1 /* $OpenBSD: dsa_ossl.c,v 1.53 2023/08/03 18:53:55 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 /* Original version from Steven Schoch <schoch@sheba.arc.nasa.gov> */ 60 61 #include <stdio.h> 62 63 #include <openssl/asn1.h> 64 #include <openssl/bn.h> 65 #include <openssl/dsa.h> 66 #include <openssl/err.h> 67 #include <openssl/sha.h> 68 69 #include "bn_local.h" 70 #include "dsa_local.h" 71 72 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa); 73 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 74 BIGNUM **rp); 75 static int dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, 76 DSA *dsa); 77 static int dsa_init(DSA *dsa); 78 static int dsa_finish(DSA *dsa); 79 80 static DSA_METHOD openssl_dsa_meth = { 81 .name = "OpenSSL DSA method", 82 .dsa_do_sign = dsa_do_sign, 83 .dsa_sign_setup = dsa_sign_setup, 84 .dsa_do_verify = dsa_do_verify, 85 .init = dsa_init, 86 .finish = dsa_finish, 87 }; 88 89 const DSA_METHOD * 90 DSA_OpenSSL(void) 91 { 92 return &openssl_dsa_meth; 93 } 94 LCRYPTO_ALIAS(DSA_OpenSSL); 95 96 /* 97 * Since DSA parameters are entirely arbitrary and checking them to be 98 * consistent is very expensive, we cannot do so on every sign operation. 99 * Instead, cap the number of retries so we do not loop indefinitely if 100 * the generator of the multiplicative group happens to be nilpotent. 101 * The probability of needing a retry with valid parameters is negligible, 102 * so trying 32 times is amply enough. 103 */ 104 #define DSA_MAX_SIGN_ITERATIONS 32 105 106 static DSA_SIG * 107 dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa) 108 { 109 BIGNUM *b = NULL, *bm = NULL, *bxr = NULL, *binv = NULL, *m = NULL; 110 BIGNUM *kinv = NULL, *r = NULL, *s = NULL; 111 BN_CTX *ctx = NULL; 112 int reason = ERR_R_BN_LIB; 113 DSA_SIG *ret = NULL; 114 int attempts = 0; 115 int noredo = 0; 116 117 if (!dsa_check_key(dsa)) { 118 reason = DSA_R_INVALID_PARAMETERS; 119 goto err; 120 } 121 122 if ((s = BN_new()) == NULL) 123 goto err; 124 125 if ((ctx = BN_CTX_new()) == NULL) 126 goto err; 127 128 BN_CTX_start(ctx); 129 130 if ((b = BN_CTX_get(ctx)) == NULL) 131 goto err; 132 if ((binv = BN_CTX_get(ctx)) == NULL) 133 goto err; 134 if ((bm = BN_CTX_get(ctx)) == NULL) 135 goto err; 136 if ((bxr = BN_CTX_get(ctx)) == NULL) 137 goto err; 138 if ((m = BN_CTX_get(ctx)) == NULL) 139 goto err; 140 141 /* 142 * If the digest length is greater than N (the bit length of q), the 143 * leftmost N bits of the digest shall be used, see FIPS 186-3, 4.2. 144 * In this case the digest length is given in bytes. 145 */ 146 if (dlen > BN_num_bytes(dsa->q)) 147 dlen = BN_num_bytes(dsa->q); 148 if (BN_bin2bn(dgst, dlen, m) == NULL) 149 goto err; 150 151 redo: 152 if (dsa->kinv == NULL || dsa->r == NULL) { 153 if (!DSA_sign_setup(dsa, ctx, &kinv, &r)) 154 goto err; 155 } else { 156 kinv = dsa->kinv; 157 dsa->kinv = NULL; 158 r = dsa->r; 159 dsa->r = NULL; 160 noredo = 1; 161 } 162 163 /* 164 * Compute: 165 * 166 * s = inv(k)(m + xr) mod q 167 * 168 * In order to reduce the possibility of a side-channel attack, the 169 * following is calculated using a blinding value: 170 * 171 * s = inv(b)(bm + bxr)inv(k) mod q 172 * 173 * Where b is a random value in the range [1, q). 