dh_gen.c revision 296341
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 73static int dh_builtin_genparams(DH *ret, int prime_len, int generator, 74 BN_GENCB *cb); 75 76int 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 */ 122static 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} 205