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dh_check.c

/* 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.
 */

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);
      }

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);
      }

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