Annotation of src/usr.bin/ssh/kexgex.c, Revision 1.9.2.1
1.1 markus 1: /*
2: * Copyright (c) 2000 Niels Provos. All rights reserved.
3: * Copyright (c) 2001 Markus Friedl. All rights reserved.
4: *
5: * Redistribution and use in source and binary forms, with or without
6: * modification, are permitted provided that the following conditions
7: * are met:
8: * 1. Redistributions of source code must retain the above copyright
9: * notice, this list of conditions and the following disclaimer.
10: * 2. Redistributions in binary form must reproduce the above copyright
11: * notice, this list of conditions and the following disclaimer in the
12: * documentation and/or other materials provided with the distribution.
13: *
14: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24: */
25:
26: #include "includes.h"
1.9.2.1 ! jason 27: RCSID("$OpenBSD: kexgex.c,v 1.20 2002/02/28 15:46:33 markus Exp $");
1.1 markus 28:
29: #include <openssl/bn.h>
30:
31: #include "xmalloc.h"
32: #include "buffer.h"
33: #include "bufaux.h"
34: #include "key.h"
35: #include "kex.h"
36: #include "log.h"
37: #include "packet.h"
38: #include "dh.h"
39: #include "ssh2.h"
40: #include "compat.h"
41:
1.8 itojun 42: static u_char *
1.1 markus 43: kexgex_hash(
44: char *client_version_string,
45: char *server_version_string,
46: char *ckexinit, int ckexinitlen,
47: char *skexinit, int skexinitlen,
1.9 stevesk 48: u_char *serverhostkeyblob, int sbloblen,
1.1 markus 49: int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen,
50: BIGNUM *client_dh_pub,
51: BIGNUM *server_dh_pub,
52: BIGNUM *shared_secret)
53: {
54: Buffer b;
55: static u_char digest[EVP_MAX_MD_SIZE];
1.9.2.1 ! jason 56: const EVP_MD *evp_md = EVP_sha1();
1.1 markus 57: EVP_MD_CTX md;
58:
59: buffer_init(&b);
1.6 markus 60: buffer_put_cstring(&b, client_version_string);
61: buffer_put_cstring(&b, server_version_string);
1.1 markus 62:
63: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
64: buffer_put_int(&b, ckexinitlen+1);
65: buffer_put_char(&b, SSH2_MSG_KEXINIT);
66: buffer_append(&b, ckexinit, ckexinitlen);
67: buffer_put_int(&b, skexinitlen+1);
68: buffer_put_char(&b, SSH2_MSG_KEXINIT);
69: buffer_append(&b, skexinit, skexinitlen);
70:
71: buffer_put_string(&b, serverhostkeyblob, sbloblen);
1.5 markus 72: if (min == -1 || max == -1)
1.1 markus 73: buffer_put_int(&b, wantbits);
74: else {
75: buffer_put_int(&b, min);
76: buffer_put_int(&b, wantbits);
77: buffer_put_int(&b, max);
78: }
79: buffer_put_bignum2(&b, prime);
80: buffer_put_bignum2(&b, gen);
81: buffer_put_bignum2(&b, client_dh_pub);
82: buffer_put_bignum2(&b, server_dh_pub);
83: buffer_put_bignum2(&b, shared_secret);
84:
85: #ifdef DEBUG_KEXDH
86: buffer_dump(&b);
87: #endif
88: EVP_DigestInit(&md, evp_md);
89: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
90: EVP_DigestFinal(&md, digest, NULL);
91:
92: buffer_free(&b);
93:
94: #ifdef DEBUG_KEXDH
1.9.2.1 ! jason 95: dump_digest("hash", digest, EVP_MD_size(evp_md));
1.1 markus 96: #endif
97: return digest;
98: }
99:
100: /* client */
101:
1.8 itojun 102: static void
1.1 markus 103: kexgex_client(Kex *kex)
104: {
1.2 markus 105: BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
106: BIGNUM *p = NULL, *g = NULL;
107: Key *server_host_key;
108: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
109: u_int klen, kout, slen, sbloblen;
1.9.2.1 ! jason 110: int min, max, nbits;
1.2 markus 111: DH *dh;
1.1 markus 112:
1.2 markus 113: nbits = dh_estimate(kex->we_need * 8);
