1 /* $OpenBSD: ecdh.c,v 1.10 2023/07/28 09:31:21 tb Exp $ */
2 /* ====================================================================
3 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
4 *
5 * The Elliptic Curve Public-Key Crypto Library (ECC Code) included
6 * herein is developed by SUN MICROSYSTEMS, INC., and is contributed
7 * to the OpenSSL project.
8 *
9 * The ECC Code is licensed pursuant to the OpenSSL open source
10 * license provided below.
11 *
12 * The ECDH software is originally written by Douglas Stebila of
13 * Sun Microsystems Laboratories.
14 *
15 */
16 /* ====================================================================
17 * Copyright (c) 1998-2003 The OpenSSL Project. All rights reserved.
18 *
19 * Redistribution and use in source and binary forms, with or without
20 * modification, are permitted provided that the following conditions
21 * are met:
22 *
23 * 1. Redistributions of source code must retain the above copyright
24 * notice, this list of conditions and the following disclaimer.
25 *
26 * 2. Redistributions in binary form must reproduce the above copyright
27 * notice, this list of conditions and the following disclaimer in
28 * the documentation and/or other materials provided with the
29 * distribution.
30 *
31 * 3. All advertising materials mentioning features or use of this
32 * software must display the following acknowledgment:
33 * "This product includes software developed by the OpenSSL Project
34 * for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
35 *
36 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
37 * endorse or promote products derived from this software without
38 * prior written permission. For written permission, please contact
39 * openssl-core@OpenSSL.org.
40 *
41 * 5. Products derived from this software may not be called "OpenSSL"
42 * nor may "OpenSSL" appear in their names without prior written
43 * permission of the OpenSSL Project.
44 *
45 * 6. Redistributions of any form whatsoever must retain the following
46 * acknowledgment:
47 * "This product includes software developed by the OpenSSL Project
48 * for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
49 *
50 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
51 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
52 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
53 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
54 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
55 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
56 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
57 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
58 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
59 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
60 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
61 * OF THE POSSIBILITY OF SUCH DAMAGE.
62 * ====================================================================
63 *
64 * This product includes cryptographic software written by Eric Young
65 * (eay@cryptsoft.com). This product includes software written by Tim
66 * Hudson (tjh@cryptsoft.com).
67 *
68 */
69
70 #include <limits.h>
71 #include <stdlib.h>
72 #include <string.h>
73
74 #include <openssl/bn.h>
75 #include <openssl/ec.h>
76 #include <openssl/err.h>
77 #include <openssl/evp.h>
78
79 #include "ec_local.h"
80
81 /*
82 * Key derivation function from X9.63/SECG.
83 */
84
85 /* Way more than we will ever need */
86 #define ECDH_KDF_MAX (1 << 30)
87
88 int
ecdh_KDF_X9_63(unsigned char * out,size_t outlen,const unsigned char * Z,size_t Zlen,const unsigned char * sinfo,size_t sinfolen,const EVP_MD * md)89 ecdh_KDF_X9_63(unsigned char *out, size_t outlen, const unsigned char *Z,
90 size_t Zlen, const unsigned char *sinfo, size_t sinfolen, const EVP_MD *md)
91 {
92 EVP_MD_CTX *mctx = NULL;
93 unsigned int i;
94 size_t mdlen;
95 unsigned char ctr[4];
96 int rv = 0;
97
98 if (sinfolen > ECDH_KDF_MAX || outlen > ECDH_KDF_MAX ||
99 Zlen > ECDH_KDF_MAX)
100 return 0;
101 mctx = EVP_MD_CTX_new();
102 if (mctx == NULL)
103 return 0;
104 mdlen = EVP_MD_size(md);
105 for (i = 1;; i++) {
106 unsigned char mtmp[EVP_MAX_MD_SIZE];
107 if (!EVP_DigestInit_ex(mctx, md, NULL))
108 goto err;
109 ctr[3] = i & 0xFF;
110 ctr[2] = (i >> 8) & 0xFF;
111 ctr[1] = (i >> 16) & 0xFF;
112 ctr[0] = (i >> 24) & 0xFF;
113 if (!EVP_DigestUpdate(mctx, Z, Zlen))
114 goto err;
115 if (!EVP_DigestUpdate(mctx, ctr, sizeof(ctr)))
116 goto err;
117 if (!EVP_DigestUpdate(mctx, sinfo, sinfolen))
118 goto err;
119 if (outlen >= mdlen) {
120 if (!EVP_DigestFinal(mctx, out, NULL))
121 goto err;
122 outlen -= mdlen;
123 if (outlen == 0)
124 break;
125 out += mdlen;
126 } else {
127 if (!EVP_DigestFinal(mctx, mtmp, NULL))
128 goto err;
129 memcpy(out, mtmp, outlen);
130 explicit_bzero(mtmp, mdlen);
131 break;
132 }
133 }
134 rv = 1;
135
136 err:
137 EVP_MD_CTX_free(mctx);
138
139 return rv;
140 }
141
142 /*
143 * Based on the ECKAS-DH1 and ECSVDP-DH primitives in the IEEE 1363 standard.
