1 /*
2 * Copyright 2002-2021 The OpenSSL Project Authors. All Rights Reserved.
3 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
4 *
5 * Licensed under the Apache License 2.0 (the "License"). You may not use
6 * this file except in compliance with the License. You can obtain a copy
7 * in the file LICENSE in the source distribution or at
8 * https://www.openssl.org/source/license.html
9 */
10
11 /*
12 * ECDH low level APIs are deprecated for public use, but still ok for
13 * internal use.
14 */
15 #include "internal/deprecated.h"
16
17 #include <string.h>
18 #include <limits.h>
19
20 #include "internal/cryptlib.h"
21
22 #include <openssl/err.h>
23 #include <openssl/bn.h>
24 #include <openssl/objects.h>
25 #include <openssl/ec.h>
26 #include "ec_local.h"
27
ossl_ecdh_compute_key(unsigned char ** psec,size_t * pseclen,const EC_POINT * pub_key,const EC_KEY * ecdh)28 int ossl_ecdh_compute_key(unsigned char **psec, size_t *pseclen,
29 const EC_POINT *pub_key, const EC_KEY *ecdh)
30 {
31 if (ecdh->group->meth->ecdh_compute_key == NULL) {
32 ERR_raise(ERR_LIB_EC, EC_R_CURVE_DOES_NOT_SUPPORT_ECDH);
33 return 0;
34 }
35
36 return ecdh->group->meth->ecdh_compute_key(psec, pseclen, pub_key, ecdh);
37 }
38
39 /*-
40 * This implementation is based on the following primitives in the
41 * IEEE 1363 standard:
42 * - ECKAS-DH1
43 * - ECSVDP-DH
44 *
45 * It also conforms to SP800-56A r3
46 * See Section 5.7.1.2 "Elliptic Curve Cryptography Cofactor Diffie-Hellman
47 * (ECC CDH) Primitive:". The steps listed below refer to SP800-56A.
48 */
ossl_ecdh_simple_compute_key(unsigned char ** pout,size_t * poutlen,const EC_POINT * pub_key,const EC_KEY * ecdh)49 int ossl_ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
50 const EC_POINT *pub_key, const EC_KEY *ecdh)
51 {
52 BN_CTX *ctx;
53 EC_POINT *tmp = NULL;
54 BIGNUM *x = NULL;
55 const BIGNUM *priv_key;
56 const EC_GROUP *group;
57 int ret = 0;
58 size_t buflen, len;
59 unsigned char *buf = NULL;
60
61 if ((ctx = BN_CTX_new_ex(ecdh->libctx)) == NULL)
62 goto err;
63 BN_CTX_start(ctx);
64 x = BN_CTX_get(ctx);
65 if (x == NULL) {
66 ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
67 goto err;
68 }
69
70 priv_key = EC_KEY_get0_private_key(ecdh);
71 if (priv_key == NULL) {
72 ERR_raise(ERR_LIB_EC, EC_R_MISSING_PRIVATE_KEY);
73 goto err;
74 }
75
76 group = EC_KEY_get0_group(ecdh);
77
78 /*
79 * Step(1) - Compute the point tmp = cofactor * owners_private_key
80 * * peer_public_key.
81 */
82 if (EC_KEY_get_flags(ecdh) & EC_FLAG_COFACTOR_ECDH) {
83 if (!EC_GROUP_get_cofactor(group, x, NULL)) {
84 ERR_raise(ERR_LIB_EC, ERR_R_EC_LIB);
85 goto err;
86 }
87 if (!BN_mul(x, x, priv_key, ctx)) {
88 ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
89 goto err;
90 }
91 priv_key = x;
92 }
93
94 if ((tmp = EC_POINT_new(group)) == NULL) {
95 ERR_raise(ERR_LIB_EC, ERR_R_EC_LIB);
96 goto err;
97 }
98
99 if (!EC_POINT_mul(group, tmp, NULL, pub_key, priv_key, ctx)) {
100 ERR_raise(ERR_LIB_EC, EC_R_POINT_ARITHMETIC_FAILURE);
101 goto err;
102 }
103
104 /*
105 * Step(2) : If point tmp is at infinity then clear intermediate values and
106 * exit. Note: getting affine coordinates returns 0 if point is at infinity.
107 * Step(3a) : Get x-coordinate of point x = tmp.x
108 */
109 if (!EC_POINT_get_affine_coordinates(group, tmp, x, NULL, ctx)) {
110 ERR_raise(ERR_LIB_EC, EC_R_POINT_ARITHMETIC_FAILURE);
111 goto err;
112 }
113
114 /*
115 * Step(3b) : convert x to a byte string, using the field-element-to-byte
116 * string conversion routine defined in Appendix C.2
117 */
118 buflen = (EC_GROUP_get_degree(group) + 7) / 8;
119 len = BN_num_bytes(x);
120 if (len > buflen) {
121 ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
122 goto err;
123 }
124 if ((buf = OPENSSL_malloc(buflen)) == NULL)
125 goto err;
126
127 memset(buf, 0, buflen - len);
128 if (len != (size_t)BN_bn2bin(x, buf + buflen - len)) {
129 ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
130 goto err;
131 }
132
133 *pout = buf;
134 *poutlen = buflen;
135 buf = NULL;
136
137 ret = 1;
138
139 err:
140 /* Step(4) : Destroy all intermediate calculations */
141 BN_clear(x);
142 EC_POINT_clear_free(tmp);
143 BN_CTX_end(ctx);
144 BN_CTX_free(ctx);
145 OPENSSL_free(buf);
146 return ret;
147 }
148
