| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: mpmont.c,v 1.2 1999/11/19 13:17:26 mdw Exp $ |
| 4 | * |
| 5 | * Montgomery reduction |
| 6 | * |
| 7 | * (c) 1999 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 11 | * |
| 12 | * This file is part of Catacomb. |
| 13 | * |
| 14 | * Catacomb is free software; you can redistribute it and/or modify |
| 15 | * it under the terms of the GNU Library General Public License as |
| 16 | * published by the Free Software Foundation; either version 2 of the |
| 17 | * License, or (at your option) any later version. |
| 18 | * |
| 19 | * Catacomb is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 22 | * GNU Library General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU Library General Public |
| 25 | * License along with Catacomb; if not, write to the Free |
| 26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 27 | * MA 02111-1307, USA. |
| 28 | */ |
| 29 | |
| 30 | /*----- Revision history --------------------------------------------------* |
| 31 | * |
| 32 | * $Log: mpmont.c,v $ |
| 33 | * Revision 1.2 1999/11/19 13:17:26 mdw |
| 34 | * Add extra interface to exponentiation which returns a Montgomerized |
| 35 | * result. |
| 36 | * |
| 37 | * Revision 1.1 1999/11/17 18:02:16 mdw |
| 38 | * New multiprecision integer arithmetic suite. |
| 39 | * |
| 40 | */ |
| 41 | |
| 42 | /*----- Header files ------------------------------------------------------*/ |
| 43 | |
| 44 | #include "mp.h" |
| 45 | #include "mpmont.h" |
| 46 | |
| 47 | /*----- Main code ---------------------------------------------------------*/ |
| 48 | |
| 49 | /* --- @mpmont_create@ --- * |
| 50 | * |
| 51 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
| 52 | * @mp *m@ = modulus to use |
| 53 | * |
| 54 | * Returns: --- |
| 55 | * |
| 56 | * Use: Initializes a Montgomery reduction context ready for use. |
| 57 | */ |
| 58 | |
| 59 | void mpmont_create(mpmont *mm, mp *m) |
| 60 | { |
| 61 | /* --- Take a copy of the modulus --- */ |
| 62 | |
| 63 | mp_shrink(m); |
| 64 | mm->m = MP_COPY(m); |
| 65 | |
| 66 | /* --- Find the magic value @mi@ --- * |
| 67 | * |
| 68 | * This is a slightly grungy way of solving the problem, but it does work. |
| 69 | */ |
| 70 | |
| 71 | { |
| 72 | mpw av[2] = { 0, 1 }; |
| 73 | mp a, b; |
| 74 | mp *i; |
| 75 | mpw mi; |
| 76 | |
| 77 | mp_build(&a, av, av + 2); |
| 78 | mp_build(&b, m->v, m->v + 1); |
| 79 | mp_gcd(0, 0, &i, &a, &b); |
| 80 | mi = i->v[0]; |
| 81 | if (!(i->f & MP_NEG)) |
| 82 | mi = MPW(-mi); |
| 83 | mm->mi = mi; |
| 84 | MP_DROP(i); |
| 85 | } |
| 86 | |
| 87 | /* --- Discover the values %$R \bmod m$% and %$R^2 \bmod m$% --- */ |
| 88 | |
| 89 | { |
| 90 | size_t l = MP_LEN(m); |
| 91 | mp *r = mp_create(l + 1); |
| 92 | |
| 93 | mm->shift = l * MPW_BITS; |
| 94 | MPX_ZERO(r->v, r->vl - 1); |
| 95 | r->vl[-1] = 1; |
| 96 | mm->r = mm->r2 = MP_NEW; |
| 97 | mp_div(0, &mm->r, r, m); |
| 98 | r = mp_sqr(r, mm->r); |
| 99 | mp_div(0, &mm->r2, r, m); |
| 100 | MP_DROP(r); |
| 101 | } |
| 102 | } |
| 103 | |
| 104 | /* --- @mpmont_destroy@ --- * |
| 105 | * |
| 106 | * Arguments: @mpmont *mm@ = pointer to a Montgomery reduction context |
| 107 | * |
| 108 | * Returns: --- |
| 109 | * |
| 110 | * Use: Disposes of a context when it's no longer of any use to |
| 111 | * anyone. |
| 112 | */ |
| 113 | |
| 114 | void mpmont_destroy(mpmont *mm) |
| 115 | { |
| 116 | MP_DROP(mm->m); |
| 117 | MP_DROP(mm->r); |
| 118 | MP_DROP(mm->r2); |
| 119 | } |
| 120 | |
| 121 | /* --- @mpmont_reduce@ --- * |
| 122 | * |
| 123 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
| 124 | * @mp *d@ = destination |
