1 /* $OpenBSD: dh_check.c,v 1.20 2021/11/29 19:54:07 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 64 #include "bn_lcl.h" 65 66 #define DH_NUMBER_ITERATIONS_FOR_PRIME 64 67 68 int 69 DH_check_params(const DH *dh, int *flags) 70 { 71 BN_CTX *ctx = NULL; 72 BIGNUM *max_g; 73 int ok = 0; 74 75 *flags = 0; 76 77 if ((ctx = BN_CTX_new()) == NULL) 78 goto err; 79 BN_CTX_start(ctx); 80 if ((max_g = BN_CTX_get(ctx)) == NULL) 81 goto err; 82 83 if (!BN_is_odd(dh->p)) 84 *flags |= DH_CHECK_P_NOT_PRIME; 85 86 /* 87 * Check that 1 < dh->g < p - 1 88 */ 89 90 if (BN_cmp(dh->g, BN_value_one()) <= 0) 91 *flags |= DH_NOT_SUITABLE_GENERATOR; 92 /* max_g = p - 1 */ 93 if (BN_copy(max_g, dh->p) == NULL) 94 goto err; 95 if (!BN_sub_word(max_g, 1)) 96 goto err; 97 /* check that g < max_g */ 98 if (BN_cmp(dh->g, max_g) >= 0) 99 *flags |= DH_NOT_SUITABLE_GENERATOR; 100 101 ok = 1; 102 103 err: 104 BN_CTX_end(ctx); 105 BN_CTX_free(ctx); 106 107 return ok; 108 } 109 110 /* 111 * Check that p is a safe prime and that g is a suitable generator. 112 */ 113 114 int 115 DH_check(const DH *dh, int *flags) 116 { 117 BN_CTX *ctx = NULL; 118 int is_prime; 119 int ok = 0; 120 121 *flags = 0; 122 123 if (!DH_check_params(dh, flags)) 124 goto err; 125 126 ctx = BN_CTX_new(); 127 if (ctx == NULL) 128 goto err; 129 BN_CTX_start(ctx); 130 131 if (dh->q != NULL) { 132 BIGNUM *quotient, *residue; 133 134 if ((quotient = BN_CTX_get(ctx)) == NULL) 135 goto err; 136 if ((residue = BN_CTX_get(ctx)) == NULL) 137 goto err; 138 if ((*flags & DH_NOT_SUITABLE_GENERATOR) == 0) { 139 /* Check g^q == 1 mod p */ 140 if (!BN_mod_exp_ct(residue, dh->g, dh->q, dh->p, ctx)) 141 goto err; 142 if (!BN_is_one(residue)) 143 *flags |= DH_NOT_SUITABLE_GENERATOR; 144 } 145 is_prime = BN_is_prime_ex(dh->q, DH_NUMBER_ITERATIONS_FOR_PRIME, 146 ctx, NULL); 147 if (is_prime < 0) 148 goto err; 149 if (is_prime == 0) 150 *flags |= DH_CHECK_Q_NOT_PRIME; 151 /* Check p == 1 mod q, i.e., q divides p - 1 */ 152 if (!BN_div_ct(quotient, residue, dh->p, dh->q, ctx)) 153 goto err; 154 if (!BN_is_one(residue)) 155 *flags |= DH_CHECK_INVALID_Q_VALUE; 156 if (dh->j != NULL && BN_cmp(dh->j, quotient) != 0) 157 *flags |= DH_CHECK_INVALID_J_VALUE; 158 } 159 160 is_prime = BN_is_prime_ex(dh->p, DH_NUMBER_ITERATIONS_FOR_PRIME, 161 ctx, NULL); 162 if (is_prime < 0) 163 goto err; 164 if (is_prime == 0) 165 *flags |= DH_CHECK_P_NOT_PRIME; 166 else if (dh->q == NULL) { 167 BIGNUM *q; 168 169 if ((q = BN_CTX_get(ctx)) == NULL) 170 goto err; 171 if (!BN_rshift1(q, dh->p)) 172 goto err; 173 is_prime = BN_is_prime_ex(q, DH_NUMBER_ITERATIONS_FOR_PRIME, 174 ctx, NULL); 175 if (is_prime < 0) 176 goto err; 177 if (is_prime == 0) 178 *flags |= DH_CHECK_P_NOT_SAFE_PRIME; 179 } 180 181 ok = 1; 182 183 err: 184 BN_CTX_end(ctx); 185 BN_CTX_free(ctx); 186 return ok; 187 } 188 189 int 190 DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret) 191 { 192 BIGNUM *q = NULL; 193 194 *ret = 0; 195 q = BN_new(); 196 if (q == NULL) 197 return 0; 198 BN_set_word(q, 1); 199 if (BN_cmp(pub_key, q) <= 0) 200 *ret |= DH_CHECK_PUBKEY_TOO_SMALL; 201 BN_copy(q, dh->p); 202 BN_sub_word(q, 1); 203 if (BN_cmp(pub_key, q) >= 0) 204 *ret |= DH_CHECK_PUBKEY_TOO_LARGE; 205 206 BN_free(q); 207 return 1; 208 } 209