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 #ifdef OPENSSL_FIPS
  70 # include <openssl/fips.h>
  71 #endif
  72
  73 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
  74                                 BN_GENCB *cb);
  75
  76 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
  77                               BN_GENCB *cb)
  78 {
  79 #ifdef OPENSSL_FIPS
  80     if (FIPS_mode() && !(ret->meth->flags & DH_FLAG_FIPS_METHOD)
  81         && !(ret->flags & DH_FLAG_NON_FIPS_ALLOW)) {
  82         DHerr(DH_F_DH_GENERATE_PARAMETERS_EX, DH_R_NON_FIPS_METHOD);
  83         return 0;
  84     }
  85 #endif
  86     if (ret->meth->generate_params)
  87         return ret->meth->generate_params(ret, prime_len, generator, cb);
  88 #ifdef OPENSSL_FIPS
  89     if (FIPS_mode())
  90         return FIPS_dh_generate_parameters_ex(ret, prime_len, generator, cb);
  91 #endif
  92     return dh_builtin_genparams(ret, prime_len, generator, cb);
  93 }
  94
  95 /*-
  96  * We generate DH parameters as follows
  97  * find a prime q which is prime_len/2 bits long.
  98  * p=(2*q)+1 or (p-1)/2 = q
  99  * For this case, g is a generator if
 100  * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
 101  * Since the factors of p-1 are q and 2, we just need to check
 102  * g^2 mod p != 1 and g^q mod p != 1.
 103  *
 104  * Having said all that,
 105  * there is another special case method for the generators 2, 3 and 5.
 106  * for 2, p mod 24 == 11
 107  * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
 108  * for 5, p mod 10 == 3 or 7
 109  *
 110  * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
 111  * special generators and for answering some of my questions.
 112  *
 113  * I've implemented the second simple method :-).
 114  * Since DH should be using a safe prime (both p and q are prime),
 115  * this generator function can take a very very long time to run.
 116  */
 117 /*
 118  * Actually there is no reason to insist that 'generator' be a generator.
 119  * It's just as OK (and in some sense better) to use a generator of the
 120  * order-q subgroup.
 121  */
 122 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
 123                                 BN_GENCB *cb)
 124 {
 125     BIGNUM *t1, *t2;
 126     int g, ok = -1;
 127     BN_CTX *ctx = NULL;
 128
 129     ctx = BN_CTX_new();
 130     if (ctx == NULL)
 131         goto err;
 132     BN_CTX_start(ctx);
 133     t1 = BN_CTX_get(ctx);
 134     t2 = BN_CTX_get(ctx);
 135     if (t1 == NULL || t2 == NULL)
 136         goto err;
 137
 138     /* Make sure 'ret' has the necessary elements */
 139     if (!ret->p && ((ret->p = BN_new()) == NULL))
 140         goto err;
 141     if (!ret->g && ((ret->g = BN_new()) == NULL))
 142         goto err;
 143
 144     if (generator <= 1) {
 145         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
 146         goto err;
 147     }
 148     if (generator == DH_GENERATOR_2) {
 149         if (!BN_set_word(t1, 24))
 150             goto err;
 151         if (!BN_set_word(t2, 11))
 152             goto err;
 153         g = 2;
 154     }
 155 #if 0                           /* does not work for safe primes */
 156     else if (generator == DH_GENERATOR_3) {
 157         if (!BN_set_word(t1, 12))
 158             goto err;
 159         if (!BN_set_word(t2, 5))
 160             goto err;
 161         g = 3;
 162     }
 163 #endif
 164     else if (generator == DH_GENERATOR_5) {
 165         if (!BN_set_word(t1, 10))
 166             goto err;
 167         if (!BN_set_word(t2, 3))
 168             goto err;
 169         /*
 170          * BN_set_word(t3,7); just have to miss out on these ones :-(
 171          */
 172         g = 5;
 173     } else {
 174         /*
 175          * in the general case, don't worry if 'generator' is a generator or
 176          * not: since we are using safe primes, it will generate either an
 177          * order-q or an order-2q group, which both is OK
 178          */
 179         if (!BN_set_word(t1, 2))
 180             goto err;
 181         if (!BN_set_word(t2, 1))
 182             goto err;
 183         g = generator;
 184     }
 185
 186     if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
 187         goto err;
 188     if (!BN_GENCB_call(cb, 3, 0))
 189         goto err;
 190     if (!BN_set_word(ret->g, g))
 191         goto err;
 192     ok = 1;
 193  err:
 194     if (ok == -1) {
 195         DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
 196         ok = 0;
 197     }
 198
 199     if (ctx != NULL) {
 200         BN_CTX_end(ctx);
 201         BN_CTX_free(ctx);
 202     }
 203     return ok;
 204 }