dsa_ossl.c revision 340704
1/* crypto/dsa/dsa_ossl.c */ 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#include "cryptlib.h" 63#include <openssl/bn.h> 64#include <openssl/sha.h> 65#include <openssl/dsa.h> 66#include <openssl/rand.h> 67#include <openssl/asn1.h> 68 69static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa); 70static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 71 BIGNUM **rp); 72static int dsa_do_verify(const unsigned char *dgst, int dgst_len, 73 DSA_SIG *sig, DSA *dsa); 74static int dsa_init(DSA *dsa); 75static int dsa_finish(DSA *dsa); 76static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q, 77 BN_CTX *ctx); 78 79static DSA_METHOD openssl_dsa_meth = { 80 "OpenSSL DSA method", 81 dsa_do_sign, 82 dsa_sign_setup, 83 dsa_do_verify, 84 NULL, /* dsa_mod_exp, */ 85 NULL, /* dsa_bn_mod_exp, */ 86 dsa_init, 87 dsa_finish, 88 0, 89 NULL, 90 NULL, 91 NULL 92}; 93 94/*- 95 * These macro wrappers replace attempts to use the dsa_mod_exp() and 96 * bn_mod_exp() handlers in the DSA_METHOD structure. We avoid the problem of 97 * having a the macro work as an expression by bundling an "err_instr". So; 98 * 99 * if (!dsa->meth->bn_mod_exp(dsa, r,dsa->g,&k,dsa->p,ctx, 100 * dsa->method_mont_p)) goto err; 101 * 102 * can be replaced by; 103 * 104 * DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, &k, dsa->p, ctx, 105 * dsa->method_mont_p); 106 */ 107 108#define DSA_MOD_EXP(err_instr,dsa,rr,a1,p1,a2,p2,m,ctx,in_mont) \ 109 do { \ 110 int _tmp_res53; \ 111 if ((dsa)->meth->dsa_mod_exp) \ 112 _tmp_res53 = (dsa)->meth->dsa_mod_exp((dsa), (rr), (a1), (p1), \ 113 (a2), (p2), (m), (ctx), (in_mont)); \ 114 else \ 115 _tmp_res53 = BN_mod_exp2_mont((rr), (a1), (p1), (a2), (p2), \ 116 (m), (ctx), (in_mont)); \ 117 if (!_tmp_res53) err_instr; \ 118 } while(0) 119#define DSA_BN_MOD_EXP(err_instr,dsa,r,a,p,m,ctx,m_ctx) \ 120 do { \ 121 int _tmp_res53; \ 122 if ((dsa)->meth->bn_mod_exp) \ 123 _tmp_res53 = (dsa)->meth->bn_mod_exp((dsa), (r), (a), (p), \ 124 (m), (ctx), (m_ctx)); \ 125 else \ 126 _tmp_res53 = BN_mod_exp_mont((r), (a), (p), (m), (ctx), (m_ctx)); \ 127 if (!_tmp_res53) err_instr; \ 128 } while(0) 129 130const DSA_METHOD *DSA_OpenSSL(void) 131{ 132 return &openssl_dsa_meth; 133} 134 135static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa) 136{ 137 BIGNUM *kinv = NULL, *r = NULL, *s = NULL; 138 BIGNUM *m, *blind, *blindm, *tmp; 139 BN_CTX *ctx = NULL; 140 int reason = ERR_R_BN_LIB; 141 DSA_SIG *ret = NULL; 142 int noredo = 0; 143 144 if (dsa->p == NULL || dsa->q == NULL || dsa->g == NULL) { 145 reason = DSA_R_MISSING_PARAMETERS; 146 goto err; 147 } 148 149 s = BN_new(); 150 if (s == NULL) 151 goto err; 152 ctx = BN_CTX_new(); 153 if (ctx == NULL) 154 goto err; 155 m = BN_CTX_get(ctx); 156 blind = BN_CTX_get(ctx); 157 blindm = BN_CTX_get(ctx); 158 tmp = BN_CTX_get(ctx); 159 if (tmp == NULL) 160 goto err; 161 162 redo: 163 if ((dsa->kinv == NULL) || (dsa->r == NULL)) { 164 if (!DSA_sign_setup(dsa, ctx, &kinv, &r)) 165 goto err; 166 } else { 167 kinv = dsa->kinv; 168 dsa->kinv = NULL; 169 r = dsa->r; 170 dsa->r = NULL; 171 noredo = 1; 172 } 173 174 if (dlen > BN_num_bytes(dsa->q)) 175 /* 176 * if the digest length is greater than the size of q use the 177 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3, 178 * 4.2 179 */ 180 dlen = BN_num_bytes(dsa->q); 181 if (BN_bin2bn(dgst, dlen, m) == NULL) 182 goto err; 183 184 /* 185 * The normal signature calculation is: 186 * 187 * s := k^-1 * (m + r * priv_key) mod q 188 * 189 * We will blind this to protect against side channel attacks 190 * 191 * s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q 192 */ 193 194 /* Generate a blinding value */ 195 do { 196 if (!BN_rand(blind, BN_num_bits(dsa->q) - 1, -1, 