crypto/ec/ecdh_ossl.c

   1 /*
   2  * Copyright 2002-2018 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 #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_lcl.h"
  21
  22 int 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  */
  38 int 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_ex(ecdh->libctx)) == 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 }