Annotation of src/usr.bin/ssh/kexdh.c, Revision 1.18
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"
1.18 ! provos 26: RCSID("$OpenBSD: kexdh.c,v 1.17 2002/02/28 15:46:33 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"
1.18 ! provos 40: #include "monitor_wrap.h"
1.1 markus 41:
1.6 itojun 42: static u_char *
1.1 markus 43: kex_dh_hash(
44: char *client_version_string,
45: char *server_version_string,
46: char *ckexinit, int ckexinitlen,
47: char *skexinit, int skexinitlen,
1.7 stevesk 48: u_char *serverhostkeyblob, int sbloblen,
1.1 markus 49: BIGNUM *client_dh_pub,
50: BIGNUM *server_dh_pub,
51: BIGNUM *shared_secret)
52: {
53: Buffer b;
54: static u_char digest[EVP_MAX_MD_SIZE];
1.17 markus 55: const EVP_MD *evp_md = EVP_sha1();
1.1 markus 56: EVP_MD_CTX md;
57:
58: buffer_init(&b);
1.4 markus 59: buffer_put_cstring(&b, client_version_string);
60: buffer_put_cstring(&b, server_version_string);
1.1 markus 61:
62: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
63: buffer_put_int(&b, ckexinitlen+1);
64: buffer_put_char(&b, SSH2_MSG_KEXINIT);
65: buffer_append(&b, ckexinit, ckexinitlen);
66: buffer_put_int(&b, skexinitlen+1);
67: buffer_put_char(&b, SSH2_MSG_KEXINIT);
68: buffer_append(&b, skexinit, skexinitlen);
69:
70: buffer_put_string(&b, serverhostkeyblob, sbloblen);
71: buffer_put_bignum2(&b, client_dh_pub);
72: buffer_put_bignum2(&b, server_dh_pub);
73: buffer_put_bignum2(&b, shared_secret);
74:
75: #ifdef DEBUG_KEX
76: buffer_dump(&b);
77: #endif
78: EVP_DigestInit(&md, evp_md);
79: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
80: EVP_DigestFinal(&md, digest, NULL);
81:
82: buffer_free(&b);
83:
84: #ifdef DEBUG_KEX
1.13 markus 85: dump_digest("hash", digest, EVP_MD_size(evp_md));
1.1 markus 86: #endif
87: return digest;
88: }
89:
90: /* client */
91:
1.6 itojun 92: static void
1.1 markus 93: kexdh_client(Kex *kex)
94: {
1.2 markus 95: BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
96: DH *dh;
97: Key *server_host_key;
1.7 stevesk 98: u_char *server_host_key_blob = NULL, *signature = NULL;
1.2 markus 99: u_char *kbuf, *hash;
100: u_int klen, kout, slen, sbloblen;
1.1 markus 101:
102: /* generate and send 'e', client DH public key */
1.2 markus 103: dh = dh_new_group1();
104: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 105: packet_start(SSH2_MSG_KEXDH_INIT);
1.2 markus 106: packet_put_bignum2(dh->pub_key);
1.1 markus 107: packet_send();
108:
1.2 markus 109: debug("sending SSH2_MSG_KEXDH_INIT");
1.1 markus 110: #ifdef DEBUG_KEXDH
1.2 markus 111: DHparams_print_fp(stderr, dh);
1.1 markus 112: fprintf(stderr, "pub= ");
1.2 markus 113: BN_print_fp(stderr, dh->pub_key);
1.1 markus 114: fprintf(stderr, "\n");
115: #endif
116:
1.2 markus 117: debug("expecting SSH2_MSG_KEXDH_REPLY");
1.12 markus 118: packet_read_expect(SSH2_MSG_KEXDH_REPLY);
1.1 markus 119:
120: /* key, cert */
121: server_host_key_blob = packet_get_string(&sbloblen);
122: server_host_key = key_from_blob(server_host_key_blob, sbloblen);
123: if (server_host_key == NULL)
124: fatal("cannot decode server_host_key_blob");
1.14 markus 125: if (server_host_key->type != kex->hostkey_type)
126: fatal("type mismatch for decoded server_host_key_blob");
1.5 markus 127: if (kex->verify_host_key == NULL)
128: fatal("cannot verify server_host_key");
129: if (kex->verify_host_key(server_host_key) == -1)
130: fatal("server_host_key verification failed");
1.1 markus 131:
132: /* DH paramter f, server public DH key */
1.8 markus 133: if ((dh_server_pub = BN_new()) == NULL)
1.1 markus 134: fatal("dh_server_pub == NULL");
1.11 markus 135: packet_get_bignum2(dh_server_pub);
1.1 markus 136:
137: #ifdef DEBUG_KEXDH
138: fprintf(stderr, "dh_server_pub= ");
139: BN_print_fp(stderr, dh_server_pub);
140: fprintf(stderr, "\n");
141: debug("bits %d", BN_num_bits(dh_server_pub));
142: #endif
143:
144: /* signed H */
145: signature = packet_get_string(&slen);
1.10 markus 146: packet_check_eom();
1.1 markus 147:
1.2 markus 148: if (!dh_pub_is_valid(dh, dh_server_pub))
1.1 markus 149: packet_disconnect("bad server public DH value");
150:
1.2 markus 151: klen = DH_size(dh);
1.1 markus 152: kbuf = xmalloc(klen);
1.2 markus 153: kout = DH_compute_key(kbuf, dh_server_pub, dh);
1.1 markus 154: #ifdef DEBUG_KEXDH
155: dump_digest("shared secret", kbuf, kout);
156: #endif
1.8 markus 157: if ((shared_secret = BN_new()) == NULL)
158: fatal("kexdh_client: BN_new failed");
1.1 markus 159: BN_bin2bn(kbuf, kout, shared_secret);
160: memset(kbuf, 0, klen);
161: xfree(kbuf);
162:
163: /* calc and verify H */
164: hash = kex_dh_hash(
165: kex->client_version_string,