1.1 markus 114:
115: if (datafellows & SSH_OLD_DHGEX) {
116: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
117:
118: /* Old GEX request */
119: packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
1.2 markus 120: packet_put_int(nbits);
121: min = DH_GRP_MIN;
122: max = DH_GRP_MAX;
1.1 markus 123: } else {
124: debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
125:
126: /* New GEX request */
1.2 markus 127: min = DH_GRP_MIN;
128: max = DH_GRP_MAX;
1.1 markus 129: packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
1.2 markus 130: packet_put_int(min);
131: packet_put_int(nbits);
132: packet_put_int(max);
1.1 markus 133: }
134: #ifdef DEBUG_KEXDH
135: fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
1.2 markus 136: min, nbits, max);
1.1 markus 137: #endif
138: packet_send();
139:
1.2 markus 140: debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
1.9.2.1 ! jason 141: packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
1.1 markus 142:
143: if ((p = BN_new()) == NULL)
144: fatal("BN_new");
1.9.2.1 ! jason 145: packet_get_bignum2(p);
1.1 markus 146: if ((g = BN_new()) == NULL)
147: fatal("BN_new");
1.9.2.1 ! jason 148: packet_get_bignum2(g);
! 149: packet_check_eom();
1.1 markus 150:
1.2 markus 151: if (BN_num_bits(p) < min || BN_num_bits(p) > max)
1.1 markus 152: fatal("DH_GEX group out of range: %d !< %d !< %d",
1.2 markus 153: min, BN_num_bits(p), max);
1.1 markus 154:
155: dh = dh_new_group(g, p);
156: dh_gen_key(dh, kex->we_need * 8);
157:
158: #ifdef DEBUG_KEXDH
159: DHparams_print_fp(stderr, dh);
160: fprintf(stderr, "pub= ");
161: BN_print_fp(stderr, dh->pub_key);
162: fprintf(stderr, "\n");
163: #endif
164:
165: debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
166: /* generate and send 'e', client DH public key */
167: packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
168: packet_put_bignum2(dh->pub_key);
169: packet_send();
170:
1.2 markus 171: debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
1.9.2.1 ! jason 172: packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
1.1 markus 173:
174: /* key, cert */
175: server_host_key_blob = packet_get_string(&sbloblen);
176: server_host_key = key_from_blob(server_host_key_blob, sbloblen);
177: if (server_host_key == NULL)
178: fatal("cannot decode server_host_key_blob");
1.9.2.1 ! jason 179: if (server_host_key->type != kex->hostkey_type)
! 180: fatal("type mismatch for decoded server_host_key_blob");
1.7 markus 181: if (kex->verify_host_key == NULL)
182: fatal("cannot verify server_host_key");
183: if (kex->verify_host_key(server_host_key) == -1)
184: fatal("server_host_key verification failed");
1.1 markus 185:
186: /* DH paramter f, server public DH key */
1.9.2.1 ! jason 187: if ((dh_server_pub = BN_new()) == NULL)
1.1 markus 188: fatal("dh_server_pub == NULL");
1.9.2.1 ! jason 189: packet_get_bignum2(dh_server_pub);
1.1 markus 190:
191: #ifdef DEBUG_KEXDH
192: fprintf(stderr, "dh_server_pub= ");
193: BN_print_fp(stderr, dh_server_pub);
194: fprintf(stderr, "\n");
195: debug("bits %d", BN_num_bits(dh_server_pub));
196: #endif
197:
198: /* signed H */
199: signature = packet_get_string(&slen);
1.9.2.1 ! jason 200: packet_check_eom();
1.1 markus 201:
202: if (!dh_pub_is_valid(dh, dh_server_pub))
203: packet_disconnect("bad server public DH value");
204:
205: klen = DH_size(dh);
206: kbuf = xmalloc(klen);
207: kout = DH_compute_key(kbuf, dh_server_pub, dh);
208: #ifdef DEBUG_KEXDH
