/*
 *      Copyright (C) 2000 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 <defines.h>
#include <gnutls_int.h>
#include <gnutls_errors.h>

/* Taken from gsti */

static const uint8 diffie_hellman_group1_prime[130] = { 0x04, 0x00,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2,
	0x21, 0x68, 0xC2, 0x34, 0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1,
	0x29, 0x02, 0x4E, 0x08, 0x8A, 0x67, 0xCC, 0x74, 0x02, 0x0B, 0xBE, 0xA6,
	0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A, 0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD,
	0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B, 0x30, 0x2B, 0x0A, 0x6D,
	0xF2, 0x5F, 0x14, 0x37, 0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51, 0xC2, 0x45,
	0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6, 0xF4, 0x4C, 0x42, 0xE9,
	0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED,
	0xEE, 0x38, 0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11,
	0x7C, 0x4B, 0x1F, 0xE6, 0x49, 0x28, 0x66, 0x51, 0xEC, 0xE6, 0x53, 0x81,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
};

/* 
	--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 for it
	X = gnutls_calc_dh_secret(&x);
//      now we can calculate the shared secret
	key = gnutls_calc_dh_key(Y, x);
	gnutls_mpi_release(x);
	gnutls_mpi_release(g);
*/

/* #define E_SIZE 1024 */
#define X_SIZE 512

#define gcry_mpi_alloc_like(x) gcry_mpi_new(gcry_mpi_get_nbits(x))

/****************
 * Choose a random value x and calculate e = g^x mod p.
 * Return: e and if ret_x is not NULL x.
 * It also returns g and p.
 */
MPI gnutls_calc_dh_secret(MPI * ret_x)
{
	MPI e, g, x, prime;
	size_t n = sizeof diffie_hellman_group1_prime;

	if (gcry_mpi_scan(&prime, GCRYMPI_FMT_USG,
			  diffie_hellman_group1_prime, &n)) {
		gnutls_assert();
		abort();
	}
	/*_gnutls_dump_mpi(stderr, "prime=", prime ); */

	g = mpi_set_ui(NULL, 2);
	x = mpi_new(X_SIZE);	/* FIXME: allocate in secure memory */
	gcry_mpi_randomize(x, X_SIZE, GCRY_STRONG_RANDOM);
	/* fixme: set high bit of x and select a larger one */

/*	e = mpi_new(E_SIZE); */
	e = gcry_mpi_alloc_like(prime);
	/* e = g^x mod prime */

	mpi_powm(e, g, x, prime);

	if (ret_x)
		*ret_x = x;
	else
		mpi_release(x);
	mpi_release(g);
	mpi_release(prime);
	return e;
}

MPI _gnutls_calc_dh_secret(MPI * ret_x, MPI g, MPI prime)
{
	MPI e, x;

	x = mpi_new(X_SIZE);	/* FIXME: allocate in secure memory */
	gcry_mpi_randomize(x, X_SIZE, GCRY_STRONG_RANDOM);
	/* fixme: set high bit of x and select a larger one */

	e = gcry_mpi_alloc_like(prime);
/*	e = mpi_new(E_SIZE); */ 
	mpi_powm(e, g, x, prime);

	if (ret_x)
		*ret_x = x;
	else
		mpi_release(x);
	return e;
}

/* returns g and p */
MPI gnutls_get_dh_params(MPI * ret_p)
{
	MPI g, prime;
	size_t n = sizeof diffie_hellman_group1_prime;

	if (gcry_mpi_scan(&prime, GCRYMPI_FMT_USG,
			  diffie_hellman_group1_prime, &n)) {
		gnutls_assert();
		abort();
	}

	g = mpi_set_ui(NULL, 2);

	if (ret_p)
		*ret_p = prime;
	else
		mpi_release(prime);
	return g;
}


MPI gnutls_calc_dh_key(MPI f, MPI x)
{
	MPI k, prime;
	size_t n = sizeof diffie_hellman_group1_prime;

	if (gcry_mpi_scan(&prime, GCRYMPI_FMT_USG,
			  diffie_hellman_group1_prime, &n)) {
		gnutls_assert();
		abort();
	}
	/*_gnutls_dump_mpi(stderr, "prime=", prime ); */

	k = gcry_mpi_alloc_like(prime);
/*	k = mpi_new(E_SIZE);	 FIXME: allocate in secure memory */
	mpi_powm(k, f, x, prime);
	mpi_release(prime);
	return k;
}

MPI _gnutls_calc_dh_key(MPI f, MPI x, MPI prime)
{
	MPI k;

/*	k = mpi_new(E_SIZE);	 FIXME: allocate in secure memory */
	k = gcry_mpi_alloc_like(prime);
	mpi_powm(k, f, x, prime);
	return k;
}