Annotation of src/usr.bin/ssh/kex.c, Revision 1.18
1.1 markus 1: /*
2: * Copyright (c) 2000 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"
1.18 ! markus 26: RCSID("$OpenBSD: kex.c,v 1.17 2001/01/08 21:48:17 markus Exp $");
! 27:
! 28: #include <openssl/crypto.h>
! 29: #include <openssl/bio.h>
! 30: #include <openssl/bn.h>
! 31: #include <openssl/dh.h>
! 32: #include <openssl/pem.h>
1.1 markus 33:
34: #include "ssh2.h"
35: #include "xmalloc.h"
36: #include "buffer.h"
37: #include "bufaux.h"
1.7 markus 38: #include "packet.h"
1.1 markus 39: #include "compat.h"
1.18 ! markus 40: #include "cipher.h"
1.1 markus 41: #include "kex.h"
1.13 markus 42: #include "key.h"
1.18 ! markus 43: #include "log.h"
1.1 markus 44:
1.7 markus 45: #define KEX_COOKIE_LEN 16
46:
1.1 markus 47: Buffer *
48: kex_init(char *myproposal[PROPOSAL_MAX])
49: {
1.7 markus 50: int first_kex_packet_follows = 0;
1.15 markus 51: u_char cookie[KEX_COOKIE_LEN];
1.1 markus 52: u_int32_t rand = 0;
53: int i;
54: Buffer *ki = xmalloc(sizeof(*ki));
1.7 markus 55: for (i = 0; i < KEX_COOKIE_LEN; i++) {
1.1 markus 56: if (i % 4 == 0)
57: rand = arc4random();
58: cookie[i] = rand & 0xff;
59: rand >>= 8;
60: }
61: buffer_init(ki);
62: buffer_append(ki, (char *)cookie, sizeof cookie);
63: for (i = 0; i < PROPOSAL_MAX; i++)
64: buffer_put_cstring(ki, myproposal[i]);
1.7 markus 65: buffer_put_char(ki, first_kex_packet_follows);
66: buffer_put_int(ki, 0); /* uint32 reserved */
1.1 markus 67: return ki;
68: }
69:
1.7 markus 70: /* send kexinit, parse and save reply */
71: void
72: kex_exchange_kexinit(
73: Buffer *my_kexinit, Buffer *peer_kexint,
74: char *peer_proposal[PROPOSAL_MAX])
75: {
76: int i;
77: char *ptr;
78: int plen;
79:
80: debug("send KEXINIT");
81: packet_start(SSH2_MSG_KEXINIT);
82: packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
83: packet_send();
84: packet_write_wait();
85: debug("done");
86:
87: /*
88: * read and save raw KEXINIT payload in buffer. this is used during
89: * computation of the session_id and the session keys.
90: */
91: debug("wait KEXINIT");
92: packet_read_expect(&plen, SSH2_MSG_KEXINIT);
93: ptr = packet_get_raw(&plen);
94: buffer_append(peer_kexint, ptr, plen);
95:
96: /* parse packet and save algorithm proposal */
97: /* skip cookie */
98: for (i = 0; i < KEX_COOKIE_LEN; i++)
99: packet_get_char();
100: /* extract kex init proposal strings */
101: for (i = 0; i < PROPOSAL_MAX; i++) {
102: peer_proposal[i] = packet_get_string(NULL);
103: debug("got kexinit: %s", peer_proposal[i]);
104: }
105: /* first kex follow / reserved */
106: i = packet_get_char();
107: debug("first kex follow: %d ", i);
108: i = packet_get_int();
109: debug("reserved: %d ", i);
110: packet_done();
111: debug("done");
112: }
113:
1.1 markus 114: /* diffie-hellman-group1-sha1 */
115:
1.3 markus 116: int
117: dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
118: {
119: int i;
120: int n = BN_num_bits(dh_pub);
121: int bits_set = 0;
122:
123: if (dh_pub->neg) {
124: log("invalid public DH value: negativ");
125: return 0;
126: }
127: for (i = 0; i <= n; i++)
128: if (BN_is_bit_set(dh_pub, i))
129: bits_set++;
130: debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
131:
132: /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
133: if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
134: return 1;
135: log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
136: return 0;
137: }
138:
1.14 provos 139: void
1.11 provos 140: dh_gen_key(DH *dh)
141: {
142: int tries = 0;
143:
144: do {
145: if (DH_generate_key(dh) == 0)
146: fatal("DH_generate_key");
147: if (tries++ > 10)
148: fatal("dh_new_group1: too many bad keys: giving up");
149: } while (!dh_pub_is_valid(dh, dh->pub_key));
150: }
151:
152: DH *
153: dh_new_group_asc(const char *gen, const char *modulus)
154: {
155: DH *dh;
156: int ret;
157:
158: dh = DH_new();
159: if (dh == NULL)
160: fatal("DH_new");
161:
162: if ((ret = BN_hex2bn(&dh->p, modulus)) < 0)
163: fatal("BN_hex2bn p");
164: if ((ret = BN_hex2bn(&dh->g, gen)) < 0)
165: fatal("BN_hex2bn g");
166:
1.14 provos 167: return (dh);
1.11 provos 168: }
169:
1.14 provos 170: /*
171: * This just returns the group, we still need to generate the exchange
172: * value.
