/* crypto/dh/dh_check.c */

/* Copyright (C) 1995-1998 Eric Young ([email protected])

 * All rights reserved.

 *

 * This package is an SSL implementation written

 * by Eric Young ([email protected]).

 * 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 ([email protected]).

 *

 * 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 ([email protected])"

 *    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 ([email protected])"

 *

 * 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.

 */

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

{

    int ok = 0;

    BN_CTX *ctx = NULL;

    BN_ULONG l;

    BIGNUM *t1 = NULL, *t2 = NULL;

    *ret = 0;

    ctx = BN_CTX_new();

    if (ctx == NULL)

        goto err;

    BN_CTX_start(ctx);

    t1 = BN_CTX_get(ctx);

    if (t1 == NULL)

        goto err;

    t2 = BN_CTX_get(ctx);

    if (t2 == NULL)

        goto err;

    if (dh->q) {

        if (BN_cmp(dh->g, BN_value_one()) <= 0)

            *ret |= DH_NOT_SUITABLE_GENERATOR;

        else if (BN_cmp(dh->g, dh->p) >= 0)

            *ret |= DH_NOT_SUITABLE_GENERATOR;

        else {

            /* Check g^q == 1 mod p */

            if (!BN_mod_exp(t1, dh->g, dh->q, dh->p, ctx))

                goto err;

            if (!BN_is_one(t1))

                *ret |= DH_NOT_SUITABLE_GENERATOR;

        }

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

            *ret |= DH_CHECK_P_NOT_SAFE_PRIME;

        /* Check p == 1 mod q  i.e. q divides p - 1 */

        if (!BN_div(t1, t2, dh->p, dh->q, ctx))

            goto err;

        if (!BN_is_one(t2))

            *ret |= DH_CHECK_P_NOT_SAFE_PRIME;

        if (dh->j && BN_cmp(dh->j, t1))

            *ret |= DH_CHECK_P_NOT_SAFE_PRIME;

    } else 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 (!dh->q) {

        if (!BN_rshift1(t1, dh->p))

            goto err;

        if (!BN_is_prime_ex(t1, BN_prime_checks, ctx, NULL))

            *ret |= DH_CHECK_P_NOT_SAFE_PRIME;

    }

    ok = 1;

 err:

    if (ctx != NULL) {

        BN_CTX_end(ctx);

        BN_CTX_free(ctx);

    }

    return (ok);

}

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

{

    int ok = 0;

    BIGNUM *tmp = NULL;

    BN_CTX *ctx = NULL;

    *ret = 0;

    ctx = BN_CTX_new();

    if (ctx == NULL)

        goto err;

    BN_CTX_start(ctx);

    tmp = BN_CTX_get(ctx);

    if (tmp == NULL || !BN_set_word(tmp, 1))

        goto err;

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

        *ret |= DH_CHECK_PUBKEY_TOO_SMALL;

    if (BN_copy(tmp, dh->p) == NULL || !BN_sub_word(tmp, 1))

        goto err;

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

        *ret |= DH_CHECK_PUBKEY_TOO_LARGE;

    if (dh->q != NULL) {

        /* Check pub_key^q == 1 mod p */

        if (!BN_mod_exp(tmp, pub_key, dh->q, dh->p, ctx))

            goto err;

        if (!BN_is_one(tmp))

            *ret |= DH_CHECK_PUBKEY_TOO_LARGE;

    }

    ok = 1;

 err:

    if (ctx != NULL) {

        BN_CTX_end(ctx);

        BN_CTX_free(ctx);

    }

    return (ok);

}