2 * Copyright 2002-2018 The OpenSSL Project Authors. All Rights Reserved.
3 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
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
12 * ECDH low level APIs are deprecated for public use, but still ok for
15 #include "internal/deprecated.h"
20 #include "internal/cryptlib.h"
22 #include <openssl/err.h>
23 #include <openssl/bn.h>
24 #include <openssl/objects.h>
25 #include <openssl/ec.h>
28 int ossl_ecdh_compute_key(unsigned char **psec, size_t *pseclen,
29 const EC_POINT *pub_key, const EC_KEY *ecdh)
31 if (ecdh->group->meth->ecdh_compute_key == NULL) {
32 ECerr(EC_F_OSSL_ECDH_COMPUTE_KEY, EC_R_CURVE_DOES_NOT_SUPPORT_ECDH);
36 return ecdh->group->meth->ecdh_compute_key(psec, pseclen, pub_key, ecdh);
40 * This implementation is based on the following primitives in the
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.
49 int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
50 const EC_POINT *pub_key, const EC_KEY *ecdh)
55 const BIGNUM *priv_key;
56 const EC_GROUP *group;
59 unsigned char *buf = NULL;
61 if ((ctx = BN_CTX_new_ex(ecdh->libctx)) == NULL)
66 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
70 priv_key = EC_KEY_get0_private_key(ecdh);
71 if (priv_key == NULL) {
72 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_MISSING_PRIVATE_KEY);
76 group = EC_KEY_get0_group(ecdh);
79 * Step(1) - Compute the point tmp = cofactor * owners_private_key
82 if (EC_KEY_get_flags(ecdh) & EC_FLAG_COFACTOR_ECDH) {
83 if (!EC_GROUP_get_cofactor(group, x, NULL) ||
84 !BN_mul(x, x, priv_key, ctx)) {
85 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
91 if ((tmp = EC_POINT_new(group)) == NULL) {
92 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
96 if (!EC_POINT_mul(group, tmp, NULL, pub_key, priv_key, ctx)) {
97 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
102 * Step(2) : If point tmp is at infinity then clear intermediate values and
103 * exit. Note: getting affine coordinates returns 0 if point is at infinity.
104 * Step(3a) : Get x-coordinate of point x = tmp.x
106 if (!EC_POINT_get_affine_coordinates(group, tmp, x, NULL, ctx)) {
107 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
112 * Step(3b) : convert x to a byte string, using the field-element-to-byte
113 * string conversion routine defined in Appendix C.2
115 buflen = (EC_GROUP_get_degree(group) + 7) / 8;
116 len = BN_num_bytes(x);
118 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_INTERNAL_ERROR);
121 if ((buf = OPENSSL_malloc(buflen)) == NULL) {
122 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
126 memset(buf, 0, buflen - len);
127 if (len != (size_t)BN_bn2bin(x, buf + buflen - len)) {
128 ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_BN_LIB);
139 /* Step(4) : Destroy all intermediate calculations */
141 EC_POINT_clear_free(tmp);