173: */
174:
1.11 provos 175: DH *
176: dh_new_group(BIGNUM *gen, BIGNUM *modulus)
177: {
178: DH *dh;
179:
180: dh = DH_new();
181: if (dh == NULL)
182: fatal("DH_new");
183: dh->p = modulus;
184: dh->g = gen;
185:
1.14 provos 186: return (dh);
1.11 provos 187: }
188:
189: DH *
1.16 markus 190: dh_new_group1(void)
1.1 markus 191: {
1.11 provos 192: static char *gen = "2", *group1 =
1.1 markus 193: "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
194: "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
195: "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
196: "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
197: "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
198: "FFFFFFFF" "FFFFFFFF";
1.11 provos 199:
200: return (dh_new_group_asc(gen, group1));
1.1 markus 201: }
202:
203: void
1.15 markus 204: dump_digest(u_char *digest, int len)
1.1 markus 205: {
206: int i;
1.5 markus 207: for (i = 0; i< len; i++){
208: fprintf(stderr, "%02x", digest[i]);
1.1 markus 209: if(i%2!=0)
210: fprintf(stderr, " ");
211: }
1.5 markus 212: fprintf(stderr, "\n");
1.1 markus 213: }
214:
1.15 markus 215: u_char *
1.1 markus 216: kex_hash(
217: char *client_version_string,
218: char *server_version_string,
219: char *ckexinit, int ckexinitlen,
220: char *skexinit, int skexinitlen,
221: char *serverhostkeyblob, int sbloblen,
222: BIGNUM *client_dh_pub,
223: BIGNUM *server_dh_pub,
224: BIGNUM *shared_secret)
225: {
226: Buffer b;
1.15 markus 227: static u_char digest[EVP_MAX_MD_SIZE];
1.1 markus 228: EVP_MD *evp_md = EVP_sha1();
229: EVP_MD_CTX md;
230:
231: buffer_init(&b);
232: buffer_put_string(&b, client_version_string, strlen(client_version_string));
233: buffer_put_string(&b, server_version_string, strlen(server_version_string));
234:
235: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
236: buffer_put_int(&b, ckexinitlen+1);
237: buffer_put_char(&b, SSH2_MSG_KEXINIT);
238: buffer_append(&b, ckexinit, ckexinitlen);
239: buffer_put_int(&b, skexinitlen+1);
240: buffer_put_char(&b, SSH2_MSG_KEXINIT);
241: buffer_append(&b, skexinit, skexinitlen);
242:
243: buffer_put_string(&b, serverhostkeyblob, sbloblen);
244: buffer_put_bignum2(&b, client_dh_pub);
245: buffer_put_bignum2(&b, server_dh_pub);
246: buffer_put_bignum2(&b, shared_secret);
247:
248: #ifdef DEBUG_KEX
249: buffer_dump(&b);
250: #endif
251:
252: EVP_DigestInit(&md, evp_md);
253: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
254: EVP_DigestFinal(&md, digest, NULL);
255:
256: buffer_free(&b);
257:
258: #ifdef DEBUG_KEX
1.5 markus 259: dump_digest(digest, evp_md->md_size);
1.1 markus 260: #endif
261: return digest;
262: }
263:
1.15 markus 264: u_char *
1.11 provos 265: kex_hash_gex(
266: char *client_version_string,
267: char *server_version_string,
268: char *ckexinit, int ckexinitlen,
269: char *skexinit, int skexinitlen,
270: char *serverhostkeyblob, int sbloblen,
271: int minbits, BIGNUM *prime, BIGNUM *gen,
272: BIGNUM *client_dh_pub,
273: BIGNUM *server_dh_pub,
274: BIGNUM *shared_secret)
275: {
276: Buffer b;
1.15 markus 277: static u_char digest[EVP_MAX_MD_SIZE];
1.11 provos 278: EVP_MD *evp_md = EVP_sha1();
279: EVP_MD_CTX md;
280:
281: buffer_init(&b);
282: buffer_put_string(&b, client_version_string, strlen(client_version_string));
283: buffer_put_string(&b, server_version_string, strlen(server_version_string));
284:
285: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
286: buffer_put_int(&b, ckexinitlen+1);
287: buffer_put_char(&b, SSH2_MSG_KEXINIT);
288: buffer_append(&b, ckexinit, ckexinitlen);
289: buffer_put_int(&b, skexinitlen+1);
290: buffer_put_char(&b, SSH2_MSG_KEXINIT);
291: buffer_append(&b, skexinit, skexinitlen);
