Annotation of src/usr.bin/ssh/kexgex.c, Revision 1.8
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"
1.8 ! itojun 27: RCSID("$OpenBSD: kexgex.c,v 1.7 2001/06/23 02:34:29 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,
48: char *serverhostkeyblob, int sbloblen,
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];
56: EVP_MD *evp_md = EVP_sha1();
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
95: dump_digest("hash", digest, evp_md->md_size);
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;
110: int dlen, plen, min, max, nbits;
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");
141: packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_GROUP);
1.1 markus 142:
143: if ((p = BN_new()) == NULL)
144: fatal("BN_new");
145: packet_get_bignum2(p, &dlen);
146: if ((g = BN_new()) == NULL)
147: fatal("BN_new");
148: packet_get_bignum2(g, &dlen);
1.2 markus 149: packet_done();
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");
172: packet_read_expect(&plen, 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");
179:
1.7 markus 180: if (kex->verify_host_key == NULL)
181: fatal("cannot verify server_host_key");
182: if (kex->verify_host_key(server_host_key) == -1)
183: fatal("server_host_key verification failed");
1.1 markus 184:
185: /* DH paramter f, server public DH key */
186: dh_server_pub = BN_new();
187: if (dh_server_pub == NULL)
188: fatal("dh_server_pub == NULL");
189: packet_get_bignum2(dh_server_pub, &dlen);
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);
200: packet_done();
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
211: shared_secret = BN_new();
212: BN_bin2bn(kbuf, kout, shared_secret);
213: memset(kbuf, 0, klen);
214: xfree(kbuf);
215:
1.2 markus 216: if (datafellows & SSH_OLD_DHGEX)
1.1 markus 217: min = max = -1;
218:
219: /* calc and verify H */
220: hash = kexgex_hash(
221: kex->client_version_string,
222: kex->server_version_string,
223: buffer_ptr(&kex->my), buffer_len(&kex->my),
224: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
225: server_host_key_blob, sbloblen,
1.2 markus 226: min, nbits, max,
1.1 markus 227: dh->p, dh->g,
228: dh->pub_key,
229: dh_server_pub,
230: shared_secret
231: );
1.3 markus 232: /* have keys, free DH */
233: DH_free(dh);
1.1 markus 234: xfree(server_host_key_blob);
235: BN_free(dh_server_pub);
236:
237: if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1)
238: fatal("key_verify failed for server_host_key");
239: key_free(server_host_key);
240: xfree(signature);
241:
1.2 markus 242: /* save session id */
243: if (kex->session_id == NULL) {
244: kex->session_id_len = 20;
245: kex->session_id = xmalloc(kex->session_id_len);
246: memcpy(kex->session_id, hash, kex->session_id_len);
247: }
1.1 markus 248: kex_derive_keys(kex, hash, shared_secret);
249: BN_clear_free(shared_secret);
250:
1.3 markus 251: kex_finish(kex);
1.1 markus 252: }
253:
254: /* server */
255:
1.8 ! itojun 256: static void
1.1 markus 257: kexgex_server(Kex *kex)
258: {
1.2 markus 259: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
260: Key *server_host_key;
261: DH *dh = dh;
262: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
263: u_int sbloblen, klen, kout;
264: int min = -1, max = -1, nbits = -1, type, plen, dlen, slen;
1.1 markus 265:
1.2 markus 266: if (kex->load_host_key == NULL)
267: fatal("Cannot load hostkey");
268: server_host_key = kex->load_host_key(kex->hostkey_type);
269: if (server_host_key == NULL)
270: fatal("Unsupported hostkey type %d", kex->hostkey_type);
1.1 markus 271:
1.2 markus 272: type = packet_read(&plen);
1.1 markus 273: switch(type){
274: case SSH2_MSG_KEX_DH_GEX_REQUEST:
275: debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
276: min = packet_get_int();
1.2 markus 277: nbits = packet_get_int();
1.1 markus 278: max = packet_get_int();
279: min = MAX(DH_GRP_MIN, min);
280: max = MIN(DH_GRP_MAX, max);
281: break;
282: case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
283: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
