crypto/dh/dh_gen.c

   1 /* crypto/dh/dh_gen.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 "bn.h"
  62 #include "dh.h"
  63
  64 /* We generate DH parameters as follows
  65  * find a prime q which is prime_len/2 bits long.
  66  * p=(2*q)+1 or (p-1)/2 = q
  67  * For this case, g is a generator if
  68  * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
  69  * Since the factors of p-1 are q and 2, we just need to check
  70  * g^2 mod p != 1 and g^q mod p != 1.
  71  *
  72  * Having said all that,
  73  * there is another special case method for the generators 2, 3 and 5.
  74  * for 2, p mod 24 == 11
  75  * for 3, p mod 12 == 5  <<<<< does not work for strong primes.
  76  * for 5, p mod 10 == 3 or 7
  77  *
  78  * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
  79  * special generators and for answering some of my questions.
  80  *
  81  * I've implemented the second simple method :-).
  82  * Since DH should be using a strong prime (both p and q are prime),
  83  * this generator function can take a very very long time to run.
  84  */
  85
  86 DH *DH_generate_parameters(prime_len,generator,callback,cb_arg)
  87 int prime_len;
  88 int generator;
  89 void (*callback)(P_I_I_P);
  90 char *cb_arg;
  91         {
  92         BIGNUM *p=NULL,*t1,*t2;
  93         DH *ret=NULL;
  94         int g,ok= -1;
  95         BN_CTX *ctx=NULL;
  96
  97         ret=DH_new();
  98         ctx=BN_CTX_new();
  99         if (ctx == NULL) goto err;
 100         t1= &(ctx->bn[0]);
 101         t2= &(ctx->bn[1]);
 102         ctx->tos=2;
 103
 104         if (generator == DH_GENERATOR_2)
 105                 {
 106                 BN_set_word(t1,24);
 107                 BN_set_word(t2,11);
 108                 g=2;
 109                 }
 110 #ifdef undef  /* does not work for strong primes */
 111         else if (generator == DH_GENERATOR_3)
 112                 {
 113                 BN_set_word(t1,12);
 114                 BN_set_word(t2,5);
 115                 g=3;
 116                 }
 117 #endif
 118         else if (generator == DH_GENERATOR_5)
 119                 {
 120                 BN_set_word(t1,10);
 121                 BN_set_word(t2,3);
 122                 /* BN_set_word(t3,7); just have to miss
 123                  * out on these ones :-( */
 124                 g=5;
 125                 }
 126         else
 127                 g=generator;
 128
 129         p=BN_generate_prime(NULL,prime_len,1,t1,t2,callback,cb_arg);
 130         if (p == NULL) goto err;
 131         if (callback != NULL) callback(3,0,cb_arg);
 132         ret->p=p;
 133         ret->g=BN_new();
 134         if (!BN_set_word(ret->g,g)) goto err;
 135         ok=1;
 136 err:
 137         if (ok == -1)
 138                 {
 139                 DHerr(DH_F_DH_GENERATE_PARAMETERS,ERR_R_BN_LIB);
 140                 ok=0;
 141                 }
 142
 143         if (ctx != NULL) BN_CTX_free(ctx);
 144         if (!ok && (ret != NULL))
 145                 {
 146                 DH_free(ret);
 147                 ret=NULL;
 148                 }
 149         return(ret);
 150         }