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 86 DH *DH_generate_parameters(int prime_len, int generator, 87 void (*callback)(int,int,void *), void *cb_arg) 88 { 89 BIGNUM *p=NULL,*t1,*t2; 90 DH *ret=NULL; 91 int g,ok= -1; 92 BN_CTX *ctx=NULL; 93 94 ret=DH_new(); 95 if (ret == NULL) goto err; 96 ctx=BN_CTX_new(); 97 if (ctx == NULL) goto err; 98 BN_CTX_start(ctx); 99 t1 = BN_CTX_get(ctx); 100 t2 = BN_CTX_get(ctx); 101 if (t1 == NULL || t2 == NULL) goto err; 102 103 if (generator == DH_GENERATOR_2) 104 { 105 BN_set_word(t1,24); 106 BN_set_word(t2,11); 107 g=2; 108 } 109 #ifdef undef /* does not work for safe primes */ 110 else if (generator == DH_GENERATOR_3) 111 { 112 BN_set_word(t1,12); 113 BN_set_word(t2,5); 114 g=3; 115 } 116 #endif 117 else if (generator == DH_GENERATOR_5) 118 { 119 BN_set_word(t1,10); 120 BN_set_word(t2,3); 121 /* BN_set_word(t3,7); just have to miss 122 * out on these ones :-( */ 123 g=5; 124 } 125 else 126 g=generator; 127 128 p=BN_generate_prime(NULL,prime_len,1,t1,t2,callback,cb_arg); 129 if (p == NULL) goto err; 130 if (callback != NULL) callback(3,0,cb_arg); 131 ret->p=p; 132 ret->g=BN_new(); 133 if (!BN_set_word(ret->g,g)) goto err; 134 ok=1; 135 err: 136 if (ok == -1) 137 { 138 DHerr(DH_F_DH_GENERATE_PARAMETERS,ERR_R_BN_LIB); 139 ok=0; 140 } 141 142 if (ctx != NULL) 143 { 144 BN_CTX_end(ctx); 145 BN_CTX_free(ctx); 146 } 147 if (!ok && (ret != NULL)) 148 { 149 DH_free(ret); 150 ret=NULL; 151 } 152 return(ret); 153 } 154