Annotation of src/usr.bin/ssh/kexdh.c, Revision 1.13
1.1 markus 1: /*
2: * Copyright (c) 2001 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"
1.13 ! markus 26: RCSID("$OpenBSD: kexdh.c,v 1.12 2001/12/28 14:50:54 markus Exp $");
1.1 markus 27:
28: #include <openssl/crypto.h>
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:
1.6 itojun 41: static u_char *
1.1 markus 42: kex_dh_hash(
43: char *client_version_string,
44: char *server_version_string,
45: char *ckexinit, int ckexinitlen,
46: char *skexinit, int skexinitlen,
1.7 stevesk 47: u_char *serverhostkeyblob, int sbloblen,
1.1 markus 48: BIGNUM *client_dh_pub,
49: BIGNUM *server_dh_pub,
50: BIGNUM *shared_secret)
51: {
52: Buffer b;
53: static u_char digest[EVP_MAX_MD_SIZE];
54: EVP_MD *evp_md = EVP_sha1();
55: EVP_MD_CTX md;
56:
57: buffer_init(&b);
1.4 markus 58: buffer_put_cstring(&b, client_version_string);
59: buffer_put_cstring(&b, server_version_string);
1.1 markus 60:
61: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
62: buffer_put_int(&b, ckexinitlen+1);
63: buffer_put_char(&b, SSH2_MSG_KEXINIT);
64: buffer_append(&b, ckexinit, ckexinitlen);
65: buffer_put_int(&b, skexinitlen+1);
66: buffer_put_char(&b, SSH2_MSG_KEXINIT);
67: buffer_append(&b, skexinit, skexinitlen);
68:
69: buffer_put_string(&b, serverhostkeyblob, sbloblen);
70: buffer_put_bignum2(&b, client_dh_pub);
71: buffer_put_bignum2(&b, server_dh_pub);
72: buffer_put_bignum2(&b, shared_secret);
73:
74: #ifdef DEBUG_KEX
75: buffer_dump(&b);
76: #endif
77: EVP_DigestInit(&md, evp_md);
78: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
79: EVP_DigestFinal(&md, digest, NULL);
80:
81: buffer_free(&b);
82:
83: #ifdef DEBUG_KEX
1.13 ! markus 84: dump_digest("hash", digest, EVP_MD_size(evp_md));
1.1 markus 85: #endif
86: return digest;
87: }
88:
89: /* client */
90:
1.6 itojun 91: static void
1.1 markus 92: kexdh_client(Kex *kex)
93: {
1.2 markus 94: BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
95: DH *dh;
96: Key *server_host_key;
1.7 stevesk 97: u_char *server_host_key_blob = NULL, *signature = NULL;
1.2 markus 98: u_char *kbuf, *hash;
99: u_int klen, kout, slen, sbloblen;
1.1 markus 100:
101: /* generate and send 'e', client DH public key */
1.2 markus 102: dh = dh_new_group1();
103: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 104: packet_start(SSH2_MSG_KEXDH_INIT);
1.2 markus 105: packet_put_bignum2(dh->pub_key);
1.1 markus 106: packet_send();
107:
1.2 markus 108: debug("sending SSH2_MSG_KEXDH_INIT");
1.1 markus 109: #ifdef DEBUG_KEXDH
1.2 markus 110: DHparams_print_fp(stderr, dh);
1.1 markus 111: fprintf(stderr, "pub= ");
1.2 markus 112: BN_print_fp(stderr, dh->pub_key);
1.1 markus 113: fprintf(stderr, "\n");
114: #endif
115:
1.2 markus 116: debug("expecting SSH2_MSG_KEXDH_REPLY");
1.12 markus 117: packet_read_expect(SSH2_MSG_KEXDH_REPLY);
1.1 markus 118:
119: /* key, cert */
120: server_host_key_blob = packet_get_string(&sbloblen);
121: server_host_key = key_from_blob(server_host_key_blob, sbloblen);
122: if (server_host_key == NULL)
123: fatal("cannot decode server_host_key_blob");
124:
1.5 markus 125: if (kex->verify_host_key == NULL)
126: fatal("cannot verify server_host_key");
127: if (kex->verify_host_key(server_host_key) == -1)
128: fatal("server_host_key verification failed");
1.1 markus 129:
130: /* DH paramter f, server public DH key */
1.8 markus 131: if ((dh_server_pub = BN_new()) == NULL)
1.1 markus 132: fatal("dh_server_pub == NULL");
1.11 markus 133: packet_get_bignum2(dh_server_pub);
1.1 markus 134:
135: #ifdef DEBUG_KEXDH
136: fprintf(stderr, "dh_server_pub= ");
137: BN_print_fp(stderr, dh_server_pub);
138: fprintf(stderr, "\n");
139: debug("bits %d", BN_num_bits(dh_server_pub));
140: #endif
141:
142: /* signed H */
143: signature = packet_get_string(&slen);
1.10 markus 144: packet_check_eom();
1.1 markus 145:
1.2 markus 146: if (!dh_pub_is_valid(dh, dh_server_pub))
1.1 markus 147: packet_disconnect("bad server public DH value");
148:
1.2 markus 149: klen = DH_size(dh);
1.1 markus 150: kbuf = xmalloc(klen);
1.2 markus 151: kout = DH_compute_key(kbuf, dh_server_pub, dh);
1.1 markus 152: #ifdef DEBUG_KEXDH
153: dump_digest("shared secret", kbuf, kout);
154: #endif
1.8 markus 155: if ((shared_secret = BN_new()) == NULL)
156: fatal("kexdh_client: BN_new failed");
1.1 markus 157: BN_bin2bn(kbuf, kout, shared_secret);
158: memset(kbuf, 0, klen);
159: xfree(kbuf);
160:
161: /* calc and verify H */
162: hash = kex_dh_hash(
163: kex->client_version_string,
164: kex->server_version_string,