1.2 markus 284: nbits = packet_get_int();
1.1 markus 285: min = DH_GRP_MIN;
286: max = DH_GRP_MAX;
287: /* unused for old GEX */
288: break;
1.2 markus 289: default:
1.4 markus 290: fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
1.1 markus 291: }
292: packet_done();
293:
1.2 markus 294: if (max < min || nbits < min || max < nbits)
1.1 markus 295: fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
1.2 markus 296: min, nbits, max);
1.1 markus 297:
1.2 markus 298: dh = choose_dh(min, nbits, max);
299: if (dh == NULL)
1.1 markus 300: packet_disconnect("Protocol error: no matching DH grp found");
301:
302: debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
303: packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
1.2 markus 304: packet_put_bignum2(dh->p);
305: packet_put_bignum2(dh->g);
1.1 markus 306: packet_send();
307:
308: /* flush */
309: packet_write_wait();
310:
311: /* Compute our exchange value in parallel with the client */
1.2 markus 312: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 313:
1.2 markus 314: debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
315: packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT);
1.1 markus 316:
317: /* key, cert */
318: dh_client_pub = BN_new();
319: if (dh_client_pub == NULL)
320: fatal("dh_client_pub == NULL");
321: packet_get_bignum2(dh_client_pub, &dlen);
322:
323: #ifdef DEBUG_KEXDH
324: fprintf(stderr, "dh_client_pub= ");
325: BN_print_fp(stderr, dh_client_pub);
326: fprintf(stderr, "\n");
327: debug("bits %d", BN_num_bits(dh_client_pub));
328: #endif
329:
330: #ifdef DEBUG_KEXDH
331: DHparams_print_fp(stderr, dh);
332: fprintf(stderr, "pub= ");
333: BN_print_fp(stderr, dh->pub_key);
334: fprintf(stderr, "\n");
335: #endif
336: if (!dh_pub_is_valid(dh, dh_client_pub))
337: packet_disconnect("bad client public DH value");
338:
339: klen = DH_size(dh);
340: kbuf = xmalloc(klen);
341: kout = DH_compute_key(kbuf, dh_client_pub, dh);
342: #ifdef DEBUG_KEXDH
1.5 markus 343: dump_digest("shared secret", kbuf, kout);
1.1 markus 344: #endif
345: shared_secret = BN_new();
346: BN_bin2bn(kbuf, kout, shared_secret);
347: memset(kbuf, 0, klen);
348: xfree(kbuf);
349:
350: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
351:
1.2 markus 352: if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
353: min = max = -1;
354:
1.1 markus 355: /* calc H */ /* XXX depends on 'kex' */
356: hash = kexgex_hash(
357: kex->client_version_string,
358: kex->server_version_string,
359: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
360: buffer_ptr(&kex->my), buffer_len(&kex->my),
361: (char *)server_host_key_blob, sbloblen,
1.2 markus 362: min, nbits, max,
1.1 markus 363: dh->p, dh->g,
364: dh_client_pub,
365: dh->pub_key,
366: shared_secret
367: );
368: BN_free(dh_client_pub);
369:
370: /* save session id := H */
371: /* XXX hashlen depends on KEX */
1.2 markus 372: if (kex->session_id == NULL) {
373: kex->session_id_len = 20;
374: kex->session_id = xmalloc(kex->session_id_len);
375: memcpy(kex->session_id, hash, kex->session_id_len);
376: }
1.1 markus 377:
378: /* sign H */
379: /* XXX hashlen depends on KEX */
380: key_sign(server_host_key, &signature, &slen, hash, 20);
381:
382: /* destroy_sensitive_data(); */
383:
384: /* send server hostkey, DH pubkey 'f' and singed H */
385: debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
386: packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
387: packet_put_string((char *)server_host_key_blob, sbloblen);
388: packet_put_bignum2(dh->pub_key); /* f */
389: packet_put_string((char *)signature, slen);
390: packet_send();
391: xfree(signature);
392: xfree(server_host_key_blob);
1.3 markus 393: /* have keys, free DH */
394: DH_free(dh);
1.1 markus 395:
396: kex_derive_keys(kex, hash, shared_secret);
397: BN_clear_free(shared_secret);
398:
1.3 markus 399: kex_finish(kex);
1.1 markus 400: }
401:
402: void
403: kexgex(Kex *kex)
404: {
405: if (kex->server)
406: kexgex_server(kex);
407: else
408: kexgex_client(kex);
409: }
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