Annotation of src/usr.bin/ssh/kex.c, Revision 1.17
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"
1.17 ! markus 26: RCSID("$OpenBSD: kex.c,v 1.16 2000/12/20 19:37:22 markus Exp $");
1.1 markus 27:
28: #include "ssh.h"
29: #include "ssh2.h"
30: #include "xmalloc.h"
31: #include "buffer.h"
32: #include "bufaux.h"
1.7 markus 33: #include "packet.h"
1.1 markus 34: #include "compat.h"
35:
1.4 markus 36: #include <openssl/bn.h>
37: #include <openssl/dh.h>
1.1 markus 38:
1.4 markus 39: #include <openssl/crypto.h>
40: #include <openssl/bio.h>
41: #include <openssl/bn.h>
42: #include <openssl/dh.h>
43: #include <openssl/pem.h>
1.1 markus 44:
45: #include "kex.h"
1.13 markus 46: #include "key.h"
1.1 markus 47:
1.7 markus 48: #define KEX_COOKIE_LEN 16
49:
1.1 markus 50: Buffer *
51: kex_init(char *myproposal[PROPOSAL_MAX])
52: {
1.7 markus 53: int first_kex_packet_follows = 0;
1.15 markus 54: u_char cookie[KEX_COOKIE_LEN];
1.1 markus 55: u_int32_t rand = 0;
56: int i;
57: Buffer *ki = xmalloc(sizeof(*ki));
1.7 markus 58: for (i = 0; i < KEX_COOKIE_LEN; i++) {
1.1 markus 59: if (i % 4 == 0)
60: rand = arc4random();
61: cookie[i] = rand & 0xff;
62: rand >>= 8;
63: }
64: buffer_init(ki);
65: buffer_append(ki, (char *)cookie, sizeof cookie);
66: for (i = 0; i < PROPOSAL_MAX; i++)
67: buffer_put_cstring(ki, myproposal[i]);
1.7 markus 68: buffer_put_char(ki, first_kex_packet_follows);
69: buffer_put_int(ki, 0); /* uint32 reserved */
1.1 markus 70: return ki;
71: }
72:
1.7 markus 73: /* send kexinit, parse and save reply */
74: void
75: kex_exchange_kexinit(
76: Buffer *my_kexinit, Buffer *peer_kexint,
77: char *peer_proposal[PROPOSAL_MAX])
78: {
79: int i;
80: char *ptr;
81: int plen;
82:
83: debug("send KEXINIT");
84: packet_start(SSH2_MSG_KEXINIT);
85: packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
86: packet_send();
87: packet_write_wait();
88: debug("done");
89:
90: /*
91: * read and save raw KEXINIT payload in buffer. this is used during
92: * computation of the session_id and the session keys.
93: */
94: debug("wait KEXINIT");
95: packet_read_expect(&plen, SSH2_MSG_KEXINIT);
96: ptr = packet_get_raw(&plen);
97: buffer_append(peer_kexint, ptr, plen);
98:
99: /* parse packet and save algorithm proposal */
100: /* skip cookie */
101: for (i = 0; i < KEX_COOKIE_LEN; i++)
102: packet_get_char();
103: /* extract kex init proposal strings */
104: for (i = 0; i < PROPOSAL_MAX; i++) {
105: peer_proposal[i] = packet_get_string(NULL);
106: debug("got kexinit: %s", peer_proposal[i]);
107: }
108: /* first kex follow / reserved */
109: i = packet_get_char();
110: debug("first kex follow: %d ", i);
111: i = packet_get_int();
112: debug("reserved: %d ", i);
113: packet_done();
114: debug("done");
115: }
116:
1.1 markus 117: /* diffie-hellman-group1-sha1 */
118:
1.3 markus 119: int
120: dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
121: {
122: int i;
123: int n = BN_num_bits(dh_pub);
124: int bits_set = 0;
125:
126: if (dh_pub->neg) {
127: log("invalid public DH value: negativ");
128: return 0;
129: }
130: for (i = 0; i <= n; i++)
131: if (BN_is_bit_set(dh_pub, i))
132: bits_set++;
133: debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
134:
135: /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
136: if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
137: return 1;
138: log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
139: return 0;
140: }
141:
1.14 provos 142: void
1.11 provos 143: dh_gen_key(DH *dh)
144: {
145: int tries = 0;
146:
147: do {
148: if (DH_generate_key(dh) == 0)
149: fatal("DH_generate_key");
150: if (tries++ > 10)
151: fatal("dh_new_group1: too many bad keys: giving up");
152: } while (!dh_pub_is_valid(dh, dh->pub_key));
153: }
154:
155: DH *
156: dh_new_group_asc(const char *gen, const char *modulus)
157: {
158: DH *dh;
159: int ret;
160:
161: dh = DH_new();
162: if (dh == NULL)
163: fatal("DH_new");
164:
165: if ((ret = BN_hex2bn(&dh->p, modulus)) < 0)
166: fatal("BN_hex2bn p");
167: if ((ret = BN_hex2bn(&dh->g, gen)) < 0)
168: fatal("BN_hex2bn g");
169:
1.14 provos 170: return (dh);
1.11 provos 171: }
172:
1.14 provos 173: /*
174: * This just returns the group, we still need to generate the exchange
175: * value.