1.5 markus 209: dump_digest("shared secret", kbuf, kout);
1.1 markus 210: #endif
1.9.2.1 ! jason 211: if ((shared_secret = BN_new()) == NULL)
! 212: fatal("kexgex_client: BN_new failed");
1.1 markus 213: BN_bin2bn(kbuf, kout, shared_secret);
214: memset(kbuf, 0, klen);
215: xfree(kbuf);
216:
1.2 markus 217: if (datafellows & SSH_OLD_DHGEX)
1.1 markus 218: min = max = -1;
219:
220: /* calc and verify H */
221: hash = kexgex_hash(
222: kex->client_version_string,
223: kex->server_version_string,
224: buffer_ptr(&kex->my), buffer_len(&kex->my),
225: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
226: server_host_key_blob, sbloblen,
1.2 markus 227: min, nbits, max,
1.1 markus 228: dh->p, dh->g,
229: dh->pub_key,
230: dh_server_pub,
231: shared_secret
232: );
1.3 markus 233: /* have keys, free DH */
234: DH_free(dh);
1.1 markus 235: xfree(server_host_key_blob);
1.9.2.1 ! jason 236: BN_clear_free(dh_server_pub);
1.1 markus 237:
1.9 stevesk 238: if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
1.1 markus 239: fatal("key_verify failed for server_host_key");
240: key_free(server_host_key);
241: xfree(signature);
242:
1.2 markus 243: /* save session id */
244: if (kex->session_id == NULL) {
245: kex->session_id_len = 20;
246: kex->session_id = xmalloc(kex->session_id_len);
247: memcpy(kex->session_id, hash, kex->session_id_len);
248: }
1.1 markus 249: kex_derive_keys(kex, hash, shared_secret);
250: BN_clear_free(shared_secret);
251:
1.3 markus 252: kex_finish(kex);
1.1 markus 253: }
254:
255: /* server */
256:
1.8 itojun 257: static void
1.1 markus 258: kexgex_server(Kex *kex)
259: {
1.2 markus 260: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
261: Key *server_host_key;
262: DH *dh = dh;
263: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
1.9.2.1 ! jason 264: u_int sbloblen, klen, kout, slen;
! 265: int min = -1, max = -1, nbits = -1, type;
1.1 markus 266:
1.2 markus 267: if (kex->load_host_key == NULL)
268: fatal("Cannot load hostkey");
269: server_host_key = kex->load_host_key(kex->hostkey_type);
270: if (server_host_key == NULL)
271: fatal("Unsupported hostkey type %d", kex->hostkey_type);
1.1 markus 272:
1.9.2.1 ! jason 273: type = packet_read();
! 274: switch (type) {
1.1 markus 275: case SSH2_MSG_KEX_DH_GEX_REQUEST:
276: debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
277: min = packet_get_int();
1.2 markus 278: nbits = packet_get_int();
1.1 markus 279: max = packet_get_int();
280: min = MAX(DH_GRP_MIN, min);
281: max = MIN(DH_GRP_MAX, max);
282: break;
283: case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
284: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
1.2 markus 285: nbits = packet_get_int();
1.1 markus 286: min = DH_GRP_MIN;
287: max = DH_GRP_MAX;
288: /* unused for old GEX */
289: break;
1.2 markus 290: default:
1.4 markus 291: fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
1.1 markus 292: }
1.9.2.1 ! jason 293: packet_check_eom();
1.1 markus 294:
1.2 markus 295: if (max < min || nbits < min || max < nbits)
1.1 markus 296: fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
1.2 markus 297: min, nbits, max);
1.1 markus 298:
1.2 markus 299: dh = choose_dh(min, nbits, max);
300: if (dh == NULL)
1.1 markus 301: packet_disconnect("Protocol error: no matching DH grp found");
302:
303: debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
304: packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
1.2 markus 305: packet_put_bignum2(dh->p);
306: packet_put_bignum2(dh->g);
