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 69static int dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb); 70 71int 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@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 */ 103static 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; 162err: 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