Annotation of src/usr.bin/ssh/kexgex.c, Revision 1.5.2.3
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"
1.5.2.3 ! miod 27: RCSID("$OpenBSD: kexgex.c,v 1.22 2002/03/24 17:27:03 stevesk 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"
1.5.2.3 ! miod 41: #include "monitor_wrap.h"
1.1 markus 42:
1.5.2.1 jason 43: static u_char *
1.1 markus 44: kexgex_hash(
45: char *client_version_string,
46: char *server_version_string,
47: char *ckexinit, int ckexinitlen,
48: char *skexinit, int skexinitlen,
1.5.2.1 jason 49: u_char *serverhostkeyblob, int sbloblen,
1.1 markus 50: int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen,
51: BIGNUM *client_dh_pub,
52: BIGNUM *server_dh_pub,
53: BIGNUM *shared_secret)
54: {
55: Buffer b;
56: static u_char digest[EVP_MAX_MD_SIZE];
1.5.2.2 miod 57: const EVP_MD *evp_md = EVP_sha1();
1.1 markus 58: EVP_MD_CTX md;
59:
60: buffer_init(&b);
1.5.2.1 jason 61: buffer_put_cstring(&b, client_version_string);
62: buffer_put_cstring(&b, server_version_string);
1.1 markus 63:
64: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
65: buffer_put_int(&b, ckexinitlen+1);
66: buffer_put_char(&b, SSH2_MSG_KEXINIT);
67: buffer_append(&b, ckexinit, ckexinitlen);
68: buffer_put_int(&b, skexinitlen+1);
69: buffer_put_char(&b, SSH2_MSG_KEXINIT);
70: buffer_append(&b, skexinit, skexinitlen);
71:
72: buffer_put_string(&b, serverhostkeyblob, sbloblen);
1.5 markus 73: if (min == -1 || max == -1)
1.1 markus 74: buffer_put_int(&b, wantbits);
75: else {
76: buffer_put_int(&b, min);
77: buffer_put_int(&b, wantbits);
78: buffer_put_int(&b, max);
79: }
80: buffer_put_bignum2(&b, prime);
81: buffer_put_bignum2(&b, gen);
82: buffer_put_bignum2(&b, client_dh_pub);
83: buffer_put_bignum2(&b, server_dh_pub);
84: buffer_put_bignum2(&b, shared_secret);
85:
86: #ifdef DEBUG_KEXDH
87: buffer_dump(&b);
88: #endif
89: EVP_DigestInit(&md, evp_md);
90: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
91: EVP_DigestFinal(&md, digest, NULL);
92:
93: buffer_free(&b);
94:
95: #ifdef DEBUG_KEXDH
1.5.2.2 miod 96: dump_digest("hash", digest, EVP_MD_size(evp_md));
1.1 markus 97: #endif
98: return digest;
99: }
100:
101: /* client */
102:
1.5.2.1 jason 103: static void
1.1 markus 104: kexgex_client(Kex *kex)
105: {
1.2 markus 106: BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
107: BIGNUM *p = NULL, *g = NULL;
108: Key *server_host_key;
109: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
110: u_int klen, kout, slen, sbloblen;
1.5.2.2 miod 111: int min, max, nbits;
1.2 markus 112: DH *dh;
1.1 markus 113:
1.2 markus 114: nbits = dh_estimate(kex->we_need * 8);
1.1 markus 115:
116: if (datafellows & SSH_OLD_DHGEX) {
117: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
118:
119: /* Old GEX request */
120: packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
1.2 markus 121: packet_put_int(nbits);
122: min = DH_GRP_MIN;
123: max = DH_GRP_MAX;
1.1 markus 124: } else {
125: debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
126:
127: /* New GEX request */
1.2 markus 128: min = DH_GRP_MIN;
129: max = DH_GRP_MAX;
1.1 markus 130: packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
1.2 markus 131: packet_put_int(min);
132: packet_put_int(nbits);
133: packet_put_int(max);
1.1 markus 134: }
135: #ifdef DEBUG_KEXDH
136: fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
1.2 markus 137: min, nbits, max);
1.1 markus 138: #endif
139: packet_send();
140:
1.2 markus 141: debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
1.5.2.2 miod 142: packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
1.1 markus 143:
144: if ((p = BN_new()) == NULL)
145: fatal("BN_new");
1.5.2.2 miod 146: packet_get_bignum2(p);
1.1 markus 147: if ((g = BN_new()) == NULL)
148: fatal("BN_new");
1.5.2.2 miod 149: packet_get_bignum2(g);
150: packet_check_eom();
1.1 markus 151:
1.2 markus 152: if (BN_num_bits(p) < min || BN_num_bits(p) > max)
1.1 markus 153: fatal("DH_GEX group out of range: %d !< %d !< %d",
1.2 markus 154: min, BN_num_bits(p), max);
1.1 markus 155:
156: dh = dh_new_group(g, p);
157: dh_gen_key(dh, kex->we_need * 8);
158:
159: #ifdef DEBUG_KEXDH
160: DHparams_print_fp(stderr, dh);
161: fprintf(stderr, "pub= ");
162: BN_print_fp(stderr, dh->pub_key);
163: fprintf(stderr, "\n");
164: #endif
165:
166: debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
