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#include <stdio.h> 60#include "cryptlib.h" 61#include <openssl/bn.h> 62#include <openssl/dh.h> 63 64/* We generate DH parameters as follows 65 * find a prime q which is prime_len/2 bits long. 66 * p=(2*q)+1 or (p-1)/2 = q 67 * For this case, g is a generator if 68 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1. 69 * Since the factors of p-1 are q and 2, we just need to check 70 * g^2 mod p != 1 and g^q mod p != 1. 71 * 72 * Having said all that, 73 * there is another special case method for the generators 2, 3 and 5. 74 * for 2, p mod 24 == 11 75 * for 3, p mod 12 == 5 <<<<< does not work for safe primes. 76 * for 5, p mod 10 == 3 or 7 77 * 78 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the 79 * special generators and for answering some of my questions. 80 * 81 * I've implemented the second simple method :-). 82 * Since DH should be using a safe prime (both p and q are prime), 83 * this generator function can take a very very long time to run. 84 */ 85/* Actually there is no reason to insist that 'generator' be a generator. 86 * It's just as OK (and in some sense better) to use a generator of the 87 * order-q subgroup. 88 */ 89 90#ifndef OPENSSL_FIPS 91 92DH *DH_generate_parameters(int prime_len, int generator, 93 void (*callback)(int,int,void *), void *cb_arg) 94 { 95 BIGNUM *p=NULL,*t1,*t2; 96 DH *ret=NULL; 97 int g,ok= -1; 98 BN_CTX *ctx=NULL; 99 100 ret=DH_new(); 101 if (ret == NULL) goto err; 102 ctx=BN_CTX_new(); 103 if (ctx == NULL) goto err; 104 BN_CTX_start(ctx); 105 t1 = BN_CTX_get(ctx); 106 t2 = BN_CTX_get(ctx); 107 if (t1 == NULL || t2 == NULL) goto err; 108 109 if (generator <= 1) 110 { 111 DHerr(DH_F_DH_GENERATE_PARAMETERS, DH_R_BAD_GENERATOR); 112 goto err; 113 } 114 if (generator == DH_GENERATOR_2) 115 { 116 if (!BN_set_word(t1,24)) goto err; 117 if (!BN_set_word(t2,11)) goto err; 118 g=2; 119 } 120#if 0 /* does not work for safe primes */ 121 else if (generator == DH_GENERATOR_3) 122 { 123 if (!BN_set_word(t1,12)) goto err; 124 if (!BN_set_word(t2,5)) goto err; 125 g=3; 126 } 127#endif 128 else if (generator == DH_GENERATOR_5) 129 { 130 if (!BN_set_word(t1,10)) goto err; 131 if (!BN_set_word(t2,3)) goto err; 132 /* BN_set_word(t3,7); just have to miss 133 * out on these ones :-( */ 134 g=5; 135 } 136 else 137 { 138 /* in the general case, don't worry if 'generator' is a 139 * generator or not: since we are using safe primes, 140 * it will generate either an order-q or an order-2q group, 141 * which both is OK */ 142 if (!BN_set_word(t1,2)) goto err; 143 if (!BN_set_word(t2,1)) goto err; 144 g=generator; 145 } 146 147 p=BN_generate_prime(NULL,prime_len,1,t1,t2,callback,cb_arg); 148 if (p == NULL) goto err; 149 if (callback != NULL) callback(3,0,cb_arg); 150 ret->p=p; 151 ret->g=BN_new(); 152 if (ret->g == NULL) goto err; 153 if (!BN_set_word(ret->g,g)) goto err; 154 ok=1; 155err: 156 if (ok == -1) 157 { 158 DHerr(DH_F_DH_GENERATE_PARAMETERS,ERR_R_BN_LIB); 159 ok=0; 160 } 161 162 if (ctx != NULL) 163 { 164 BN_CTX_end(ctx); 165 BN_CTX_free(ctx); 166 } 167 if (!ok && (ret != NULL)) 168 { 169 DH_free(ret); 170 ret=NULL; 171 } 172 return(ret); 173 } 174 175#endif 176