165: buffer_ptr(&kex->my), buffer_len(&kex->my),
166: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
167: server_host_key_blob, sbloblen,
1.2 markus 168: dh->pub_key,
1.1 markus 169: dh_server_pub,
170: shared_secret
171: );
172: xfree(server_host_key_blob);
1.9 markus 173: BN_clear_free(dh_server_pub);
1.2 markus 174: DH_free(dh);
1.1 markus 175:
1.7 stevesk 176: if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
1.1 markus 177: fatal("key_verify failed for server_host_key");
178: key_free(server_host_key);
179: xfree(signature);
180:
1.2 markus 181: /* save session id */
182: if (kex->session_id == NULL) {
183: kex->session_id_len = 20;
184: kex->session_id = xmalloc(kex->session_id_len);
185: memcpy(kex->session_id, hash, kex->session_id_len);
186: }
187:
1.1 markus 188: kex_derive_keys(kex, hash, shared_secret);
189: BN_clear_free(shared_secret);
1.3 markus 190: kex_finish(kex);
1.1 markus 191: }
192:
193: /* server */
194:
1.6 itojun 195: static void
1.1 markus 196: kexdh_server(Kex *kex)
197: {
198: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
1.2 markus 199: DH *dh;
1.1 markus 200: Key *server_host_key;
201: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
202: u_int sbloblen, klen, kout;
1.12 markus 203: int slen;
1.2 markus 204:
205: /* generate server DH public key */
206: dh = dh_new_group1();
207: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 208:
1.2 markus 209: debug("expecting SSH2_MSG_KEXDH_INIT");
1.12 markus 210: packet_read_expect(SSH2_MSG_KEXDH_INIT);
1.1 markus 211:
212: if (kex->load_host_key == NULL)
213: fatal("Cannot load hostkey");
214: server_host_key = kex->load_host_key(kex->hostkey_type);
215: if (server_host_key == NULL)
216: fatal("Unsupported hostkey type %d", kex->hostkey_type);
217:
218: /* key, cert */
1.8 markus 219: if ((dh_client_pub = BN_new()) == NULL)
1.1 markus 220: fatal("dh_client_pub == NULL");
1.11 markus 221: packet_get_bignum2(dh_client_pub);
1.1 markus 222:
223: #ifdef DEBUG_KEXDH
224: fprintf(stderr, "dh_client_pub= ");
225: BN_print_fp(stderr, dh_client_pub);
226: fprintf(stderr, "\n");
227: debug("bits %d", BN_num_bits(dh_client_pub));
228: #endif
229:
230: #ifdef DEBUG_KEXDH
231: DHparams_print_fp(stderr, dh);
232: fprintf(stderr, "pub= ");
233: BN_print_fp(stderr, dh->pub_key);
234: fprintf(stderr, "\n");
235: #endif
236: if (!dh_pub_is_valid(dh, dh_client_pub))
237: packet_disconnect("bad client public DH value");
238:
239: klen = DH_size(dh);
240: kbuf = xmalloc(klen);
241: kout = DH_compute_key(kbuf, dh_client_pub, dh);
242: #ifdef DEBUG_KEXDH
243: dump_digest("shared secret", kbuf, kout);
244: #endif
1.8 markus 245: if ((shared_secret = BN_new()) == NULL)
246: fatal("kexdh_server: BN_new failed");
1.1 markus 247: BN_bin2bn(kbuf, kout, shared_secret);
248: memset(kbuf, 0, klen);
249: xfree(kbuf);
250:
251: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
252:
253: /* calc H */
254: hash = kex_dh_hash(
255: kex->client_version_string,
256: kex->server_version_string,
257: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
258: buffer_ptr(&kex->my), buffer_len(&kex->my),
1.7 stevesk 259: server_host_key_blob, sbloblen,
1.1 markus 260: dh_client_pub,
261: dh->pub_key,
262: shared_secret
263: );
1.9 markus 264: BN_clear_free(dh_client_pub);
1.1 markus 265:
266: /* save session id := H */
267: /* XXX hashlen depends on KEX */
1.2 markus 268: if (kex->session_id == NULL) {
269: kex->session_id_len = 20;
270: kex->session_id = xmalloc(kex->session_id_len);
271: memcpy(kex->session_id, hash, kex->session_id_len);
272: }
1.1 markus 273:
274: /* sign H */
275: /* XXX hashlen depends on KEX */
276: key_sign(server_host_key, &signature, &slen, hash, 20);
277:
278: /* destroy_sensitive_data(); */
279:
280: /* send server hostkey, DH pubkey 'f' and singed H */
281: packet_start(SSH2_MSG_KEXDH_REPLY);
1.7 stevesk 282: packet_put_string(server_host_key_blob, sbloblen);
1.1 markus 283: packet_put_bignum2(dh->pub_key); /* f */
1.7 stevesk 284: packet_put_string(signature, slen);
1.1 markus 285: packet_send();
1.3 markus 286:
1.1 markus 287: xfree(signature);
288: xfree(server_host_key_blob);
1.3 markus 289: /* have keys, free DH */
290: DH_free(dh);
1.1 markus 291:
292: kex_derive_keys(kex, hash, shared_secret);
293: BN_clear_free(shared_secret);
1.3 markus 294: kex_finish(kex);
1.1 markus 295: }
296:
297: void
298: kexdh(Kex *kex)
299: {
300: if (kex->server)
301: kexdh_server(kex);
302: else
303: kexdh_client(kex);
304: }
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