1 /* $OpenBSD: kexgexc.c,v 1.23 2016/09/12 01:22:38 deraadt Exp $ */
2 /*
3 * Copyright (c) 2000 Niels Provos. All rights reserved.
4 * Copyright (c) 2001 Markus Friedl. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 #include "includes.h"
28
29 #ifdef WITH_OPENSSL
30
31 #include <sys/types.h>
32
33 #include <openssl/dh.h>
34
35 #include <stdarg.h>
36 #include <stdio.h>
37 #include <string.h>
38 #include <signal.h>
39
40 #include "sshkey.h"
41 #include "cipher.h"
42 #include "digest.h"
43 #include "kex.h"
44 #include "log.h"
45 #include "packet.h"
46 #include "dh.h"
47 #include "ssh2.h"
48 #include "compat.h"
49 #include "dispatch.h"
50 #include "ssherr.h"
51 #include "sshbuf.h"
52 #include "misc.h"
53
54 static int input_kex_dh_gex_group(int, u_int32_t, void *);
55 static int input_kex_dh_gex_reply(int, u_int32_t, void *);
56
57 int
kexgex_client(struct ssh * ssh)58 kexgex_client(struct ssh *ssh)
59 {
60 struct kex *kex = ssh->kex;
61 int r;
62 u_int nbits;
63
64 nbits = dh_estimate(kex->dh_need * 8);
65
66 kex->min = DH_GRP_MIN;
67 kex->max = DH_GRP_MAX;
68 kex->nbits = nbits;
69 if (datafellows & SSH_BUG_DHGEX_LARGE)
70 kex->nbits = MINIMUM(kex->nbits, 4096);
71 /* New GEX request */
72 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
73 (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
74 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
75 (r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
76 (r = sshpkt_send(ssh)) != 0)
77 goto out;
78 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
79 kex->min, kex->nbits, kex->max);
80 #ifdef DEBUG_KEXDH
81 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
82 kex->min, kex->nbits, kex->max);
83 #endif
84 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
85 &input_kex_dh_gex_group);
86 r = 0;
87 out:
88 return r;
89 }
90
91 static int
input_kex_dh_gex_group(int type,u_int32_t seq,void * ctxt)92 input_kex_dh_gex_group(int type, u_int32_t seq, void *ctxt)
93 {
94 struct ssh *ssh = ctxt;
95 struct kex *kex = ssh->kex;
96 BIGNUM *p = NULL, *g = NULL;
97 int r, bits;
98
99 debug("got SSH2_MSG_KEX_DH_GEX_GROUP");
100
101 if ((p = BN_new()) == NULL ||
102 (g = BN_new()) == NULL) {
103 r = SSH_ERR_ALLOC_FAIL;
104 goto out;
105 }
106 if ((r = sshpkt_get_bignum2(ssh, p)) != 0 ||
107 (r = sshpkt_get_bignum2(ssh, g)) != 0 ||
108 (r = sshpkt_get_end(ssh)) != 0)
109 goto out;
110 if ((bits = BN_num_bits(p)) < 0 ||
111 (u_int)bits < kex->min || (u_int)bits > kex->max) {
112 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
113 goto out;
114 }
115 if ((kex->dh = dh_new_group(g, p)) == NULL) {
116 r = SSH_ERR_ALLOC_FAIL;
117 goto out;
118 }
119 p = g = NULL; /* belong to kex->dh now */
120
121 /* generate and send 'e', client DH public key */
122 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0 ||
123 (r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
124 (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 ||
125 (r = sshpkt_send(ssh)) != 0)
126 goto out;
127 debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
128 #ifdef DEBUG_KEXDH
129 DHparams_print_fp(stderr, kex->dh);
130 fprintf(stderr, "pub= ");
131 BN_print_fp(stderr, kex->dh->pub_key);
132 fprintf(stderr, "\n");
133 #endif
134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL);
135 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
136 r = 0;
137 out:
138 if (p)
139 BN_clear_free(p);
140 if (g)
141 BN_clear_free(g);
142 return r;
143 }
144
145 static int
input_kex_dh_gex_reply(int type,u_int32_t seq,void * ctxt)146 input_kex_dh_gex_reply(int type, u_int32_t seq, void *ctxt)
147 {
148 struct ssh *ssh = ctxt;
