1 /* crypto/ec/ec_mult.c */ 2 /* ==================================================================== 3 * Copyright (c) 1998-2001 The OpenSSL Project. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in 14 * the documentation and/or other materials provided with the 15 * distribution. 16 * 17 * 3. All advertising materials mentioning features or use of this 18 * software must display the following acknowledgment: 19 * "This product includes software developed by the OpenSSL Project 20 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 21 * 22 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 23 * endorse or promote products derived from this software without 24 * prior written permission. For written permission, please contact 25 * openssl-core@openssl.org. 26 * 27 * 5. Products derived from this software may not be called "OpenSSL" 28 * nor may "OpenSSL" appear in their names without prior written 29 * permission of the OpenSSL Project. 30 * 31 * 6. Redistributions of any form whatsoever must retain the following 32 * acknowledgment: 33 * "This product includes software developed by the OpenSSL Project 34 * for use in the OpenSSL Toolkit (http://www.openssl.org/)" 35 * 36 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 37 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 38 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 39 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 40 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 41 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 42 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 43 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 44 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 45 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 46 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 47 * OF THE POSSIBILITY OF SUCH DAMAGE. 48 * ==================================================================== 49 * 50 * This product includes cryptographic software written by Eric Young 51 * (eay@cryptsoft.com). This product includes software written by Tim 52 * Hudson (tjh@cryptsoft.com). 53 * 54 */ 55 56 #include <openssl/err.h> 57 58 #include "ec_lcl.h" 59 60 61 /* TODO: optional precomputation of multiples of the generator */ 62 63 64 65 /* 66 * wNAF-based interleaving multi-exponentation method 67 * (<URL:http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#multiexp>) 68 */ 69 70 71 /* Determine the width-(w+1) Non-Adjacent Form (wNAF) of 'scalar'. 72 * This is an array r[] of values that are either zero or odd with an 73 * absolute value less than 2^w satisfying 74 * scalar = \sum_j r[j]*2^j 75 * where at most one of any w+1 consecutive digits is non-zero. 76 */ 77 static signed char *compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len, BN_CTX *ctx) 78 { 79 BIGNUM *c; 80 int ok = 0; 81 signed char *r = NULL; 82 int sign = 1; 83 int bit, next_bit, mask; 84 size_t len = 0, j; 85 86 BN_CTX_start(ctx); 87 c = BN_CTX_get(ctx); 88 if (c == NULL) goto err; 89 90 if (w <= 0 || w > 7) /* 'signed char' can represent integers with absolute values less than 2^7 */ 91 { 92 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR); 93 goto err; 94 } 95 bit = 1 << w; /* at most 128 */ 96 next_bit = bit << 1; /* at most 256 */ 97 mask = next_bit - 1; /* at most 255 */ 98 99 if (!BN_copy(c, scalar)) goto err; 100 if (c->neg) 101 { 102 sign = -1; 103 c->neg = 0; 104 } 105 106 len = BN_num_bits(c) + 1; /* wNAF may be one digit longer than binary representation */ 107 r = OPENSSL_malloc(len); 108 if (r == NULL) goto err; 109 110 j = 0; 111 while (!BN_is_zero(c)) 112 { 113 int u = 0; 114 115 if (BN_is_odd(c)) 116 { 117 if (c->d == NULL || c->top == 0) 118 { 119 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR); 120 goto err; 121 } 122 u = c->d[0] & mask; 123 if (u & bit) 124 { 125 u -= next_bit; 126 /* u < 0 */ 127 if (!BN_add_word(c, -u)) goto err; 128 } 129 else 130 { 131 /* u > 0 */ 132 if (!BN_sub_word(c, u)) goto err; 133 } 134 135 if (u <= -bit || u >= bit || !