Annotation of src/usr.bin/ssh/kexdh.c, Revision 1.5
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"
1.5 ! markus 26: RCSID("$OpenBSD: kexdh.c,v 1.4 2001/06/07 20:23:04 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:
41: u_char *
42: kex_dh_hash(
43: char *client_version_string,
44: char *server_version_string,
45: char *ckexinit, int ckexinitlen,
46: char *skexinit, int skexinitlen,
47: char *serverhostkeyblob, int sbloblen,
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
84: dump_digest("hash", digest, evp_md->md_size);
85: #endif
86: return digest;
87: }
88:
89: /* client */
90:
91: void
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;
97: char *server_host_key_blob = NULL, *signature = NULL;
98: u_char *kbuf, *hash;
99: u_int klen, kout, slen, sbloblen;
100: int dlen, plen;
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");
118: packet_read_expect(&plen, 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");
125:
1.5 ! markus 126: if (kex->verify_host_key == NULL)
! 127: fatal("cannot verify server_host_key");
! 128: if (kex->verify_host_key(server_host_key) == -1)
! 129: fatal("server_host_key verification failed");
1.1 markus 130:
131: /* DH paramter f, server public DH key */
132: dh_server_pub = BN_new();
133: if (dh_server_pub == NULL)
134: fatal("dh_server_pub == NULL");
135: packet_get_bignum2(dh_server_pub, &dlen);
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);
146: packet_done();
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
157: shared_secret = BN_new();
158: BN_bin2bn(kbuf, kout, shared_secret);
159: memset(kbuf, 0, klen);
160: xfree(kbuf);
161:
162: /* calc and verify H */
163: hash = kex_dh_hash(
164: kex->client_version_string,
165: kex->server_version_string,
166: buffer_ptr(&kex->my), buffer_len(&kex->my),
167: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
168: server_host_key_blob, sbloblen,
1.2 markus 169: dh->pub_key,
1.1 markus 170: dh_server_pub,
171: shared_secret
172: );
173: xfree(server_host_key_blob);
1.3 markus 174: BN_free(dh_server_pub);
1.2 markus 175: DH_free(dh);
1.1 markus 176:
177: if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1)
178: fatal("key_verify failed for server_host_key");
179: key_free(server_host_key);
180: xfree(signature);
181:
1.2 markus 182: /* save session id */
183: if (kex->session_id == NULL) {
184: kex->session_id_len = 20;
185: kex->session_id = xmalloc(kex->session_id_len);
186: memcpy(kex->session_id, hash, kex->session_id_len);
187: }
188:
1.1 markus 189: kex_derive_keys(kex, hash, shared_secret);
190: BN_clear_free(shared_secret);
1.3 markus 191: kex_finish(kex);
1.1 markus 192: }
193:
194: /* server */
195:
196: void
197: kexdh_server(Kex *kex)
198: {
199: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
1.2 markus 200: DH *dh;
1.1 markus 201: Key *server_host_key;
202: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
203: u_int sbloblen, klen, kout;
1.2 markus 204: int dlen, slen, plen;
205:
206: /* generate server DH public key */
207: dh = dh_new_group1();
208: dh_gen_key(dh, kex->we_need * 8);
1.1 markus 209:
1.2 markus 210: debug("expecting SSH2_MSG_KEXDH_INIT");
211: packet_read_expect(&plen, SSH2_MSG_KEXDH_INIT);
1.1 markus 212:
213: if (kex->load_host_key == NULL)
214: fatal("Cannot load hostkey");
215: server_host_key = kex->load_host_key(kex->hostkey_type);
216: if (server_host_key == NULL)
217: fatal("Unsupported hostkey type %d", kex->hostkey_type);
218:
219: /* key, cert */
220: dh_client_pub = BN_new();
221: if (dh_client_pub == NULL)
222: fatal("dh_client_pub == NULL");
223: packet_get_bignum2(dh_client_pub, &dlen);
224:
225: #ifdef DEBUG_KEXDH
226: fprintf(stderr, "dh_client_pub= ");
227: BN_print_fp(stderr, dh_client_pub);
228: fprintf(stderr, "\n");
229: debug("bits %d", BN_num_bits(dh_client_pub));
230: #endif
231:
232: #ifdef DEBUG_KEXDH
233: DHparams_print_fp(stderr, dh);
234: fprintf(stderr, "pub= ");
235: BN_print_fp(stderr, dh->pub_key);
236: fprintf(stderr, "\n");
237: #endif
238: if (!dh_pub_is_valid(dh, dh_client_pub))
239: packet_disconnect("bad client public DH value");
240:
241: klen = DH_size(dh);
242: kbuf = xmalloc(klen);
243: kout = DH_compute_key(kbuf, dh_client_pub, dh);
244: #ifdef DEBUG_KEXDH
245: dump_digest("shared secret", kbuf, kout);
246: #endif
247: shared_secret = BN_new();
248: BN_bin2bn(kbuf, kout, shared_secret);
249: memset(kbuf, 0, klen);
250: xfree(kbuf);
251:
252: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
253:
254: /* calc H */
255: hash = kex_dh_hash(
256: kex->client_version_string,
257: kex->server_version_string,
258: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
259: buffer_ptr(&kex->my), buffer_len(&kex->my),
260: (char *)server_host_key_blob, sbloblen,
261: dh_client_pub,
262: dh->pub_key,
263: shared_secret
264: );
265: BN_free(dh_client_pub);
266:
267: /* save session id := H */
268: /* XXX hashlen depends on KEX */
1.2 markus 269: if (kex->session_id == NULL) {
270: kex->session_id_len = 20;
271: kex->session_id = xmalloc(kex->session_id_len);
272: memcpy(kex->session_id, hash, kex->session_id_len);
273: }
1.1 markus 274:
275: /* sign H */
276: /* XXX hashlen depends on KEX */
277: key_sign(server_host_key, &signature, &slen, hash, 20);
278:
279: /* destroy_sensitive_data(); */
280:
281: /* send server hostkey, DH pubkey 'f' and singed H */
282: packet_start(SSH2_MSG_KEXDH_REPLY);
283: packet_put_string((char *)server_host_key_blob, sbloblen);
284: packet_put_bignum2(dh->pub_key); /* f */
285: packet_put_string((char *)signature, slen);
286: packet_send();
1.3 markus 287:
1.1 markus 288: xfree(signature);
289: xfree(server_host_key_blob);
1.3 markus 290: /* have keys, free DH */
291: DH_free(dh);
1.1 markus 292:
293: kex_derive_keys(kex, hash, shared_secret);
294: BN_clear_free(shared_secret);
1.3 markus 295: kex_finish(kex);
1.1 markus 296: }
297:
298: void
299: kexdh(Kex *kex)
300: {
301: if (kex->server)
302: kexdh_server(kex);
303: else
304: kexdh_client(kex);
305: }
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