1 /* $OpenBSD: dh_check.c,v 1.30 2024/11/29 15:59:57 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 #define DH_NUMBER_ITERATIONS_FOR_PRIME 64 69 70 /* 71 * Check that p is odd and 1 < g < p - 1. 72 */ 73 74 static int 75 DH_check_params(const DH *dh, int *flags) 76 { 77 BIGNUM *max_g = NULL; 78 int ok = 0; 79 80 *flags = 0; 81 82 if (!BN_is_odd(dh->p)) 83 *flags |= DH_CHECK_P_NOT_PRIME; 84 85 /* 86 * Check that 1 < dh->g < p - 1 87 */ 88 89 if (BN_cmp(dh->g, BN_value_one()) <= 0) 90 *flags |= DH_NOT_SUITABLE_GENERATOR; 91 /* max_g = p - 1 */ 92 if ((max_g = BN_dup(dh->p)) == NULL) 93 goto err; 94 if (!BN_sub_word(max_g, 1)) 95 goto err; 96 /* check that g < max_g */ 97 if (BN_cmp(dh->g, max_g) >= 0) 98 *flags |= DH_NOT_SUITABLE_GENERATOR; 99 100 ok = 1; 101 102 err: 103 BN_free(max_g); 104 105 return ok; 106 } 107 108 /* 109 * Check that p is a safe prime and that g is a suitable generator. 110 */ 111 112 int 113 DH_check(const DH *dh, int *flags) 114 { 115 BN_CTX *ctx = NULL; 116 int is_prime; 117 int ok = 0; 118 119 *flags = 0; 120 121 if (!DH_check_params(dh, flags)) 122 goto err; 123 124 ctx = BN_CTX_new(); 125 if (ctx == NULL) 126 goto err; 127 BN_CTX_start(ctx); 128 129 if (dh->q != NULL) { 130 BIGNUM *residue; 131 132 if ((residue = BN_CTX_get(ctx)) == NULL) 133 goto err; 134 if ((*flags & DH_NOT_SUITABLE_GENERATOR) == 0) { 135 /* Check g^q == 1 mod p */ 136 if (!BN_mod_exp_ct(residue, dh->g, dh->q, dh->p, ctx)) 137 goto err; 138 if (!BN_is_one(residue)) 139 *flags |= DH_NOT_SUITABLE_GENERATOR; 140 } 141 is_prime = BN_is_prime_ex(dh->q, DH_NUMBER_ITERATIONS_FOR_PRIME, 142 ctx, NULL); 143 if (is_prime < 0) 144 goto err; 145 if (is_prime == 0) 146 *flags |= DH_CHECK_Q_NOT_PRIME; 147 /* Check p == 1 mod q, i.e., q divides p - 1 */ 148 if (!BN_div_ct(NULL, residue, dh->p, dh->q, ctx)) 149 goto err; 150 if (!BN_is_one(residue)) 151 *flags |= DH_CHECK_INVALID_Q_VALUE; 152 } 153 154 is_prime = BN_is_prime_ex(dh->p, DH_NUMBER_ITERATIONS_FOR_PRIME, 155 ctx, NULL); 156 if (is_prime < 0) 157 goto err; 158 if (is_prime == 0) 159 *flags |= DH_CHECK_P_NOT_PRIME; 160 else if (dh->q == NULL) { 161 BIGNUM *q; 162 163 if ((q = BN_CTX_get(ctx)) == NULL) 164 goto err; 165 if (!BN_rshift1(q, dh->p)) 166 goto err; 167 is_prime = BN_is_prime_ex(q, DH_NUMBER_ITERATIONS_FOR_PRIME, 168 ctx, NULL); 169 if (is_prime < 0) 170 goto err; 171 if (is_prime == 0) 172 *flags |= DH_CHECK_P_NOT_SAFE_PRIME; 173 } 174 175 ok = 1; 176 177 err: 178 BN_CTX_end(ctx); 179 BN_CTX_free(ctx); 180 return ok; 181 } 182 LCRYPTO_ALIAS(DH_check); 183 184 int 185 DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *flags) 186 { 187 BN_CTX *ctx = NULL; 188 BIGNUM *max_pub_key; 189 int ok = 0; 190 191 *flags = 0; 192 193 if ((ctx = BN_CTX_new()) == NULL) 194 goto err; 195 BN_CTX_start(ctx); 196 if ((max_pub_key = BN_CTX_get(ctx)) == NULL) 197 goto err; 198 199 /* 200 * Check that 1 < pub_key < dh->p - 1 201 */ 202 203 if (BN_cmp(pub_key, BN_value_one()) <= 0) 204 *flags |= DH_CHECK_PUBKEY_TOO_SMALL; 205 206 /* max_pub_key = dh->p - 1 */ 207 if (!BN_sub(max_pub_key, dh->p, BN_value_one())) 208 goto err; 209 210 if (BN_cmp(pub_key, max_pub_key) >= 0) 211 *flags |= DH_CHECK_PUBKEY_TOO_LARGE; 212 213 /* 214 * If dh->q is set, check that pub_key^q == 1 mod p 215 */ 216 217 if (dh->q != NULL) { 218 BIGNUM *residue; 219 220 if ((residue = BN_CTX_get(ctx)) == NULL) 221 goto err; 222 223 if (!BN_mod_exp_ct(residue, pub_key, dh->q, dh->p, ctx)) 224 goto err; 225 if (!BN_is_one(residue)) 226 *flags |= DH_CHECK_PUBKEY_INVALID; 227 } 228 229 ok = 1; 230 231 err: 232 BN_CTX_end(ctx); 233 BN_CTX_free(ctx); 234 235 return ok; 236 } 237 LCRYPTO_ALIAS(DH_check_pub_key); 238