166: kex->server_version_string,
167: buffer_ptr(&kex->my), buffer_len(&kex->my),
168: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
169: server_host_key_blob, sbloblen,
1.2 markus 170: dh->pub_key,
1.1 markus 171: dh_server_pub,
172: shared_secret
173: );
174: xfree(server_host_key_blob);
1.9 markus 175: BN_clear_free(dh_server_pub);
1.2 markus 176: DH_free(dh);
1.1 markus 177:
1.7 stevesk 178: if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
1.1 markus 179: fatal("key_verify failed for server_host_key");
180: key_free(server_host_key);
181: xfree(signature);
182:
1.2 markus 183: /* save session id */
184: if (kex->session_id == NULL) {
185: kex->session_id_len = 20;
186: kex->session_id = xmalloc(kex->session_id_len);
187: memcpy(kex->session_id, hash, kex->session_id_len);
188: }
189:
1.1 markus 190: kex_derive_keys(kex, hash, shared_secret);
191: BN_clear_free(shared_secret);
1.3 markus 192: kex_finish(kex);
1.1 markus 193: }
194:
195: /* server */
196:
1.6 itojun 197: static void
1.1 markus 198: kexdh_server(Kex *kex)
199: {
200: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
1.2 markus 201: DH *dh;
1.1 markus 202: Key *server_host_key;
203: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
204: u_int sbloblen, klen, kout;
1.16 markus 205: u_int slen;
1.2 markus 206:
207: /* generate server DH public key */
208: dh = dh_new_group1();
209: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 210:
1.2 markus 211: debug("expecting SSH2_MSG_KEXDH_INIT");
1.12 markus 212: packet_read_expect(SSH2_MSG_KEXDH_INIT);
1.1 markus 213:
214: if (kex->load_host_key == NULL)
215: fatal("Cannot load hostkey");
216: server_host_key = kex->load_host_key(kex->hostkey_type);
217: if (server_host_key == NULL)
218: fatal("Unsupported hostkey type %d", kex->hostkey_type);
219:
220: /* key, cert */
1.8 markus 221: if ((dh_client_pub = BN_new()) == NULL)
1.1 markus 222: fatal("dh_client_pub == NULL");
1.11 markus 223: packet_get_bignum2(dh_client_pub);
1.15 markus 224: packet_check_eom();
1.1 markus 225:
226: #ifdef DEBUG_KEXDH
227: fprintf(stderr, "dh_client_pub= ");
228: BN_print_fp(stderr, dh_client_pub);
229: fprintf(stderr, "\n");
230: debug("bits %d", BN_num_bits(dh_client_pub));
231: #endif
232:
233: #ifdef DEBUG_KEXDH
234: DHparams_print_fp(stderr, dh);
235: fprintf(stderr, "pub= ");
236: BN_print_fp(stderr, dh->pub_key);
237: fprintf(stderr, "\n");
238: #endif
239: if (!dh_pub_is_valid(dh, dh_client_pub))
240: packet_disconnect("bad client public DH value");
241:
242: klen = DH_size(dh);
243: kbuf = xmalloc(klen);
244: kout = DH_compute_key(kbuf, dh_client_pub, dh);
245: #ifdef DEBUG_KEXDH
246: dump_digest("shared secret", kbuf, kout);
247: #endif
1.8 markus 248: if ((shared_secret = BN_new()) == NULL)
249: fatal("kexdh_server: BN_new failed");
1.1 markus 250: BN_bin2bn(kbuf, kout, shared_secret);
251: memset(kbuf, 0, klen);
252: xfree(kbuf);
253:
254: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
255:
256: /* calc H */
257: hash = kex_dh_hash(
258: kex->client_version_string,
259: kex->server_version_string,
260: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
261: buffer_ptr(&kex->my), buffer_len(&kex->my),
1.7 stevesk 262: server_host_key_blob, sbloblen,
1.1 markus 263: dh_client_pub,
264: dh->pub_key,
265: shared_secret
266: );
1.9 markus 267: BN_clear_free(dh_client_pub);
1.1 markus 268:
269: /* save session id := H */
270: /* XXX hashlen depends on KEX */
1.2 markus 271: if (kex->session_id == NULL) {
272: kex->session_id_len = 20;
273: kex->session_id = xmalloc(kex->session_id_len);
274: memcpy(kex->session_id, hash, kex->session_id_len);
275: }
1.1 markus 276:
277: /* sign H */
278: /* XXX hashlen depends on KEX */
1.18 ! provos 279: PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20));
1.1 markus 280:
281: /* destroy_sensitive_data(); */
282:
283: /* send server hostkey, DH pubkey 'f' and singed H */
284: packet_start(SSH2_MSG_KEXDH_REPLY);
1.7 stevesk 285: packet_put_string(server_host_key_blob, sbloblen);
1.1 markus 286: packet_put_bignum2(dh->pub_key); /* f */
1.7 stevesk 287: packet_put_string(signature, slen);
1.1 markus 288: packet_send();
1.3 markus 289:
1.1 markus 290: xfree(signature);
291: xfree(server_host_key_blob);
1.3 markus 292: /* have keys, free DH */
293: DH_free(dh);
1.1 markus 294:
295: kex_derive_keys(kex, hash, shared_secret);
296: BN_clear_free(shared_secret);
1.3 markus 297: kex_finish(kex);
1.1 markus 298: }
299:
300: void
301: kexdh(Kex *kex)
302: {
303: if (kex->server)
304: kexdh_server(kex);
305: else
306: kexdh_client(kex);
307: }
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