176: */
177:
1.11 provos 178: DH *
179: dh_new_group(BIGNUM *gen, BIGNUM *modulus)
180: {
181: DH *dh;
182:
183: dh = DH_new();
184: if (dh == NULL)
185: fatal("DH_new");
186: dh->p = modulus;
187: dh->g = gen;
188:
1.14 provos 189: return (dh);
1.11 provos 190: }
191:
192: DH *
1.16 markus 193: dh_new_group1(void)
1.1 markus 194: {
1.11 provos 195: static char *gen = "2", *group1 =
1.1 markus 196: "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
197: "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
198: "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
199: "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
200: "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
201: "FFFFFFFF" "FFFFFFFF";
1.11 provos 202:
203: return (dh_new_group_asc(gen, group1));
1.1 markus 204: }
205:
206: void
1.15 markus 207: dump_digest(u_char *digest, int len)
1.1 markus 208: {
209: int i;
1.5 markus 210: for (i = 0; i< len; i++){
211: fprintf(stderr, "%02x", digest[i]);
1.1 markus 212: if(i%2!=0)
213: fprintf(stderr, " ");
214: }
1.5 markus 215: fprintf(stderr, "\n");
1.1 markus 216: }
217:
1.15 markus 218: u_char *
1.1 markus 219: kex_hash(
220: char *client_version_string,
221: char *server_version_string,
222: char *ckexinit, int ckexinitlen,
223: char *skexinit, int skexinitlen,
224: char *serverhostkeyblob, int sbloblen,
225: BIGNUM *client_dh_pub,
226: BIGNUM *server_dh_pub,
227: BIGNUM *shared_secret)
228: {
229: Buffer b;
1.15 markus 230: static u_char digest[EVP_MAX_MD_SIZE];
1.1 markus 231: EVP_MD *evp_md = EVP_sha1();
232: EVP_MD_CTX md;
233:
234: buffer_init(&b);
235: buffer_put_string(&b, client_version_string, strlen(client_version_string));
236: buffer_put_string(&b, server_version_string, strlen(server_version_string));
237:
238: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
239: buffer_put_int(&b, ckexinitlen+1);
240: buffer_put_char(&b, SSH2_MSG_KEXINIT);
241: buffer_append(&b, ckexinit, ckexinitlen);
242: buffer_put_int(&b, skexinitlen+1);
243: buffer_put_char(&b, SSH2_MSG_KEXINIT);
244: buffer_append(&b, skexinit, skexinitlen);
245:
246: buffer_put_string(&b, serverhostkeyblob, sbloblen);
247: buffer_put_bignum2(&b, client_dh_pub);
248: buffer_put_bignum2(&b, server_dh_pub);
249: buffer_put_bignum2(&b, shared_secret);
250:
251: #ifdef DEBUG_KEX
252: buffer_dump(&b);
253: #endif
254:
255: EVP_DigestInit(&md, evp_md);
256: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
257: EVP_DigestFinal(&md, digest, NULL);
258:
259: buffer_free(&b);
260:
261: #ifdef DEBUG_KEX
1.5 markus 262: dump_digest(digest, evp_md->md_size);
1.1 markus 263: #endif
264: return digest;
265: }
266:
1.15 markus 267: u_char *
1.11 provos 268: kex_hash_gex(
269: char *client_version_string,
270: char *server_version_string,
271: char *ckexinit, int ckexinitlen,
272: char *skexinit, int skexinitlen,
273: char *serverhostkeyblob, int sbloblen,
274: int minbits, BIGNUM *prime, BIGNUM *gen,
275: BIGNUM *client_dh_pub,
276: BIGNUM *server_dh_pub,
277: BIGNUM *shared_secret)
278: {
279: Buffer b;
1.15 markus 280: static u_char digest[EVP_MAX_MD_SIZE];
1.11 provos 281: EVP_MD *evp_md = EVP_sha1();
282: EVP_MD_CTX md;
283:
284: buffer_init(&b);
285: buffer_put_string(&b, client_version_string, strlen(client_version_string));
286: buffer_put_string(&b, server_version_string, strlen(server_version_string));
287:
288: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
289: buffer_put_int(&b, ckexinitlen+1);
290: buffer_put_char(&b, SSH2_MSG_KEXINIT);
291: buffer_append(&b, ckexinit, ckexinitlen);
292: buffer_put_int(&b, skexinitlen+1);
293: buffer_put_char(&b, SSH2_MSG_KEXINIT);
294: buffer_append(&b, skexinit, skexinitlen);
