xref: /freebsd/crypto/openssh/kexgexs.c (revision 1fb62fb074788ca4713551be09d6569966a3abee)
1 /* $OpenBSD: kexgexs.c,v 1.26 2015/12/04 16:41:28 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/param.h>	/* MIN MAX */
32 
33 #include <stdarg.h>
34 #include <stdio.h>
35 #include <string.h>
36 #include <signal.h>
37 
38 #include <openssl/dh.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 #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 
57 static int input_kex_dh_gex_request(int, u_int32_t, void *);
58 static int input_kex_dh_gex_init(int, u_int32_t, void *);
59 
60 int
61 kexgex_server(struct ssh *ssh)
62 {
63 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
64 	    &input_kex_dh_gex_request);
65 	debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST");
66 	return 0;
67 }
68 
69 static int
70 input_kex_dh_gex_request(int type, u_int32_t seq, void *ctxt)
71 {
72 	struct ssh *ssh = ctxt;
73 	struct kex *kex = ssh->kex;
74 	int r;
75 	u_int min = 0, max = 0, nbits = 0;
76 
77 	debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
78 	if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
79 	    (r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
80 	    (r = sshpkt_get_u32(ssh, &max)) != 0 ||
81 	    (r = sshpkt_get_end(ssh)) != 0)
82 		goto out;
83 	kex->nbits = nbits;
84 	kex->min = min;
85 	kex->max = max;
86 	min = MAX(DH_GRP_MIN, min);
87 	max = MIN(DH_GRP_MAX, max);
88 	nbits = MAX(DH_GRP_MIN, nbits);
89 	nbits = MIN(DH_GRP_MAX, nbits);
90 
91 	if (kex->max < kex->min || kex->nbits < kex->min ||
92 	    kex->max < kex->nbits) {
93 		r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
94 		goto out;
95 	}
96 
97 	/* Contact privileged parent */
98 	kex->dh = PRIVSEP(choose_dh(min, nbits, max));
99 	if (kex->dh == NULL) {
100 		sshpkt_disconnect(ssh, "no matching DH grp found");
101 		r = SSH_ERR_ALLOC_FAIL;
102 		goto out;
103 	}
104 	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
105 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
106 	    (r = sshpkt_put_bignum2(ssh, kex->dh->p)) != 0 ||
107 	    (r = sshpkt_put_bignum2(ssh, kex->dh->g)) != 0 ||
108 	    (r = sshpkt_send(ssh)) != 0)
109 		goto out;
110 
111 	/* Compute our exchange value in parallel with the client */
112 	if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
113 		goto out;
114 
115 	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
116 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
117 	r = 0;
118  out:
119 	return r;
120 }
121 
122 static int
123 input_kex_dh_gex_init(int type, u_int32_t seq, void *ctxt)
124 {
125 	struct ssh *ssh = ctxt;
126 	struct kex *kex = ssh->kex;
127 	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
128 	struct sshkey *server_host_public, *server_host_private;
129 	u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
130 	u_char hash[SSH_DIGEST_MAX_LENGTH];
131 	size_t sbloblen, slen;
132 	size_t klen = 0, hashlen;
133 	int kout, r;
134 
135 	if (kex->load_host_public_key == NULL ||
136 	    kex->load_host_private_key == NULL) {
137 		r = SSH_ERR_INVALID_ARGUMENT;
138 		goto out;
139 	}
140 	server_host_public = kex->load_host_public_key(kex->hostkey_type,
141 	    kex->hostkey_nid, ssh);
142 	server_host_private = kex->load_host_private_key(kex->hostkey_type,
143 	    kex->hostkey_nid, ssh);
144 	if (server_host_public == NULL) {
145 		r = SSH_ERR_NO_HOSTKEY_LOADED;
146 		goto out;
147 	}
148 
149 	/* key, cert */
150 	if ((dh_client_pub = BN_new()) == NULL) {
151 		r = SSH_ERR_ALLOC_FAIL;
152 		goto out;
153 	}
154 	if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 ||
155 	    (r = sshpkt_get_end(ssh)) != 0)
156 		goto out;
157 
158 #ifdef DEBUG_KEXDH
159 	fprintf(stderr, "dh_client_pub= ");
160 	BN_print_fp(stderr, dh_client_pub);
161 	fprintf(stderr, "\n");
162 	debug("bits %d", BN_num_bits(dh_client_pub));
163 #endif
164 
165 #ifdef DEBUG_KEXDH
166 	DHparams_print_fp(stderr, kex->dh);
167 	fprintf(stderr, "pub= ");
168 	BN_print_fp(stderr, kex->dh->pub_key);
169 	fprintf(stderr, "\n");
170 #endif
171 	if (!dh_pub_is_valid(kex->dh, dh_client_pub)) {
172 		sshpkt_disconnect(ssh, "bad client public DH value");
173 		r = SSH_ERR_MESSAGE_INCOMPLETE;
174 		goto out;
175 	}
176 
177 	klen = DH_size(kex->dh);
178 	if ((kbuf = malloc(klen)) == NULL ||
179 	    (shared_secret = BN_new()) == NULL) {
180 		r = SSH_ERR_ALLOC_FAIL;
181 		goto out;
182 	}
183 	if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 ||
184 	    BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
185 		r = SSH_ERR_LIBCRYPTO_ERROR;
186 		goto out;
187 	}
188 #ifdef DEBUG_KEXDH
189 	dump_digest("shared secret", kbuf, kout);
190 #endif
191 	if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
192 	    &sbloblen)) != 0)
193 		goto out;
194 	/* calc H */
195 	hashlen = sizeof(hash);
196 	if ((r = kexgex_hash(
197 	    kex->hash_alg,
198 	    kex->client_version_string,
199 	    kex->server_version_string,
200 	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
201 	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
202 	    server_host_key_blob, sbloblen,
203 	    kex->min, kex->nbits, kex->max,
204 	    kex->dh->p, kex->dh->g,
205 	    dh_client_pub,
206 	    kex->dh->pub_key,
207 	    shared_secret,
208 	    hash, &hashlen)) != 0)
209 		goto out;
210 
211 	/* save session id := H */
212 	if (kex->session_id == NULL) {
213 		kex->session_id_len = hashlen;
214 		kex->session_id = malloc(kex->session_id_len);
215 		if (kex->session_id == NULL) {
216 			r = SSH_ERR_ALLOC_FAIL;
217 			goto out;
218 		}
219 		memcpy(kex->session_id, hash, kex->session_id_len);
220 	}
221 
222 	/* sign H */
223 	if ((r = kex->sign(server_host_private, server_host_public, &signature,
224 	     &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
225 		goto out;
226 
227 	/* destroy_sensitive_data(); */
228 
229 	/* send server hostkey, DH pubkey 'f' and singed H */
230 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
231 	    (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
232 	    (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 ||     /* f */
233 	    (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
234 	    (r = sshpkt_send(ssh)) != 0)
235 		goto out;
236 
237 	if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
238 		r = kex_send_newkeys(ssh);
239  out:
240 	DH_free(kex->dh);
241 	kex->dh = NULL;
242 	if (dh_client_pub)
243 		BN_clear_free(dh_client_pub);
244 	if (kbuf) {
245 		explicit_bzero(kbuf, klen);
246 		free(kbuf);
247 	}
248 	if (shared_secret)
249 		BN_clear_free(shared_secret);
250 	free(server_host_key_blob);
251 	free(signature);
252 	return r;
253 }
254 #endif /* WITH_OPENSSL */
255