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1c14df9e | 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 | RCSID("$OpenBSD: kexgexs.c,v 1.1 2003/02/16 17:09:57 markus Exp $"); | |
28 | ||
29 | #include "xmalloc.h" | |
30 | #include "key.h" | |
31 | #include "kex.h" | |
32 | #include "log.h" | |
33 | #include "packet.h" | |
34 | #include "dh.h" | |
35 | #include "ssh2.h" | |
36 | #include "compat.h" | |
37 | #include "monitor_wrap.h" | |
38 | ||
39 | void | |
40 | kexgex_server(Kex *kex) | |
41 | { | |
42 | BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; | |
43 | Key *server_host_key; | |
44 | DH *dh; | |
45 | u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; | |
46 | u_int sbloblen, klen, kout, slen; | |
47 | int min = -1, max = -1, nbits = -1, type; | |
48 | ||
49 | if (kex->load_host_key == NULL) | |
50 | fatal("Cannot load hostkey"); | |
51 | server_host_key = kex->load_host_key(kex->hostkey_type); | |
52 | if (server_host_key == NULL) | |
53 | fatal("Unsupported hostkey type %d", kex->hostkey_type); | |
54 | ||
55 | type = packet_read(); | |
56 | switch (type) { | |
57 | case SSH2_MSG_KEX_DH_GEX_REQUEST: | |
58 | debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); | |
59 | min = packet_get_int(); | |
60 | nbits = packet_get_int(); | |
61 | max = packet_get_int(); | |
62 | min = MAX(DH_GRP_MIN, min); | |
63 | max = MIN(DH_GRP_MAX, max); | |
64 | break; | |
65 | case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: | |
66 | debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); | |
67 | nbits = packet_get_int(); | |
68 | min = DH_GRP_MIN; | |
69 | max = DH_GRP_MAX; | |
70 | /* unused for old GEX */ | |
71 | break; | |
72 | default: | |
73 | fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); | |
74 | } | |
75 | packet_check_eom(); | |
76 | ||
77 | if (max < min || nbits < min || max < nbits) | |
78 | fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", | |
79 | min, nbits, max); | |
80 | ||
81 | /* Contact privileged parent */ | |
82 | dh = PRIVSEP(choose_dh(min, nbits, max)); | |
83 | if (dh == NULL) | |
84 | packet_disconnect("Protocol error: no matching DH grp found"); | |
85 | ||
86 | debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); | |
87 | packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); | |
88 | packet_put_bignum2(dh->p); | |
89 | packet_put_bignum2(dh->g); | |
90 | packet_send(); | |
91 | ||
92 | /* flush */ | |
93 | packet_write_wait(); | |
94 | ||
95 | /* Compute our exchange value in parallel with the client */ | |
96 | dh_gen_key(dh, kex->we_need * 8); | |
97 | ||
98 | debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); | |
99 | packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); | |
100 | ||
101 | /* key, cert */ | |
102 | if ((dh_client_pub = BN_new()) == NULL) | |
103 | fatal("dh_client_pub == NULL"); | |
104 | packet_get_bignum2(dh_client_pub); | |
105 | packet_check_eom(); | |
106 | ||
107 | #ifdef DEBUG_KEXDH | |
108 | fprintf(stderr, "dh_client_pub= "); | |
109 | BN_print_fp(stderr, dh_client_pub); | |
110 | fprintf(stderr, "\n"); | |
111 | debug("bits %d", BN_num_bits(dh_client_pub)); | |
112 | #endif | |
113 | ||
114 | #ifdef DEBUG_KEXDH | |
115 | DHparams_print_fp(stderr, dh); | |
116 | fprintf(stderr, "pub= "); | |
117 | BN_print_fp(stderr, dh->pub_key); | |
118 | fprintf(stderr, "\n"); | |
119 | #endif | |
120 | if (!dh_pub_is_valid(dh, dh_client_pub)) | |
121 | packet_disconnect("bad client public DH value"); | |
122 | ||
123 | klen = DH_size(dh); | |
124 | kbuf = xmalloc(klen); | |
125 | kout = DH_compute_key(kbuf, dh_client_pub, dh); | |
126 | #ifdef DEBUG_KEXDH | |
127 | dump_digest("shared secret", kbuf, kout); | |
128 | #endif | |
129 | if ((shared_secret = BN_new()) == NULL) | |
130 | fatal("kexgex_server: BN_new failed"); | |
131 | BN_bin2bn(kbuf, kout, shared_secret); | |
132 | memset(kbuf, 0, klen); | |
133 | xfree(kbuf); | |
134 | ||
135 | key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); | |
136 | ||
137 | if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) | |
138 | min = max = -1; | |
139 | ||
140 | /* calc H */ /* XXX depends on 'kex' */ | |
141 | hash = kexgex_hash( | |
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, | |
151 | shared_secret | |
152 | ); | |
153 | BN_clear_free(dh_client_pub); | |
154 | ||
155 | /* save session id := H */ | |
156 | /* XXX hashlen depends on KEX */ | |
157 | if (kex->session_id == NULL) { | |
158 | kex->session_id_len = 20; | |
159 | kex->session_id = xmalloc(kex->session_id_len); | |
160 | memcpy(kex->session_id, hash, kex->session_id_len); | |
161 | } | |
162 | ||
163 | /* sign H */ | |
164 | /* XXX hashlen depends on KEX */ | |
165 | PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20)); | |
166 | ||
167 | /* destroy_sensitive_data(); */ | |
168 | ||
169 | /* send server hostkey, DH pubkey 'f' and singed H */ | |
170 | debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); | |
171 | packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); | |
172 | packet_put_string(server_host_key_blob, sbloblen); | |
173 | packet_put_bignum2(dh->pub_key); /* f */ | |
174 | packet_put_string(signature, slen); | |
175 | packet_send(); | |
176 | ||
177 | xfree(signature); | |
178 | xfree(server_host_key_blob); | |
179 | /* have keys, free DH */ | |
180 | DH_free(dh); | |
181 | ||
182 | kex_derive_keys(kex, hash, shared_secret); | |
183 | BN_clear_free(shared_secret); | |
184 | ||
185 | kex_finish(kex); | |
186 | } |