packet_check_eom();
1.26 markus 143: debug("SSH2_MSG_NEWKEYS received");
1.32 markus 144:
1.30 markus 145: kex->done = 1;
1.26 markus 146: buffer_clear(&kex->peer);
1.27 markus 147: /* buffer_clear(&kex->my); */
1.26 markus 148: kex->flags &= ~KEX_INIT_SENT;
1.32 markus 149: xfree(kex->name);
150: kex->name = NULL;
1.26 markus 151: }
1.1 markus 152:
1.26 markus 153: void
154: kex_send_kexinit(Kex *kex)
155: {
1.49 markus 156: u_int32_t rand = 0;
157: u_char *cookie;
158: int i;
159:
1.29 markus 160: if (kex == NULL) {
161: error("kex_send_kexinit: no kex, cannot rekey");
162: return;
163: }
1.28 markus 164: if (kex->flags & KEX_INIT_SENT) {
165: debug("KEX_INIT_SENT");
166: return;
167: }
1.30 markus 168: kex->done = 0;
1.49 markus 169:
170: /* generate a random cookie */
171: if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
172: fatal("kex_send_kexinit: kex proposal too short");
173: cookie = buffer_ptr(&kex->my);
174: for (i = 0; i < KEX_COOKIE_LEN; i++) {
175: if (i % 4 == 0)
176: rand = arc4random();
177: cookie[i] = rand;
178: rand >>= 8;
179: }
1.26 markus 180: packet_start(SSH2_MSG_KEXINIT);
181: packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
182: packet_send();
183: debug("SSH2_MSG_KEXINIT sent");
184: kex->flags |= KEX_INIT_SENT;
1.1 markus 185: }
186:
1.26 markus 187: void
1.41 markus 188: kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
1.11 provos 189: {
1.26 markus 190: char *ptr;
191: int dlen;
1.31 markus 192: int i;
1.26 markus 193: Kex *kex = (Kex *)ctxt;
1.11 provos 194:
1.26 markus 195: debug("SSH2_MSG_KEXINIT received");
1.29 markus 196: if (kex == NULL)
197: fatal("kex_input_kexinit: no kex, cannot rekey");
1.11 provos 198:
1.26 markus 199: ptr = packet_get_raw(&dlen);
200: buffer_append(&kex->peer, ptr, dlen);
1.31 markus 201:
202: /* discard packet */
203: for (i = 0; i < KEX_COOKIE_LEN; i++)
204: packet_get_char();
205: for (i = 0; i < PROPOSAL_MAX; i++)
206: xfree(packet_get_string(NULL));
1.51 markus 207: (void) packet_get_char();
208: (void) packet_get_int();
1.39 markus 209: packet_check_eom();
1.19 stevesk 210:
1.26 markus 211: kex_kexinit_finish(kex);
212: }
1.11 provos 213:
1.26 markus 214: Kex *
1.28 markus 215: kex_setup(char *proposal[PROPOSAL_MAX])
1.26 markus 216: {
217: Kex *kex;
1.11 provos 218:
1.26 markus 219: kex = xmalloc(sizeof(*kex));
220: memset(kex, 0, sizeof(*kex));
221: buffer_init(&kex->peer);
222: buffer_init(&kex->my);
223: kex_prop2buf(&kex->my, proposal);
1.30 markus 224: kex->done = 0;
1.26 markus 225:
226: kex_send_kexinit(kex); /* we start */
1.44 markus 227: kex_reset_dispatch();
1.26 markus 228:
229: return kex;
1.11 provos 230: }
231:
1.35 itojun 232: static void
1.26 markus 233: kex_kexinit_finish(Kex *kex)
1.1 markus 234: {
1.26 markus 235: if (!(kex->flags & KEX_INIT_SENT))
236: kex_send_kexinit(kex);
1.1 markus 237:
1.26 markus 238: kex_choose_conf(kex);
1.1 markus 239:
1.37 deraadt 240: switch (kex->kex_type) {
1.26 markus 241: case DH_GRP1_SHA1:
242: kexdh(kex);
243: break;
244: case DH_GEX_SHA1:
245: kexgex(kex);
246: break;
247: default:
248: fatal("Unsupported key exchange %d", kex->kex_type);
1.1 markus 249: }
250: }
251:
1.35 itojun 252: static void
1.1 markus 253: choose_enc(Enc *enc, char *client, char *server)
254: {
1.23 markus 255: char *name = match_list(client, server, NULL);
1.1 markus 256: if (name == NULL)
257: fatal("no matching cipher found: client %s server %s", client, server);
1.45 markus 258: if ((enc->cipher = cipher_by_name(name)) == NULL)
1.12 markus 259: fatal("matching cipher is not supported: %s", name);
1.1 markus 260: enc->name = name;
261: enc->enabled = 0;
262: enc->iv = NULL;
263: enc->key = NULL;
1.45 markus 264: enc->key_len = cipher_keylen(enc->cipher);
265: enc->block_size = cipher_blocksize(enc->cipher);
1.1 markus 266: }
1.35 itojun 267: static void
1.1 markus 268: choose_mac(Mac *mac, char *client, char *server)
269: {
1.23 markus 270: char *name = match_list(client, server, NULL);
1.1 markus 271: if (name == NULL)
272: fatal("no matching mac found: client %s server %s", client, server);