292:
293: buffer_put_string(&b, serverhostkeyblob, sbloblen);
294: buffer_put_int(&b, minbits);
295: buffer_put_bignum2(&b, prime);
296: buffer_put_bignum2(&b, gen);
297: buffer_put_bignum2(&b, client_dh_pub);
298: buffer_put_bignum2(&b, server_dh_pub);
299: buffer_put_bignum2(&b, shared_secret);
300:
301: #ifdef DEBUG_KEX
302: buffer_dump(&b);
303: #endif
304:
305: EVP_DigestInit(&md, evp_md);
306: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
307: EVP_DigestFinal(&md, digest, NULL);
308:
309: buffer_free(&b);
310:
311: #ifdef DEBUG_KEX
312: dump_digest(digest, evp_md->md_size);
313: #endif
314: return digest;
315: }
316:
1.15 markus 317: u_char *
318: derive_key(int id, int need, u_char *hash, BIGNUM *shared_secret)
1.1 markus 319: {
320: Buffer b;
321: EVP_MD *evp_md = EVP_sha1();
322: EVP_MD_CTX md;
323: char c = id;
324: int have;
325: int mdsz = evp_md->md_size;
1.15 markus 326: u_char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);
1.1 markus 327:
328: buffer_init(&b);
329: buffer_put_bignum2(&b, shared_secret);
330:
331: EVP_DigestInit(&md, evp_md);
332: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
333: EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
334: EVP_DigestUpdate(&md, &c, 1); /* key id */
335: EVP_DigestUpdate(&md, hash, mdsz); /* session id */
336: EVP_DigestFinal(&md, digest, NULL);
337:
338: /* expand */
339: for (have = mdsz; need > have; have += mdsz) {
340: EVP_DigestInit(&md, evp_md);
341: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
342: EVP_DigestUpdate(&md, hash, mdsz);
343: EVP_DigestUpdate(&md, digest, have);
344: EVP_DigestFinal(&md, digest + have, NULL);
345: }
346: buffer_free(&b);
347: #ifdef DEBUG_KEX
348: fprintf(stderr, "Digest '%c'== ", c);
349: dump_digest(digest, need);
350: #endif
351: return digest;
352: }
353:
354: #define NKEYS 6
355:
356: #define MAX_PROP 20
357: #define SEP ","
358:
359: char *
360: get_match(char *client, char *server)
361: {
362: char *sproposals[MAX_PROP];
1.9 ho 363: char *c, *s, *p, *ret, *cp, *sp;
1.1 markus 364: int i, j, nproposals;
365:
1.9 ho 366: c = cp = xstrdup(client);
367: s = sp = xstrdup(server);
1.7 markus 368:
1.9 ho 369: for ((p = strsep(&sp, SEP)), i=0; p && *p != '\0';
370: (p = strsep(&sp, SEP)), i++) {
1.1 markus 371: if (i < MAX_PROP)
372: sproposals[i] = p;
373: else
374: break;
375: }
376: nproposals = i;
377:
1.9 ho 378: for ((p = strsep(&cp, SEP)), i=0; p && *p != '\0';
379: (p = strsep(&cp, SEP)), i++) {
1.7 markus 380: for (j = 0; j < nproposals; j++) {
381: if (strcmp(p, sproposals[j]) == 0) {
382: ret = xstrdup(p);
383: xfree(c);
384: xfree(s);
385: return ret;
386: }
387: }
1.1 markus 388: }
1.7 markus 389: xfree(c);
390: xfree(s);
1.1 markus 391: return NULL;
392: }
393: void
394: choose_enc(Enc *enc, char *client, char *server)
395: {
396: char *name = get_match(client, server);
397: if (name == NULL)
398: fatal("no matching cipher found: client %s server %s", client, server);
1.12 markus 399: enc->cipher = cipher_by_name(name);
400: if (enc->cipher == NULL)
401: fatal("matching cipher is not supported: %s", name);
1.1 markus 402: enc->name = name;
403: enc->enabled = 0;
404: enc->iv = NULL;
405: enc->key = NULL;
406: }
407: void
408: choose_mac(Mac *mac, char *client, char *server)
409: {
410: char *name = get_match(client, server);
411: if (name == NULL)
412: fatal("no matching mac found: client %s server %s", client, server);
413: if (strcmp(name, "hmac-md5") == 0) {
414: mac->md = EVP_md5();
415: } else if (strcmp(name, "hmac-sha1") == 0) {
416: mac->md = EVP_sha1();
417: } else if (strcmp(name, "hmac-ripemd160@openssh.com") == 0) {
418: mac->md = EVP_ripemd160();
