/* crypto/dh/dh_gen.c */

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)

 * All rights reserved.

 *

 * This package is an SSL implementation written

 * by Eric Young (eay@cryptsoft.com).

 * The implementation was written so as to conform with Netscapes SSL.

 * 

 * This library is free for commercial and non-commercial use as long as

 * the following conditions are aheared to.  The following conditions

 * apply to all code found in this distribution, be it the RC4, RSA,

 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation

 * included with this distribution is covered by the same copyright terms

 * except that the holder is Tim Hudson (tjh@cryptsoft.com).

 * 

 * Copyright remains Eric Young's, and as such any Copyright notices in

 * the code are not to be removed.

 * If this package is used in a product, Eric Young should be given attribution

 * as the author of the parts of the library used.

 * This can be in the form of a textual message at program startup or

 * in documentation (online or textual) provided with the package.

 * 

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. All advertising materials mentioning features or use of this software

 *    must display the following acknowledgement:

 *    "This product includes cryptographic software written by

 *     Eric Young (eay@cryptsoft.com)"

 *    The word 'cryptographic' can be left out if the rouines from the library

 *    being used are not cryptographic related :-).

 * 4. If you include any Windows specific code (or a derivative thereof) from 

 *    the apps directory (application code) you must include an acknowledgement:

 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"

 * 

 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 * 

 * The licence and distribution terms for any publically available version or

 * derivative of this code cannot be changed.  i.e. this code cannot simply be

 * copied and put under another distribution licence

 * [including the GNU Public Licence.]

 */

/* NB: These functions have been upgraded - the previous prototypes are in

 * dh_depr.c as wrappers to these ones.

 *  - Geoff

 */

#include <stdio.h>

#include "cryptlib.h"

#include <openssl/bn.h>

#include <openssl/dh.h>

static int dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb);

EXPORT_C int DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb)

	{

	if(ret->meth->generate_params)

		return ret->meth->generate_params(ret, prime_len, generator, cb);

	return dh_builtin_genparams(ret, prime_len, generator, cb);

	}

/* We generate DH parameters as follows

 * find a prime q which is prime_len/2 bits long.

 * p=(2*q)+1 or (p-1)/2 = q

 * For this case, g is a generator if

 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.

 * Since the factors of p-1 are q and 2, we just need to check

 * g^2 mod p != 1 and g^q mod p != 1.

 *

 * Having said all that,

 * there is another special case method for the generators 2, 3 and 5.

 * for 2, p mod 24 == 11

 * for 3, p mod 12 == 5  <<<<< does not work for safe primes.

 * for 5, p mod 10 == 3 or 7

 *

 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the

 * special generators and for answering some of my questions.

 *

 * I've implemented the second simple method :-).

 * Since DH should be using a safe prime (both p and q are prime),

 * this generator function can take a very very long time to run.

 */

/* Actually there is no reason to insist that 'generator' be a generator.

 * It's just as OK (and in some sense better) to use a generator of the

 * order-q subgroup.

 */

static int dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb)

	{

	BIGNUM *t1,*t2;

	int g,ok= -1;

	BN_CTX *ctx=NULL;

	ctx=BN_CTX_new();

	if (ctx == NULL) goto err;

	BN_CTX_start(ctx);

	t1 = BN_CTX_get(ctx);

	t2 = BN_CTX_get(ctx);

	if (t1 == NULL || t2 == NULL) goto err;

	/* Make sure 'ret' has the necessary elements */

	if(!ret->p && ((ret->p = BN_new()) == NULL)) goto err;

	if(!ret->g && ((ret->g = BN_new()) == NULL)) goto err;

	if (generator <= 1)

		{

		DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);

		goto err;

		}

	if (generator == DH_GENERATOR_2)

		{

		if (!BN_set_word(t1,24)) goto err;

		if (!BN_set_word(t2,11)) goto err;

		g=2;

		}

#if 0 /* does not work for safe primes */

	else if (generator == DH_GENERATOR_3)

		{

		if (!BN_set_word(t1,12)) goto err;

		if (!BN_set_word(t2,5)) goto err;

		g=3;

		}

#endif

	else if (generator == DH_GENERATOR_5)

		{

		if (!BN_set_word(t1,10)) goto err;

		if (!BN_set_word(t2,3)) goto err;

		/* BN_set_word(t3,7); just have to miss

		 * out on these ones :-( */

		g=5;

		}

	else

		{

		/* in the general case, don't worry if 'generator' is a

		 * generator or not: since we are using safe primes,

		 * it will generate either an order-q or an order-2q group,

		 * which both is OK */

		if (!BN_set_word(t1,2)) goto err;

		if (!BN_set_word(t2,1)) goto err;

		g=generator;

		}

	if(!BN_generate_prime_ex(ret->p,prime_len,1,t1,t2,cb)) goto err;

	if(!BN_GENCB_call(cb, 3, 0)) goto err;

	if (!BN_set_word(ret->g,g)) goto err;

	ok=1;

err:

	if (ok == -1)

		{

		DHerr(DH_F_DH_BUILTIN_GENPARAMS,ERR_R_BN_LIB);

		ok=0;

		}

	if (ctx != NULL)

		{

		BN_CTX_end(ctx);

		BN_CTX_free(ctx);

		}

	return ok;

	}