1 /* $OpenBSD: dsa_ossl.c,v 1.40 2018/11/06 07:02:33 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 71 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa); 72 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 73 BIGNUM **rp); 74 static int dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, 75 DSA *dsa); 76 static int dsa_init(DSA *dsa); 77 static int dsa_finish(DSA *dsa); 78 79 static DSA_METHOD openssl_dsa_meth = { 80 .name = "OpenSSL DSA method", 81 .dsa_do_sign = dsa_do_sign, 82 .dsa_sign_setup = dsa_sign_setup, 83 .dsa_do_verify = dsa_do_verify, 84 .init = dsa_init, 85 .finish = dsa_finish, 86 }; 87 88 const DSA_METHOD * 89 DSA_OpenSSL(void) 90 { 91 return &openssl_dsa_meth; 92 } 93 94 static DSA_SIG * 95 dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa) 96 { 97 BIGNUM b, bm, bxr, binv, m, *kinv = NULL, *r = NULL, *s = NULL; 98 BN_CTX *ctx = NULL; 99 int reason = ERR_R_BN_LIB; 100 DSA_SIG *ret = NULL; 101 int noredo = 0; 102 103 BN_init(&b); 104 BN_init(&binv); 105 BN_init(&bm); 106 BN_init(&bxr); 107 BN_init(&m); 108 109 if (!dsa->p || !dsa->q || !dsa->g) { 110 reason = DSA_R_MISSING_PARAMETERS; 111 goto err; 112 } 113 114 s = BN_new(); 115 if (s == NULL) 116 goto err; 117 ctx = BN_CTX_new(); 118 if (ctx == NULL) 119 goto err; 120 121 /* 122 * If the digest length is greater than N (the bit length of q), the 123 * leftmost N bits of the digest shall be used, see FIPS 186-3, 4.2. 124 * In this case the digest length is given in bytes. 125 */ 126 if (dlen > BN_num_bytes(dsa->q)) 127 dlen = BN_num_bytes(dsa->q); 128 if (BN_bin2bn(dgst, dlen, &m) == NULL) 129 goto err; 130 131 redo: 132 if (dsa->kinv == NULL || dsa->r == NULL) { 133 if (!DSA_sign_setup(dsa, ctx, &kinv, &r)) 134 goto err; 135 } else { 136 kinv = dsa->kinv; 137 dsa->kinv = NULL; 138 r = dsa->r; 139 dsa->r = NULL; 140 noredo = 1; 141 } 142 143 /* 144 * Compute: 145 * 146 * s = inv(k)(m + xr) mod q 147 * 148 * In order to reduce the possibility of a side-channel attack, the 149 * following is calculated using a blinding value: 150 * 151 * s = inv(k)inv(b)(bm + bxr) mod q 152 * 153 * Where b is a random value in the range [1, q). 154 */ 155 if (!bn_rand_interval(&b, BN_value_one(), dsa->q)) 156 goto err; 157 if (BN_mod_inverse_ct(&binv, &b, dsa->q, ctx) == NULL) 158 goto err; 159 160 if (!BN_mod_mul(&bxr, &b, dsa->priv_key, dsa->q, ctx)) /* bx */ 161 goto err; 162 if (!BN_mod_mul(&bxr, &bxr, r, dsa->q, ctx)) /* bxr */ 163 goto err; 164 if (!BN_mod_mul(&bm, &b, &m, dsa->q, ctx)) /* bm */ 165 goto err; 166 if (!BN_mod_add(s, &bxr, &bm, dsa->q, ctx)) /* s = bm + bxr */ 167 goto err; 168 if (!BN_mod_mul(s, s, &binv, dsa->q, ctx)) /* s = m + xr */ 169 goto err; 170 if (!BN_mod_mul(s, s, kinv, dsa->q, ctx)) 171 goto err; 172 173 /* 174 * Redo if r or s is zero as required by FIPS 186-3: this is very 175 * unlikely. 