1 /* $OpenBSD: kexgexc.c,v 1.38 2021/12/19 22:08:06 djm 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 <sys/types.h>
28
29 #include <openssl/dh.h>
30
31 #include <stdio.h>
32 #include <string.h>
33 #include <signal.h>
34
35 #include "sshkey.h"
36 #include "cipher.h"
37 #include "digest.h"
38 #include "kex.h"
39 #include "log.h"
40 #include "packet.h"
41 #include "dh.h"
42 #include "ssh2.h"
43 #include "compat.h"
44 #include "dispatch.h"
45 #include "ssherr.h"
46 #include "sshbuf.h"
47 #include "misc.h"
48
49 static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *);
50 static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *);
51
52 int
kexgex_client(struct ssh * ssh)53 kexgex_client(struct ssh *ssh)
54 {
55 struct kex *kex = ssh->kex;
56 int r;
57 u_int nbits;
58
59 nbits = dh_estimate(kex->dh_need * 8);
60
61 kex->min = DH_GRP_MIN;
62 kex->max = DH_GRP_MAX;
63 kex->nbits = nbits;
64 if (ssh->compat & SSH_BUG_DHGEX_LARGE)
65 kex->nbits = MINIMUM(kex->nbits, 4096);
66 /* New GEX request */
67 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
68 (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
69 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
70 (r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
71 (r = sshpkt_send(ssh)) != 0)
72 goto out;
73 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
74 kex->min, kex->nbits, kex->max);
75 #ifdef DEBUG_KEXDH
76 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
77 kex->min, kex->nbits, kex->max);
78 #endif
79 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
80 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
81 &input_kex_dh_gex_group);
82 r = 0;
83 out:
84 return r;
85 }
86
87 static int
input_kex_dh_gex_group(int type,u_int32_t seq,struct ssh * ssh)88 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
89 {
90 struct kex *kex = ssh->kex;
91 BIGNUM *p = NULL, *g = NULL;
92 const BIGNUM *pub_key;
93 int r, bits;
94
95 debug("SSH2_MSG_KEX_DH_GEX_GROUP received");
96 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, &kex_protocol_error);
97
98 if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 ||
99 (r = sshpkt_get_bignum2(ssh, &g)) != 0 ||
100 (r = sshpkt_get_end(ssh)) != 0)
101 goto out;
102 if ((bits = BN_num_bits(p)) < 0 ||
103 (u_int)bits < kex->min || (u_int)bits > kex->max) {
104 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
105 goto out;
106 }
107 if ((kex->dh = dh_new_group(g, p)) == NULL) {
108 r = SSH_ERR_ALLOC_FAIL;
109 goto out;
110 }
111 p = g = NULL; /* belong to kex->dh now */
112
113 /* generate and send 'e', client DH public key */
114 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
115 goto out;
116 DH_get0_key(kex->dh, &pub_key, NULL);
117 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
118 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
119 (r = sshpkt_send(ssh)) != 0)
120 goto out;
121 debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
122 #ifdef DEBUG_KEXDH
123 DHparams_print_fp(stderr, kex->dh);
124 fprintf(stderr, "pub= ");
125 BN_print_fp(stderr, pub_key);
126 fprintf(stderr, "\n");
127 #endif
128 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
129 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
130 r = 0;
131 out:
132 BN_clear_free(p);
133 BN_clear_free(g);
134 return r;
135 }
136
137 static int
input_kex_dh_gex_reply(int type,u_int32_t seq,struct ssh * ssh)138 input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
139 {
140 struct kex *kex = ssh->kex;
141 BIGNUM *dh_server_pub = NULL;
142 const BIGNUM *pub_key, *dh_p, *dh_g;
143 struct sshbuf *shared_secret = NULL;
144 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
145 struct sshkey *server_host_key = NULL;
146 u_char *signature = NULL;
147 u_char hash[SSH_DIGEST_MAX_LENGTH];
148 size_t slen, hashlen;
149 int r;
150
151 debug("SSH2_MSG_KEX_DH_GEX_REPLY received");
152 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &kex_protocol_error);
153
154 /* key, cert */
155 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
156 goto out;
157 /* sshkey_fromb() consumes its buffer, so make a copy */
158 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
159 r = SSH_ERR_ALLOC_FAIL;
160 goto out;
161 }
162 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 ||
163 (r = kex_verify_host_key(ssh, server_host_key)) != 0)
164 goto out;
165 /* DH parameter f, server public DH key, signed H */
166 if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 ||
167 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
168 (r = sshpkt_get_end(ssh)) != 0)
169 goto out;
170 if ((shared_secret = sshbuf_new()) == NULL) {
171 r = SSH_ERR_ALLOC_FAIL;
172 goto out;
173 }
174 if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0)
175 goto out;
176 if (ssh->compat & SSH_OLD_DHGEX)
177 kex->min = kex->max = -1;
178
179 /* calc and verify H */
180 DH_get0_key(kex->dh, &pub_key, NULL);
181 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
182 hashlen = sizeof(hash);
183 if ((r = kexgex_hash(
184 kex->hash_alg,
185 kex->client_version,
186 kex->server_version,
187 kex->my,
188 kex->peer,
189 server_host_key_blob,
190 kex->min, kex->nbits, kex->max,
191 dh_p, dh_g,
192 pub_key,
193 dh_server_pub,
194 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
195 hash, &hashlen)) != 0)
196 goto out;
197
198 if ((r = sshkey_verify(server_host_key, signature, slen, hash,
199 hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0)
200 goto out;
201
202 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
203 (r = kex_send_newkeys(ssh)) != 0)
204 goto out;
205
206 /* save initial signature and hostkey */
207 if ((kex->flags & KEX_INITIAL) != 0) {
208 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
209 r = SSH_ERR_INTERNAL_ERROR;
210 goto out;
211 }
212 if ((kex->initial_sig = sshbuf_new()) == NULL) {
213 r = SSH_ERR_ALLOC_FAIL;
214 goto out;
215 }
216 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
217 goto out;
218 kex->initial_hostkey = server_host_key;
219 server_host_key = NULL;
220 }
221 /* success */
222 out:
223 explicit_bzero(hash, sizeof(hash));
224 DH_free(kex->dh);
225 kex->dh = NULL;
226 BN_clear_free(dh_server_pub);
227 sshbuf_free(shared_secret);
228 sshkey_free(server_host_key);
229 sshbuf_free(tmp);
230 sshbuf_free(server_host_key_blob);
231 free(signature);
232 return r;
233 }
234