1 /* $OpenBSD: dh_check.c,v 1.25 2022/07/13 18:38:20 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_lcl.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. The _ex version removes the need of 72 * inspecting flags and pushes errors on the stack instead. 73 */ 74 75 int 76 DH_check_params_ex(const DH *dh) 77 { 78 int flags = 0; 79 80 if (!DH_check_params(dh, &flags)) 81 return 0; 82 83 if ((flags & DH_CHECK_P_NOT_PRIME) != 0) 84 DHerror(DH_R_CHECK_P_NOT_PRIME); 85 if ((flags & DH_NOT_SUITABLE_GENERATOR) != 0) 86 DHerror(DH_R_NOT_SUITABLE_GENERATOR); 87 88 return flags == 0; 89 } 90 91 int 92 DH_check_params(const DH *dh, int *flags) 93 { 94 BIGNUM *max_g = NULL; 95 int ok = 0; 96 97 *flags = 0; 98 99 if (!BN_is_odd(dh->p)) 100 *flags |= DH_CHECK_P_NOT_PRIME; 101 102 /* 103 * Check that 1 < dh->g < p - 1 104 */ 105 106 if (BN_cmp(dh->g, BN_value_one()) <= 0) 107 *flags |= DH_NOT_SUITABLE_GENERATOR; 108 /* max_g = p - 1 */ 109 if ((max_g = BN_dup(dh->p)) == NULL) 110 goto err; 111 if (!BN_sub_word(max_g, 1)) 112 goto err; 113 /* check that g < max_g */ 114 if (BN_cmp(dh->g, max_g) >= 0) 115 *flags |= DH_NOT_SUITABLE_GENERATOR; 116 117 ok = 1; 118 119 err: 120 BN_free(max_g); 121 122 return ok; 123 } 124 125 /* 126 * Check that p is a safe prime and that g is a suitable generator. 127 * The _ex version puts errors on the stack instead of returning flags. 128 */ 129 130 int 131 DH_check_ex(const DH *dh) 132 { 133 int flags = 0; 134 135 if (!DH_check(dh, &flags)) 136 return 0; 137 138 if ((flags & DH_NOT_SUITABLE_GENERATOR) != 0) 139 DHerror(DH_R_NOT_SUITABLE_GENERATOR); 140 if ((flags & DH_CHECK_Q_NOT_PRIME) != 0) 141 DHerror(DH_R_CHECK_Q_NOT_PRIME); 142 if ((flags & DH_CHECK_INVALID_Q_VALUE) != 0) 143 DHerror(DH_R_CHECK_INVALID_Q_VALUE); 144 if ((flags & DH_CHECK_INVALID_J_VALUE) != 0) 145 DHerror(DH_R_CHECK_INVALID_J_VALUE); 146 if ((flags & DH_UNABLE_TO_CHECK_GENERATOR) != 0) 147 DHerror(DH_R_UNABLE_TO_CHECK_GENERATOR); 148 if ((flags & DH_CHECK_P_NOT_PRIME) != 0) 149 DHerror(DH_R_CHECK_P_NOT_PRIME); 150 if ((flags & DH_CHECK_P_NOT_SAFE_PRIME) != 0) 151 DHerror(DH_R_CHECK_P_NOT_SAFE_PRIME); 152 153 return flags == 0; 154 } 155 156 int 157 DH_check(const DH *dh, int *flags) 158 { 159 BN_CTX *ctx = NULL; 160 int is_prime; 161 int ok = 0; 162 163 *flags = 0; 164 165 if (!DH_check_params(dh, flags)) 166 goto err; 167 168 ctx = BN_CTX_new(); 169 if (ctx == NULL) 170 goto err; 171 BN_CTX_start(ctx); 172 173 if (dh->q != NULL) { 174 BIGNUM *quotient, *residue; 175 176 if ((quotient = BN_CTX_get(ctx)) == NULL) 177 goto err; 178 if ((residue = BN_CTX_get(ctx)) == NULL) 179 goto err; 180 if ((*flags & DH_NOT_SUITABLE_GENERATOR) == 0) { 181 /* Check g^q == 1 mod p */ 182 if (!BN_mod_exp_ct(residue, dh->g, dh->q, dh->p, ctx)) 