crypto/dh/dh_check.c

   1 /* crypto/dh/dh_check.c */
   2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   3  * All rights reserved.
   4  *
   5  * This package is an SSL implementation written
   6  * by Eric Young (eay@cryptsoft.com).
   7  * The implementation was written so as to conform with Netscapes SSL.
   8  *
   9  * This library is free for commercial and non-commercial use as long as
  10  * the following conditions are aheared to.  The following conditions
  11  * apply to all code found in this distribution, be it the RC4, RSA,
  12  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  13  * included with this distribution is covered by the same copyright terms
  14  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  15  *
  16  * Copyright remains Eric Young's, and as such any Copyright notices in
  17  * the code are not to be removed.
  18  * If this package is used in a product, Eric Young should be given attribution
  19  * as the author of the parts of the library used.
  20  * This can be in the form of a textual message at program startup or
  21  * in documentation (online or textual) provided with the package.
  22  *
  23  * Redistribution and use in source and binary forms, with or without
  24  * modification, are permitted provided that the following conditions
  25  * are met:
  26  * 1. Redistributions of source code must retain the copyright
  27  *    notice, this list of conditions and the following disclaimer.
  28  * 2. Redistributions in binary form must reproduce the above copyright
  29  *    notice, this list of conditions and the following disclaimer in the
  30  *    documentation and/or other materials provided with the distribution.
  31  * 3. All advertising materials mentioning features or use of this software
  32  *    must display the following acknowledgement:
  33  *    "This product includes cryptographic software written by
  34  *     Eric Young (eay@cryptsoft.com)"
  35  *    The word 'cryptographic' can be left out if the rouines from the library
  36  *    being used are not cryptographic related :-).
  37  * 4. If you include any Windows specific code (or a derivative thereof) from
  38  *    the apps directory (application code) you must include an acknowledgement:
  39  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  40  *
  41  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  42  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  43  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  44  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  45  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  46  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  47  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  48  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  49  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  50  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  51  * SUCH DAMAGE.
  52  *
  53  * The licence and distribution terms for any publically available version or
  54  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  55  * copied and put under another distribution licence
  56  * [including the GNU Public Licence.]
  57  */
  58
  59 #include <stdio.h>
  60 #include "cryptlib.h"
  61 #include <openssl/bn.h>
  62 #include <openssl/dh.h>
  63
  64 /* Check that p is a strong prime and
  65  * if g is 2, 3 or 5, check that is is a suitable generator
  66  * where
  67  * for 2, p mod 24 == 11
  68  * for 3, p mod 12 == 5
  69  * for 5, p mod 10 == 3 or 7
  70  * should hold.
  71  */
  72
  73 int DH_check(DH *dh, int *ret)
  74         {
  75         int ok=0;
  76         BN_CTX *ctx=NULL;
  77         BN_ULONG l;
  78         BIGNUM *q=NULL;
  79
  80         *ret=0;
  81         ctx=BN_CTX_new();
  82         if (ctx == NULL) goto err;
  83         q=BN_new();
  84         if (q == NULL) goto err;
  85
  86         if (BN_is_word(dh->g,DH_GENERATOR_2))
  87                 {
  88                 l=BN_mod_word(dh->p,24);
  89                 if (l != 11) *ret|=DH_NOT_SUITABLE_GENERATOR;
  90                 }
  91 /*      else if (BN_is_word(dh->g,DH_GENERATOR_3))
  92                 {
  93                 l=BN_mod_word(dh->p,12);
  94                 if (l != 5) *ret|=DH_NOT_SUITABLE_GENERATOR;
  95                 }*/
  96         else if (BN_is_word(dh->g,DH_GENERATOR_5))
  97                 {
  98                 l=BN_mod_word(dh->p,10);
  99                 if ((l != 3) && (l != 7))
 100                         *ret|=DH_NOT_SUITABLE_GENERATOR;
 101                 }
 102         else
 103                 *ret|=DH_UNABLE_TO_CHECK_GENERATOR;
 104
 105         if (!BN_is_prime(dh->p,BN_prime_checks,NULL,ctx,NULL))
 106                 *ret|=DH_CHECK_P_NOT_PRIME;
 107         else
 108                 {
 109                 if (!BN_rshift1(q,dh->p)) goto err;
 110                 if (!BN_is_prime(q,BN_prime_checks,NULL,ctx,NULL))
 111                         *ret|=DH_CHECK_P_NOT_STRONG_PRIME;
 112                 }
 113         ok=1;
 114 err:
 115         if (ctx != NULL) BN_CTX_free(ctx);
 116         if (q != NULL) BN_free(q);
 117         return(ok);
 118         }