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/*
* Copyright (C) 2000,2001,2002 Nikos Mavroyanopoulos
*
* This file is part of GNUTLS.
* someday was part of gsti
*
* GNUTLS is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* GNUTLS 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include <gnutls_int.h>
#include <gnutls_errors.h>
#include <gnutls_gcry.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 = gnutls_calc_dh_secret(&x, g, p);
// now we can calculate the shared secret
key = gnutls_calc_dh_key(Y, x, g, p);
_gnutls_mpi_release(x);
_gnutls_mpi_release(g);
*/
/* This function should return a resonable size for X
* (DH secret key). The input is the number of bits of
* the modulus.
* FIXME: This function is not correct
*/
static int get_x_size(int bits)
{
if (bits <= 2048)
return 512;
if (bits <= 4096)
return 768;
return 1024;
}
/* returns the public value (X), and the secret (ret_x).
*/
GNUTLS_MPI gnutls_calc_dh_secret(GNUTLS_MPI * ret_x, GNUTLS_MPI g, GNUTLS_MPI prime)
{
GNUTLS_MPI e, x;
int x_size = get_x_size(_gnutls_mpi_get_nbits(prime));
x = _gnutls_mpi_new(x_size); /* FIXME: allocate in secure memory */
if (x == NULL) {
gnutls_assert();
if (ret_x)
*ret_x = NULL;
return NULL;
}
_gnutls_mpi_randomize(x, x_size, GCRY_STRONG_RANDOM);
/* fixme: set high bit of x and select a larger one */
e = _gnutls_mpi_alloc_like(prime);
if (e == NULL) {
gnutls_assert();
if (ret_x)
*ret_x = NULL;
_gnutls_mpi_release( &x);
return NULL;
}
_gnutls_mpi_powm(e, g, x, prime);
if (ret_x)
*ret_x = x;
else
_gnutls_mpi_release(&x);
return e;
}
GNUTLS_MPI gnutls_calc_dh_key(GNUTLS_MPI f, GNUTLS_MPI x, GNUTLS_MPI prime)
{
GNUTLS_MPI k;
k = _gnutls_mpi_alloc_like(prime);
if (k == NULL)
return NULL;
_gnutls_mpi_powm(k, f, x, prime);
return k;
}
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