1 /* $OpenBSD: kexgexs.c,v 1.47 2024/05/17 00:30:23 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 "includes.h"
28
29 #ifdef WITH_OPENSSL
30
31
32 #include <stdarg.h>
33 #include <stdio.h>
34 #include <string.h>
35 #include <signal.h>
36
37 #include <openssl/dh.h>
38
39 #include "openbsd-compat/openssl-compat.h"
40
41 #include "sshkey.h"
42 #include "cipher.h"
43 #include "digest.h"
44 #include "kex.h"
45 #include "log.h"
46 #include "packet.h"
47 #include "dh.h"
48 #include "ssh2.h"
49 #ifdef GSSAPI
50 #include "ssh-gss.h"
51 #endif
52 #include "monitor_wrap.h"
53 #include "dispatch.h"
54 #include "ssherr.h"
55 #include "sshbuf.h"
56 #include "misc.h"
57
58 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *);
59 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *);
60
61 int
kexgex_server(struct ssh * ssh)62 kexgex_server(struct ssh *ssh)
63 {
64 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
65 &input_kex_dh_gex_request);
66 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST");
67 return 0;
68 }
69
70 static int
input_kex_dh_gex_request(int type,u_int32_t seq,struct ssh * ssh)71 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh)
72 {
73 struct kex *kex = ssh->kex;
74 int r;
75 u_int min = 0, max = 0, nbits = 0;
76 const BIGNUM *dh_p, *dh_g;
77
78 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
79 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error);
80
81 if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
82 (r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
83 (r = sshpkt_get_u32(ssh, &max)) != 0 ||
84 (r = sshpkt_get_end(ssh)) != 0)
85 goto out;
86 kex->nbits = nbits;
87 kex->min = min;
88 kex->max = max;
89 min = MAXIMUM(DH_GRP_MIN, min);
90 max = MINIMUM(DH_GRP_MAX, max);
91 nbits = MAXIMUM(DH_GRP_MIN, nbits);
92 nbits = MINIMUM(DH_GRP_MAX, nbits);
93
94 if (kex->max < kex->min || kex->nbits < kex->min ||
95 kex->max < kex->nbits || kex->max < DH_GRP_MIN) {
96 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
97 goto out;
98 }
99
100 /* Contact privileged parent */
101 kex->dh = mm_choose_dh(min, nbits, max);
102 if (kex->dh == NULL) {
103 (void)sshpkt_disconnect(ssh, "no matching DH grp found");
104 r = SSH_ERR_ALLOC_FAIL;
105 goto out;
106 }
107 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
108 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
109 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
110 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
111 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
112 (r = sshpkt_send(ssh)) != 0)
113 goto out;
114
115 /* Compute our exchange value in parallel with the client */
116 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
117 goto out;
118
119 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
120 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
121 r = 0;
122 out:
123 return r;
124 }
125
126 static int
input_kex_dh_gex_init(int type,u_int32_t seq,struct ssh * ssh)127 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
128 {
129 struct kex *kex = ssh->kex;
130 BIGNUM *dh_client_pub = NULL;
131 const BIGNUM *pub_key, *dh_p, *dh_g;
132 struct sshbuf *shared_secret = NULL;
133 struct sshbuf *server_host_key_blob = NULL;
134 struct sshkey *server_host_public, *server_host_private;
135 u_char *signature = NULL;
136 u_char hash[SSH_DIGEST_MAX_LENGTH];
137 size_t slen, hashlen;
138 int r;
139
140 debug("SSH2_MSG_KEX_DH_GEX_INIT received");
141 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error);
142
143 if ((r = kex_load_hostkey(ssh, &server_host_private,
144 &server_host_public)) != 0)
145 goto out;
146
147 /* key, cert */
148 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
149 (r = sshpkt_get_end(ssh)) != 0)
150 goto out;
151 if ((shared_secret = sshbuf_new()) == NULL) {
152 r = SSH_ERR_ALLOC_FAIL;
153 goto out;
154 }
155 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
156 goto out;
157 if ((server_host_key_blob = sshbuf_new()) == NULL) {
158 r = SSH_ERR_ALLOC_FAIL;
159 goto out;
160 }
161 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
162 goto out;
163
164 /* calc H */
165 DH_get0_key(kex->dh, &pub_key, NULL);
166 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
167 hashlen = sizeof(hash);
168 if ((r = kexgex_hash(
169 kex->hash_alg,
170 kex->client_version,
171 kex->server_version,
172 kex->peer,
173 kex->my,
174 server_host_key_blob,
175 kex->min, kex->nbits, kex->max,
176 dh_p, dh_g,
177 dh_client_pub,
178 pub_key,
179 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
180 hash, &hashlen)) != 0)
181 goto out;
182
183 /* sign H */
184 if ((r = kex->sign(ssh, server_host_private, server_host_public,
185 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0)
186 goto out;
187
188 /* send server hostkey, DH pubkey 'f' and signed H */
189 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
190 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
191 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */
192 (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
193 (r = sshpkt_send(ssh)) != 0)
194 goto out;
195
196 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
197 (r = kex_send_newkeys(ssh)) != 0)
198 goto out;
199
200 /* retain copy of hostkey used at initial KEX */
201 if (kex->initial_hostkey == NULL &&
202 (r = sshkey_from_private(server_host_public,
203 &kex->initial_hostkey)) != 0)
204 goto out;
205 /* success */
206 out:
207 explicit_bzero(hash, sizeof(hash));
208 DH_free(kex->dh);
209 kex->dh = NULL;
210 BN_clear_free(dh_client_pub);
211 sshbuf_free(shared_secret);
212 sshbuf_free(server_host_key_blob);
213 free(signature);
214 return r;
215 }
216 #endif /* WITH_OPENSSL */
217