• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 /* $OpenBSD: kexdhc.c,v 1.19 2016/05/02 10:26:04 djm Exp $ */
2 /*
3  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24  */
25 
26 #include "includes.h"
27 
28 #ifdef WITH_OPENSSL
29 
30 #include <sys/types.h>
31 
32 #include <openssl/dh.h>
33 
34 #include <stdarg.h>
35 #include <stdio.h>
36 #include <string.h>
37 #include <signal.h>
38 
39 #include "sshkey.h"
40 #include "cipher.h"
41 #include "digest.h"
42 #include "kex.h"
43 #include "log.h"
44 #include "packet.h"
45 #include "dh.h"
46 #include "ssh2.h"
47 #include "dispatch.h"
48 #include "compat.h"
49 #include "ssherr.h"
50 #include "sshbuf.h"
51 
52 static int input_kex_dh(int, u_int32_t, void *);
53 
54 int
kexdh_client(struct ssh * ssh)55 kexdh_client(struct ssh *ssh)
56 {
57 	struct kex *kex = ssh->kex;
58 	int r;
59 
60 	/* generate and send 'e', client DH public key */
61 	switch (kex->kex_type) {
62 	case KEX_DH_GRP1_SHA1:
63 		kex->dh = dh_new_group1();
64 		break;
65 	case KEX_DH_GRP14_SHA1:
66 	case KEX_DH_GRP14_SHA256:
67 		kex->dh = dh_new_group14();
68 		break;
69 	case KEX_DH_GRP16_SHA512:
70 		kex->dh = dh_new_group16();
71 		break;
72 	case KEX_DH_GRP18_SHA512:
73 		kex->dh = dh_new_group18();
74 		break;
75 	default:
76 		r = SSH_ERR_INVALID_ARGUMENT;
77 		goto out;
78 	}
79 	if (kex->dh == NULL) {
80 		r = SSH_ERR_ALLOC_FAIL;
81 		goto out;
82 	}
83 	debug("sending SSH2_MSG_KEXDH_INIT");
84 	if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0 ||
85 	    (r = sshpkt_start(ssh, SSH2_MSG_KEXDH_INIT)) != 0 ||
86 	    (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 ||
87 	    (r = sshpkt_send(ssh)) != 0)
88 		goto out;
89 #ifdef DEBUG_KEXDH
90 	DHparams_print_fp(stderr, kex->dh);
91 	fprintf(stderr, "pub= ");
92 	BN_print_fp(stderr, kex->dh->pub_key);
93 	fprintf(stderr, "\n");
94 #endif
95 	debug("expecting SSH2_MSG_KEXDH_REPLY");
96 	ssh_dispatch_set(ssh, SSH2_MSG_KEXDH_REPLY, &input_kex_dh);
97 	r = 0;
98  out:
99 	return r;
100 }
101 
102 static int
input_kex_dh(int type,u_int32_t seq,void * ctxt)103 input_kex_dh(int type, u_int32_t seq, void *ctxt)
104 {
105 	struct ssh *ssh = ctxt;
106 	struct kex *kex = ssh->kex;
107 	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
108 	struct sshkey *server_host_key = NULL;
109 	u_char *kbuf = NULL, *server_host_key_blob = NULL, *signature = NULL;
110 	u_char hash[SSH_DIGEST_MAX_LENGTH];
111 	size_t klen = 0, slen, sbloblen, hashlen;
112 	int kout, r;
113 
114 	if (kex->verify_host_key == NULL) {
115 		r = SSH_ERR_INVALID_ARGUMENT;
116 		goto out;
117 	}
118 	/* key, cert */
119 	if ((r = sshpkt_get_string(ssh, &server_host_key_blob,
120 	    &sbloblen)) != 0 ||
121 	    (r = sshkey_from_blob(server_host_key_blob, sbloblen,
122 	    &server_host_key)) != 0)
123 		goto out;
124 	if (server_host_key->type != kex->hostkey_type ||
125 	    (kex->hostkey_type == KEY_ECDSA &&
126 	    server_host_key->ecdsa_nid != kex->hostkey_nid)) {
127 		r = SSH_ERR_KEY_TYPE_MISMATCH;
128 		goto out;
129 	}
130 	if (kex->verify_host_key(server_host_key, ssh) == -1) {
131 		r = SSH_ERR_SIGNATURE_INVALID;
132 		goto out;
133 	}
134 	/* DH parameter f, server public DH key */
135 	if ((dh_server_pub = BN_new()) == NULL) {
136 		r = SSH_ERR_ALLOC_FAIL;
137 		goto out;
138 	}
139 	/* signed H */
140 	if ((r = sshpkt_get_bignum2(ssh, dh_server_pub)) != 0 ||
141 	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
142 	    (r = sshpkt_get_end(ssh)) != 0)
143 		goto out;
144 #ifdef DEBUG_KEXDH
145 	fprintf(stderr, "dh_server_pub= ");
146 	BN_print_fp(stderr, dh_server_pub);
147 	fprintf(stderr, "\n");
148 	debug("bits %d", BN_num_bits(dh_server_pub));
149 #endif
150 	if (!dh_pub_is_valid(kex->dh, dh_server_pub)) {
151 		sshpkt_disconnect(ssh, "bad server public DH value");
152 		r = SSH_ERR_MESSAGE_INCOMPLETE;
153 		goto out;
154 	}
155 
156 	klen = DH_size(kex->dh);
157 	if ((kbuf = malloc(klen)) == NULL ||
158 	    (shared_secret = BN_new()) == NULL) {
159 		r = SSH_ERR_ALLOC_FAIL;
160 		goto out;
161 	}
162 	if ((kout = DH_compute_key(kbuf, dh_server_pub, kex->dh)) < 0 ||
163 	    BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
164 		r = SSH_ERR_LIBCRYPTO_ERROR;
165 		goto out;
166 	}
167 #ifdef DEBUG_KEXDH
168 	dump_digest("shared secret", kbuf, kout);
169 #endif
170 
171 	/* calc and verify H */
172 	hashlen = sizeof(hash);
173 	if ((r = kex_dh_hash(
174 	    kex->hash_alg,
175 	    kex->client_version_string,
176 	    kex->server_version_string,
177 	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
178 	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
179 	    server_host_key_blob, sbloblen,
180 	    kex->dh->pub_key,
181 	    dh_server_pub,
182 	    shared_secret,
183 	    hash, &hashlen)) != 0)
184 		goto out;
185 
186 	if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen,
187 	    ssh->compat)) != 0)
188 		goto out;
189 
190 	/* save session id */
191 	if (kex->session_id == NULL) {
192 		kex->session_id_len = hashlen;
193 		kex->session_id = malloc(kex->session_id_len);
194 		if (kex->session_id == NULL) {
195 			r = SSH_ERR_ALLOC_FAIL;
196 			goto out;
197 		}
198 		memcpy(kex->session_id, hash, kex->session_id_len);
199 	}
200 
201 	if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
202 		r = kex_send_newkeys(ssh);
203  out:
204 	explicit_bzero(hash, sizeof(hash));
205 	DH_free(kex->dh);
206 	kex->dh = NULL;
207 	if (dh_server_pub)
208 		BN_clear_free(dh_server_pub);
209 	if (kbuf) {
210 		explicit_bzero(kbuf, klen);
211 		free(kbuf);
212 	}
213 	if (shared_secret)
214 		BN_clear_free(shared_secret);
215 	sshkey_free(server_host_key);
216 	free(server_host_key_blob);
217 	free(signature);
218 	return r;
219 }
220 #endif /* WITH_OPENSSL */
221