1 /* $OpenBSD: dh_gen.c,v 1.20 2023/04/13 15:18:29 tb Exp $ */ 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 61 #include <openssl/bn.h> 62 #include <openssl/dh.h> 63 #include <openssl/err.h> 64 65 #include "bn_local.h" 66 #include "dh_local.h" 67 68 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, 69 BN_GENCB *cb); 70 71 int 72 DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb) 73 { 74 if (ret->meth->generate_params) 75 return ret->meth->generate_params(ret, prime_len, generator, cb); 76 return dh_builtin_genparams(ret, prime_len, generator, cb); 77 } 78 79 /* 80 * We generate DH parameters as follows: 81 * find a prime q which is prime_len/2 bits long. 82 * p=(2*q)+1 or (p-1)/2 = q 83 * For this case, g is a generator if 84 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1. 85 * Since the factors of p-1 are q and 2, we just need to check 86 * g^2 mod p != 1 and g^q mod p != 1. 87 * 88 * Having said all that, 89 * there is another special case method for the generators 2, 3 and 5. 90 * for 2, p mod 24 == 11 91 * for 3, p mod 12 == 5 <<<<< does not work for safe primes. 92 * for 5, p mod 10 == 3 or 7 93 * 94 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the 95 * special generators and for answering some of my questions. 96 * 97 * I've implemented the second simple method :-). 98 * Since DH should be using a safe prime (both p and q are prime), 99 * this generator function can take a very very long time to run. 100 */ 101 /* Actually there is no reason to insist that 'generator' be a generator. 102 * It's just as OK (and in some sense better) to use a generator of the 103 * order-q subgroup. 104 */ 105 static int 106 dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb) 107 { 108 BIGNUM *t1, *t2; 109 int g, ok = -1; 110 BN_CTX *ctx = NULL; 111 112 ctx = BN_CTX_new(); 113 if (ctx == NULL) 114 goto err; 115 BN_CTX_start(ctx); 116 if ((t1 = BN_CTX_get(ctx)) == NULL) 117 goto err; 118 if ((t2 = BN_CTX_get(ctx)) == NULL) 119 goto err; 120 121 /* Make sure 'ret' has the necessary elements */ 122 if (!ret->p && ((ret->p = BN_new()) == NULL)) 123 goto err; 124 if (!ret->g && ((ret->g = BN_new()) == NULL)) 125 goto err; 126 127 if (generator <= 1) { 128 DHerror(DH_R_BAD_GENERATOR); 129 goto err; 130 } 131 if (generator == DH_GENERATOR_2) { 132 if (!BN_set_word(t1, 24)) 133 goto err; 134 if (!BN_set_word(t2, 11)) 135 goto err; 136 g = 2; 137 } else if (generator == DH_GENERATOR_5) { 138 if (!BN_set_word(t1, 10)) 139 goto err; 140 if (!BN_set_word(t2, 3)) 141 goto err; 142 /* BN_set_word(t3,7); just have to miss 143 * out on these ones :-( */ 144 g = 5; 145 } else { 146 /* 147 * in the general case, don't worry if 'generator' is a 148 * generator or not: since we are using safe primes, 149 * it will generate either an order-q or an order-2q group, 150 * which both is OK 151 */ 152 if (!BN_set_word(t1, 2)) 153 goto err; 154 if (!BN_set_word(t2, 1)) 155 goto err; 156 g = generator; 157 } 158 159 if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb)) 160 goto err; 161 if (!BN_GENCB_call(cb, 3, 0)) 162 goto err; 163 if (!BN_set_word(ret->g, g)) 164 goto err; 165 ok = 1; 166 err: 167 if (ok == -1) { 168 DHerror(ERR_R_BN_LIB); 169 ok = 0; 170 } 171 172 if (ctx != NULL) { 173 BN_CTX_end(ctx); 174 BN_CTX_free(ctx); 175 } 176 return ok; 177 } 178 179 DH * 180 DH_generate_parameters(int prime_len, int generator, 181 void (*callback)(int, int, void *), void *cb_arg) 182 { 183 BN_GENCB cb; 184 DH *ret = NULL; 185 186 if ((ret = DH_new()) == NULL) 187 return NULL; 188 189 BN_GENCB_set_old(&cb, callback, cb_arg); 190 191 if (DH_generate_parameters_ex(ret, prime_len, generator, &cb)) 192 return ret; 193 DH_free(ret); 194 return NULL; 195 } 196