(u & 1) || c->neg) 136 { 137 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR); 138 goto err; 139 } 140 } 141 142 r[j++] = sign * u; 143 144 if (BN_is_odd(c)) 145 { 146 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR); 147 goto err; 148 } 149 if (!BN_rshift1(c, c)) goto err; 150 } 151 152 if (j > len) 153 { 154 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR); 155 goto err; 156 } 157 len = j; 158 ok = 1; 159 160 err: 161 BN_CTX_end(ctx); 162 if (!ok) 163 { 164 OPENSSL_free(r); 165 r = NULL; 166 } 167 if (ok) 168 *ret_len = len; 169 return r; 170 } 171 172 173 /* TODO: table should be optimised for the wNAF-based implementation, 174 * sometimes smaller windows will give better performance 175 * (thus the boundaries should be increased) 176 */ 177 #define EC_window_bits_for_scalar_size(b) \ 178 ((size_t) \ 179 ((b) >= 2000 ? 6 : \ 180 (b) >= 800 ? 5 : \ 181 (b) >= 300 ? 4 : \ 182 (b) >= 70 ? 3 : \ 183 (b) >= 20 ? 2 : \ 184 1)) 185 186 /* Compute 187 * \sum scalars[i]*points[i], 188 * also including 189 * scalar*generator 190 * in the addition if scalar != NULL 191 */ 192 int EC_POINTs_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, 193 size_t num, const EC_POINT *points[], const BIGNUM *scalars[], BN_CTX *ctx) 194 { 195 BN_CTX *new_ctx = NULL; 196 EC_POINT *generator = NULL; 197 EC_POINT *tmp = NULL; 198 size_t totalnum; 199 size_t i, j; 200 int k; 201 int r_is_inverted = 0; 202 int r_is_at_infinity = 1; 203 size_t *wsize = NULL; /* individual window sizes */ 204 signed char **wNAF = NULL; /* individual wNAFs */ 205 size_t *wNAF_len = NULL; 206 size_t max_len = 0; 207 size_t num_val; 208 EC_POINT **val = NULL; /* precomputation */ 209 EC_POINT **v; 210 EC_POINT ***val_sub = NULL; /* pointers to sub-arrays of 'val' */ 211 int ret = 0; 212 213 if (group->meth != r->meth) 214 { 215 ECerr(EC_F_EC_POINTS_MUL, EC_R_INCOMPATIBLE_OBJECTS); 216 return 0; 217 } 218 219 if ((scalar == NULL) && (num == 0)) 220 { 221 return EC_POINT_set_to_infinity(group, r); 222 } 223 224 if (scalar != NULL) 225 { 226 generator = EC_GROUP_get0_generator(group); 227 if (generator == NULL) 228 { 229 ECerr(EC_F_EC_POINTS_MUL, EC_R_UNDEFINED_GENERATOR); 230 return 0; 231 } 232 } 233 234 for (i = 0; i < num; i++) 235 { 236 if (group->meth != points[i]->meth) 237 { 238 ECerr(EC_F_EC_POINTS_MUL, EC_R_INCOMPATIBLE_OBJECTS); 239 return 0; 240 } 241 } 242 243 totalnum = num + (scalar != NULL); 244 245 wsize = OPENSSL_malloc(totalnum * sizeof wsize[0]); 246 wNAF_len = OPENSSL_malloc(totalnum * sizeof wNAF_len[0]); 247 wNAF = OPENSSL_malloc((totalnum + 1) * sizeof wNAF[0]); 248 if (wNAF != NULL) 249 { 250 wNAF[0] = NULL; /* preliminary pivot */ 251 } 252 if (wsize == NULL || wNAF_len == NULL || wNAF == NULL) goto err; 253 254 /* num_val := total number of points to precompute */ 255 num_val = 0; 256 for (i = 0; i < totalnum; i++) 257 { 258 size_t bits; 259 260 bits = i < num ? BN_num_bits(scalars[i]) : BN_num_bits(scalar); 261 wsize[i] = EC_window_bits_for_scalar_size(bits); 262 num_val += 1u << (wsize[i] - 1); 263 } 264 265 /* all precomputed points go into a single array 'val', 266 * 'val_sub[i]' is a pointer to the subarray for the i-th point */ 267 val = OPENSSL_malloc((num_val + 1) * sizeof val[0]); 268 if (val == NULL) goto err; 269 val[num_val] = NULL; /* pivot element */ 270 271 val_sub = OPENSSL_malloc(totalnum * sizeof val_sub[0]); 272 if (val_sub == NULL) goto err; 273 274 /* allocate points for precomputation */ 275 v = val; 276 for (i = 0; i < totalnum; i++) 277 { 278 val_sub[i] = v; 279 for (j = 0; j < (1u << (wsize[i] - 1)); j++) 280 { 281 *v = EC_POINT_new(group); 282 if (*v == NULL) goto err; 283 v++; 284 } 285 } 286 if (!