144 */
145 int
ecdh_compute_key(unsigned char ** out,size_t * out_len,const EC_POINT * pub_key,const EC_KEY * ecdh)146 ecdh_compute_key(unsigned char **out, size_t *out_len, const EC_POINT *pub_key,
147 const EC_KEY *ecdh)
148 {
149 BN_CTX *ctx;
150 BIGNUM *x;
151 const BIGNUM *priv_key;
152 const EC_GROUP *group;
153 EC_POINT *point = NULL;
154 unsigned char *buf = NULL;
155 int buf_len = 0;
156 int ret = 0;
157
158 *out = NULL;
159 *out_len = 0;
160
161 if ((ctx = BN_CTX_new()) == NULL)
162 goto err;
163
164 BN_CTX_start(ctx);
165
166 if ((x = BN_CTX_get(ctx)) == NULL)
167 goto err;
168
169 if ((group = EC_KEY_get0_group(ecdh)) == NULL)
170 goto err;
171
172 if (EC_POINT_is_on_curve(group, pub_key, ctx) <= 0)
173 goto err;
174
175 if ((point = EC_POINT_new(group)) == NULL) {
176 ECerror(ERR_R_MALLOC_FAILURE);
177 goto err;
178 }
179
180 if ((priv_key = EC_KEY_get0_private_key(ecdh)) == NULL) {
181 ECerror(EC_R_MISSING_PRIVATE_KEY);
182 goto err;
183 }
184
185 if (!EC_POINT_mul(group, point, NULL, pub_key, priv_key, ctx)) {
186 ECerror(EC_R_POINT_ARITHMETIC_FAILURE);
187 goto err;
188 }
189
190 if (!EC_POINT_get_affine_coordinates(group, point, x, NULL, ctx)) {
191 ECerror(EC_R_POINT_ARITHMETIC_FAILURE);
192 goto err;
193 }
194
195 if ((buf_len = ECDH_size(ecdh)) < BN_num_bytes(x)) {
196 ECerror(ERR_R_INTERNAL_ERROR);
197 goto err;
198 }
199 if ((buf = calloc(1, buf_len)) == NULL) {
200 ECerror(ERR_R_MALLOC_FAILURE);
201 goto err;
202 }
203 if (BN_bn2binpad(x, buf, buf_len) != buf_len) {
204 ECerror(ERR_R_BN_LIB);
205 goto err;
206 }
207
208 *out = buf;
209 *out_len = buf_len;
210 buf = NULL;
211 buf_len = 0;
212
213 ret = 1;
214
215 err:
216 EC_POINT_free(point);
217 BN_CTX_end(ctx);
218 BN_CTX_free(ctx);
219 freezero(buf, buf_len);
220
221 return ret;
222 }
223
224 int
ECDH_compute_key(void * out,size_t out_len,const EC_POINT * pub_key,EC_KEY * eckey,void * (* KDF)(const void * in,size_t inlen,void * out,size_t * out_len))225 ECDH_compute_key(void *out, size_t out_len, const EC_POINT *pub_key,
226 EC_KEY *eckey,
227 void *(*KDF)(const void *in, size_t inlen, void *out, size_t *out_len))
228 {
229 unsigned char *secret = NULL;
230 size_t secret_len = 0;
231 int ret = 0;
232
233 if (eckey->meth->compute_key == NULL) {
234 ECerror(EC_R_NOT_IMPLEMENTED);
235 goto err;
236 }
237
238 if (out_len > INT_MAX) {
239 ECerror(EC_R_INVALID_OUTPUT_LENGTH);
240 goto err;
241 }
242
243 if (!eckey->meth->compute_key(&secret, &secret_len, pub_key, eckey))
244 goto err;
245
246 memset(out, 0, out_len);
247 if (KDF != NULL) {
248 if (KDF(secret, secret_len, out, &out_len) == NULL) {
249 ECerror(EC_R_KDF_FAILED);
250 goto err;
251 }
252 } else {
253 if (out_len < secret_len) {
254 /* The resulting key would be truncated. */
255 ECerror(EC_R_KEY_TRUNCATION);
256 goto err;
257 }
258 out_len = secret_len;
259 memcpy(out, secret, out_len);
260 }
261
262 if (out_len > INT_MAX) {
263 ECerror(EC_R_INVALID_OUTPUT_LENGTH);
264 goto err;
265 }
266
267 ret = out_len;
268
269 err:
270 freezero(secret, secret_len);
271
272 return ret;
273 }
274 LCRYPTO_ALIAS(ECDH_compute_key);
275
276 int
ECDH_size(const EC_KEY * d)277 ECDH_size(const EC_KEY *d)
278 {
279 return (EC_GROUP_get_degree(EC_KEY_get0_group(d)) + 7) / 8;
280 }
281 LCRYPTO_ALIAS(ECDH_size);
282