1 /* $OpenBSD: dh_gen.c,v 1.17 2022/01/07 09:27:13 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 /* NB: These functions have been upgraded - the previous prototypes are in 60 * dh_depr.c as wrappers to these ones. 61 * - Geoff 62 */ 63 64 #include <stdio.h> 65 66 #include <openssl/bn.h> 67 #include <openssl/dh.h> 68 #include <openssl/err.h> 69 70 #include "dh_local.h" 71 72 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, 73 BN_GENCB *cb); 74 75 int 76 DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb) 77 { 78 if (ret->meth->generate_params) 79 return ret->meth->generate_params(ret, prime_len, generator, cb); 80 return dh_builtin_genparams(ret, prime_len, generator, cb); 81 } 82 83 /* 84 * We generate DH parameters as follows: 85 * find a prime q which is prime_len/2 bits long. 86 * p=(2*q)+1 or (p-1)/2 = q 87 * For this case, g is a generator if 88 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1. 89 * Since the factors of p-1 are q and 2, we just need to check 90 * g^2 mod p != 1 and g^q mod p != 1. 91 * 92 * Having said all that, 93 * there is another special case method for the generators 2, 3 and 5. 94 * for 2, p mod 24 == 11 95 * for 3, p mod 12 == 5 <<<<< does not work for safe primes. 96 * for 5, p mod 10 == 3 or 7 97 * 98 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the 99 * special generators and for answering some of my questions. 100 * 101 * I've implemented the second simple method :-). 102 * Since DH should be using a safe prime (both p and q are prime), 103 * this generator function can take a very very long time to run. 104 */ 105 /* Actually there is no reason to insist that 'generator' be a generator. 106 * It's just as OK (and in some sense better) to use a generator of the 107 * order-q subgroup. 108 */ 109 static int 110 dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb) 111 { 112 BIGNUM *t1, *t2; 113 int g, ok = -1; 114 BN_CTX *ctx = NULL; 115 116 ctx = BN_CTX_new(); 117 if (ctx == NULL) 118 goto err; 119 BN_CTX_start(ctx); 120 if ((t1 = BN_CTX_get(ctx)) == NULL) 121 goto err; 122 if ((t2 = BN_CTX_get(ctx)) == NULL) 123 goto err; 124 125 /* Make sure 'ret' has the necessary elements */ 126 if (!ret->p && ((ret->p = BN_new()) == NULL)) 127 goto err; 128 if (!ret->g && ((ret->g = BN_new()) == NULL)) 129 goto err; 130 131 if (generator <= 1) { 132 DHerror(DH_R_BAD_GENERATOR); 133 goto err; 134 } 135 if (generator == DH_GENERATOR_2) { 136 if (!BN_set_word(t1, 24)) 137 goto err; 138 if (!BN_set_word(t2, 11)) 139 goto err; 140 g = 2; 141 } else if (generator == DH_GENERATOR_5) { 142 if (!BN_set_word(t1, 10)) 143 goto err; 144 if (!BN_set_word(t2, 3)) 145 goto err; 146 /* BN_set_word(t3,7); just have to miss 147 * out on these ones :-( */ 148 g = 5; 149 } else { 150 /* 151 * in the general case, don't worry if 'generator' is a 152 * generator or not: since we are using safe primes, 153 * it will generate either an order-q or an order-2q group, 154 * which both is OK 155 */ 156 if (!BN_set_word(t1, 2)) 157 goto err; 158 if (!BN_set_word(t2, 1)) 159 goto err; 160 g = generator; 161 } 162 163 if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb)) 164 goto err; 165 if (!BN_GENCB_call(cb, 3, 0)) 166 goto err; 167 if (!BN_set_word(ret->g, g)) 168 goto err; 169 ok = 1; 170 err: 171 if (ok == -1) { 172 DHerror(ERR_R_BN_LIB); 173 ok = 0; 174 } 175 176 if (ctx != NULL) { 177 BN_CTX_end(ctx); 178 BN_CTX_free(ctx); 179 } 180 return ok; 181 } 182