1 /* $OpenBSD: dsa_ossl.c,v 1.44 2022/02/24 08:35:45 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_lcl.h" 70 #include "dsa_locl.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 95 static DSA_SIG * 96 dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa) 97 { 98 BIGNUM b, bm, bxr, binv, m, *kinv = NULL, *r = NULL, *s = NULL; 99 BN_CTX *ctx = NULL; 100 int reason = ERR_R_BN_LIB; 101 DSA_SIG *ret = NULL; 102 int noredo = 0; 103 104 BN_init(&b); 105 BN_init(&binv); 106 BN_init(&bm); 107 BN_init(&bxr); 108 BN_init(&m); 109 110 if (!dsa->p || !dsa->q || !dsa->g) { 111 reason = DSA_R_MISSING_PARAMETERS; 112 goto err; 113 } 114 115 s = BN_new(); 116 if (s == NULL) 117 goto err; 118 ctx = BN_CTX_new(); 119 if (ctx == NULL) 120 goto err; 121 122 /* 123 * If the digest length is greater than N (the bit length of q), the 124 * leftmost N bits of the digest shall be used, see FIPS 186-3, 4.2. 125 * In this case the digest length is given in bytes. 126 */ 127 if (dlen > BN_num_bytes(dsa->q)) 128 dlen = BN_num_bytes(dsa->q); 129 if (BN_bin2bn(dgst, dlen, &m) == NULL) 130 goto err; 131 132 redo: 133 if (dsa->kinv == NULL || dsa->r == NULL) { 134 if (!DSA_sign_setup(dsa, ctx, &kinv, &r)) 135 goto err; 136 } else { 137 kinv = dsa->kinv; 138 dsa->kinv = NULL; 139 r = dsa->r; 140 dsa->r = NULL; 141 noredo = 1; 142 } 143 144 /* 145 * Compute: 146 * 147 * s = inv(k)(m + xr) mod q 148 * 149 * In order to reduce the possibility of a side-channel attack, the 150 * following is calculated using a blinding value: 151 * 152 * s = inv(b)(bm + bxr)inv(k) mod q 153 * 154 * Where b is a random value in the range [1, q). 155 */ 156 if (!bn_rand_interval(&b, BN_value_one(), dsa->q)) 157 goto err; 158 if (BN_mod_inverse_ct(&binv, &b, dsa->q, ctx) == NULL) 159 goto err; 160 161 if (!BN_mod_mul(&bxr, &b, dsa->priv_key, dsa->q, ctx)) /* bx */ 162 goto err; 163 if (!BN_mod_mul(&bxr, &bxr, r, dsa->q, ctx)) /* bxr */ 164 goto err; 165 if (!BN_mod_mul(&bm, &b, &m, dsa->q, ctx)) /* bm */ 166 goto err; 167 if (!BN_mod_add(s, &bxr, &bm, dsa->q, ctx)) /* s = bm + bxr */ 168 goto err; 169 if (!BN_mod_mul(s, s, kinv, dsa->q, ctx)) /* s = b(m + xr)k^-1 */ 170 goto err; 171 if (!BN_mod_mul(s, s, &binv, dsa->q, ctx)) /* s = (m + xr)k^-1 */ 172 goto err; 173 174 /* 175 * Redo if r or s is zero as required by FIPS 186-3: this is very 176 * unlikely. 177 */ 178 if (BN_is_zero(r) || BN_is_zero(s)) { 179 if (noredo) { 180 reason = DSA_R_NEED_NEW_SETUP_VALUES; 181 goto err; 182 } 183 goto redo; 184 } 185 186 if ((ret = DSA_SIG_new()) == NULL) { 187 reason = ERR_R_MALLOC_FAILURE; 188 goto err; 189 } 190 ret->r = r; 191 ret->s = s; 192 193 err: 194 if (!ret) { 195 DSAerror(reason); 196 BN_free(r); 197 BN_free(s); 198 } 199 BN_CTX_free(ctx); 200 BN_clear_free(&b); 201 BN_clear_free(&bm); 202 BN_clear_free(&bxr); 203 BN_clear_free(&binv); 204 BN_clear_free(&m); 205 BN_clear_free(kinv); 206 207 return ret; 208 } 209 210 static int 211 dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp) 212 { 213 BN_CTX *ctx; 214 BIGNUM k, l, m, *kinv = NULL, *r = NULL; 215 int q_bits, ret = 0; 216 217 if (!dsa->p || !dsa->q || !dsa->g) { 218 DSAerror(DSA_R_MISSING_PARAMETERS); 219 return 0; 220 } 221 222 BN_init(&k); 223 BN_init(&l); 224 BN_init(&m); 225 226 if (ctx_in == NULL) { 227 if ((ctx = BN_CTX_new()) == NULL) 228 goto err; 229 } else 230 ctx = ctx_in; 231 232 if ((r = BN_new()) == NULL) 233 goto err; 234 235 /* Preallocate space */ 236 q_bits = BN_num_bits(dsa->q); 237 if (!BN_set_bit(&k, q_bits) || 238 !BN_set_bit(&l, q_bits) || 239 !BN_set_bit(&m, q_bits)) 240 goto err; 241 242 if (!bn_rand_interval(&k, BN_value_one(), dsa->q)) 243 goto err; 244 245 BN_set_flags(&k, BN_FLG_CONSTTIME); 246 247 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 248 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p, 249 CRYPTO_LOCK_DSA, dsa->p, ctx)) 250 goto err; 251 } 252 253 /* Compute r = (g^k mod p) mod q */ 254 255 /* 256 * We do not want timing information to leak the length of k, 257 * so we compute G^k using an equivalent exponent of fixed 258 * bit-length. 