183 goto err; 184 if (!BN_is_one(residue)) 185 *flags |= DH_NOT_SUITABLE_GENERATOR; 186 } 187 is_prime = BN_is_prime_ex(dh->q, DH_NUMBER_ITERATIONS_FOR_PRIME, 188 ctx, NULL); 189 if (is_prime < 0) 190 goto err; 191 if (is_prime == 0) 192 *flags |= DH_CHECK_Q_NOT_PRIME; 193 /* Check p == 1 mod q, i.e., q divides p - 1 */ 194 if (!BN_div_ct(quotient, residue, dh->p, dh->q, ctx)) 195 goto err; 196 if (!BN_is_one(residue)) 197 *flags |= DH_CHECK_INVALID_Q_VALUE; 198 if (dh->j != NULL && BN_cmp(dh->j, quotient) != 0) 199 *flags |= DH_CHECK_INVALID_J_VALUE; 200 } 201 202 is_prime = BN_is_prime_ex(dh->p, DH_NUMBER_ITERATIONS_FOR_PRIME, 203 ctx, NULL); 204 if (is_prime < 0) 205 goto err; 206 if (is_prime == 0) 207 *flags |= DH_CHECK_P_NOT_PRIME; 208 else if (dh->q == NULL) { 209 BIGNUM *q; 210 211 if ((q = BN_CTX_get(ctx)) == NULL) 212 goto err; 213 if (!BN_rshift1(q, dh->p)) 214 goto err; 215 is_prime = BN_is_prime_ex(q, DH_NUMBER_ITERATIONS_FOR_PRIME, 216 ctx, NULL); 217 if (is_prime < 0) 218 goto err; 219 if (is_prime == 0) 220 *flags |= DH_CHECK_P_NOT_SAFE_PRIME; 221 } 222 223 ok = 1; 224 225 err: 226 BN_CTX_end(ctx); 227 BN_CTX_free(ctx); 228 return ok; 229 } 230 231 int 232 DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key) 233 { 234 int flags = 0; 235 236 if (!DH_check_pub_key(dh, pub_key, &flags)) 237 return 0; 238 239 if ((flags & DH_CHECK_PUBKEY_TOO_SMALL) != 0) 240 DHerror(DH_R_CHECK_PUBKEY_TOO_SMALL); 241 if ((flags & DH_CHECK_PUBKEY_TOO_LARGE) != 0) 242 DHerror(DH_R_CHECK_PUBKEY_TOO_LARGE); 243 if ((flags & DH_CHECK_PUBKEY_INVALID) != 0) 244 DHerror(DH_R_CHECK_PUBKEY_INVALID); 245 246 return flags == 0; 247 } 248 249 int 250 DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *flags) 251 { 252 BN_CTX *ctx = NULL; 253 BIGNUM *max_pub_key; 254 int ok = 0; 255 256 *flags = 0; 257 258 if ((ctx = BN_CTX_new()) == NULL) 259 goto err; 260 BN_CTX_start(ctx); 261 if ((max_pub_key = BN_CTX_get(ctx)) == NULL) 262 goto err; 263 264 /* 265 * Check that 1 < pub_key < dh->p - 1 266 */ 267 268 if (BN_cmp(pub_key, BN_value_one()) <= 0) 269 *flags |= DH_CHECK_PUBKEY_TOO_SMALL; 270 271 /* max_pub_key = dh->p - 1 */ 272 if (!BN_sub(max_pub_key, dh->p, BN_value_one())) 273 goto err; 274 275 if (BN_cmp(pub_key, max_pub_key) >= 0) 276 *flags |= DH_CHECK_PUBKEY_TOO_LARGE; 277 278 /* 279 * If dh->q is set, check that pub_key^q == 1 mod p 280 */ 281 282 if (dh->q != NULL) { 283 BIGNUM *residue; 284 285 if ((residue = BN_CTX_get(ctx)) == NULL) 286 goto err; 287 288 if (!BN_mod_exp_ct(residue, pub_key, dh->q, dh->p, ctx)) 289 goto err; 290 if (!BN_is_one(residue)) 291 *flags = DH_CHECK_PUBKEY_INVALID; 292 } 293 294 ok = 1; 295 296 err: 297 BN_CTX_end(ctx); 298 BN_CTX_free(ctx); 299 300 return ok; 301 } 302