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/*
* Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation
*
* Author: Nikos Mavrogiannopoulos
*
* 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 2.1 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 library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA
*
*/
#include <gnutls_int.h>
#include <gnutls_errors.h>
/*
--Example--
you: X = g ^ x mod p;
peer:Y = g ^ y mod p;
your_key = Y ^ x mod p;
his_key = X ^ y mod p;
// generate our secret and the public value (X) for it
X = mhd_gtls_calc_dh_secret(&x, g, p);
// now we can calculate the shared secret
key = mhd_gtls_calc_dh_key(Y, x, g, p);
mhd_gtls_mpi_release(x);
mhd_gtls_mpi_release(g);
*/
#define MAX_BITS 18000
/* returns the public value (X), and the secret (ret_x).
*/
mpi_t
mhd_gtls_calc_dh_secret (mpi_t * ret_x, mpi_t g, mpi_t prime)
{
mpi_t e, x;
int x_size = _gnutls_mpi_get_nbits (prime) - 1;
/* The size of the secret key is less than
* prime/2
*/
if (x_size > MAX_BITS || x_size <= 0)
{
gnutls_assert ();
return NULL;
}
x = _gnutls_mpi_new (x_size);
if (x == NULL)
{
gnutls_assert ();
if (ret_x)
*ret_x = NULL;
return NULL;
}
/* FIXME: (x_size/8)*8 is there to overcome a bug in libgcrypt
* which does not really check the bits given but the bytes.
*/
do
{
_gnutls_mpi_randomize (x, (x_size / 8) * 8, GCRY_STRONG_RANDOM);
/* Check whether x is zero.
*/
}
while (_gnutls_mpi_cmp_ui (x, 0) == 0);
e = _gnutls_mpi_alloc_like (prime);
if (e == NULL)
{
gnutls_assert ();
if (ret_x)
*ret_x = NULL;
mhd_gtls_mpi_release (&x);
return NULL;
}
_gnutls_mpi_powm (e, g, x, prime);
if (ret_x)
*ret_x = x;
else
mhd_gtls_mpi_release (&x);
return e;
}
mpi_t
mhd_gtls_calc_dh_key (mpi_t f, mpi_t x, mpi_t prime)
{
mpi_t k;
int bits;
bits = _gnutls_mpi_get_nbits (prime);
if (bits <= 0 || bits > MAX_BITS)
{
gnutls_assert ();
return NULL;
}
k = _gnutls_mpi_alloc_like (prime);
if (k == NULL)
return NULL;
_gnutls_mpi_powm (k, f, x, prime);
return k;
}
/*-
* mhd_gtls_get_dh_params - Returns the DH parameters pointer
* @dh_params: is an DH parameters structure, or NULL.
* @func: is a callback function to receive the parameters or NULL.
* @session: a gnutls session.
*
* This function will return the dh parameters pointer.
*
-*/
mhd_gtls_dh_params_t
mhd_gtls_get_dh_params (mhd_gtls_dh_params_t dh_params,
gnutls_params_function * func,
mhd_gtls_session_t session)
{
gnutls_params_st params;
int ret;
/* if cached return the cached */
if (session->internals.params.dh_params)
return session->internals.params.dh_params;
if (dh_params)
{
session->internals.params.dh_params = dh_params;
}
else if (func)
{
ret = func (session, GNUTLS_PARAMS_DH, ¶ms);
if (ret == 0 && params.type == GNUTLS_PARAMS_DH)
{
session->internals.params.dh_params = params.params.dh;
session->internals.params.free_dh_params = params.deinit;
}
}
return session->internals.params.dh_params;
}
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