crypto/dh/dh_gen.c

   1 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   2  * All rights reserved.
   3  *
   4  * This package is an SSL implementation written
   5  * by Eric Young (eay@cryptsoft.com).
   6  * The implementation was written so as to conform with Netscapes SSL.
   7  *
   8  * This library is free for commercial and non-commercial use as long as
   9  * the following conditions are aheared to.  The following conditions
  10  * apply to all code found in this distribution, be it the RC4, RSA,
  11  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  12  * included with this distribution is covered by the same copyright terms
  13  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  14  *
  15  * Copyright remains Eric Young's, and as such any Copyright notices in
  16  * the code are not to be removed.
  17  * If this package is used in a product, Eric Young should be given attribution
  18  * as the author of the parts of the library used.
  19  * This can be in the form of a textual message at program startup or
  20  * in documentation (online or textual) provided with the package.
  21  *
  22  * Redistribution and use in source and binary forms, with or without
  23  * modification, are permitted provided that the following conditions
  24  * are met:
  25  * 1. Redistributions of source code must retain the copyright
  26  *    notice, this list of conditions and the following disclaimer.
  27  * 2. Redistributions in binary form must reproduce the above copyright
  28  *    notice, this list of conditions and the following disclaimer in the
  29  *    documentation and/or other materials provided with the distribution.
  30  * 3. All advertising materials mentioning features or use of this software
  31  *    must display the following acknowledgement:
  32  *    "This product includes cryptographic software written by
  33  *     Eric Young (eay@cryptsoft.com)"
  34  *    The word 'cryptographic' can be left out if the rouines from the library
  35  *    being used are not cryptographic related :-).
  36  * 4. If you include any Windows specific code (or a derivative thereof) from
  37  *    the apps directory (application code) you must include an acknowledgement:
  38  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  39  *
  40  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  41  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  42  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  43  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  44  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  45  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  46  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  47  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  48  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  49  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  50  * SUCH DAMAGE.
  51  *
  52  * The licence and distribution terms for any publically available version or
  53  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  54  * copied and put under another distribution licence
  55  * [including the GNU Public Licence.]
  56  */
  57
  58 /*
  59  * NB: These functions have been upgraded - the previous prototypes are in
  60  * dh_depr.c as wrappers to these ones.  - Geoff
  61  */
  62
  63 #include <stdio.h>
  64 #include "internal/cryptlib.h"
  65 #include <openssl/bn.h>
  66 #include <openssl/dh.h>
  67
  68 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
  69                                 BN_GENCB *cb);
  70
  71 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
  72                               BN_GENCB *cb)
  73 {
  74     if (ret->meth->generate_params)
  75         return ret->meth->generate_params(ret, prime_len, generator, cb);
  76     return dh_builtin_genparams(ret, prime_len, generator, cb);
  77 }
  78
  79 /*-
  80  * We generate DH parameters as follows
  81  * find a prime q which is prime_len/2 bits long.
  82  * p=(2*q)+1 or (p-1)/2 = q
  83  * For this case, g is a generator if
  84  * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
  85  * Since the factors of p-1 are q and 2, we just need to check
  86  * g^2 mod p != 1 and g^q mod p != 1.
  87  *
  88  * Having said all that,
  89  * there is another special case method for the generators 2, 3 and 5.
  90  * for 2, p mod 24 == 11
  91  * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
  92  * for 5, p mod 10 == 3 or 7
  93  *
  94  * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
  95  * special generators and for answering some of my questions.
  96  *
  97  * I've implemented the second simple method :-).
  98  * Since DH should be using a safe prime (both p and q are prime),
  99  * this generator function can take a very very long time to run.
 100  */
 101 /*
 102  * Actually there is no reason to insist that 'generator' be a generator.
 103  * It's just as OK (and in some sense better) to use a generator of the
 104  * order-q subgroup.
 105  */
 106 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
 107                                 BN_GENCB *cb)
 108 {
 109     BIGNUM *t1, *t2;
 110     int g, ok = -1;
 111     BN_CTX *ctx = NULL;
 112
 113     ctx = BN_CTX_new();
 114     if (ctx == NULL)
 115         goto err;
 116     BN_CTX_start(ctx);
 117     t1 = BN_CTX_get(ctx);
 118     t2 = BN_CTX_get(ctx);
 119     if (t1 == NULL || t2 == NULL)
 120         goto err;
 121
 122     /* Make sure 'ret' has the necessary elements */
 123     if (!ret->p && ((ret->p = BN_new()) == NULL))
 124         goto err;
 125     if (!ret->g && ((ret->g = BN_new()) == NULL))
 126         goto err;
 127
 128     if (generator <= 1) {
 129         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
 130         goto err;
 131     }
 132     if (generator == DH_GENERATOR_2) {
 133         if (!BN_set_word(t1, 24))
 134             goto err;
 135         if (!BN_set_word(t2, 11))
 136             goto err;
 137         g = 2;
 138     } else if (generator == DH_GENERATOR_5) {
 139         if (!BN_set_word(t1, 10))
 140             goto err;
 141         if (!BN_set_word(t2, 3))
 142             goto err;
 143         /*
 144          * BN_set_word(t3,7); just have to miss out on these ones :-(
 145          */
 146         g = 5;
 147     } else {
 148         /*
 149          * in the general case, don't worry if 'generator' is a generator or
 150          * not: since we are using safe primes, it will generate either an
 151          * order-q or an order-2q group, which both is OK
 152          */
 153         if (!BN_set_word(t1, 2))
 154             goto err;
 155         if (!BN_set_word(t2, 1))
 156             goto err;
 157         g = generator;
 158     }
 159
 160     if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
 161         goto err;
 162     if (!BN_GENCB_call(cb, 3, 0))
 163         goto err;
 164     if (!BN_set_word(ret->g, g))
 165         goto err;
 166     ok = 1;
 167  err:
 168     if (ok == -1) {
 169         DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
 170         ok = 0;
 171     }
 172
 173     if (ctx != NULL) {
 174         BN_CTX_end(ctx);
 175         BN_CTX_free(ctx);
 176     }
 177     return ok;
 178 }