1/*
2 * Copyright 2002-2019 The OpenSSL Project Authors. All Rights Reserved.
3 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
4 *
5 * Licensed under the OpenSSL license (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#include <string.h>
12#include <limits.h>
13
14#include "internal/cryptlib.h"
15
16#include <openssl/err.h>
17#include <openssl/bn.h>
18#include <openssl/objects.h>
19#include <openssl/ec.h>
20#include "ec_local.h"
21
22int ossl_ecdh_compute_key(unsigned char **psec, size_t *pseclen,
23                          const EC_POINT *pub_key, const EC_KEY *ecdh)
24{
25    if (ecdh->group->meth->ecdh_compute_key == NULL) {
26        ECerr(EC_F_OSSL_ECDH_COMPUTE_KEY, EC_R_CURVE_DOES_NOT_SUPPORT_ECDH);
27        return 0;
28    }
29
30    return ecdh->group->meth->ecdh_compute_key(psec, pseclen, pub_key, ecdh);
31}
32
33/*-
34 * This implementation is based on the following primitives in the IEEE 1363 standard:
35 *  - ECKAS-DH1
36 *  - ECSVDP-DH
37 */
38int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
39                            const EC_POINT *pub_key, const EC_KEY *ecdh)
40{
41    BN_CTX *ctx;
42    EC_POINT *tmp = NULL;
43    BIGNUM *x = NULL;
44    const BIGNUM *priv_key;
45    const EC_GROUP *group;
46    int ret = 0;
47    size_t buflen, len;
48    unsigned char *buf = NULL;
49
50    if ((ctx = BN_CTX_new()) == NULL)
51        goto err;
52    BN_CTX_start(ctx);
53    x = BN_CTX_get(ctx);
54    if (x == NULL) {
55        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
56        goto err;
57    }
58
59    priv_key = EC_KEY_get0_private_key(ecdh);
60    if (priv_key == NULL) {
61        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_MISSING_PRIVATE_KEY);
62        goto err;
63    }
64
65    group = EC_KEY_get0_group(ecdh);
66
67    if (EC_KEY_get_flags(ecdh) & EC_FLAG_COFACTOR_ECDH) {
68        if (!EC_GROUP_get_cofactor(group, x, NULL) ||
69            !BN_mul(x, x, priv_key, ctx)) {
70            ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
71            goto err;
72        }
73        priv_key = x;
74    }
75
76    if ((tmp = EC_POINT_new(group)) == NULL) {
77        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
78        goto err;
79    }
80
81    if (!EC_POINT_mul(group, tmp, NULL, pub_key, priv_key, ctx)) {
82        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
83        goto err;
84    }
85
86    if (!EC_POINT_get_affine_coordinates(group, tmp, x, NULL, ctx)) {
87        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
88        goto err;
89    }
90
91    buflen = (EC_GROUP_get_degree(group) + 7) / 8;
92    len = BN_num_bytes(x);
93    if (len > buflen) {
94        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_INTERNAL_ERROR);
95        goto err;
96    }
97    if ((buf = OPENSSL_malloc(buflen)) == NULL) {
98        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
99        goto err;
100    }
101
102    memset(buf, 0, buflen - len);
103    if (len != (size_t)BN_bn2bin(x, buf + buflen - len)) {
104        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_BN_LIB);
105        goto err;
106    }
107
108    *pout = buf;
109    *poutlen = buflen;
110    buf = NULL;
111
112    ret = 1;
113
114 err:
115    EC_POINT_clear_free(tmp);
116    BN_CTX_end(ctx);
117    BN_CTX_free(ctx);
118    OPENSSL_free(buf);
119    return ret;
120}
121