1 /* $OpenBSD: kexgexc.c,v 1.35 2019/11/25 00:51:37 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 #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 "openbsd-compat/openssl-compat.h"
41
42 #include "sshkey.h"
43 #include "cipher.h"
44 #include "digest.h"
45 #include "kex.h"
46 #include "log.h"
47 #include "packet.h"
48 #include "dh.h"
49 #include "ssh2.h"
50 #include "compat.h"
51 #include "dispatch.h"
52 #include "ssherr.h"
53 #include "sshbuf.h"
54 #include "misc.h"
55
56 static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *);
57 static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *);
58
59 int
kexgex_client(struct ssh * ssh)60 kexgex_client(struct ssh *ssh)
61 {
62 struct kex *kex = ssh->kex;
63 int r;
64 u_int nbits;
65
66 nbits = dh_estimate(kex->dh_need * 8);
67
68 kex->min = DH_GRP_MIN;
69 kex->max = DH_GRP_MAX;
70 kex->nbits = nbits;
71 if (datafellows & SSH_BUG_DHGEX_LARGE)
72 kex->nbits = MINIMUM(kex->nbits, 4096);
73 /* New GEX request */
74 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
75 (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
76 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
77 (r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
78 (r = sshpkt_send(ssh)) != 0)
79 goto out;
80 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
81 kex->min, kex->nbits, kex->max);
82 #ifdef DEBUG_KEXDH
83 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
84 kex->min, kex->nbits, kex->max);
85 #endif
86 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
87 &input_kex_dh_gex_group);
88 r = 0;
89 out:
90 return r;
91 }
92
93 static int
input_kex_dh_gex_group(int type,u_int32_t seq,struct ssh * ssh)94 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
95 {
96 struct kex *kex = ssh->kex;
97 BIGNUM *p = NULL, *g = NULL;
98 const BIGNUM *pub_key;
99 int r, bits;
100
101 debug("got SSH2_MSG_KEX_DH_GEX_GROUP");
102
103 if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 ||
104 (r = sshpkt_get_bignum2(ssh, &g)) != 0 ||
105 (r = sshpkt_get_end(ssh)) != 0)
106 goto out;
107 if ((bits = BN_num_bits(p)) < 0 ||
108 (u_int)bits < kex->min || (u_int)bits > kex->max) {
109 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
110 goto out;
111 }
112 if ((kex->dh = dh_new_group(g, p)) == NULL) {
113 r = SSH_ERR_ALLOC_FAIL;
114 goto out;
115 }
116 p = g = NULL; /* belong to kex->dh now */
117
118 /* generate and send 'e', client DH public key */
119 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
120 goto out;
121 DH_get0_key(kex->dh, &pub_key, NULL);
122 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
123 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
124 (r = sshpkt_send(ssh)) != 0)
125 goto out;
126 debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
127 #ifdef DEBUG_KEXDH
128 DHparams_print_fp(stderr, kex->dh);
129 fprintf(stderr, "pub= ");
130 BN_print_fp(stderr, pub_key);
131 fprintf(stderr, "\n");
132 #endif
133 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL);
134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
135 r = 0;
136 out:
137 BN_clear_free(p);
138 BN_clear_free(g);
139 return r;
140 }
141
142 static int
input_kex_dh_gex_reply(int type,u_int32_t seq,struct ssh * ssh)143 input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
144 {
145 struct kex *kex = ssh->kex;
146 BIGNUM *dh_server_pub = NULL;
147 const BIGNUM *pub_key, *dh_p, *dh_g;
148 struct sshbuf *shared_secret = NULL;
149 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
150 struct sshkey *server_host_key = NULL;
151 u_char *signature = NULL;
152 u_char hash[SSH_DIGEST_MAX_LENGTH];
153 size_t slen, hashlen;
154 int r;
155
156 debug("got SSH2_MSG_KEX_DH_GEX_REPLY");
157 /* key, cert */
158 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
159 goto out;
160 /* sshkey_fromb() consumes its buffer, so make a copy */
161 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
162 r = SSH_ERR_ALLOC_FAIL;
163 goto out;
164 }
165 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 ||
166 (r = kex_verify_host_key(ssh, server_host_key)) != 0)
167 goto out;
168 /* DH parameter f, server public DH key, signed H */
169 if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 ||
170 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
171 (r = sshpkt_get_end(ssh)) != 0)
172 goto out;
173 if ((shared_secret = sshbuf_new()) == NULL) {
174 r = SSH_ERR_ALLOC_FAIL;
175 goto out;
176 }
177 if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0)
178 goto out;
179 if (ssh->compat & SSH_OLD_DHGEX)
180 kex->min = kex->max = -1;
181
182 /* calc and verify H */
183 DH_get0_key(kex->dh, &pub_key, NULL);
184 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
185 hashlen = sizeof(hash);
186 if ((r = kexgex_hash(
187 kex->hash_alg,
188 kex->client_version,
189 kex->server_version,
190 kex->my,
191 kex->peer,
192 server_host_key_blob,
193 kex->min, kex->nbits, kex->max,
194 dh_p, dh_g,
195 pub_key,
196 dh_server_pub,
197 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
198 hash, &hashlen)) != 0)
199 goto out;
200
201 if ((r = sshkey_verify(server_host_key, signature, slen, hash,
202 hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0)
203 goto out;
204
205 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
206 r = kex_send_newkeys(ssh);
207 out:
208 explicit_bzero(hash, sizeof(hash));
209 DH_free(kex->dh);
210 kex->dh = NULL;
211 BN_clear_free(dh_server_pub);
212 sshbuf_free(shared_secret);
213 sshkey_free(server_host_key);
214 sshbuf_free(tmp);
215 sshbuf_free(server_host_key_blob);
216 free(signature);
217 return r;
218 }
219 #endif /* WITH_OPENSSL */
220