1.1 markus 307: packet_send();
308:
309: /* flush */
310: packet_write_wait();
311:
312: /* Compute our exchange value in parallel with the client */
1.2 markus 313: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 314:
1.2 markus 315: debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
1.9.2.1 ! jason 316: packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
1.1 markus 317:
318: /* key, cert */
1.9.2.1 ! jason 319: if ((dh_client_pub = BN_new()) == NULL)
1.1 markus 320: fatal("dh_client_pub == NULL");
1.9.2.1 ! jason 321: packet_get_bignum2(dh_client_pub);
! 322: packet_check_eom();
1.1 markus 323:
324: #ifdef DEBUG_KEXDH
325: fprintf(stderr, "dh_client_pub= ");
326: BN_print_fp(stderr, dh_client_pub);
327: fprintf(stderr, "\n");
328: debug("bits %d", BN_num_bits(dh_client_pub));
329: #endif
330:
331: #ifdef DEBUG_KEXDH
332: DHparams_print_fp(stderr, dh);
333: fprintf(stderr, "pub= ");
334: BN_print_fp(stderr, dh->pub_key);
335: fprintf(stderr, "\n");
336: #endif
337: if (!dh_pub_is_valid(dh, dh_client_pub))
338: packet_disconnect("bad client public DH value");
339:
340: klen = DH_size(dh);
341: kbuf = xmalloc(klen);
342: kout = DH_compute_key(kbuf, dh_client_pub, dh);
343: #ifdef DEBUG_KEXDH
1.5 markus 344: dump_digest("shared secret", kbuf, kout);
1.1 markus 345: #endif
1.9.2.1 ! jason 346: if ((shared_secret = BN_new()) == NULL)
! 347: fatal("kexgex_server: BN_new failed");
1.1 markus 348: BN_bin2bn(kbuf, kout, shared_secret);
349: memset(kbuf, 0, klen);
350: xfree(kbuf);
351:
352: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
353:
1.2 markus 354: if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
355: min = max = -1;
356:
1.1 markus 357: /* calc H */ /* XXX depends on 'kex' */
358: hash = kexgex_hash(
359: kex->client_version_string,
360: kex->server_version_string,
361: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
362: buffer_ptr(&kex->my), buffer_len(&kex->my),
1.9 stevesk 363: server_host_key_blob, sbloblen,
1.2 markus 364: min, nbits, max,
1.1 markus 365: dh->p, dh->g,
366: dh_client_pub,
367: dh->pub_key,
368: shared_secret
369: );
1.9.2.1 ! jason 370: BN_clear_free(dh_client_pub);
1.1 markus 371:
372: /* save session id := H */
373: /* XXX hashlen depends on KEX */
1.2 markus 374: if (kex->session_id == NULL) {
375: kex->session_id_len = 20;
376: kex->session_id = xmalloc(kex->session_id_len);
377: memcpy(kex->session_id, hash, kex->session_id_len);
378: }
1.1 markus 379:
380: /* sign H */
381: /* XXX hashlen depends on KEX */
382: key_sign(server_host_key, &signature, &slen, hash, 20);
383:
384: /* destroy_sensitive_data(); */
385:
386: /* send server hostkey, DH pubkey 'f' and singed H */
387: debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
388: packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
1.9 stevesk 389: packet_put_string(server_host_key_blob, sbloblen);
1.1 markus 390: packet_put_bignum2(dh->pub_key); /* f */
1.9 stevesk 391: packet_put_string(signature, slen);
1.1 markus 392: packet_send();
393: xfree(signature);
394: xfree(server_host_key_blob);
1.3 markus 395: /* have keys, free DH */
396: DH_free(dh);
1.1 markus 397:
398: kex_derive_keys(kex, hash, shared_secret);
399: BN_clear_free(shared_secret);
400:
1.3 markus 401: kex_finish(kex);
1.1 markus 402: }
403:
404: void
405: kexgex(Kex *kex)
406: {
407: if (kex->server)
408: kexgex_server(kex);
409: else
410: kexgex_client(kex);
411: }
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