259 * 260 * We unconditionally perform both of these additions to prevent a 261 * small timing information leakage. We then choose the sum that is 262 * one bit longer than the modulus. 263 * 264 * TODO: revisit the BN_copy aiming for a memory access agnostic 265 * conditional copy. 266 */ 267 268 if (!BN_add(&l, &k, dsa->q) || 269 !BN_add(&m, &l, dsa->q) || 270 !BN_copy(&k, BN_num_bits(&l) > q_bits ? &l : &m)) 271 goto err; 272 273 if (dsa->meth->bn_mod_exp != NULL) { 274 if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, &k, dsa->p, ctx, 275 dsa->method_mont_p)) 276 goto err; 277 } else { 278 if (!BN_mod_exp_mont_ct(r, dsa->g, &k, dsa->p, ctx, 279 dsa->method_mont_p)) 280 goto err; 281 } 282 283 if (!BN_mod_ct(r, r, dsa->q, ctx)) 284 goto err; 285 286 /* Compute part of 's = inv(k) (m + xr) mod q' */ 287 if ((kinv = BN_mod_inverse_ct(NULL, &k, dsa->q, ctx)) == NULL) 288 goto err; 289 290 BN_clear_free(*kinvp); 291 *kinvp = kinv; 292 kinv = NULL; 293 BN_clear_free(*rp); 294 *rp = r; 295 296 ret = 1; 297 298 err: 299 if (!ret) { 300 DSAerror(ERR_R_BN_LIB); 301 BN_clear_free(r); 302 } 303 if (ctx_in == NULL) 304 BN_CTX_free(ctx); 305 BN_clear_free(&k); 306 BN_clear_free(&l); 307 BN_clear_free(&m); 308 309 return ret; 310 } 311 312 static int 313 dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, DSA *dsa) 314 { 315 BN_CTX *ctx; 316 BIGNUM u1, u2, t1; 317 BN_MONT_CTX *mont = NULL; 318 int qbits; 319 int ret = -1; 320 321 if (!dsa->p || !dsa->q || !dsa->g) { 322 DSAerror(DSA_R_MISSING_PARAMETERS); 323 return -1; 324 } 325 326 /* FIPS 186-3 allows only three different sizes for q. */ 327 qbits = BN_num_bits(dsa->q); 328 if (qbits != 160 && qbits != 224 && qbits != 256) { 329 DSAerror(DSA_R_BAD_Q_VALUE); 330 return -1; 331 } 332 if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) { 333 DSAerror(DSA_R_MODULUS_TOO_LARGE); 334 return -1; 335 } 336 337 BN_init(&u1); 338 BN_init(&u2); 339 BN_init(&t1); 340 341 if ((ctx = BN_CTX_new()) == NULL) 342 goto err; 343 344 if (BN_is_zero(sig->r) || BN_is_negative(sig->r) || 345 BN_ucmp(sig->r, dsa->q) >= 0) { 346 ret = 0; 347 goto err; 348 } 349 if (BN_is_zero(sig->s) || BN_is_negative(sig->s) || 350 BN_ucmp(sig->s, dsa->q) >= 0) { 351 ret = 0; 352 goto err; 353 } 354 355 /* Calculate w = inv(s) mod q, saving w in u2. */ 356 if ((BN_mod_inverse_ct(&u2, sig->s, dsa->q, ctx)) == NULL) 357 goto err; 358 359 /* 360 * If the digest length is greater than the size of q use the 361 * BN_num_bits(dsa->q) leftmost bits of the digest, see FIPS 186-3, 4.2. 362 */ 363 if (dgst_len > (qbits >> 3)) 364 dgst_len = (qbits >> 3); 365 366 /* Save m in u1. */ 367 if (BN_bin2bn(dgst, dgst_len, &u1) == NULL) 368 goto err; 369 370 /* u1 = m * w mod q */ 371 if (!BN_mod_mul(&u1, &u1, &u2, dsa->q, ctx)) 372 goto err; 373 374 /* u2 = r * w mod q */ 375 if (!BN_mod_mul(&u2, sig->r, &u2, dsa->q, ctx)) 376 goto err; 377 378 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 379 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p, 380 CRYPTO_LOCK_DSA, dsa->p, ctx); 381 if (!mont) 382 goto err; 383 } 384 385 if (dsa->meth->dsa_mod_exp != NULL) { 386 if (!dsa->meth->dsa_mod_exp(dsa, &t1, dsa->g, &u1, dsa->pub_key, 387 &u2, dsa->p, ctx, mont)) 388 goto err; 389 } else { 390 if (!BN_mod_exp2_mont(&t1, dsa->g, &u1, dsa->pub_key, &u2, 391 dsa->p, ctx, mont)) 392 goto err; 393 } 394 395 /* BN_copy(&u1,&t1); */ 396 /* let u1 = u1 mod q */ 397 if (!BN_mod_ct(&u1, &t1, dsa->q, ctx)) 398 goto err; 399 400 /* v is in u1 - if the signature is correct, it will be equal to r. */ 401 ret = BN_ucmp(&u1, sig->r) == 0; 402 403 err: 404 if (ret < 0) 405 DSAerror(ERR_R_BN_LIB); 406 BN_CTX_free(ctx); 407 BN_free(&u1); 408 BN_free(&u2); 409 BN_free(&t1); 410 411 return ret; 412 } 413 414 static int 415 dsa_init(DSA *dsa) 416 { 417 dsa->flags |= DSA_FLAG_CACHE_MONT_P; 418 return 1; 419 } 420 421 static int 422 dsa_finish(DSA *dsa) 423 { 424 BN_MONT_CTX_free(dsa->method_mont_p); 425 return 1; 426 } 427 428