Annotation of src/usr.bin/ssh/kex.c, Revision 1.20
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"
1.20 ! itojun 26: RCSID("$OpenBSD: kex.c,v 1.19 2001/02/04 15:32:23 stevesk Exp $");
1.18 markus 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);
1.19 stevesk 82: packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
1.7 markus 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:
1.20 ! itojun 203: #ifdef DEBUG_KEX
1.1 markus 204: void
1.15 markus 205: dump_digest(u_char *digest, int len)
1.1 markus 206: {
207: int i;
1.5 markus 208: for (i = 0; i< len; i++){
209: fprintf(stderr, "%02x", digest[i]);
1.1 markus 210: if(i%2!=0)
211: fprintf(stderr, " ");
212: }
1.5 markus 213: fprintf(stderr, "\n");
1.1 markus 214: }
1.20 ! itojun 215: #endif
1.1 markus 216:
1.15 markus 217: u_char *
1.1 markus 218: kex_hash(
219: char *client_version_string,
220: char *server_version_string,
221: char *ckexinit, int ckexinitlen,
222: char *skexinit, int skexinitlen,
223: char *serverhostkeyblob, int sbloblen,
224: BIGNUM *client_dh_pub,
225: BIGNUM *server_dh_pub,
226: BIGNUM *shared_secret)
227: {
228: Buffer b;
1.15 markus 229: static u_char digest[EVP_MAX_MD_SIZE];
1.1 markus 230: EVP_MD *evp_md = EVP_sha1();
231: EVP_MD_CTX md;
232:
233: buffer_init(&b);
234: buffer_put_string(&b, client_version_string, strlen(client_version_string));
235: buffer_put_string(&b, server_version_string, strlen(server_version_string));
236:
237: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
238: buffer_put_int(&b, ckexinitlen+1);
239: buffer_put_char(&b, SSH2_MSG_KEXINIT);
240: buffer_append(&b, ckexinit, ckexinitlen);
241: buffer_put_int(&b, skexinitlen+1);
242: buffer_put_char(&b, SSH2_MSG_KEXINIT);
243: buffer_append(&b, skexinit, skexinitlen);
244:
245: buffer_put_string(&b, serverhostkeyblob, sbloblen);
246: buffer_put_bignum2(&b, client_dh_pub);
247: buffer_put_bignum2(&b, server_dh_pub);
248: buffer_put_bignum2(&b, shared_secret);
1.19 stevesk 249:
1.1 markus 250: #ifdef DEBUG_KEX
251: buffer_dump(&b);
252: #endif
253:
254: EVP_DigestInit(&md, evp_md);
255: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
256: EVP_DigestFinal(&md, digest, NULL);
257:
258: buffer_free(&b);
259:
260: #ifdef DEBUG_KEX
1.5 markus 261: dump_digest(digest, evp_md->md_size);
1.1 markus 262: #endif
263: return digest;
264: }
265:
1.15 markus 266: u_char *
1.11 provos 267: kex_hash_gex(
268: char *client_version_string,
269: char *server_version_string,
270: char *ckexinit, int ckexinitlen,
271: char *skexinit, int skexinitlen,
272: char *serverhostkeyblob, int sbloblen,
273: int minbits, BIGNUM *prime, BIGNUM *gen,
274: BIGNUM *client_dh_pub,
275: BIGNUM *server_dh_pub,
276: BIGNUM *shared_secret)
277: {
278: Buffer b;
1.15 markus 279: static u_char digest[EVP_MAX_MD_SIZE];
1.11 provos 280: EVP_MD *evp_md = EVP_sha1();
281: EVP_MD_CTX md;
282:
283: buffer_init(&b);
284: buffer_put_string(&b, client_version_string, strlen(client_version_string));
285: buffer_put_string(&b, server_version_string, strlen(server_version_string));
286:
287: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
288: buffer_put_int(&b, ckexinitlen+1);
289: buffer_put_char(&b, SSH2_MSG_KEXINIT);
290: buffer_append(&b, ckexinit, ckexinitlen);
291: buffer_put_int(&b, skexinitlen+1);
292: buffer_put_char(&b, SSH2_MSG_KEXINIT);
293: buffer_append(&b, skexinit, skexinitlen);
294:
295: buffer_put_string(&b, serverhostkeyblob, sbloblen);
296: buffer_put_int(&b, minbits);
297: buffer_put_bignum2(&b, prime);
298: buffer_put_bignum2(&b, gen);
299: buffer_put_bignum2(&b, client_dh_pub);
