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      1 /* crypto/dh/dh_gen.c */
      2 /* Copyright (C) 1995-1998 Eric Young (eay (at) cryptsoft.com)
      3  * All rights reserved.
      4  *
      5  * This package is an SSL implementation written
      6  * by Eric Young (eay (at) 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 (at) 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 (at) 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 (at) 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 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb);
     70 
     71 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb)
     72 	{
     73 	if(ret->meth->generate_params)
     74 		return ret->meth->generate_params(ret, prime_len, generator, cb);
     75 	return dh_builtin_genparams(ret, prime_len, generator, cb);
     76 	}
     77 
     78 /* We generate DH parameters as follows
     79  * find a prime q which is prime_len/2 bits long.
     80  * p=(2*q)+1 or (p-1)/2 = q
     81  * For this case, g is a generator if
     82  * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
     83  * Since the factors of p-1 are q and 2, we just need to check
     84  * g^2 mod p != 1 and g^q mod p != 1.
     85  *
     86  * Having said all that,
     87  * there is another special case method for the generators 2, 3 and 5.
     88  * for 2, p mod 24 == 11
     89  * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
     90  * for 5, p mod 10 == 3 or 7
     91  *
     92  * Thanks to Phil Karn <karn (at) qualcomm.com> for the pointers about the
     93  * special generators and for answering some of my questions.
     94  *
     95  * I've implemented the second simple method :-).
     96  * Since DH should be using a safe prime (both p and q are prime),
     97  * this generator function can take a very very long time to run.
     98  */
     99 /* Actually there is no reason to insist that 'generator' be a generator.
    100  * It's just as OK (and in some sense better) to use a generator of the
    101  * order-q subgroup.
    102  */
    103 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb)
    104 	{
    105 	BIGNUM *t1,*t2;
    106 	int g,ok= -1;
    107 	BN_CTX *ctx=NULL;
    108 
    109 	ctx=BN_CTX_new();
    110 	if (ctx == NULL) goto err;
    111 	BN_CTX_start(ctx);
    112 	t1 = BN_CTX_get(ctx);
    113 	t2 = BN_CTX_get(ctx);
    114 	if (t1 == NULL || t2 == NULL) goto err;
    115 
    116 	/* Make sure 'ret' has the necessary elements */
    117 	if(!ret->p && ((ret->p = BN_new()) == NULL)) goto err;
    118 	if(!ret->g && ((ret->g = BN_new()) == NULL)) goto err;
    119 
    120 	if (generator <= 1)
    121 		{
    122 		DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
    123 		goto err;
    124 		}
    125 	if (generator == DH_GENERATOR_2)
    126 		{
    127 		if (!BN_set_word(t1,24)) goto err;
    128 		if (!BN_set_word(t2,11)) goto err;
    129 		g=2;
    130 		}
    131 #if 0 /* does not work for safe primes */
    132 	else if (generator == DH_GENERATOR_3)
    133 		{
    134 		if (!BN_set_word(t1,12)) goto err;
    135 		if (!BN_set_word(t2,5)) goto err;
    136 		g=3;
    137 		}
    138 #endif
    139 	else if (generator == DH_GENERATOR_5)
    140 		{
    141 		if (!BN_set_word(t1,10)) goto err;
    142 		if (!BN_set_word(t2,3)) goto err;
    143 		/* BN_set_word(t3,7); just have to miss
    144 		 * out on these ones :-( */
    145 		g=5;
    146 		}
    147 	else
    148 		{
    149 		/* in the general case, don't worry if 'generator' is a
    150 		 * generator or not: since we are using safe primes,
    151 		 * it will generate either an order-q or an order-2q group,
    152 		 * which both is OK */
    153 		if (!BN_set_word(t1,2)) goto err;
    154 		if (!BN_set_word(t2,1)) goto err;
    155 		g=generator;
    156 		}
    157 
    158 	if(!BN_generate_prime_ex(ret->p,prime_len,1,t1,t2,cb)) goto err;
    159 	if(!BN_GENCB_call(cb, 3, 0)) goto err;
    160 	if (!BN_set_word(ret->g,g)) goto err;
    161 	ok=1;
    162 err:
    163 	if (ok == -1)
    164 		{
    165 		DHerr(DH_F_DH_BUILTIN_GENPARAMS,ERR_R_BN_LIB);
    166 		ok=0;
    167 		}
    168 
    169 	if (ctx != NULL)
    170 		{
    171 		BN_CTX_end(ctx);
    172 		BN_CTX_free(ctx);
    173 		}
    174 	return ok;
    175 	}
    176