1.21 markus 273: if (mac_init(mac, name) < 0)
1.1 markus 274: fatal("unsupported mac %s", name);
1.21 markus 275: /* truncate the key */
276: if (datafellows & SSH_BUG_HMAC)
277: mac->key_len = 16;
1.1 markus 278: mac->name = name;
279: mac->key = NULL;
280: mac->enabled = 0;
281: }
1.35 itojun 282: static void
1.1 markus 283: choose_comp(Comp *comp, char *client, char *server)
284: {
1.23 markus 285: char *name = match_list(client, server, NULL);
1.1 markus 286: if (name == NULL)
287: fatal("no matching comp found: client %s server %s", client, server);
288: if (strcmp(name, "zlib") == 0) {
289: comp->type = 1;
290: } else if (strcmp(name, "none") == 0) {
291: comp->type = 0;
292: } else {
293: fatal("unsupported comp %s", name);
294: }
295: comp->name = name;
296: }
1.35 itojun 297: static void
1.1 markus 298: choose_kex(Kex *k, char *client, char *server)
299: {
1.23 markus 300: k->name = match_list(client, server, NULL);
1.1 markus 301: if (k->name == NULL)
302: fatal("no kex alg");
1.11 provos 303: if (strcmp(k->name, KEX_DH1) == 0) {
304: k->kex_type = DH_GRP1_SHA1;
305: } else if (strcmp(k->name, KEX_DHGEX) == 0) {
306: k->kex_type = DH_GEX_SHA1;
307: } else
1.1 markus 308: fatal("bad kex alg %s", k->name);
309: }
1.35 itojun 310: static void
1.1 markus 311: choose_hostkeyalg(Kex *k, char *client, char *server)
312: {
1.23 markus 313: char *hostkeyalg = match_list(client, server, NULL);
1.13 markus 314: if (hostkeyalg == NULL)
1.1 markus 315: fatal("no hostkey alg");
1.13 markus 316: k->hostkey_type = key_type_from_name(hostkeyalg);
317: if (k->hostkey_type == KEY_UNSPEC)
318: fatal("bad hostkey alg '%s'", hostkeyalg);
1.17 markus 319: xfree(hostkeyalg);
1.1 markus 320: }
321:
1.53 ! markus 322: static int
! 323: proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
! 324: {
! 325: static int check[] = {
! 326: PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
! 327: };
! 328: int *idx;
! 329: char *p;
! 330:
! 331: for (idx = &check[0]; *idx != -1; idx++) {
! 332: if ((p = strchr(my[*idx], ',')) != NULL)
! 333: *p = '\0';
! 334: if ((p = strchr(peer[*idx], ',')) != NULL)
! 335: *p = '\0';
! 336: if (strcmp(my[*idx], peer[*idx]) != 0) {
! 337: debug2("proposal mismatch: my %s peer %s",
! 338: my[*idx], peer[*idx]);
! 339: return (0);
! 340: }
! 341: }
! 342: debug2("proposals match");
! 343: return (1);
! 344: }
! 345:
1.35 itojun 346: static void
1.27 markus 347: kex_choose_conf(Kex *kex)
1.1 markus 348: {
1.27 markus 349: Newkeys *newkeys;
1.26 markus 350: char **my, **peer;
351: char **cprop, **sprop;
1.27 markus 352: int nenc, nmac, ncomp;
1.1 markus 353: int mode;
354: int ctos; /* direction: if true client-to-server */
355: int need;
1.53 ! markus 356: int first_kex_follows, type;
1.1 markus 357:
1.53 ! markus 358: my = kex_buf2prop(&kex->my, NULL);
! 359: peer = kex_buf2prop(&kex->peer, &first_kex_follows);
1.26 markus 360:
1.27 markus 361: if (kex->server) {
1.26 markus 362: cprop=peer;
363: sprop=my;
364: } else {
365: cprop=my;
366: sprop=peer;
367: }
1.1 markus 368:
1.30 markus 369: /* Algorithm Negotiation */
1.1 markus 370: for (mode = 0; mode < MODE_MAX; mode++) {
1.27 markus 371: newkeys = xmalloc(sizeof(*newkeys));
372: memset(newkeys, 0, sizeof(*newkeys));
1.30 markus 373: kex->newkeys[mode] = newkeys;
1.27 markus 374: ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
1.1 markus 375: nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
376: nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
377: ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
1.27 markus 378: choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
379: choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
380: choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
1.2 markus 381: debug("kex: %s %s %s %s",
1.1 markus 382: ctos ? "client->server" : "server->client",
1.27 markus 383: newkeys->enc.name,
384: newkeys->mac.name,
385: newkeys->comp.name);
1.1 markus 386: }
1.27 markus 387: choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
388: choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
