xref: /openssh-portable/kexdh.c (revision d5520393)
1 /* $OpenBSD: kexdh.c,v 1.32 2019/01/21 10:40:11 djm Exp $ */
2 /*
3  * Copyright (c) 2019 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 <signal.h>
33 #include <stdio.h>
34 #include <string.h>
35 
36 #include "openbsd-compat/openssl-compat.h"
37 #include <openssl/dh.h>
38 
39 #include "sshkey.h"
40 #include "kex.h"
41 #include "sshbuf.h"
42 #include "digest.h"
43 #include "ssherr.h"
44 #include "dh.h"
45 
46 int
kex_dh_keygen(struct kex * kex)47 kex_dh_keygen(struct kex *kex)
48 {
49 	switch (kex->kex_type) {
50 	case KEX_DH_GRP1_SHA1:
51 		kex->dh = dh_new_group1();
52 		break;
53 	case KEX_DH_GRP14_SHA1:
54 	case KEX_DH_GRP14_SHA256:
55 		kex->dh = dh_new_group14();
56 		break;
57 	case KEX_DH_GRP16_SHA512:
58 		kex->dh = dh_new_group16();
59 		break;
60 	case KEX_DH_GRP18_SHA512:
61 		kex->dh = dh_new_group18();
62 		break;
63 	default:
64 		return SSH_ERR_INVALID_ARGUMENT;
65 	}
66 	if (kex->dh == NULL)
67 		return SSH_ERR_ALLOC_FAIL;
68 	return (dh_gen_key(kex->dh, kex->we_need * 8));
69 }
70 
71 int
kex_dh_compute_key(struct kex * kex,BIGNUM * dh_pub,struct sshbuf * out)72 kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
73 {
74 	BIGNUM *shared_secret = NULL;
75 	u_char *kbuf = NULL;
76 	size_t klen = 0;
77 	int kout, r;
78 
79 #ifdef DEBUG_KEXDH
80 	fprintf(stderr, "dh_pub= ");
81 	BN_print_fp(stderr, dh_pub);
82 	fprintf(stderr, "\n");
83 	debug("bits %d", BN_num_bits(dh_pub));
84 	DHparams_print_fp(stderr, kex->dh);
85 	fprintf(stderr, "\n");
86 #endif
87 
88 	if (!dh_pub_is_valid(kex->dh, dh_pub)) {
89 		r = SSH_ERR_MESSAGE_INCOMPLETE;
90 		goto out;
91 	}
92 	klen = DH_size(kex->dh);
93 	if ((kbuf = malloc(klen)) == NULL ||
94 	    (shared_secret = BN_new()) == NULL) {
95 		r = SSH_ERR_ALLOC_FAIL;
96 		goto out;
97 	}
98 	if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
99 	    BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
100 		r = SSH_ERR_LIBCRYPTO_ERROR;
101 		goto out;
102 	}
103 #ifdef DEBUG_KEXDH
104 	dump_digest("shared secret", kbuf, kout);
105 #endif
106 	r = sshbuf_put_bignum2(out, shared_secret);
107  out:
108 	freezero(kbuf, klen);
109 	BN_clear_free(shared_secret);
110 	return r;
111 }
112 
113 int
kex_dh_keypair(struct kex * kex)114 kex_dh_keypair(struct kex *kex)
115 {
116 	const BIGNUM *pub_key;
117 	struct sshbuf *buf = NULL;
118 	int r;
119 
120 	if ((r = kex_dh_keygen(kex)) != 0)
121 		return r;
122 	DH_get0_key(kex->dh, &pub_key, NULL);
123 	if ((buf = sshbuf_new()) == NULL)
124 		return SSH_ERR_ALLOC_FAIL;
125 	if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
126 	    (r = sshbuf_get_u32(buf, NULL)) != 0)
127 		goto out;
128 #ifdef DEBUG_KEXDH
129 	DHparams_print_fp(stderr, kex->dh);
130 	fprintf(stderr, "pub= ");
131 	BN_print_fp(stderr, pub_key);
132 	fprintf(stderr, "\n");
133 #endif
134 	kex->client_pub = buf;
135 	buf = NULL;
136  out:
137 	sshbuf_free(buf);
138 	return r;
139 }
140 
141 int
kex_dh_enc(struct kex * kex,const struct sshbuf * client_blob,struct sshbuf ** server_blobp,struct sshbuf ** shared_secretp)142 kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
143     struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
144 {
145 	const BIGNUM *pub_key;
146 	struct sshbuf *server_blob = NULL;
147 	int r;
148 
149 	*server_blobp = NULL;
150 	*shared_secretp = NULL;
151 
152 	if ((r = kex_dh_keygen(kex)) != 0)
153 		goto out;
154 	DH_get0_key(kex->dh, &pub_key, NULL);
155 	if ((server_blob = sshbuf_new()) == NULL) {
156 		r = SSH_ERR_ALLOC_FAIL;
157 		goto out;
158 	}
159 	if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
160 	    (r = sshbuf_get_u32(server_blob, NULL)) != 0)
161 		goto out;
162 	if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
163 		goto out;
164 	*server_blobp = server_blob;
165 	server_blob = NULL;
166  out:
167 	DH_free(kex->dh);
168 	kex->dh = NULL;
169 	sshbuf_free(server_blob);
170 	return r;
171 }
172 
173 int
kex_dh_dec(struct kex * kex,const struct sshbuf * dh_blob,struct sshbuf ** shared_secretp)174 kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
175     struct sshbuf **shared_secretp)
176 {
177 	struct sshbuf *buf = NULL;
178 	BIGNUM *dh_pub = NULL;
179 	int r;
180 
181 	*shared_secretp = NULL;
182 
183 	if ((buf = sshbuf_new()) == NULL) {
184 		r = SSH_ERR_ALLOC_FAIL;
185 		goto out;
186 	}
187 	if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
188 	    (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
189 		goto out;
190 	sshbuf_reset(buf);
191 	if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
192 		goto out;
193 	*shared_secretp = buf;
194 	buf = NULL;
195  out:
196 	DH_free(kex->dh);
197 	kex->dh = NULL;
198 	sshbuf_free(buf);
199 	return r;
200 }
201 #endif /* WITH_OPENSSL */
202