295:
296: buffer_put_string(&b, serverhostkeyblob, sbloblen);
297: buffer_put_int(&b, minbits);
298: buffer_put_bignum2(&b, prime);
299: buffer_put_bignum2(&b, gen);
300: buffer_put_bignum2(&b, client_dh_pub);
301: buffer_put_bignum2(&b, server_dh_pub);
302: buffer_put_bignum2(&b, shared_secret);
303:
304: #ifdef DEBUG_KEX
305: buffer_dump(&b);
306: #endif
307:
308: EVP_DigestInit(&md, evp_md);
309: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
310: EVP_DigestFinal(&md, digest, NULL);
311:
312: buffer_free(&b);
313:
314: #ifdef DEBUG_KEX
315: dump_digest(digest, evp_md->md_size);
316: #endif
317: return digest;
318: }
319:
1.15 markus 320: u_char *
321: derive_key(int id, int need, u_char *hash, BIGNUM *shared_secret)
1.1 markus 322: {
323: Buffer b;
324: EVP_MD *evp_md = EVP_sha1();
325: EVP_MD_CTX md;
326: char c = id;
327: int have;
328: int mdsz = evp_md->md_size;
1.15 markus 329: u_char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);
1.1 markus 330:
331: buffer_init(&b);
332: buffer_put_bignum2(&b, shared_secret);
333:
334: EVP_DigestInit(&md, evp_md);
335: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
336: EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
337: EVP_DigestUpdate(&md, &c, 1); /* key id */
338: EVP_DigestUpdate(&md, hash, mdsz); /* session id */
339: EVP_DigestFinal(&md, digest, NULL);
340:
341: /* expand */
342: for (have = mdsz; need > have; have += mdsz) {
343: EVP_DigestInit(&md, evp_md);
344: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
345: EVP_DigestUpdate(&md, hash, mdsz);
346: EVP_DigestUpdate(&md, digest, have);
347: EVP_DigestFinal(&md, digest + have, NULL);
348: }
349: buffer_free(&b);
350: #ifdef DEBUG_KEX
351: fprintf(stderr, "Digest '%c'== ", c);
352: dump_digest(digest, need);
353: #endif
354: return digest;
355: }
356:
357: #define NKEYS 6
358:
359: #define MAX_PROP 20
360: #define SEP ","
361:
362: char *
363: get_match(char *client, char *server)
364: {
365: char *sproposals[MAX_PROP];
1.9 ho 366: char *c, *s, *p, *ret, *cp, *sp;
1.1 markus 367: int i, j, nproposals;
368:
1.9 ho 369: c = cp = xstrdup(client);
370: s = sp = xstrdup(server);
1.7 markus 371:
1.9 ho 372: for ((p = strsep(&sp, SEP)), i=0; p && *p != '\0';
373: (p = strsep(&sp, SEP)), i++) {
1.1 markus 374: if (i < MAX_PROP)
375: sproposals[i] = p;
376: else
377: break;
378: }
379: nproposals = i;
380:
1.9 ho 381: for ((p = strsep(&cp, SEP)), i=0; p && *p != '\0';
382: (p = strsep(&cp, SEP)), i++) {
1.7 markus 383: for (j = 0; j < nproposals; j++) {
384: if (strcmp(p, sproposals[j]) == 0) {
385: ret = xstrdup(p);
386: xfree(c);
387: xfree(s);
388: return ret;
389: }
390: }
1.1 markus 391: }
1.7 markus 392: xfree(c);
393: xfree(s);
1.1 markus 394: return NULL;
395: }
396: void
397: choose_enc(Enc *enc, char *client, char *server)
398: {
399: char *name = get_match(client, server);
400: if (name == NULL)
401: fatal("no matching cipher found: client %s server %s", client, server);
1.12 markus 402: enc->cipher = cipher_by_name(name);
403: if (enc->cipher == NULL)
404: fatal("matching cipher is not supported: %s", name);
1.1 markus 405: enc->name = name;
406: enc->enabled = 0;
407: enc->iv = NULL;
408: enc->key = NULL;
409: }
410: void
411: choose_mac(Mac *mac, char *client, char *server)
412: {
413: char *name = get_match(client, server);
414: if (name == NULL)
415: fatal("no matching mac found: client %s server %s", client, server);
416: if (strcmp(name, "hmac-md5") == 0) {
417: mac->md = EVP_md5();
418: } else if (strcmp(name, "hmac-sha1") == 0) {
419: mac->md = EVP_sha1();
420: } else if (strcmp(name, "hmac-ripemd160@openssh.com") == 0) {
421: mac->md = EVP_ripemd160();