(v == val + num_val)) 287 { 288 ECerr(EC_F_EC_POINTS_MUL, ERR_R_INTERNAL_ERROR); 289 goto err; 290 } 291 292 if (ctx == NULL) 293 { 294 ctx = new_ctx = BN_CTX_new(); 295 if (ctx == NULL) 296 goto err; 297 } 298 299 tmp = EC_POINT_new(group); 300 if (tmp == NULL) goto err; 301 302 /* prepare precomputed values: 303 * val_sub[i][0] := points[i] 304 * val_sub[i][1] := 3 * points[i] 305 * val_sub[i][2] := 5 * points[i] 306 * ... 307 */ 308 for (i = 0; i < totalnum; i++) 309 { 310 if (i < num) 311 { 312 if (!EC_POINT_copy(val_sub[i][0], points[i])) goto err; 313 } 314 else 315 { 316 if (!EC_POINT_copy(val_sub[i][0], generator)) goto err; 317 } 318 319 if (wsize[i] > 1) 320 { 321 if (!EC_POINT_dbl(group, tmp, val_sub[i][0], ctx)) goto err; 322 for (j = 1; j < (1u << (wsize[i] - 1)); j++) 323 { 324 if (!EC_POINT_add(group, val_sub[i][j], val_sub[i][j - 1], tmp, ctx)) goto err; 325 } 326 } 327 328 wNAF[i + 1] = NULL; /* make sure we always have a pivot */ 329 wNAF[i] = compute_wNAF((i < num ? scalars[i] : scalar), wsize[i], &wNAF_len[i], ctx); 330 if (wNAF[i] == NULL) goto err; 331 if (wNAF_len[i] > max_len) 332 max_len = wNAF_len[i]; 333 } 334 335 #if 1 /* optional; EC_window_bits_for_scalar_size assumes we do this step */ 336 if (!EC_POINTs_make_affine(group, num_val, val, ctx)) goto err; 337 #endif 338 339 r_is_at_infinity = 1; 340 341 for (k = max_len - 1; k >= 0; k--) 342 { 343 if (!r_is_at_infinity) 344 { 345 if (!EC_POINT_dbl(group, r, r, ctx)) goto err; 346 } 347 348 for (i = 0; i < totalnum; i++) 349 { 350 if (wNAF_len[i] > (size_t)k) 351 { 352 int digit = wNAF[i][k]; 353 int is_neg; 354 355 if (digit) 356 { 357 is_neg = digit < 0; 358 359 if (is_neg) 360 digit = -digit; 361 362 if (is_neg != r_is_inverted) 363 { 364 if (!r_is_at_infinity) 365 { 366 if (!EC_POINT_invert(group, r, ctx)) goto err; 367 } 368 r_is_inverted = !r_is_inverted; 369 } 370 371 /* digit > 0 */ 372 373 if (r_is_at_infinity) 374 { 375 if (!EC_POINT_copy(r, val_sub[i][digit >> 1])) goto err; 376 r_is_at_infinity = 0; 377 } 378 else 379 { 380 if (!EC_POINT_add(group, r, r, val_sub[i][digit >> 1], ctx)) goto err; 381 } 382 } 383 } 384 } 385 } 386 387 if (r_is_at_infinity) 388 { 389 if (!EC_POINT_set_to_infinity(group, r)) goto err; 390 } 391 else 392 { 393 if (r_is_inverted) 394 if (!EC_POINT_invert(group, r, ctx)) goto err; 395 } 396 397 ret = 1; 398 399 err: 400 if (new_ctx != NULL) 401 BN_CTX_free(new_ctx); 402 if (tmp != NULL) 403 EC_POINT_free(tmp); 404 if (wsize != NULL) 405 OPENSSL_free(wsize); 406 if (wNAF_len != NULL) 407 OPENSSL_free(wNAF_len); 408 if (wNAF != NULL) 409 { 410 signed char **w; 411 412 for (w = wNAF; *w != NULL; w++) 413 OPENSSL_free(*w); 414 415 OPENSSL_free(wNAF); 416 } 417 if (val != NULL) 418 { 419 for (v = val; *v != NULL; v++) 420 EC_POINT_clear_free(*v); 421 422 OPENSSL_free(val); 423 } 424 if (val_sub != NULL) 425 { 426 OPENSSL_free(val_sub); 427 } 428 return ret; 429 } 430 431 432 int EC_POINT_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *g_scalar, const EC_POINT *point, const BIGNUM *p_scalar, BN_CTX *ctx) 433 { 434 const EC_POINT *points[1]; 435 const BIGNUM *scalars[1]; 436 437 points[0] = point; 438 scalars[0] = p_scalar; 439 440 return EC_POINTs_mul(group, r, g_scalar, (point != NULL && p_scalar != NULL), points, scalars, ctx); 441 } 442 443 444 int EC_GROUP_precompute_mult(EC_GROUP *group, BN_CTX *ctx) 445 { 446 const EC_POINT *generator; 447 BN_CTX *new_ctx = NULL; 448 BIGNUM *order; 449 int ret = 0; 450 451 generator = EC_GROUP_get0_generator(group); 452 if (generator == NULL) 453 { 454 ECerr(EC_F_EC_GROUP_PRECOMPUTE_MULT, EC_R_UNDEFINED_GENERATOR); 455 return 0; 456 } 457 458 if (ctx == NULL) 459 { 460 ctx = new_ctx = BN_CTX_new(); 461 if (ctx == NULL) 462 return 0; 463 } 464 465 BN_CTX_start(ctx); 466 order = BN_CTX_get(ctx); 467 if (order == NULL) goto err; 468 469 if (!EC_GROUP_get_order(group, order, ctx)) return 0; 470 if (BN_is_zero(order)) 471 { 472 ECerr(EC_F_EC_GROUP_PRECOMPUTE_MULT, EC_R_UNKNOWN_ORDER); 473 goto err; 474 } 475 476 /* TODO */ 477 478 ret = 1; 479 480 err: 481 BN_CTX_end(ctx); 482 if (new_ctx != NULL) 483 BN_CTX_free(new_ctx); 484 return ret; 485 } 486