174 */ 175 if (!bn_rand_interval(b, 1, dsa->q)) 176 goto err; 177 if (BN_mod_inverse_ct(binv, b, dsa->q, ctx) == NULL) 178 goto err; 179 180 if (!BN_mod_mul(bxr, b, dsa->priv_key, dsa->q, ctx)) /* bx */ 181 goto err; 182 if (!BN_mod_mul(bxr, bxr, r, dsa->q, ctx)) /* bxr */ 183 goto err; 184 if (!BN_mod_mul(bm, b, m, dsa->q, ctx)) /* bm */ 185 goto err; 186 if (!BN_mod_add(s, bxr, bm, dsa->q, ctx)) /* s = bm + bxr */ 187 goto err; 188 if (!BN_mod_mul(s, s, kinv, dsa->q, ctx)) /* s = b(m + xr)k^-1 */ 189 goto err; 190 if (!BN_mod_mul(s, s, binv, dsa->q, ctx)) /* s = (m + xr)k^-1 */ 191 goto err; 192 193 /* 194 * Redo if r or s is zero as required by FIPS 186-3: this is very 195 * unlikely. 196 */ 197 if (BN_is_zero(r) || BN_is_zero(s)) { 198 if (noredo) { 199 reason = DSA_R_NEED_NEW_SETUP_VALUES; 200 goto err; 201 } 202 if (++attempts > DSA_MAX_SIGN_ITERATIONS) { 203 reason = DSA_R_INVALID_PARAMETERS; 204 goto err; 205 } 206 goto redo; 207 } 208 209 if ((ret = DSA_SIG_new()) == NULL) { 210 reason = ERR_R_MALLOC_FAILURE; 211 goto err; 212 } 213 ret->r = r; 214 ret->s = s; 215 216 err: 217 if (!ret) { 218 DSAerror(reason); 219 BN_free(r); 220 BN_free(s); 221 } 222 BN_CTX_end(ctx); 223 BN_CTX_free(ctx); 224 BN_free(kinv); 225 226 return ret; 227 } 228 229 static int 230 dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp) 231 { 232 BIGNUM *k = NULL, *l = NULL, *m = NULL, *kinv = NULL, *r = NULL; 233 BN_CTX *ctx = NULL; 234 int q_bits; 235 int ret = 0; 236 237 if (!dsa_check_key(dsa)) 238 goto err; 239 240 if ((r = BN_new()) == NULL) 241 goto err; 242 243 if ((ctx = ctx_in) == NULL) 244 ctx = BN_CTX_new(); 245 if (ctx == NULL) 246 goto err; 247 248 BN_CTX_start(ctx); 249 250 if ((k = BN_CTX_get(ctx)) == NULL) 251 goto err; 252 if ((l = BN_CTX_get(ctx)) == NULL) 253 goto err; 254 if ((m = BN_CTX_get(ctx)) == NULL) 255 goto err; 256 257 /* Preallocate space */ 258 q_bits = BN_num_bits(dsa->q); 259 if (!BN_set_bit(k, q_bits) || 260 !BN_set_bit(l, q_bits) || 261 !BN_set_bit(m, q_bits)) 262 goto err; 263 264 if (!bn_rand_interval(k, 1, dsa->q)) 265 goto err; 266 267 BN_set_flags(k, BN_FLG_CONSTTIME); 268 269 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 270 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p, 271 CRYPTO_LOCK_DSA, dsa->p, ctx)) 272 goto err; 273 } 274 275 /* Compute r = (g^k mod p) mod q */ 276 277 /* 278 * We do not want timing information to leak the length of k, 279 * so we compute G^k using an equivalent exponent of fixed 280 * bit-length. 281 * 282 * We unconditionally perform both of these additions to prevent a 283 * small timing information leakage. We then choose the sum that is 284 * one bit longer than the modulus. 285 * 286 * TODO: revisit the bn_copy aiming for a memory access agnostic 287 * conditional copy. 288 */ 289 290 if (!BN_add(l, k, dsa->q) || 291 !BN_add(m, l, dsa->q) || 292 !bn_copy(k, BN_num_bits(l) > q_bits ? l : m)) 293 goto err; 294 295 if (dsa->meth->bn_mod_exp != NULL) { 296 if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx, 297 dsa->method_mont_p)) 298 goto err; 299 } else { 300 if (!BN_mod_exp_mont_ct(r, dsa->g, k, dsa->p, ctx, 301 dsa->method_mont_p)) 302 goto err; 303 } 304 305 if (!BN_mod_ct(r, r, dsa->q, ctx)) 306 goto err; 307 308 /* Compute part of 's = inv(k) (m + xr) mod q' */ 309 if ((kinv = BN_mod_inverse_ct(NULL, k, dsa->q, ctx)) == NULL) 310 goto err; 311 312 BN_free(*kinvp); 313 *kinvp = kinv; 314 kinv = NULL; 315 316 BN_free(*rp); 317 *rp = r; 318 319 ret = 1; 320 321 err: 322 if (!ret) { 323 DSAerror(ERR_R_BN_LIB); 324 BN_free(r); 325 } 326 BN_CTX_end(ctx); 