167: /* generate and send 'e', client DH public key */
168: packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
169: packet_put_bignum2(dh->pub_key);
170: packet_send();
171:
1.2 markus 172: debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
1.5.2.2 miod 173: packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
1.1 markus 174:
175: /* key, cert */
176: server_host_key_blob = packet_get_string(&sbloblen);
177: server_host_key = key_from_blob(server_host_key_blob, sbloblen);
178: if (server_host_key == NULL)
179: fatal("cannot decode server_host_key_blob");
1.5.2.2 miod 180: if (server_host_key->type != kex->hostkey_type)
181: fatal("type mismatch for decoded server_host_key_blob");
1.5.2.1 jason 182: if (kex->verify_host_key == NULL)
183: fatal("cannot verify server_host_key");
184: if (kex->verify_host_key(server_host_key) == -1)
185: fatal("server_host_key verification failed");
1.1 markus 186:
187: /* DH paramter f, server public DH key */
1.5.2.2 miod 188: if ((dh_server_pub = BN_new()) == NULL)
1.1 markus 189: fatal("dh_server_pub == NULL");
1.5.2.2 miod 190: packet_get_bignum2(dh_server_pub);
1.1 markus 191:
192: #ifdef DEBUG_KEXDH
193: fprintf(stderr, "dh_server_pub= ");
194: BN_print_fp(stderr, dh_server_pub);
195: fprintf(stderr, "\n");
196: debug("bits %d", BN_num_bits(dh_server_pub));
197: #endif
198:
199: /* signed H */
200: signature = packet_get_string(&slen);
1.5.2.2 miod 201: packet_check_eom();
1.1 markus 202:
203: if (!dh_pub_is_valid(dh, dh_server_pub))
204: packet_disconnect("bad server public DH value");
205:
206: klen = DH_size(dh);
207: kbuf = xmalloc(klen);
208: kout = DH_compute_key(kbuf, dh_server_pub, dh);
209: #ifdef DEBUG_KEXDH
1.5 markus 210: dump_digest("shared secret", kbuf, kout);
1.1 markus 211: #endif
1.5.2.2 miod 212: if ((shared_secret = BN_new()) == NULL)
213: fatal("kexgex_client: BN_new failed");
1.1 markus 214: BN_bin2bn(kbuf, kout, shared_secret);
215: memset(kbuf, 0, klen);
216: xfree(kbuf);
217:
1.2 markus 218: if (datafellows & SSH_OLD_DHGEX)
1.1 markus 219: min = max = -1;
220:
221: /* calc and verify H */
222: hash = kexgex_hash(
223: kex->client_version_string,
224: kex->server_version_string,
225: buffer_ptr(&kex->my), buffer_len(&kex->my),
226: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
227: server_host_key_blob, sbloblen,
1.2 markus 228: min, nbits, max,
1.1 markus 229: dh->p, dh->g,
230: dh->pub_key,
231: dh_server_pub,
232: shared_secret
233: );
1.3 markus 234: /* have keys, free DH */
235: DH_free(dh);
1.1 markus 236: xfree(server_host_key_blob);
1.5.2.2 miod 237: BN_clear_free(dh_server_pub);
1.1 markus 238:
1.5.2.1 jason 239: if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
1.1 markus 240: fatal("key_verify failed for server_host_key");
241: key_free(server_host_key);
242: xfree(signature);
243:
1.2 markus 244: /* save session id */
245: if (kex->session_id == NULL) {
246: kex->session_id_len = 20;
247: kex->session_id = xmalloc(kex->session_id_len);
248: memcpy(kex->session_id, hash, kex->session_id_len);
249: }
1.1 markus 250: kex_derive_keys(kex, hash, shared_secret);
251: BN_clear_free(shared_secret);
252:
1.3 markus 253: kex_finish(kex);
1.1 markus 254: }
255:
256: /* server */
257:
1.5.2.1 jason 258: static void
1.1 markus 259: kexgex_server(Kex *kex)
260: {
1.2 markus 261: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
262: Key *server_host_key;
1.5.2.3 ! miod 263: DH *dh;
1.2 markus 264: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
1.5.2.2 miod 265: u_int sbloblen, klen, kout, slen;
266: int min = -1, max = -1, nbits = -1, type;
1.1 markus 267:
1.2 markus 268: if (kex->load_host_key == NULL)
269: fatal("Cannot load hostkey");
270: server_host_key = kex->load_host_key(kex->hostkey_type);
271: if (server_host_key == NULL)
272: fatal("Unsupported hostkey type %d", kex->hostkey_type);
1.1 markus 273:
1.5.2.2 miod 274: type = packet_read();
275: switch (type) {
1.1 markus 276: case SSH2_MSG_KEX_DH_GEX_REQUEST:
277: debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
278: min = packet_get_int();
1.2 markus 279: nbits = packet_get_int();
1.1 markus 280: max = packet_get_int();
281: min = MAX(DH_GRP_MIN, min);
282: max = MIN(DH_GRP_MAX, max);
283: break;
284: case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
285: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
