Annotation of src/usr.bin/ssh/kexgexs.c, Revision 1.3
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"
27:
28: #include "xmalloc.h"
29: #include "key.h"
30: #include "kex.h"
31: #include "log.h"
32: #include "packet.h"
33: #include "dh.h"
34: #include "ssh2.h"
35: #include "compat.h"
36: #include "monitor_wrap.h"
37:
38: void
39: kexgex_server(Kex *kex)
40: {
41: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
42: Key *server_host_key;
43: DH *dh;
44: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
1.2 djm 45: u_int sbloblen, klen, kout, slen, hashlen;
1.1 markus 46: int min = -1, max = -1, nbits = -1, type;
47:
48: if (kex->load_host_key == NULL)
49: fatal("Cannot load hostkey");
50: server_host_key = kex->load_host_key(kex->hostkey_type);
51: if (server_host_key == NULL)
52: fatal("Unsupported hostkey type %d", kex->hostkey_type);
53:
54: type = packet_read();
55: switch (type) {
56: case SSH2_MSG_KEX_DH_GEX_REQUEST:
57: debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
58: min = packet_get_int();
59: nbits = packet_get_int();
60: max = packet_get_int();
61: min = MAX(DH_GRP_MIN, min);
62: max = MIN(DH_GRP_MAX, max);
63: break;
64: case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
65: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
66: nbits = packet_get_int();
67: min = DH_GRP_MIN;
68: max = DH_GRP_MAX;
69: /* unused for old GEX */
70: break;
71: default:
72: fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
73: }
74: packet_check_eom();
75:
76: if (max < min || nbits < min || max < nbits)
77: fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
78: min, nbits, max);
79:
80: /* Contact privileged parent */
81: dh = PRIVSEP(choose_dh(min, nbits, max));
82: if (dh == NULL)
83: packet_disconnect("Protocol error: no matching DH grp found");
84:
85: debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
86: packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
87: packet_put_bignum2(dh->p);
88: packet_put_bignum2(dh->g);
89: packet_send();
90:
91: /* flush */
92: packet_write_wait();
93:
94: /* Compute our exchange value in parallel with the client */
95: dh_gen_key(dh, kex->we_need * 8);
96:
97: debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
98: packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
99:
100: /* key, cert */
101: if ((dh_client_pub = BN_new()) == NULL)
102: fatal("dh_client_pub == NULL");
103: packet_get_bignum2(dh_client_pub);
104: packet_check_eom();
105:
106: #ifdef DEBUG_KEXDH
107: fprintf(stderr, "dh_client_pub= ");
108: BN_print_fp(stderr, dh_client_pub);
109: fprintf(stderr, "\n");
110: debug("bits %d", BN_num_bits(dh_client_pub));
111: #endif
112:
113: #ifdef DEBUG_KEXDH
114: DHparams_print_fp(stderr, dh);
115: fprintf(stderr, "pub= ");
116: BN_print_fp(stderr, dh->pub_key);
117: fprintf(stderr, "\n");
118: #endif
119: if (!dh_pub_is_valid(dh, dh_client_pub))
120: packet_disconnect("bad client public DH value");
121:
122: klen = DH_size(dh);
123: kbuf = xmalloc(klen);
124: kout = DH_compute_key(kbuf, dh_client_pub, dh);
125: #ifdef DEBUG_KEXDH
126: dump_digest("shared secret", kbuf, kout);
127: #endif
128: if ((shared_secret = BN_new()) == NULL)
129: fatal("kexgex_server: BN_new failed");
130: BN_bin2bn(kbuf, kout, shared_secret);
131: memset(kbuf, 0, klen);
132: xfree(kbuf);
133:
134: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
135:
136: if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
137: min = max = -1;
138:
1.2 djm 139: /* calc H */
140: kexgex_hash(
141: kex->evp_md,
1.1 markus 142: kex->client_version_string,
143: kex->server_version_string,
144: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
145: buffer_ptr(&kex->my), buffer_len(&kex->my),
146: server_host_key_blob, sbloblen,
147: min, nbits, max,
148: dh->p, dh->g,
149: dh_client_pub,
150: dh->pub_key,
1.2 djm 151: shared_secret,
152: &hash, &hashlen
1.1 markus 153: );
154: BN_clear_free(dh_client_pub);
155:
156: /* save session id := H */
157: if (kex->session_id == NULL) {
1.2 djm 158: kex->session_id_len = hashlen;
1.1 markus 159: kex->session_id = xmalloc(kex->session_id_len);
160: memcpy(kex->session_id, hash, kex->session_id_len);
161: }
162:
163: /* sign H */
1.2 djm 164: PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
1.1 markus 165:
166: /* destroy_sensitive_data(); */
167:
168: /* send server hostkey, DH pubkey 'f' and singed H */
169: debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
170: packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
171: packet_put_string(server_host_key_blob, sbloblen);
172: packet_put_bignum2(dh->pub_key); /* f */
173: packet_put_string(signature, slen);
174: packet_send();
175:
176: xfree(signature);
177: xfree(server_host_key_blob);
178: /* have keys, free DH */
179: DH_free(dh);
180:
1.2 djm 181: kex_derive_keys(kex, hash, hashlen, shared_secret);
1.1 markus 182: BN_clear_free(shared_secret);
183:
184: kex_finish(kex);
185: }
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