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 /* NB: These functions have been upgraded - the previous prototypes are in
  60  * dh_depr.c as wrappers to these ones.
  61  *  - Geoff
  62  */
  63
  64 #include <stdio.h>
  65 #include "cryptlib.h"
  66 #include <openssl/bn.h>
  67 #include <openssl/dh.h>
  68
  69 /* We generate DH parameters as follows
  70  * find a prime q which is prime_len/2 bits long.
  71  * p=(2*q)+1 or (p-1)/2 = q
  72  * For this case, g is a generator if
  73  * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
  74  * Since the factors of p-1 are q and 2, we just need to check
  75  * g^2 mod p != 1 and g^q mod p != 1.
  76  *
  77  * Having said all that,
  78  * there is another special case method for the generators 2, 3 and 5.
  79  * for 2, p mod 24 == 11
  80  * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
  81  * for 5, p mod 10 == 3 or 7
  82  *
  83  * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
  84  * special generators and for answering some of my questions.
  85  *
  86  * I've implemented the second simple method :-).
  87  * Since DH should be using a safe prime (both p and q are prime),
  88  * this generator function can take a very very long time to run.
  89  */
  90 /* Actually there is no reason to insist that 'generator' be a generator.
  91  * It's just as OK (and in some sense better) to use a generator of the
  92  * order-q subgroup.
  93  */
  94 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb)
  95         {
  96         BIGNUM *t1,*t2;
  97         int g,ok= -1;
  98         BN_CTX *ctx=NULL;
  99
 100         ctx=BN_CTX_new();
 101         if (ctx == NULL) goto err;
 102         BN_CTX_start(ctx);
 103         t1 = BN_CTX_get(ctx);
 104         t2 = BN_CTX_get(ctx);
 105         if (t1 == NULL || t2 == NULL) goto err;
 106
 107         /* Make sure 'ret' has the necessary elements */
 108         if(!ret->p && ((ret->p = BN_new()) == NULL)) goto err;
 109         if(!ret->g && ((ret->g = BN_new()) == NULL)) goto err;
 110
 111         if (generator <= 1)
 112                 {
 113                 DHerr(DH_F_DH_GENERATE_PARAMETERS, DH_R_BAD_GENERATOR);
 114                 goto err;
 115                 }
 116         if (generator == DH_GENERATOR_2)
 117                 {
 118                 if (!BN_set_word(t1,24)) goto err;
 119                 if (!BN_set_word(t2,11)) goto err;
 120                 g=2;
 121                 }
 122 #if 0 /* does not work for safe primes */
 123         else if (generator == DH_GENERATOR_3)
 124                 {
 125                 if (!BN_set_word(t1,12)) goto err;
 126                 if (!BN_set_word(t2,5)) goto err;
 127                 g=3;
 128                 }
 129 #endif
 130         else if (generator == DH_GENERATOR_5)
 131                 {
 132                 if (!BN_set_word(t1,10)) goto err;
 133                 if (!BN_set_word(t2,3)) goto err;
 134                 /* BN_set_word(t3,7); just have to miss
 135                  * out on these ones :-( */
 136                 g=5;
 137                 }
 138         else
 139                 {
 140                 /* in the general case, don't worry if 'generator' is a
 141                  * generator or not: since we are using safe primes,
 142                  * it will generate either an order-q or an order-2q group,
 143                  * which both is OK */
 144                 if (!BN_set_word(t1,2)) goto err;
 145                 if (!BN_set_word(t2,1)) goto err;
 146                 g=generator;
 147                 }
 148
 149         if(!BN_generate_prime_ex(ret->p,prime_len,1,t1,t2,cb)) goto err;
 150         if(!BN_GENCB_call(cb, 3, 0)) goto err;
 151         if (!BN_set_word(ret->g,g)) goto err;
 152         ok=1;
 153 err:
 154         if (ok == -1)
 155                 {
 156                 DHerr(DH_F_DH_GENERATE_PARAMETERS,ERR_R_BN_LIB);
 157                 ok=0;
 158                 }
 159
 160         if (ctx != NULL)
 161                 {
 162                 BN_CTX_end(ctx);
 163                 BN_CTX_free(ctx);
 164                 }
 165         return ok;
 166         }