1.2 markus 286: nbits = packet_get_int();
1.1 markus 287: min = DH_GRP_MIN;
288: max = DH_GRP_MAX;
289: /* unused for old GEX */
290: break;
1.2 markus 291: default:
1.4 markus 292: fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
1.1 markus 293: }
1.5.2.2 miod 294: packet_check_eom();
1.1 markus 295:
1.2 markus 296: if (max < min || nbits < min || max < nbits)
1.1 markus 297: fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
1.2 markus 298: min, nbits, max);
1.1 markus 299:
1.5.2.3 ! miod 300: /* Contact privileged parent */
! 301: dh = PRIVSEP(choose_dh(min, nbits, max));
1.2 markus 302: if (dh == NULL)
1.1 markus 303: packet_disconnect("Protocol error: no matching DH grp found");
304:
305: debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
306: packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
1.2 markus 307: packet_put_bignum2(dh->p);
308: packet_put_bignum2(dh->g);
1.1 markus 309: packet_send();
310:
311: /* flush */
312: packet_write_wait();
313:
314: /* Compute our exchange value in parallel with the client */
1.2 markus 315: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 316:
1.2 markus 317: debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
1.5.2.2 miod 318: packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
1.1 markus 319:
320: /* key, cert */
1.5.2.2 miod 321: if ((dh_client_pub = BN_new()) == NULL)
1.1 markus 322: fatal("dh_client_pub == NULL");
1.5.2.2 miod 323: packet_get_bignum2(dh_client_pub);
324: packet_check_eom();
1.1 markus 325:
326: #ifdef DEBUG_KEXDH
327: fprintf(stderr, "dh_client_pub= ");
328: BN_print_fp(stderr, dh_client_pub);
329: fprintf(stderr, "\n");
330: debug("bits %d", BN_num_bits(dh_client_pub));
331: #endif
332:
333: #ifdef DEBUG_KEXDH
334: DHparams_print_fp(stderr, dh);
335: fprintf(stderr, "pub= ");
336: BN_print_fp(stderr, dh->pub_key);
337: fprintf(stderr, "\n");
338: #endif
339: if (!dh_pub_is_valid(dh, dh_client_pub))
340: packet_disconnect("bad client public DH value");
341:
342: klen = DH_size(dh);
343: kbuf = xmalloc(klen);
344: kout = DH_compute_key(kbuf, dh_client_pub, dh);
345: #ifdef DEBUG_KEXDH
1.5 markus 346: dump_digest("shared secret", kbuf, kout);
1.1 markus 347: #endif
1.5.2.2 miod 348: if ((shared_secret = BN_new()) == NULL)
349: fatal("kexgex_server: BN_new failed");
1.1 markus 350: BN_bin2bn(kbuf, kout, shared_secret);
351: memset(kbuf, 0, klen);
352: xfree(kbuf);
353:
354: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
355:
1.2 markus 356: if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
357: min = max = -1;
358:
1.1 markus 359: /* calc H */ /* XXX depends on 'kex' */
360: hash = kexgex_hash(
361: kex->client_version_string,
362: kex->server_version_string,
363: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
364: buffer_ptr(&kex->my), buffer_len(&kex->my),
1.5.2.1 jason 365: server_host_key_blob, sbloblen,
1.2 markus 366: min, nbits, max,
1.1 markus 367: dh->p, dh->g,
368: dh_client_pub,
369: dh->pub_key,
370: shared_secret
371: );
1.5.2.2 miod 372: BN_clear_free(dh_client_pub);
1.1 markus 373:
374: /* save session id := H */
375: /* XXX hashlen depends on KEX */
1.2 markus 376: if (kex->session_id == NULL) {
377: kex->session_id_len = 20;
378: kex->session_id = xmalloc(kex->session_id_len);
379: memcpy(kex->session_id, hash, kex->session_id_len);
380: }
1.1 markus 381:
382: /* sign H */
383: /* XXX hashlen depends on KEX */
1.5.2.3 ! miod 384: PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20));
1.1 markus 385:
386: /* destroy_sensitive_data(); */
387:
388: /* send server hostkey, DH pubkey 'f' and singed H */
389: debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
390: packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
1.5.2.1 jason 391: packet_put_string(server_host_key_blob, sbloblen);
1.1 markus 392: packet_put_bignum2(dh->pub_key); /* f */
1.5.2.1 jason 393: packet_put_string(signature, slen);
1.1 markus 394: packet_send();
1.5.2.3 ! miod 395:
1.1 markus 396: xfree(signature);
397: xfree(server_host_key_blob);
1.3 markus 398: /* have keys, free DH */
399: DH_free(dh);
1.1 markus 400:
401: kex_derive_keys(kex, hash, shared_secret);
402: BN_clear_free(shared_secret);
403:
1.3 markus 404: kex_finish(kex);
1.1 markus 405: }
406:
407: void
408: kexgex(Kex *kex)
409: {
410: if (kex->server)
411: kexgex_server(kex);
412: else
413: kexgex_client(kex);
414: }