422: } else {
423: fatal("unsupported mac %s", name);
424: }
425: mac->name = name;
426: mac->mac_len = mac->md->md_size;
1.6 markus 427: mac->key_len = (datafellows & SSH_BUG_HMAC) ? 16 : mac->mac_len;
1.1 markus 428: mac->key = NULL;
429: mac->enabled = 0;
430: }
431: void
432: choose_comp(Comp *comp, char *client, char *server)
433: {
434: char *name = get_match(client, server);
435: if (name == NULL)
436: fatal("no matching comp found: client %s server %s", client, server);
437: if (strcmp(name, "zlib") == 0) {
438: comp->type = 1;
439: } else if (strcmp(name, "none") == 0) {
440: comp->type = 0;
441: } else {
442: fatal("unsupported comp %s", name);
443: }
444: comp->name = name;
445: }
446: void
447: choose_kex(Kex *k, char *client, char *server)
448: {
449: k->name = get_match(client, server);
450: if (k->name == NULL)
451: fatal("no kex alg");
1.11 provos 452: if (strcmp(k->name, KEX_DH1) == 0) {
453: k->kex_type = DH_GRP1_SHA1;
454: } else if (strcmp(k->name, KEX_DHGEX) == 0) {
455: k->kex_type = DH_GEX_SHA1;
456: } else
1.1 markus 457: fatal("bad kex alg %s", k->name);
458: }
459: void
460: choose_hostkeyalg(Kex *k, char *client, char *server)
461: {
1.13 markus 462: char *hostkeyalg = get_match(client, server);
463: if (hostkeyalg == NULL)
1.1 markus 464: fatal("no hostkey alg");
1.13 markus 465: k->hostkey_type = key_type_from_name(hostkeyalg);
466: if (k->hostkey_type == KEY_UNSPEC)
467: fatal("bad hostkey alg '%s'", hostkeyalg);
1.17 ! markus 468: xfree(hostkeyalg);
1.1 markus 469: }
470:
471: Kex *
472: kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
473: {
474: int mode;
475: int ctos; /* direction: if true client-to-server */
476: int need;
477: Kex *k;
478:
479: k = xmalloc(sizeof(*k));
480: memset(k, 0, sizeof(*k));
481: k->server = server;
482:
483: for (mode = 0; mode < MODE_MAX; mode++) {
484: int nenc, nmac, ncomp;
485: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
486: nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
487: nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
488: ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
489: choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
490: choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
491: choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
1.2 markus 492: debug("kex: %s %s %s %s",
1.1 markus 493: ctos ? "client->server" : "server->client",
494: k->enc[mode].name,
495: k->mac[mode].name,
496: k->comp[mode].name);
497: }
498: choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
499: choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
500: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
501: need = 0;
502: for (mode = 0; mode < MODE_MAX; mode++) {
1.12 markus 503: if (need < k->enc[mode].cipher->key_len)
504: need = k->enc[mode].cipher->key_len;
505: if (need < k->enc[mode].cipher->block_size)
506: need = k->enc[mode].cipher->block_size;
1.1 markus 507: if (need < k->mac[mode].key_len)
508: need = k->mac[mode].key_len;
509: }
1.7 markus 510: /* XXX need runden? */
1.1 markus 511: k->we_need = need;
512: return k;
513: }
514:
515: int
1.15 markus 516: kex_derive_keys(Kex *k, u_char *hash, BIGNUM *shared_secret)
1.1 markus 517: {
518: int i;
519: int mode;
520: int ctos;
1.15 markus 521: u_char *keys[NKEYS];
1.1 markus 522:
523: for (i = 0; i < NKEYS; i++)
524: keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);
525:
526: for (mode = 0; mode < MODE_MAX; mode++) {
527: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
528: k->enc[mode].iv = keys[ctos ? 0 : 1];
529: k->enc[mode].key = keys[ctos ? 2 : 3];
530: k->mac[mode].key = keys[ctos ? 4 : 5];
531: }
532: return 0;
533: }