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 DH *DH_generate_parameters(int prime_len, int generator, 90 void (*callback)(int,int,void *), void *cb_arg) 91 { 92 BIGNUM *p=NULL,*t1,*t2; 93 DH *ret=NULL; 94 int g,ok= -1; 95 BN_CTX *ctx=NULL; 96 97 ret=DH_new(); 98 if (ret == NULL) goto err; 99 ctx=BN_CTX_new(); 100 if (ctx == NULL) goto err; 101 BN_CTX_start(ctx); 102 t1 = BN_CTX_get(ctx); 103 t2 = BN_CTX_get(ctx); 104 if (t1 == NULL || t2 == NULL) goto err; 105 106 if (generator <= 1) 107 { 108 DHerr(DH_F_DH_GENERATE_PARAMETERS, DH_R_BAD_GENERATOR); 109 goto err; 110 } 111 if (generator == DH_GENERATOR_2) 112 { 113 if (!BN_set_word(t1,24)) goto err; 114 if (!BN_set_word(t2,11)) goto err; 115 g=2; 116 } 117 #if 0 /* does not work for safe primes */ 118 else if (generator == DH_GENERATOR_3) 119 { 120 if (!BN_set_word(t1,12)) goto err; 121 if (!BN_set_word(t2,5)) goto err; 122 g=3; 123 } 124 #endif 125 else if (generator == DH_GENERATOR_5) 126 { 127 if (!BN_set_word(t1,10)) goto err; 128 if (!BN_set_word(t2,3)) goto err; 129 /* BN_set_word(t3,7); just have to miss 130 * out on these ones :-( */ 131 g=5; 132 } 133 else 134 { 135 /* in the general case, don't worry if 'generator' is a 136 * generator or not: since we are using safe primes, 137 * it will generate either an order-q or an order-2q group, 138 * which both is OK */ 139 if (!BN_set_word(t1,2)) goto err; 140 if (!BN_set_word(t2,1)) goto err; 141 g=generator; 142 } 143 144 p=BN_generate_prime(NULL,prime_len,1,t1,t2,callback,cb_arg); 145 if (p == NULL) goto err; 146 if (callback != NULL) callback(3,0,cb_arg); 147 ret->p=p; 148 ret->g=BN_new(); 149 if (!BN_set_word(ret->g,g)) goto err; 150 ok=1; 151 err: 152 if (ok == -1) 153 { 154 DHerr(DH_F_DH_GENERATE_PARAMETERS,ERR_R_BN_LIB); 155 ok=0; 156 } 157 158 if (ctx != NULL) 159 { 160 BN_CTX_end(ctx); 161 BN_CTX_free(ctx); 162 } 163 if (!ok && (ret != NULL)) 164 { 165 DH_free(ret); 166 ret=NULL; 167 } 168 return(ret); 169 } 170