0)) 197 goto err; 198 } while (BN_is_zero(blind)); 199 BN_set_flags(blind, BN_FLG_CONSTTIME); 200 BN_set_flags(blindm, BN_FLG_CONSTTIME); 201 BN_set_flags(tmp, BN_FLG_CONSTTIME); 202 203 /* tmp := blind * priv_key * r mod q */ 204 if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx)) 205 goto err; 206 if (!BN_mod_mul(tmp, tmp, r, dsa->q, ctx)) 207 goto err; 208 209 /* blindm := blind * m mod q */ 210 if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx)) 211 goto err; 212 213 /* s : = (blind * priv_key * r) + (blind * m) mod q */ 214 if (!BN_mod_add_quick(s, tmp, blindm, dsa->q)) 215 goto err; 216 217 /* s := s * k^-1 mod q */ 218 if (!BN_mod_mul(s, s, kinv, dsa->q, ctx)) 219 goto err; 220 221 /* s:= s * blind^-1 mod q */ 222 if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL) 223 goto err; 224 if (!BN_mod_mul(s, s, blind, dsa->q, ctx)) 225 goto err; 226 227 /* 228 * Redo if r or s is zero as required by FIPS 186-3: this is very 229 * unlikely. 230 */ 231 if (BN_is_zero(r) || BN_is_zero(s)) { 232 if (noredo) { 233 reason = DSA_R_NEED_NEW_SETUP_VALUES; 234 goto err; 235 } 236 goto redo; 237 } 238 ret = DSA_SIG_new(); 239 if (ret == NULL) 240 goto err; 241 ret->r = r; 242 ret->s = s; 243 244 err: 245 if (ret == NULL) { 246 DSAerr(DSA_F_DSA_DO_SIGN, reason); 247 BN_free(r); 248 BN_free(s); 249 } 250 BN_CTX_free(ctx); 251 BN_clear_free(kinv); 252 return ret; 253} 254 255static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 256 BIGNUM **rp) 257{ 258 BN_CTX *ctx; 259 BIGNUM k, kq, *K, *kinv = NULL, *r = NULL; 260 BIGNUM l, m; 261 int ret = 0; 262 int q_bits; 263 264 if (!dsa->p || !dsa->q || !dsa->g) { 265 DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS); 266 return 0; 267 } 268 269 BN_init(&k); 270 BN_init(&kq); 271 BN_init(&l); 272 BN_init(&m); 273 274 if (ctx_in == NULL) { 275 if ((ctx = BN_CTX_new()) == NULL) 276 goto err; 277 } else 278 ctx = ctx_in; 279 280 if ((r = BN_new()) == NULL) 281 goto err; 282 283 /* Preallocate space */ 284 q_bits = BN_num_bits(dsa->q) + sizeof(dsa->q->d[0]) * 16; 285 if (!BN_set_bit(&k, q_bits) 286 || !BN_set_bit(&l, q_bits) 287 || !BN_set_bit(&m, q_bits)) 288 goto err; 289 290 /* Get random k */ 291 do 292 if (!BN_rand_range(&k, dsa->q)) 293 goto err; 294 while (BN_is_zero(&k)); 295 296 if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) { 297 BN_set_flags(&k, BN_FLG_CONSTTIME); 298 BN_set_flags(&l, BN_FLG_CONSTTIME); 299 } 300 301 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 302 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p, 303 CRYPTO_LOCK_DSA, dsa->p, ctx)) 304 goto err; 305 } 306 307 /* Compute r = (g^k mod p) mod q */ 308 309 if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) { 310 /* 311 * We do not want timing information to leak the length of k, so we 312 * compute G^k using an equivalent scalar of fixed bit-length. 313 * 314 * We unconditionally perform both of these additions to prevent a 315 * small timing information leakage. We then choose the sum that is 316 * one bit longer than the modulus. 317 * 318 * TODO: revisit the BN_copy aiming for a memory access agnostic 319 * conditional copy. 320 */ 321 if (!BN_add(&l, &k, dsa->q) 322 || !BN_add(&m, &l, dsa->q) 323 || !BN_copy(&kq, BN_num_bits(&l) > q_bits ? &l : &m)) 324 goto err; 325 326 BN_set_flags(&kq, BN_FLG_CONSTTIME); 327 328 K = &kq; 329 } else { 330 K = &k; 331 } 332 333 DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, K, dsa->p, ctx, 334 dsa->method_mont_p); 335 if (!BN_mod(r, r, dsa->q, ctx)) 336 goto err; 337 338 /* Compute part of 's = inv(k) (m + xr) mod q' */ 339 if ((kinv = dsa_mod_inverse_fermat(&k, dsa->q, ctx)) == NULL) 340 goto err; 341 342 if (*kinvp != NULL) 343 BN_clear_free(*kinvp); 344 *kinvp = kinv; 345 kinv = NULL; 346 if (*rp != NULL) 347 BN_clear_free(*rp); 348 *rp = r; 349 ret = 1; 350 err: 351 if (!ret) { 352 DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB); 353 if (r != NULL) 354 BN_clear_free(r); 355 } 356 if (ctx_in == NULL) 357 BN_CTX_free(ctx); 358 BN_clear_free(&k); 359 BN_clear_free(&kq); 360 BN_clear_free(&l); 361 BN_clear_free(&m); 362 return ret; 363} 364 365static int dsa_do_verify(const unsigned char *dgst, int dgst_len, 366 DSA_SIG *sig, DSA *dsa) 367{ 368 BN_CTX *ctx; 369 BIGNUM u1, u2, t1; 370 BN_MONT_CTX *mont = NULL; 371 int ret = -1, i; 372 if (!dsa->p || !dsa->q || !dsa->g) { 373 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS); 374 return -1; 375 } 376 377 i = BN_num_bits(dsa->q); 378 /* fips 186-3 allows only different sizes for q */ 379 if (i != 160 && i != 224 && i != 256) { 380 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE); 381 return -1; 382 } 383 384 if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) { 385 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE); 386 return -1; 387 } 388 BN_init(&u1); 389 BN_init(&u2); 390 BN_init(&t1); 391 392 if ((ctx = BN_CTX_new()) == NULL) 393 goto err; 394 395 if (BN_is_zero(sig->r) || BN_is_negative(sig->r) || 396 BN_ucmp(sig->r, dsa->q) >= 0) { 397 ret = 0; 398 goto err; 399 } 400 if (BN_is_zero(sig->s) || BN_is_negative(sig->s) || 401 BN_ucmp(sig->s, dsa->q) >= 0) { 402 ret = 0; 403 goto err; 404 } 405 406 /* 407 * Calculate W = inv(S) mod Q save W in u2 408 */ 409 if ((BN_mod_inverse(&u2, sig->s, dsa->q, ctx)) == NULL) 410 goto err; 411 412 /* save M in u1 */ 413 if (dgst_len > (i >> 3)) 414 /* 415 * if the digest length is greater than the size of q use the 416 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3, 417 * 4.2 418 */ 419 dgst_len = (i >> 3); 420 if (BN_bin2bn(dgst, dgst_len, &u1) == NULL) 421 goto err; 422 423 /* u1 = M * w mod q */ 424 if (!BN_mod_mul(&u1, &u1, &u2, dsa->q, ctx)) 425 goto err; 426 427 /* u2 = r * w mod q */ 428 if (!BN_mod_mul(&u2, sig->r, &u2, dsa->q, ctx)) 429 goto err; 430 431 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { 432 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p, 433 CRYPTO_LOCK_DSA, dsa->p, ctx); 434 if (!mont) 435 goto err; 436 } 437 438 DSA_MOD_EXP(goto err, dsa, &t1, dsa->g, &u1, dsa->pub_key, &u2, dsa->p, 439 ctx, mont); 440 /* BN_copy(&u1,&t1); */ 441 /* let u1 = u1 mod q */ 442 if (!BN_mod(&u1, &t1, dsa->q, ctx)) 443 goto err; 444 445 /* 446 * V is now in u1. If the signature is correct, it will be equal to R. 447 */ 448 ret = (BN_ucmp(&u1, sig->r) == 0); 449 450 err: 451 if (ret < 0) 452 DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB); 453 if (ctx != NULL) 454 BN_CTX_free(ctx); 455 BN_free(&u1); 456 BN_free(&u2); 457 BN_free(&t1); 458 return (ret); 459} 460 461static int dsa_init(DSA *dsa) 462{ 463 dsa->flags |= DSA_FLAG_CACHE_MONT_P; 464 return (1); 465} 466 467static int dsa_finish(DSA *dsa) 468{ 469 if (dsa->method_mont_p) 470 BN_MONT_CTX_free(dsa->method_mont_p); 471 return (1); 472} 473 474/* 475 * Compute the inverse of k modulo q. 476 * Since q is prime, Fermat's Little Theorem applies, which reduces this to 477 * mod-exp operation. Both the exponent and modulus are public information 478 * so a mod-exp that doesn't leak the base is sufficient. A newly allocated 479 * BIGNUM is returned which the caller must free. 480 */ 481static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q, 482 BN_CTX *ctx) 483{ 484 BIGNUM *res = NULL; 485 BIGNUM *r, e; 486 487 if ((r = BN_new()) == NULL) 488 return NULL; 489 490 BN_init(&e); 491 492 if (BN_set_word(r, 2) 493 && BN_sub(&e, q, r) 494 && BN_mod_exp_mont(r, k, &e, q, ctx, NULL)) 495 res = r; 496 else 497 BN_free(r); 498 BN_free(&e); 499 return res; 500} 501