Annotation of src/usr.bin/ssh/kexdh.c, Revision 1.2
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"
1.2 ! markus 26: RCSID("$OpenBSD: kexdh.c,v 1.1 2001/04/03 19:53:29 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);
58: buffer_put_string(&b, client_version_string, strlen(client_version_string));
59: buffer_put_string(&b, server_version_string, strlen(server_version_string));
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:
126: if (kex->check_host_key == NULL)
127: fatal("cannot check server_host_key");
128: kex->check_host_key(server_host_key);
129:
130: /* DH paramter f, server public DH key */
131: dh_server_pub = BN_new();
132: if (dh_server_pub == NULL)
133: fatal("dh_server_pub == NULL");
134: packet_get_bignum2(dh_server_pub, &dlen);
135:
136: #ifdef DEBUG_KEXDH
137: fprintf(stderr, "dh_server_pub= ");
138: BN_print_fp(stderr, dh_server_pub);
139: fprintf(stderr, "\n");
140: debug("bits %d", BN_num_bits(dh_server_pub));
141: #endif
142:
143: /* signed H */
144: signature = packet_get_string(&slen);
145: packet_done();
146:
1.2 ! markus 147: if (!dh_pub_is_valid(dh, dh_server_pub))
1.1 markus 148: packet_disconnect("bad server public DH value");
149:
1.2 ! markus 150: klen = DH_size(dh);
1.1 markus 151: kbuf = xmalloc(klen);
1.2 ! markus 152: kout = DH_compute_key(kbuf, dh_server_pub, dh);
1.1 markus 153: #ifdef DEBUG_KEXDH
154: dump_digest("shared secret", kbuf, kout);
155: #endif
156: shared_secret = BN_new();
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);
1.2 ! markus 173: DH_free(dh);
1.1 markus 174: BN_free(dh_server_pub);
175:
176: if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1)
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);
190: kex_send_newkeys();
191: }
192:
193: /* server */
194:
195: void
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;
1.2 ! markus 203: int dlen, slen, plen;
! 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");
! 210: packet_read_expect(&plen, 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 */
219: dh_client_pub = BN_new();
220: if (dh_client_pub == NULL)
221: fatal("dh_client_pub == NULL");
222: packet_get_bignum2(dh_client_pub, &dlen);
223:
224: #ifdef DEBUG_KEXDH
225: fprintf(stderr, "dh_client_pub= ");
226: BN_print_fp(stderr, dh_client_pub);
227: fprintf(stderr, "\n");
228: debug("bits %d", BN_num_bits(dh_client_pub));
229: #endif
230:
231: #ifdef DEBUG_KEXDH
232: DHparams_print_fp(stderr, dh);
233: fprintf(stderr, "pub= ");
234: BN_print_fp(stderr, dh->pub_key);
235: fprintf(stderr, "\n");
236: #endif
237: if (!dh_pub_is_valid(dh, dh_client_pub))
238: packet_disconnect("bad client public DH value");
239:
240: klen = DH_size(dh);
241: kbuf = xmalloc(klen);
242: kout = DH_compute_key(kbuf, dh_client_pub, dh);
243: #ifdef DEBUG_KEXDH
244: dump_digest("shared secret", kbuf, kout);
245: #endif
246: shared_secret = BN_new();
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),
259: (char *)server_host_key_blob, sbloblen,
260: dh_client_pub,
261: dh->pub_key,
262: shared_secret
263: );
264: BN_free(dh_client_pub);
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);
282: packet_put_string((char *)server_host_key_blob, sbloblen);
283: packet_put_bignum2(dh->pub_key); /* f */
284: packet_put_string((char *)signature, slen);
285: packet_send();
286: xfree(signature);
287: xfree(server_host_key_blob);
288:
289: kex_derive_keys(kex, hash, shared_secret);
290: BN_clear_free(shared_secret);
291: kex_send_newkeys();
292:
293: /* have keys, free DH */
294: DH_free(dh);
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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