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/*
* Copyright (C) 2011 Free Software Foundation, Inc.
*
* This file is part of GNUTLS.
*
* The GNUTLS library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* as published by the Free Software Foundation; either version 3 of
* the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>
*
*/
/* Based on public domain code of LibTomCrypt by Tom St Denis.
* Adapted to gmp and nettle by Nikos Mavrogiannopoulos.
*/
#include "ecc.h"
#include <string.h>
/*
@file ecc_shared_secret.c
ECC Crypto, Tom St Denis
*/
/*
Create an ECC shared secret between two keys
@param private_key The private ECC key
@param public_key The public key
@param out [out] Destination of the shared secret (Conforms to EC-DH from ANSI X9.63)
@param outlen [in/out] The max size and resulting size of the shared secret
@return 0 if successful
*/
int
ecc_shared_secret (ecc_key * private_key, ecc_key * public_key,
unsigned char *out, unsigned long *outlen)
{
unsigned long x;
ecc_point *result;
int err;
if (private_key == NULL || public_key == NULL || out == NULL || outlen == NULL)
return -1;
/* type valid? */
if (private_key->type != PK_PRIVATE)
{
return -1;
}
/* make new point */
result = ecc_new_point ();
if (result == NULL)
{
return -1;
}
if ((err =
ecc_mulmod (private_key->k, &public_key->pubkey, result,
private_key->A, private_key->prime, 1)) != 0)
{
goto done;
}
x = nettle_mpz_sizeinbase_256_u (private_key->prime);
if (*outlen < x)
{
*outlen = x;
err = -1;
goto done;
}
nettle_mpz_get_str_256(x, out, result->x);
err = 0;
*outlen = x;
done:
ecc_del_point (result);
return err;
}
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_shared_secret.c,v $ */
/* $Revision: 1.10 $ */
/* $Date: 2007/05/12 14:32:35 $ */
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