1.1 markus 389: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
390: need = 0;
391: for (mode = 0; mode < MODE_MAX; mode++) {
1.30 markus 392: newkeys = kex->newkeys[mode];
1.45 markus 393: if (need < newkeys->enc.key_len)
394: need = newkeys->enc.key_len;
395: if (need < newkeys->enc.block_size)
396: need = newkeys->enc.block_size;
1.27 markus 397: if (need < newkeys->mac.key_len)
398: need = newkeys->mac.key_len;
1.1 markus 399: }
1.7 markus 400: /* XXX need runden? */
1.27 markus 401: kex->we_need = need;
1.53 ! markus 402:
! 403: /* ignore the next message if the proposals do not match */
! 404: if (first_kex_follows && !proposals_match(my, peer)) {
! 405: type = packet_read();
! 406: debug2("skipping next packet (type %u)", type);
! 407: }
1.26 markus 408:
409: kex_prop_free(my);
410: kex_prop_free(peer);
411: }
412:
1.35 itojun 413: static u_char *
1.27 markus 414: derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
1.26 markus 415: {
416: Buffer b;
1.47 markus 417: const EVP_MD *evp_md = EVP_sha1();
1.26 markus 418: EVP_MD_CTX md;
419: char c = id;
420: int have;
1.43 markus 421: int mdsz = EVP_MD_size(evp_md);
1.30 markus 422: u_char *digest = xmalloc(roundup(need, mdsz));
1.26 markus 423:
424: buffer_init(&b);
425: buffer_put_bignum2(&b, shared_secret);
426:
1.30 markus 427: /* K1 = HASH(K || H || "A" || session_id) */
1.26 markus 428: EVP_DigestInit(&md, evp_md);
1.34 markus 429: if (!(datafellows & SSH_BUG_DERIVEKEY))
430: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
1.30 markus 431: EVP_DigestUpdate(&md, hash, mdsz);
432: EVP_DigestUpdate(&md, &c, 1);
1.27 markus 433: EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
1.26 markus 434: EVP_DigestFinal(&md, digest, NULL);
435:
1.30 markus 436: /*
437: * expand key:
438: * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
439: * Key = K1 || K2 || ... || Kn
440: */
1.26 markus 441: for (have = mdsz; need > have; have += mdsz) {
442: EVP_DigestInit(&md, evp_md);
1.34 markus 443: if (!(datafellows & SSH_BUG_DERIVEKEY))
444: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
1.26 markus 445: EVP_DigestUpdate(&md, hash, mdsz);
446: EVP_DigestUpdate(&md, digest, have);
447: EVP_DigestFinal(&md, digest + have, NULL);
448: }
449: buffer_free(&b);
450: #ifdef DEBUG_KEX
451: fprintf(stderr, "key '%c'== ", c);
452: dump_digest("key", digest, need);
453: #endif
454: return digest;
1.1 markus 455: }
456:
1.30 markus 457: Newkeys *current_keys[MODE_MAX];
1.27 markus 458:
1.23 markus 459: #define NKEYS 6
1.26 markus 460: void
1.27 markus 461: kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
1.1 markus 462: {
1.15 markus 463: u_char *keys[NKEYS];
1.27 markus 464: int i, mode, ctos;
1.1 markus 465:
466: for (i = 0; i < NKEYS; i++)
1.27 markus 467: keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
1.1 markus 468:
1.52 markus 469: debug2("kex_derive_keys");
1.1 markus 470: for (mode = 0; mode < MODE_MAX; mode++) {
1.30 markus 471: current_keys[mode] = kex->newkeys[mode];
472: kex->newkeys[mode] = NULL;
1.27 markus 473: ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
1.30 markus 474: current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
475: current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
476: current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
1.1 markus 477: }
1.27 markus 478: }
479:
480: Newkeys *
481: kex_get_newkeys(int mode)
482: {
1.30 markus 483: Newkeys *ret;
484:
485: ret = current_keys[mode];
486: current_keys[mode] = NULL;
487: return ret;
1.1 markus 488: }
1.26 markus 489:
490: #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
491: void
492: dump_digest(char *msg, u_char *digest, int len)
493: {
494: int i;
495:
496: fprintf(stderr, "%s\n", msg);
1.37 deraadt 497: for (i = 0; i< len; i++) {
1.26 markus 498: fprintf(stderr, "%02x", digest[i]);
499: if (i%32 == 31)
500: fprintf(stderr, "\n");
501: else if (i%8 == 7)
502: fprintf(stderr, " ");
503: }
504: fprintf(stderr, "\n");
505: }
506: #endif
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