xref: /openssh-portable/kexgexc.c (revision 3dd0c64e)
1 /* $OpenBSD: kexgexc.c,v 1.37 2021/01/31 22:55:29 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 (ssh->compat & 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 	debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
87 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
88 	    &input_kex_dh_gex_group);
89 	r = 0;
90  out:
91 	return r;
92 }
93 
94 static int
input_kex_dh_gex_group(int type,u_int32_t seq,struct ssh * ssh)95 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
96 {
97 	struct kex *kex = ssh->kex;
98 	BIGNUM *p = NULL, *g = NULL;
99 	const BIGNUM *pub_key;
100 	int r, bits;
101 
102 	debug("SSH2_MSG_KEX_DH_GEX_GROUP received");
103 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, &kex_protocol_error);
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 		goto out;
123 	DH_get0_key(kex->dh, &pub_key, NULL);
124 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
125 	    (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
126 	    (r = sshpkt_send(ssh)) != 0)
127 		goto out;
128 	debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
129 #ifdef DEBUG_KEXDH
130 	DHparams_print_fp(stderr, kex->dh);
131 	fprintf(stderr, "pub= ");
132 	BN_print_fp(stderr, pub_key);
133 	fprintf(stderr, "\n");
134 #endif
135 	debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
136 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
137 	r = 0;
138 out:
139 	BN_clear_free(p);
140 	BN_clear_free(g);
141 	return r;
142 }
143 
144 static int
input_kex_dh_gex_reply(int type,u_int32_t seq,struct ssh * ssh)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;
149 	const BIGNUM *pub_key, *dh_p, *dh_g;
150 	struct sshbuf *shared_secret = NULL;
151 	struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
152 	struct sshkey *server_host_key = NULL;
153 	u_char *signature = NULL;
154 	u_char hash[SSH_DIGEST_MAX_LENGTH];
155 	size_t slen, hashlen;
156 	int r;
157 
158 	debug("SSH2_MSG_KEX_DH_GEX_REPLY received");
159 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &kex_protocol_error);
160 
161 	/* key, cert */
162 	if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
163 		goto out;
164 	/* sshkey_fromb() consumes its buffer, so make a copy */
165 	if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
166 		r = SSH_ERR_ALLOC_FAIL;
167 		goto out;
168 	}
169 	if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 ||
170 	    (r = kex_verify_host_key(ssh, server_host_key)) != 0)
171 		goto out;
172 	/* DH parameter f, server public DH key, signed H */
173 	if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 ||
174 	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
175 	    (r = sshpkt_get_end(ssh)) != 0)
176 		goto out;
177 	if ((shared_secret = sshbuf_new()) == NULL) {
178 		r = SSH_ERR_ALLOC_FAIL;
179 		goto out;
180 	}
181 	if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0)
182 		goto out;
183 	if (ssh->compat & SSH_OLD_DHGEX)
184 		kex->min = kex->max = -1;
185 
186 	/* calc and verify H */
187 	DH_get0_key(kex->dh, &pub_key, NULL);
188 	DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
189 	hashlen = sizeof(hash);
190 	if ((r = kexgex_hash(
191 	    kex->hash_alg,
192 	    kex->client_version,
193 	    kex->server_version,
194 	    kex->my,
195 	    kex->peer,
196 	    server_host_key_blob,
197 	    kex->min, kex->nbits, kex->max,
198 	    dh_p, dh_g,
199 	    pub_key,
200 	    dh_server_pub,
201 	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
202 	    hash, &hashlen)) != 0)
203 		goto out;
204 
205 	if ((r = sshkey_verify(server_host_key, signature, slen, hash,
206 	    hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0)
207 		goto out;
208 
209 	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
210 		r = kex_send_newkeys(ssh);
211  out:
212 	explicit_bzero(hash, sizeof(hash));
213 	DH_free(kex->dh);
214 	kex->dh = NULL;
215 	BN_clear_free(dh_server_pub);
216 	sshbuf_free(shared_secret);
217 	sshkey_free(server_host_key);
218 	sshbuf_free(tmp);
219 	sshbuf_free(server_host_key_blob);
220 	free(signature);
221 	return r;
222 }
223 #endif /* WITH_OPENSSL */
224