419: } else {
420: fatal("unsupported mac %s", name);
421: }
422: mac->name = name;
423: mac->mac_len = mac->md->md_size;
1.6 markus 424: mac->key_len = (datafellows & SSH_BUG_HMAC) ? 16 : mac->mac_len;
1.1 markus 425: mac->key = NULL;
426: mac->enabled = 0;
427: }
428: void
429: choose_comp(Comp *comp, char *client, char *server)
430: {
431: char *name = get_match(client, server);
432: if (name == NULL)
433: fatal("no matching comp found: client %s server %s", client, server);
434: if (strcmp(name, "zlib") == 0) {
435: comp->type = 1;
436: } else if (strcmp(name, "none") == 0) {
437: comp->type = 0;
438: } else {
439: fatal("unsupported comp %s", name);
440: }
441: comp->name = name;
442: }
443: void
444: choose_kex(Kex *k, char *client, char *server)
445: {
446: k->name = get_match(client, server);
447: if (k->name == NULL)
448: fatal("no kex alg");
1.11 provos 449: if (strcmp(k->name, KEX_DH1) == 0) {
450: k->kex_type = DH_GRP1_SHA1;
451: } else if (strcmp(k->name, KEX_DHGEX) == 0) {
452: k->kex_type = DH_GEX_SHA1;
453: } else
1.1 markus 454: fatal("bad kex alg %s", k->name);
455: }
456: void
457: choose_hostkeyalg(Kex *k, char *client, char *server)
458: {
1.13 markus 459: char *hostkeyalg = get_match(client, server);
460: if (hostkeyalg == NULL)
1.1 markus 461: fatal("no hostkey alg");
1.13 markus 462: k->hostkey_type = key_type_from_name(hostkeyalg);
463: if (k->hostkey_type == KEY_UNSPEC)
464: fatal("bad hostkey alg '%s'", hostkeyalg);
1.17 markus 465: xfree(hostkeyalg);
1.1 markus 466: }
467:
468: Kex *
469: kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
470: {
471: int mode;
472: int ctos; /* direction: if true client-to-server */
473: int need;
474: Kex *k;
475:
476: k = xmalloc(sizeof(*k));
477: memset(k, 0, sizeof(*k));
478: k->server = server;
479:
480: for (mode = 0; mode < MODE_MAX; mode++) {
481: int nenc, nmac, ncomp;
482: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
483: nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
484: nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
485: ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
486: choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
487: choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
488: choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
1.2 markus 489: debug("kex: %s %s %s %s",
1.1 markus 490: ctos ? "client->server" : "server->client",
491: k->enc[mode].name,
492: k->mac[mode].name,
493: k->comp[mode].name);
494: }
495: choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
496: choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
497: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
498: need = 0;
499: for (mode = 0; mode < MODE_MAX; mode++) {
1.12 markus 500: if (need < k->enc[mode].cipher->key_len)
501: need = k->enc[mode].cipher->key_len;
502: if (need < k->enc[mode].cipher->block_size)
503: need = k->enc[mode].cipher->block_size;
1.1 markus 504: if (need < k->mac[mode].key_len)
505: need = k->mac[mode].key_len;
506: }
1.7 markus 507: /* XXX need runden? */
1.1 markus 508: k->we_need = need;
509: return k;
510: }
511:
512: int
1.15 markus 513: kex_derive_keys(Kex *k, u_char *hash, BIGNUM *shared_secret)
1.1 markus 514: {
515: int i;
516: int mode;
517: int ctos;
1.15 markus 518: u_char *keys[NKEYS];
1.1 markus 519:
520: for (i = 0; i < NKEYS; i++)
521: keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);
522:
523: for (mode = 0; mode < MODE_MAX; mode++) {
524: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
525: k->enc[mode].iv = keys[ctos ? 0 : 1];
526: k->enc[mode].key = keys[ctos ? 2 : 3];
527: k->mac[mode].key = keys[ctos ? 4 : 5];
528: }
529: return 0;
530: }