Annotation of src/usr.bin/ssh/kexgex.c, Revision 1.2
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"
1.2 ! markus 27: RCSID("$OpenBSD: kexgex.c,v 1.1 2001/04/03 19:53:29 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:
42: u_char *
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);
60: buffer_put_string(&b, client_version_string, strlen(client_version_string));
61: buffer_put_string(&b, server_version_string, strlen(server_version_string));
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);
72: if (min == -1 || max == -1)
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:
102: void
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:
180: if (kex->check_host_key == NULL)
181: fatal("cannot check server_host_key");
182: kex->check_host_key(server_host_key);
183:
184: /* DH paramter f, server public DH key */
185: dh_server_pub = BN_new();
186: if (dh_server_pub == NULL)
187: fatal("dh_server_pub == NULL");
188: packet_get_bignum2(dh_server_pub, &dlen);
189:
190: #ifdef DEBUG_KEXDH
191: fprintf(stderr, "dh_server_pub= ");
192: BN_print_fp(stderr, dh_server_pub);
193: fprintf(stderr, "\n");
194: debug("bits %d", BN_num_bits(dh_server_pub));
195: #endif
196:
197: /* signed H */
198: signature = packet_get_string(&slen);
199: packet_done();
200:
201: if (!dh_pub_is_valid(dh, dh_server_pub))
202: packet_disconnect("bad server public DH value");
203:
204: klen = DH_size(dh);
205: kbuf = xmalloc(klen);
206: kout = DH_compute_key(kbuf, dh_server_pub, dh);
207: #ifdef DEBUG_KEXDH
208: dump_digest("shared secret", kbuf, kout);
209: #endif
210: shared_secret = BN_new();
211: BN_bin2bn(kbuf, kout, shared_secret);
212: memset(kbuf, 0, klen);
213: xfree(kbuf);
214:
1.2 ! markus 215: if (datafellows & SSH_OLD_DHGEX)
1.1 markus 216: min = max = -1;
217:
218: /* calc and verify H */
219: hash = kexgex_hash(
220: kex->client_version_string,
221: kex->server_version_string,
222: buffer_ptr(&kex->my), buffer_len(&kex->my),
223: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
224: server_host_key_blob, sbloblen,
1.2 ! markus 225: min, nbits, max,
1.1 markus 226: dh->p, dh->g,
227: dh->pub_key,
228: dh_server_pub,
229: shared_secret
230: );
231: xfree(server_host_key_blob);
232: BN_free(dh_server_pub);
233:
234: if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1)
235: fatal("key_verify failed for server_host_key");
236: key_free(server_host_key);
237: xfree(signature);
238:
1.2 ! markus 239: /* save session id */
! 240: if (kex->session_id == NULL) {
! 241: kex->session_id_len = 20;
! 242: kex->session_id = xmalloc(kex->session_id_len);
! 243: memcpy(kex->session_id, hash, kex->session_id_len);
! 244: }
! 245:
1.1 markus 246: kex_derive_keys(kex, hash, shared_secret);
247: BN_clear_free(shared_secret);
248:
249: kex_send_newkeys();
250:
251: /* have keys, free DH */
252: DH_free(dh);
253: }
254:
255: /* server */
256:
257: void
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;
! 264: u_int sbloblen, klen, kout;
! 265: int min = -1, max = -1, nbits = -1, type, plen, dlen, slen;
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:
1.2 ! markus 273: type = packet_read(&plen);
1.1 markus 274: switch(type){
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:
! 291: fatal("protocol error during kex, no DH_GEX_REQUEST");
1.1 markus 292: }
293: packet_done();
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");
! 316: packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT);
1.1 markus 317:
318: /* key, cert */
319: dh_client_pub = BN_new();
320: if (dh_client_pub == NULL)
321: fatal("dh_client_pub == NULL");
322: packet_get_bignum2(dh_client_pub, &dlen);
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
344: dump_digest("shared secret", kbuf, kout);
345: #endif
346: shared_secret = BN_new();
347: BN_bin2bn(kbuf, kout, shared_secret);
348: memset(kbuf, 0, klen);
349: xfree(kbuf);
350:
351: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
352:
1.2 ! markus 353: if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
! 354: min = max = -1;
! 355:
1.1 markus 356: /* calc H */ /* XXX depends on 'kex' */
357: hash = kexgex_hash(
358: kex->client_version_string,
359: kex->server_version_string,
360: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
361: buffer_ptr(&kex->my), buffer_len(&kex->my),
362: (char *)server_host_key_blob, sbloblen,
1.2 ! markus 363: min, nbits, max,
1.1 markus 364: dh->p, dh->g,
365: dh_client_pub,
366: dh->pub_key,
367: shared_secret
368: );
369: BN_free(dh_client_pub);
370:
371: /* save session id := H */
372: /* XXX hashlen depends on KEX */
1.2 ! markus 373: if (kex->session_id == NULL) {
! 374: kex->session_id_len = 20;
! 375: kex->session_id = xmalloc(kex->session_id_len);
! 376: memcpy(kex->session_id, hash, kex->session_id_len);
! 377: }
1.1 markus 378:
379: /* sign H */
380: /* XXX hashlen depends on KEX */
381: key_sign(server_host_key, &signature, &slen, hash, 20);
382:
383: /* destroy_sensitive_data(); */
384:
385: /* send server hostkey, DH pubkey 'f' and singed H */
386: debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
387: packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
388: packet_put_string((char *)server_host_key_blob, sbloblen);
389: packet_put_bignum2(dh->pub_key); /* f */
390: packet_put_string((char *)signature, slen);
391: packet_send();
392: xfree(signature);
393: xfree(server_host_key_blob);
394:
395: kex_derive_keys(kex, hash, shared_secret);
396: BN_clear_free(shared_secret);
397:
398: kex_send_newkeys();
399:
400: /* have keys, free DH */
401: DH_free(dh);
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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