300: buffer_put_bignum2(&b, server_dh_pub);
301: buffer_put_bignum2(&b, shared_secret);
1.19 stevesk 302:
1.11 provos 303: #ifdef DEBUG_KEX
304: buffer_dump(&b);
305: #endif
306:
307: EVP_DigestInit(&md, evp_md);
308: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
309: EVP_DigestFinal(&md, digest, NULL);
310:
311: buffer_free(&b);
312:
313: #ifdef DEBUG_KEX
314: dump_digest(digest, evp_md->md_size);
315: #endif
316: return digest;
317: }
318:
1.15 markus 319: u_char *
320: derive_key(int id, int need, u_char *hash, BIGNUM *shared_secret)
1.1 markus 321: {
322: Buffer b;
323: EVP_MD *evp_md = EVP_sha1();
324: EVP_MD_CTX md;
325: char c = id;
326: int have;
327: int mdsz = evp_md->md_size;
1.15 markus 328: u_char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);
1.1 markus 329:
330: buffer_init(&b);
331: buffer_put_bignum2(&b, shared_secret);
332:
333: EVP_DigestInit(&md, evp_md);
334: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
335: EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
336: EVP_DigestUpdate(&md, &c, 1); /* key id */
337: EVP_DigestUpdate(&md, hash, mdsz); /* session id */
338: EVP_DigestFinal(&md, digest, NULL);
339:
340: /* expand */
341: for (have = mdsz; need > have; have += mdsz) {
342: EVP_DigestInit(&md, evp_md);
343: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
344: EVP_DigestUpdate(&md, hash, mdsz);
345: EVP_DigestUpdate(&md, digest, have);
346: EVP_DigestFinal(&md, digest + have, NULL);
347: }
348: buffer_free(&b);
349: #ifdef DEBUG_KEX
350: fprintf(stderr, "Digest '%c'== ", c);
351: dump_digest(digest, need);
352: #endif
353: return digest;
354: }
355:
356: #define NKEYS 6
357:
358: #define MAX_PROP 20
359: #define SEP ","
360:
361: char *
362: get_match(char *client, char *server)
363: {
364: char *sproposals[MAX_PROP];
1.9 ho 365: char *c, *s, *p, *ret, *cp, *sp;
1.1 markus 366: int i, j, nproposals;
367:
1.9 ho 368: c = cp = xstrdup(client);
369: s = sp = xstrdup(server);
1.7 markus 370:
1.19 stevesk 371: for ((p = strsep(&sp, SEP)), i=0; p && *p != '\0';
1.9 ho 372: (p = strsep(&sp, SEP)), i++) {
1.1 markus 373: if (i < MAX_PROP)
374: sproposals[i] = p;
375: else
376: break;
377: }
378: nproposals = i;
379:
1.19 stevesk 380: for ((p = strsep(&cp, SEP)), i=0; p && *p != '\0';
1.9 ho 381: (p = strsep(&cp, SEP)), i++) {
1.7 markus 382: for (j = 0; j < nproposals; j++) {
383: if (strcmp(p, sproposals[j]) == 0) {
384: ret = xstrdup(p);
385: xfree(c);
386: xfree(s);
387: return ret;
388: }
389: }
1.1 markus 390: }
1.7 markus 391: xfree(c);
392: xfree(s);
1.1 markus 393: return NULL;
394: }
395: void
396: choose_enc(Enc *enc, char *client, char *server)
397: {
398: char *name = get_match(client, server);
399: if (name == NULL)
400: fatal("no matching cipher found: client %s server %s", client, server);
1.12 markus 401: enc->cipher = cipher_by_name(name);
402: if (enc->cipher == NULL)
403: fatal("matching cipher is not supported: %s", name);
1.1 markus 404: enc->name = name;
405: enc->enabled = 0;
406: enc->iv = NULL;
407: enc->key = NULL;
408: }
409: void
410: choose_mac(Mac *mac, char *client, char *server)
411: {
412: char *name = get_match(client, server);
413: if (name == NULL)
414: fatal("no matching mac found: client %s server %s", client, server);
415: if (strcmp(name, "hmac-md5") == 0) {
416: mac->md = EVP_md5();
417: } else if (strcmp(name, "hmac-sha1") == 0) {
418: mac->md = EVP_sha1();
419: } else if (strcmp(name, "hmac-ripemd160@openssh.com") == 0) {
420: mac->md = EVP_ripemd160();
421: } else {
422: fatal("unsupported mac %s", name);
423: }
424: mac->name = name;
425: mac->mac_len = mac->md->md_size;