149 struct kex *kex = ssh->kex;
150 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
151 struct sshkey *server_host_key = NULL;
152 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
153 u_char hash[SSH_DIGEST_MAX_LENGTH];
154 size_t klen = 0, slen, sbloblen, hashlen;
155 int kout, r;
156
157 debug("got SSH2_MSG_KEX_DH_GEX_REPLY");
158 if (kex->verify_host_key == NULL) {
159 r = SSH_ERR_INVALID_ARGUMENT;
160 goto out;
161 }
162 /* key, cert */
163 if ((r = sshpkt_get_string(ssh, &server_host_key_blob,
164 &sbloblen)) != 0 ||
165 (r = sshkey_from_blob(server_host_key_blob, sbloblen,
166 &server_host_key)) != 0)
167 goto out;
168 if (server_host_key->type != kex->hostkey_type) {
169 r = SSH_ERR_KEY_TYPE_MISMATCH;
170 goto out;
171 }
172 if (server_host_key->type != kex->hostkey_type ||
173 (kex->hostkey_type == KEY_ECDSA &&
174 server_host_key->ecdsa_nid != kex->hostkey_nid)) {
175 r = SSH_ERR_KEY_TYPE_MISMATCH;
176 goto out;
177 }
178 if (kex->verify_host_key(server_host_key, ssh) == -1) {
179 r = SSH_ERR_SIGNATURE_INVALID;
180 goto out;
181 }
182 /* DH parameter f, server public DH key */
183 if ((dh_server_pub = BN_new()) == NULL) {
184 r = SSH_ERR_ALLOC_FAIL;
185 goto out;
186 }
187 /* signed H */
188 if ((r = sshpkt_get_bignum2(ssh, dh_server_pub)) != 0 ||
189 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
190 (r = sshpkt_get_end(ssh)) != 0)
191 goto out;
192 #ifdef DEBUG_KEXDH
193 fprintf(stderr, "dh_server_pub= ");
194 BN_print_fp(stderr, dh_server_pub);
195 fprintf(stderr, "\n");
196 debug("bits %d", BN_num_bits(dh_server_pub));
197 #endif
198 if (!dh_pub_is_valid(kex->dh, dh_server_pub)) {
199 sshpkt_disconnect(ssh, "bad server public DH value");
200 r = SSH_ERR_MESSAGE_INCOMPLETE;
201 goto out;
202 }
203
204 klen = DH_size(kex->dh);
205 if ((kbuf = malloc(klen)) == NULL ||
206 (shared_secret = BN_new()) == NULL) {
207 r = SSH_ERR_ALLOC_FAIL;
208 goto out;
209 }
210 if ((kout = DH_compute_key(kbuf, dh_server_pub, kex->dh)) < 0 ||
211 BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
212 r = SSH_ERR_LIBCRYPTO_ERROR;
213 goto out;
214 }
215 #ifdef DEBUG_KEXDH
216 dump_digest("shared secret", kbuf, kout);
217 #endif
218 if (ssh->compat & SSH_OLD_DHGEX)
219 kex->min = kex->max = -1;
220
221 /* calc and verify H */
222 hashlen = sizeof(hash);
223 if ((r = kexgex_hash(
224 kex->hash_alg,
225 kex->client_version_string,
226 kex->server_version_string,
227 sshbuf_ptr(kex->my), sshbuf_len(kex->my),
228 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
229 server_host_key_blob, sbloblen,
230 kex->min, kex->nbits, kex->max,
231 kex->dh->p, kex->dh->g,
232 kex->dh->pub_key,
233 dh_server_pub,
234 shared_secret,
235 hash, &hashlen)) != 0)
236 goto out;
237
238 if ((r = sshkey_verify(server_host_key, signature, slen, hash,
239 hashlen, ssh->compat)) != 0)
240 goto out;
241
242 /* save session id */
243 if (kex->session_id == NULL) {
244 kex->session_id_len = hashlen;
245 kex->session_id = malloc(kex->session_id_len);
246 if (kex->session_id == NULL) {
247 r = SSH_ERR_ALLOC_FAIL;
248 goto out;
249 }
250 memcpy(kex->session_id, hash, kex->session_id_len);
251 }
252
253 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
254 r = kex_send_newkeys(ssh);
255 out:
256 explicit_bzero(hash, sizeof(hash));
257 DH_free(kex->dh);
258 kex->dh = NULL;
259 if (dh_server_pub)
260 BN_clear_free(dh_server_pub);
261 if (kbuf) {
262 explicit_bzero(kbuf, klen);
263 free(kbuf);
264 }
265 if (shared_secret)
266 BN_clear_free(shared_secret);
267 sshkey_free(server_host_key);
268 free(server_host_key_blob);
269 free(signature);
270 return r;
271 }
272 #endif /* WITH_OPENSSL */
273