/* crypto/dh/dh_check.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.]

 */

#include <stdio.h>

#include "cryptlib.h"

#include <openssl/bn.h>

#include <openssl/dh.h>

/* Check that p is a safe prime and

 * if g is 2, 3 or 5, check that it is a suitable generator

 * where

 * for 2, p mod 24 == 11

 * for 3, p mod 12 == 5

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

 * should hold.

 */

EXPORT_C int DH_check(const DH *dh, int *ret)

	{

	int ok=0;

	BN_CTX *ctx=NULL;

	BN_ULONG l;

	BIGNUM *q=NULL;

	*ret=0;

	ctx=BN_CTX_new();

	if (ctx == NULL) goto err;

	q=BN_new();

	if (q == NULL) goto err;

	if (BN_is_word(dh->g,DH_GENERATOR_2))

		{

		l=BN_mod_word(dh->p,24);

		if (l != 11) *ret|=DH_NOT_SUITABLE_GENERATOR;

		}

#if 0

	else if (BN_is_word(dh->g,DH_GENERATOR_3))

		{

		l=BN_mod_word(dh->p,12);

		if (l != 5) *ret|=DH_NOT_SUITABLE_GENERATOR;

		}

#endif

	else if (BN_is_word(dh->g,DH_GENERATOR_5))

		{

		l=BN_mod_word(dh->p,10);

		if ((l != 3) && (l != 7))

			*ret|=DH_NOT_SUITABLE_GENERATOR;

		}

	else

		*ret|=DH_UNABLE_TO_CHECK_GENERATOR;

	if (!BN_is_prime_ex(dh->p,BN_prime_checks,ctx,NULL))

		*ret|=DH_CHECK_P_NOT_PRIME;

	else

		{

		if (!BN_rshift1(q,dh->p)) goto err;

		if (!BN_is_prime_ex(q,BN_prime_checks,ctx,NULL))

			*ret|=DH_CHECK_P_NOT_SAFE_PRIME;

		}

	ok=1;

err:

	if (ctx != NULL) BN_CTX_free(ctx);

	if (q != NULL) BN_free(q);

	return(ok);

	}

EXPORT_C int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)

	{

	int ok=0;

	BIGNUM *q=NULL;

	*ret=0;

	q=BN_new();

	if (q == NULL) goto err;

	BN_set_word(q,1);

	if (BN_cmp(pub_key,q) <= 0)

		*ret|=DH_CHECK_PUBKEY_TOO_SMALL;

	BN_copy(q,dh->p);

	BN_sub_word(q,1);

	if (BN_cmp(pub_key,q) >= 0)

		*ret|=DH_CHECK_PUBKEY_TOO_LARGE;

	ok = 1;

err:

	if (q != NULL) BN_free(q);

	return(ok);

	}