1.6 markus 426: mac->key_len = (datafellows & SSH_BUG_HMAC) ? 16 : mac->mac_len;
1.1 markus 427: mac->key = NULL;
428: mac->enabled = 0;
429: }
430: void
431: choose_comp(Comp *comp, char *client, char *server)
432: {
433: char *name = get_match(client, server);
434: if (name == NULL)
435: fatal("no matching comp found: client %s server %s", client, server);
436: if (strcmp(name, "zlib") == 0) {
437: comp->type = 1;
438: } else if (strcmp(name, "none") == 0) {
439: comp->type = 0;
440: } else {
441: fatal("unsupported comp %s", name);
442: }
443: comp->name = name;
444: }
445: void
446: choose_kex(Kex *k, char *client, char *server)
447: {
448: k->name = get_match(client, server);
449: if (k->name == NULL)
450: fatal("no kex alg");
1.11 provos 451: if (strcmp(k->name, KEX_DH1) == 0) {
452: k->kex_type = DH_GRP1_SHA1;
453: } else if (strcmp(k->name, KEX_DHGEX) == 0) {
454: k->kex_type = DH_GEX_SHA1;
455: } else
1.1 markus 456: fatal("bad kex alg %s", k->name);
457: }
458: void
459: choose_hostkeyalg(Kex *k, char *client, char *server)
460: {
1.13 markus 461: char *hostkeyalg = get_match(client, server);
462: if (hostkeyalg == NULL)
1.1 markus 463: fatal("no hostkey alg");
1.13 markus 464: k->hostkey_type = key_type_from_name(hostkeyalg);
465: if (k->hostkey_type == KEY_UNSPEC)
466: fatal("bad hostkey alg '%s'", hostkeyalg);
1.17 markus 467: xfree(hostkeyalg);
1.1 markus 468: }
469:
470: Kex *
471: kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
472: {
473: int mode;
474: int ctos; /* direction: if true client-to-server */
475: int need;
476: Kex *k;
477:
478: k = xmalloc(sizeof(*k));
479: memset(k, 0, sizeof(*k));
480: k->server = server;
481:
482: for (mode = 0; mode < MODE_MAX; mode++) {
483: int nenc, nmac, ncomp;
484: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
485: nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
486: nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
487: ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
488: choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
489: choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
490: choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
1.2 markus 491: debug("kex: %s %s %s %s",
1.1 markus 492: ctos ? "client->server" : "server->client",
493: k->enc[mode].name,
494: k->mac[mode].name,
495: k->comp[mode].name);
496: }
497: choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
498: choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
499: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
500: need = 0;
501: for (mode = 0; mode < MODE_MAX; mode++) {
1.12 markus 502: if (need < k->enc[mode].cipher->key_len)
503: need = k->enc[mode].cipher->key_len;
504: if (need < k->enc[mode].cipher->block_size)
505: need = k->enc[mode].cipher->block_size;
1.1 markus 506: if (need < k->mac[mode].key_len)
507: need = k->mac[mode].key_len;
508: }
1.7 markus 509: /* XXX need runden? */
1.1 markus 510: k->we_need = need;
511: return k;
512: }
513:
514: int
1.15 markus 515: kex_derive_keys(Kex *k, u_char *hash, BIGNUM *shared_secret)
1.1 markus 516: {
517: int i;
518: int mode;
519: int ctos;
1.15 markus 520: u_char *keys[NKEYS];
1.1 markus 521:
522: for (i = 0; i < NKEYS; i++)
523: keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);
524:
525: for (mode = 0; mode < MODE_MAX; mode++) {
526: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
527: k->enc[mode].iv = keys[ctos ? 0 : 1];
528: k->enc[mode].key = keys[ctos ? 2 : 3];
529: k->mac[mode].key = keys[ctos ? 4 : 5];
530: }
531: return 0;
532: }
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