176 */ 177 if (BN_is_zero(r) || BN_is_zero(s)) { 178 if (noredo) { 179 reason = DSA_R_NEED_NEW_SETUP_VALUES; 180 goto err; 181 } 182 goto redo; 183 } 184 185 if ((ret = DSA_SIG_new()) == NULL) { 186 reason = ERR_R_MALLOC_FAILURE; 187 goto err; 188 } 189 ret->r = r; 190 ret->s = s; 191 192 err: 193 if (!ret) { 194 DSAerror(reason); 195 BN_free(r); 196 BN_free(s); 197 } 198 BN_CTX_free(ctx); 199 BN_clear_free(&b); 200 BN_clear_free(&bm); 201 BN_clear_free(&bxr); 202 BN_clear_free(&binv); 203 BN_clear_free(&m); 204 BN_clear_free(kinv); 205 206 return ret; 207 } 208 209 static int 210 dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp) 211 { 212 BN_CTX *ctx; 213 BIGNUM k, l, m, *kinv = NULL, *r = NULL; 214 int q_bits, ret = 0; 215 216 if (!dsa->p || !dsa->q || !dsa->g) { 217 DSAerror(DSA_R_MISSING_PARAMETERS); 218 return 0; 219 } 220 221 BN_init(&k); 222 BN_init(&l); 223 BN_init(&m); 224 225 if (ctx_in == NULL) { 226 if ((ctx = BN_CTX_new()) == NULL) 227 goto err; 228 } else 229 ctx = ctx_in; 230 231 if ((r = BN_new()) == NULL) 232 goto err; 233 234 /* Preallocate space */ 235 q_bits = BN_num_bits(dsa->q); 236 if (!BN_set_bit(&k, q_bits) || 237 !BN_set_bit(&l, q_bits) || 238 !BN_set_bit(&m, q_bits)) 239 goto err; 240 241 if (!bn_rand_interval(&k, BN_value_one(), dsa->q)) 242 goto err; 243 244 BN_set_flags(&k, BN_FLG_CONSTTIME); 245 246 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 247 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p, 248 CRYPTO_LOCK_DSA, dsa->p, ctx)) 249 goto err; 250 } 251 252 /* Compute r = (g^k mod p) mod q */ 253 254 /* 255 * We do not want timing information to leak the length of k, 256 * so we compute G^k using an equivalent exponent of fixed 257 * bit-length. 258 * 259 * We unconditionally perform both of these additions to prevent a 260 * small timing information leakage. We then choose the sum that is 261 * one bit longer than the modulus. 262 * 263 * TODO: revisit the BN_copy aiming for a memory access agnostic 264 * conditional copy. 265 */ 266 267 if (!BN_add(&l, &k, dsa->q) || 268 !BN_add(&m, &l, dsa->q) || 269 !BN_copy(&k, BN_num_bits(&l) > q_bits ? &l : &m)) 270 goto err; 271 272 if (dsa->meth->bn_mod_exp != NULL) { 273 if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, &k, dsa->p, ctx, 274 dsa->method_mont_p)) 275 goto err; 276 } else { 277 if (!BN_mod_exp_mont_ct(r, dsa->g, &k, dsa->p, ctx, 278 dsa->method_mont_p)) 279 goto err; 280 } 281 282 if (!BN_mod_ct(r, r, dsa->q, ctx)) 283 goto err; 284 285 /* Compute part of 's = inv(k) (m + xr) mod q' */ 286 if ((kinv = BN_mod_inverse_ct(NULL, &k, dsa->q, ctx)) == NULL) 287 goto err; 288 289 BN_clear_free(*kinvp); 290 *kinvp = kinv; 291 kinv = NULL; 292 BN_clear_free(*rp); 293 *rp = r; 294 295 ret = 1; 296 297 err: 298 if (!ret) { 299 DSAerror(ERR_R_BN_LIB); 300 BN_clear_free(r); 301 } 302 if (ctx_in == NULL) 303 BN_CTX_free(ctx); 304 BN_clear_free(&k); 305 BN_clear_free(&l); 306 BN_clear_free(&m); 307 308 return ret; 309 } 310 311 static int 312 dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, DSA *dsa) 313 { 314 BN_CTX *ctx; 315 BIGNUM u1, u2, t1; 316 BN_MONT_CTX *mont = NULL; 317 int ret = -1, i; 318 319 if (!dsa->p || !dsa->q || !dsa->g) { 320 DSAerror(DSA_R_MISSING_PARAMETERS); 321 return -1; 322 } 323 324 i = BN_num_bits(dsa->q); 325 /* FIPS 186-3 allows only three different sizes for q. */ 326 if (i != 160 && i != 224 && i != 256) { 327 DSAerror(DSA_R_BAD_Q_VALUE); 328 return -1; 329 } 330 331 if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) { 332 DSAerror(DSA_R_MODULUS_TOO_LARGE); 333 return -1; 334 } 335 BN_init(&u1); 336 BN_init(&u2); 337 BN_init(&t1); 338 339 if ((ctx = BN_CTX_new()) == NULL) 340 goto err; 341 342 if (BN_is_zero(sig->r) || BN_is_negative(sig->r) || 343 BN_ucmp(sig->r, dsa->q) >= 0) { 344 ret = 0; 345 goto err; 346 } 347 if (BN_is_zero(sig->s) || BN_is_negative(sig->s) || 348 BN_ucmp(sig->s, dsa->q) >= 0) { 349 ret = 0; 350 goto err; 351 } 352 353 /* Calculate w = inv(s) mod q, saving w in u2. */ 354 if ((BN_mod_inverse_ct(&u2, sig->s, dsa->q, ctx)) == NULL) 355 goto err; 356 357 /* 358 * If the digest length is greater than the size of q use the 359 * BN_num_bits(dsa->q) leftmost bits of the digest, see FIPS 186-3, 4.2. 360 */ 361 if (dgst_len > (i >> 3)) 362 dgst_len = (i >> 3); 363 364 /* Save m in u1. */ 365 if (BN_bin2bn(dgst, dgst_len, &u1) == NULL) 366 goto err; 367 368 /* u1 = m * w mod q */ 369 if (!BN_mod_mul(&u1, &u1, &u2, dsa->q, ctx)) 370 goto err; 371 372 /* u2 = r * w mod q */ 373 if (!BN_mod_mul(&u2, sig->r, &u2, dsa->q, ctx)) 374 goto err; 375 376 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 377 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p, 378 CRYPTO_LOCK_DSA, dsa->p, ctx); 379 if (!mont) 380 goto err; 381 } 382 383 if (dsa->meth->dsa_mod_exp != NULL) { 384 if (!dsa->meth->dsa_mod_exp(dsa, &t1, dsa->g, &u1, dsa->pub_key, 385 &u2, dsa->p, ctx, mont)) 386 goto err; 387 } else { 388 if (!BN_mod_exp2_mont(&t1, dsa->g, &u1, dsa->pub_key, &u2, 389 dsa->p, ctx, mont)) 390 goto err; 391 } 392 393 /* BN_copy(&u1,&t1); */ 394 /* let u1 = u1 mod q */ 395 if (!BN_mod_ct(&u1, &t1, dsa->q, ctx)) 396 goto err; 397 398 /* v is in u1 - if the signature is correct, it will be equal to r. */ 399 ret = BN_ucmp(&u1, sig->r) == 0; 400 401 err: 402 if (ret < 0) 403 DSAerror(ERR_R_BN_LIB); 404 BN_CTX_free(ctx); 405 BN_free(&u1); 406 BN_free(&u2); 407 BN_free(&t1); 408 409 return ret; 410 } 411 412 static int 413 dsa_init(DSA *dsa) 414 { 415 dsa->flags |= DSA_FLAG_CACHE_MONT_P; 416 return 1; 417 } 418 419 static int 420 dsa_finish(DSA *dsa) 421 { 422 BN_MONT_CTX_free(dsa->method_mont_p); 423 return 1; 424 } 425 426