xref: /freebsd/crypto/openssh/kexgexc.c (revision 4f52dfbb8d6c4d446500c5b097e3806ec219fbd4)
1 /* $OpenBSD: kexgexc.c,v 1.25 2017/05/30 14:23:52 markus 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, struct ssh *);
55 static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *);
56 
57 int
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
92 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
93 {
94 	struct kex *kex = ssh->kex;
95 	BIGNUM *p = NULL, *g = NULL;
96 	int r, bits;
97 
98 	debug("got SSH2_MSG_KEX_DH_GEX_GROUP");
99 
100 	if ((p = BN_new()) == NULL ||
101 	    (g = BN_new()) == NULL) {
102 		r = SSH_ERR_ALLOC_FAIL;
103 		goto out;
104 	}
105 	if ((r = sshpkt_get_bignum2(ssh, p)) != 0 ||
106 	    (r = sshpkt_get_bignum2(ssh, g)) != 0 ||
107 	    (r = sshpkt_get_end(ssh)) != 0)
108 		goto out;
109 	if ((bits = BN_num_bits(p)) < 0 ||
110 	    (u_int)bits < kex->min || (u_int)bits > kex->max) {
111 		r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
112 		goto out;
113 	}
114 	if ((kex->dh = dh_new_group(g, p)) == NULL) {
115 		r = SSH_ERR_ALLOC_FAIL;
116 		goto out;
117 	}
118 	p = g = NULL; /* belong to kex->dh now */
119 
120 	/* generate and send 'e', client DH public key */
121 	if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0 ||
122 	    (r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
123 	    (r = sshpkt_put_bignum2(ssh, kex->dh->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, kex->dh->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 	if (p)
138 		BN_clear_free(p);
139 	if (g)
140 		BN_clear_free(g);
141 	return r;
142 }
143 
144 static int
145 input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
146 {
147 	struct kex *kex = ssh->kex;
148 	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
149 	struct sshkey *server_host_key = NULL;
150 	u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
151 	u_char hash[SSH_DIGEST_MAX_LENGTH];
152 	size_t klen = 0, slen, sbloblen, hashlen;
153 	int kout, r;
154 
155 	debug("got SSH2_MSG_KEX_DH_GEX_REPLY");
156 	if (kex->verify_host_key == NULL) {
157 		r = SSH_ERR_INVALID_ARGUMENT;
158 		goto out;
159 	}
160 	/* key, cert */
161 	if ((r = sshpkt_get_string(ssh, &server_host_key_blob,
162 	    &sbloblen)) != 0 ||
163 	    (r = sshkey_from_blob(server_host_key_blob, sbloblen,
164 	    &server_host_key)) != 0)
165 		goto out;
166 	if (server_host_key->type != kex->hostkey_type ||
167 	    (kex->hostkey_type == KEY_ECDSA &&
168 	    server_host_key->ecdsa_nid != kex->hostkey_nid)) {
169 		r = SSH_ERR_KEY_TYPE_MISMATCH;
170 		goto out;
171 	}
172 	if (kex->verify_host_key(server_host_key, ssh) == -1) {
173 		r = SSH_ERR_SIGNATURE_INVALID;
174 		goto out;
175 	}
176 	/* DH parameter f, server public DH key */
177 	if ((dh_server_pub = BN_new()) == NULL) {
178 		r = SSH_ERR_ALLOC_FAIL;
179 		goto out;
180 	}
181 	/* signed H */
182 	if ((r = sshpkt_get_bignum2(ssh, dh_server_pub)) != 0 ||
183 	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
184 	    (r = sshpkt_get_end(ssh)) != 0)
185 		goto out;
186 #ifdef DEBUG_KEXDH
187 	fprintf(stderr, "dh_server_pub= ");
188 	BN_print_fp(stderr, dh_server_pub);
189 	fprintf(stderr, "\n");
190 	debug("bits %d", BN_num_bits(dh_server_pub));
191 #endif
192 	if (!dh_pub_is_valid(kex->dh, dh_server_pub)) {
193 		sshpkt_disconnect(ssh, "bad server public DH value");
194 		r = SSH_ERR_MESSAGE_INCOMPLETE;
195 		goto out;
196 	}
197 
198 	klen = DH_size(kex->dh);
199 	if ((kbuf = malloc(klen)) == NULL ||
200 	    (shared_secret = BN_new()) == NULL) {
201 		r = SSH_ERR_ALLOC_FAIL;
202 		goto out;
203 	}
204 	if ((kout = DH_compute_key(kbuf, dh_server_pub, kex->dh)) < 0 ||
205 	    BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
206 		r = SSH_ERR_LIBCRYPTO_ERROR;
207 		goto out;
208 	}
209 #ifdef DEBUG_KEXDH
210 	dump_digest("shared secret", kbuf, kout);
211 #endif
212 	if (ssh->compat & SSH_OLD_DHGEX)
213 		kex->min = kex->max = -1;
214 
215 	/* calc and verify H */
216 	hashlen = sizeof(hash);
217 	if ((r = kexgex_hash(
218 	    kex->hash_alg,
219 	    kex->client_version_string,
220 	    kex->server_version_string,
221 	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
222 	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
223 	    server_host_key_blob, sbloblen,
224 	    kex->min, kex->nbits, kex->max,
225 	    kex->dh->p, kex->dh->g,
226 	    kex->dh->pub_key,
227 	    dh_server_pub,
228 	    shared_secret,
229 	    hash, &hashlen)) != 0)
230 		goto out;
231 
232 	if ((r = sshkey_verify(server_host_key, signature, slen, hash,
233 	    hashlen, ssh->compat)) != 0)
234 		goto out;
235 
236 	/* save session id */
237 	if (kex->session_id == NULL) {
238 		kex->session_id_len = hashlen;
239 		kex->session_id = malloc(kex->session_id_len);
240 		if (kex->session_id == NULL) {
241 			r = SSH_ERR_ALLOC_FAIL;
242 			goto out;
243 		}
244 		memcpy(kex->session_id, hash, kex->session_id_len);
245 	}
246 
247 	if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
248 		r = kex_send_newkeys(ssh);
249  out:
250 	explicit_bzero(hash, sizeof(hash));
251 	DH_free(kex->dh);
252 	kex->dh = NULL;
253 	if (dh_server_pub)
254 		BN_clear_free(dh_server_pub);
255 	if (kbuf) {
256 		explicit_bzero(kbuf, klen);
257 		free(kbuf);
258 	}
259 	if (shared_secret)
260 		BN_clear_free(shared_secret);
261 	sshkey_free(server_host_key);
262 	free(server_host_key_blob);
263 	free(signature);
264 	return r;
265 }
266 #endif /* WITH_OPENSSL */
267