lib/nettle/ecc_shared_secret.c

   1 /*
   2  * Copyright (C) 2011-2012 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GNUTLS.
   5  *
   6  * The GNUTLS library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public License
   8  * as published by the Free Software Foundation; either version 3 of
   9  * the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>
  18  *
  19  */
  20
  21 /* Based on public domain code of LibTomCrypt by Tom St Denis.
  22  * Adapted to gmp and nettle by Nikos Mavrogiannopoulos.
  23  */
  24
  25 #include "ecc.h"
  26 #include <string.h>
  27
  28 /*
  29   @file ecc_shared_secret.c
  30   ECC Crypto, Tom St Denis
  31 */
  32
  33 /*
  34   Create an ECC shared secret between two keys
  35   @param private_key      The private ECC key
  36   @param public_key       The public key
  37   @param out              [out] Destination of the shared secret (Conforms to EC-DH from ANSI X9.63)
  38   @param outlen           [in/out] The max size and resulting size of the shared secret
  39   @return 0 if successful
  40 */
  41 int
  42 ecc_shared_secret (ecc_key * private_key, ecc_key * public_key,
  43                    unsigned char *out, unsigned long *outlen)
  44 {
  45   unsigned long x;
  46   ecc_point *result;
  47   int err;
  48
  49   if (private_key == NULL || public_key == NULL || out == NULL || outlen == NULL)
  50     return -1;
  51
  52   /* type valid? */
  53   if (private_key->type != PK_PRIVATE)
  54     {
  55       return -1;
  56     }
  57
  58   /* make new point */
  59   result = ecc_new_point ();
  60   if (result == NULL)
  61     {
  62       return -1;
  63     }
  64
  65   if ((err =
  66        ecc_mulmod (private_key->k, &public_key->pubkey, result,
  67                        private_key->A, private_key->prime, 1)) != 0)
  68     {
  69       goto done;
  70     }
  71
  72   x = nettle_mpz_sizeinbase_256_u (private_key->prime);
  73   if (*outlen < x)
  74     {
  75       *outlen = x;
  76       err = -1;
  77       goto done;
  78     }
  79   nettle_mpz_get_str_256(x, out, result->x);
  80
  81   err = 0;
  82   *outlen = x;
  83 done:
  84   ecc_del_point (result);
  85   return err;
  86 }
  87
  88 /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_shared_secret.c,v $ */
  89 /* $Revision: 1.10 $ */
  90 /* $Date: 2007/05/12 14:32:35 $ */