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 /*
  60  * NB: These functions have been upgraded - the previous prototypes are in
  61  * dh_depr.c as wrappers to these ones.  - Geoff
  62  */
  63
  64 #include <stdio.h>
  65 #include "cryptlib.h"
  66 #include <openssl/bn.h>
  67 #include <openssl/dh.h>
  68
  69 #ifndef OPENSSL_FIPS
  70
  71 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
  72                                 BN_GENCB *cb);
  73
  74 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
  75                               BN_GENCB *cb)
  76 {
  77     if (ret->meth->generate_params)
  78         return ret->meth->generate_params(ret, prime_len, generator, cb);
  79     return dh_builtin_genparams(ret, prime_len, generator, cb);
  80 }
  81
  82 /*-
  83  * We generate DH parameters as follows
  84  * find a prime q which is prime_len/2 bits long.
  85  * p=(2*q)+1 or (p-1)/2 = q
  86  * For this case, g is a generator if
  87  * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
  88  * Since the factors of p-1 are q and 2, we just need to check
  89  * g^2 mod p != 1 and g^q mod p != 1.
  90  *
  91  * Having said all that,
  92  * there is another special case method for the generators 2, 3 and 5.
  93  * for 2, p mod 24 == 11
  94  * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
  95  * for 5, p mod 10 == 3 or 7
  96  *
  97  * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
  98  * special generators and for answering some of my questions.
  99  *
 100  * I've implemented the second simple method :-).
 101  * Since DH should be using a safe prime (both p and q are prime),
 102  * this generator function can take a very very long time to run.
 103  */
 104 /*
 105  * Actually there is no reason to insist that 'generator' be a generator.
 106  * It's just as OK (and in some sense better) to use a generator of the
 107  * order-q subgroup.
 108  */
 109 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
 110                                 BN_GENCB *cb)
 111 {
 112     BIGNUM *t1, *t2;
 113     int g, ok = -1;
 114     BN_CTX *ctx = NULL;
 115
 116     ctx = BN_CTX_new();
 117     if (ctx == NULL)
 118         goto err;
 119     BN_CTX_start(ctx);
 120     t1 = BN_CTX_get(ctx);
 121     t2 = BN_CTX_get(ctx);
 122     if (t1 == NULL || t2 == NULL)
 123         goto err;
 124
 125     /* Make sure 'ret' has the necessary elements */
 126     if (!ret->p && ((ret->p = BN_new()) == NULL))
 127         goto err;
 128     if (!ret->g && ((ret->g = BN_new()) == NULL))
 129         goto err;
 130
 131     if (generator <= 1) {
 132         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
 133         goto err;
 134     }
 135     if (generator == DH_GENERATOR_2) {
 136         if (!BN_set_word(t1, 24))
 137             goto err;
 138         if (!BN_set_word(t2, 11))
 139             goto err;
 140         g = 2;
 141     }
 142 # if 0                          /* does not work for safe primes */
 143     else if (generator == DH_GENERATOR_3) {
 144         if (!BN_set_word(t1, 12))
 145             goto err;
 146         if (!BN_set_word(t2, 5))
 147             goto err;
 148         g = 3;
 149     }
 150 # endif
 151     else if (generator == DH_GENERATOR_5) {
 152         if (!BN_set_word(t1, 10))
 153             goto err;
 154         if (!BN_set_word(t2, 3))
 155             goto err;
 156         /*
 157          * BN_set_word(t3,7); just have to miss out on these ones :-(
 158          */
 159         g = 5;
 160     } else {
 161         /*
 162          * in the general case, don't worry if 'generator' is a generator or
 163          * not: since we are using safe primes, it will generate either an
 164          * order-q or an order-2q group, which both is OK
 165          */
 166         if (!BN_set_word(t1, 2))
 167             goto err;
 168         if (!BN_set_word(t2, 1))
 169             goto err;
 170         g = generator;
 171     }
 172
 173     if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
 174         goto err;
 175     if (!BN_GENCB_call(cb, 3, 0))
 176         goto err;
 177     if (!BN_set_word(ret->g, g))
 178         goto err;
 179     ok = 1;
 180  err:
 181     if (ok == -1) {
 182         DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
 183         ok = 0;
 184     }
 185
 186     if (ctx != NULL) {
 187         BN_CTX_end(ctx);
 188         BN_CTX_free(ctx);
 189     }
 190     return ok;
 191 }
 192
 193 #endif