327 if (ctx != ctx_in) 328 BN_CTX_free(ctx); 329 330 return ret; 331 } 332 333 static int 334 dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, DSA *dsa) 335 { 336 BIGNUM *u1 = NULL, *u2 = NULL, *t1 = NULL; 337 BN_CTX *ctx = NULL; 338 BN_MONT_CTX *mont = NULL; 339 int qbits; 340 int ret = -1; 341 342 if (!dsa_check_key(dsa)) 343 goto err; 344 345 if ((ctx = BN_CTX_new()) == NULL) 346 goto err; 347 348 BN_CTX_start(ctx); 349 350 if ((u1 = BN_CTX_get(ctx)) == NULL) 351 goto err; 352 if ((u2 = BN_CTX_get(ctx)) == NULL) 353 goto err; 354 if ((t1 = BN_CTX_get(ctx)) == NULL) 355 goto err; 356 357 if (BN_is_zero(sig->r) || BN_is_negative(sig->r) || 358 BN_ucmp(sig->r, dsa->q) >= 0) { 359 ret = 0; 360 goto err; 361 } 362 if (BN_is_zero(sig->s) || BN_is_negative(sig->s) || 363 BN_ucmp(sig->s, dsa->q) >= 0) { 364 ret = 0; 365 goto err; 366 } 367 368 /* Calculate w = inv(s) mod q, saving w in u2. */ 369 if ((BN_mod_inverse_ct(u2, sig->s, dsa->q, ctx)) == NULL) 370 goto err; 371 372 /* 373 * If the digest length is greater than the size of q use the 374 * BN_num_bits(dsa->q) leftmost bits of the digest, see FIPS 186-4, 4.2. 375 */ 376 qbits = BN_num_bits(dsa->q); 377 if (dgst_len > (qbits >> 3)) 378 dgst_len = (qbits >> 3); 379 380 /* Save m in u1. */ 381 if (BN_bin2bn(dgst, dgst_len, u1) == NULL) 382 goto err; 383 384 /* u1 = m * w mod q */ 385 if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx)) 386 goto err; 387 388 /* u2 = r * w mod q */ 389 if (!BN_mod_mul(u2, sig->r, u2, dsa->q, ctx)) 390 goto err; 391 392 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 393 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p, 394 CRYPTO_LOCK_DSA, dsa->p, ctx); 395 if (!mont) 396 goto err; 397 } 398 399 if (dsa->meth->dsa_mod_exp != NULL) { 400 if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, 401 u2, dsa->p, ctx, mont)) 402 goto err; 403 } else { 404 if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, 405 dsa->p, ctx, mont)) 406 goto err; 407 } 408 409 /* let u1 = u1 mod q */ 410 if (!BN_mod_ct(u1, t1, dsa->q, ctx)) 411 goto err; 412 413 /* v is in u1 - if the signature is correct, it will be equal to r. */ 414 ret = BN_ucmp(u1, sig->r) == 0; 415 416 err: 417 if (ret < 0) 418 DSAerror(ERR_R_BN_LIB); 419 BN_CTX_end(ctx); 420 BN_CTX_free(ctx); 421 422 return ret; 423 } 424 425 static int 426 dsa_init(DSA *dsa) 427 { 428 dsa->flags |= DSA_FLAG_CACHE_MONT_P; 429 return 1; 430 } 431 432 static int 433 dsa_finish(DSA *dsa) 434 { 435 BN_MONT_CTX_free(dsa->method_mont_p); 436 return 1; 437 } 438 439 DSA_SIG * 440 DSA_SIG_new(void) 441 { 442 return calloc(1, sizeof(DSA_SIG)); 443 } 444 LCRYPTO_ALIAS(DSA_SIG_new); 445 446 void 447 DSA_SIG_free(DSA_SIG *sig) 448 { 449 if (sig == NULL) 450 return; 451 452 BN_free(sig->r); 453 BN_free(sig->s); 454 free(sig); 455 } 456 LCRYPTO_ALIAS(DSA_SIG_free); 457 458 int 459 DSA_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp) 460 { 461 return dsa->meth->dsa_sign_setup(dsa, ctx_in, kinvp, rp); 462 } 463 LCRYPTO_ALIAS(DSA_sign_setup); 464 465 DSA_SIG * 466 DSA_do_sign(const unsigned char *dgst, int dlen, DSA *dsa) 467 { 468 return dsa->meth->dsa_do_sign(dgst, dlen, dsa); 469 } 470 LCRYPTO_ALIAS(DSA_do_sign); 471 472 int 473 DSA_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, DSA *dsa) 474 { 475 return dsa->meth->dsa_do_verify(dgst, dgst_len, sig, dsa); 476 } 477 LCRYPTO_ALIAS(DSA_do_verify); 478