| 125 | * @const mp *a@ = source, assumed positive |
| 126 | * |
| 127 | * Returns: Result, %$a R^{-1} \bmod m$%. |
| 128 | */ |
| 129 | |
| 130 | mp *mpmont_reduce(mpmont *mm, mp *d, const mp *a) |
| 131 | { |
| 132 | mpw *dv, *dvl; |
| 133 | const mpw *mv, *mvl; |
| 134 | size_t n; |
| 135 | |
| 136 | /* --- Initial conditioning of the arguments --- */ |
| 137 | |
| 138 | n = MP_LEN(mm->m); |
| 139 | |
| 140 | if (d == a) |
| 141 | MP_MODIFY(d, 2 * n); |
| 142 | else { |
| 143 | MP_MODIFY(d, 2 * n); |
| 144 | memcpy(d->v, a->v, MPWS(MP_LEN(a))); |
| 145 | memset(d->v + MP_LEN(a), 0, MPWS(MP_LEN(d) - MP_LEN(a))); |
| 146 | } |
| 147 | |
| 148 | dv = d->v; dvl = d->vl; |
| 149 | mv = mm->m->v; mvl = mm->m->vl; |
| 150 | |
| 151 | /* --- Let's go to work --- */ |
| 152 | |
| 153 | while (n--) { |
| 154 | mpw u = MPW(*dv * mm->mi); |
| 155 | MPX_UMLAN(dv, dvl, mv, mvl, u); |
| 156 | dv++; |
| 157 | } |
| 158 | |
| 159 | /* --- Done --- */ |
| 160 | |
| 161 | memmove(d->v, dv, MPWS(dvl - dv)); |
| 162 | d->vl -= dv - d->v; |
| 163 | MP_SHRINK(d); |
| 164 | d->f = a->f & MP_BURN; |
| 165 | if (MP_CMP(d, >=, mm->m)) |
| 166 | d = mp_sub(d, d, mm->m); |
| 167 | return (d); |
| 168 | } |
| 169 | |
| 170 | /* --- @mpmont_mul@ --- * |
| 171 | * |
| 172 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
| 173 | * @mp *d@ = destination |
| 174 | * @const mp *a, *b@ = sources, assumed positive |
| 175 | * |
| 176 | * Returns: Result, %$a b R^{-1} \bmod m$%. |
| 177 | */ |
| 178 | |
| 179 | mp *mpmont_mul(mpmont *mm, mp *d, const mp *a, const mp *b) |
| 180 | { |
| 181 | mpw *dv, *dvl; |
| 182 | const mpw *av, *avl; |
| 183 | const mpw *bv, *bvl; |
| 184 | const mpw *mv, *mvl; |
| 185 | mpw y; |
| 186 | size_t n, i; |
| 187 | |
| 188 | /* --- Initial conditioning of the arguments --- */ |
| 189 | |
| 190 | if (MP_LEN(a) > MP_LEN(b)) { |
| 191 | const mp *t = a; a = b; b = t; |
| 192 | } |
| 193 | n = MP_LEN(mm->m); |
| 194 | |
| 195 | MP_MODIFY(d, 2 * n + 1); |
| 196 | dv = d->v; dvl = d->vl; |
| 197 | MPX_ZERO(dv, dvl); |
| 198 | av = a->v; avl = a->vl; |
| 199 | bv = b->v; bvl = b->vl; |
| 200 | mv = mm->m->v; mvl = mm->m->vl; |
| 201 | y = *bv; |
| 202 | |
| 203 | /* --- Montgomery multiplication phase --- */ |
| 204 | |
| 205 | i = 0; |
| 206 | while (i < n && av < avl) { |
| 207 | mpw x = *av++; |
| 208 | mpw u = MPW((*dv + x * y) * mm->mi); |
| 209 | MPX_UMLAN(dv, dvl, bv, bvl, x); |
| 210 | MPX_UMLAN(dv, dvl, mv, mvl, u); |
| 211 | dv++; |
| 212 | i++; |
| 213 | } |
| 214 | |
| 215 | /* --- Simpler Montgomery reduction phase --- */ |
| 216 | |
| 217 | while (i < n) { |
| 218 | mpw u = MPW(*dv * mm->mi); |
| 219 | MPX_UMLAN(dv, dvl, mv, mvl, u); |
| 220 | dv++; |
| 221 | i++; |
| 222 | } |
| 223 | |
| 224 | /* --- Done --- */ |
| 225 | |
| 226 | memmove(d->v, dv, MPWS(dvl - dv)); |
| 227 | d->vl -= dv - d->v; |
| 228 | MP_SHRINK(d); |
| 229 | d->f = (a->f | b->f) & MP_BURN; |
| 230 | if (MP_CMP(d, >=, mm->m)) |
| 231 | d = mp_sub(d, d, mm->m); |
| 232 | return (d); |
| 233 | } |
| 234 | |
| 235 | /* --- @mpmont_expr@ --- * |
| 236 | * |
| 237 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
| 238 | * @const mp *a@ = base |
| 239 | * @const mp *e@ = exponent |
| 240 | * |
| 241 | * Returns: Result, %$a^e R \bmod m$%. |
| 242 | */ |
| 243 | |
| 244 | mp *mpmont_expr(mpmont *mm, const mp *a, const mp *e) |
| 245 | { |
| 246 | mpscan sc; |
| 247 | mp *ar = mpmont_mul(mm, MP_NEW, a, mm->r2); |
| 248 | mp *d = MP_COPY(mm->r); |
| 249 | mp *spare = MP_NEW; |
| 250 | |
| 251 | mp_scan(&sc, e); |
| 252 | |
| 253 | if (MP_STEP(&sc)) { |
| 254 | size_t sq = 0; |
| 255 | for (;;) { |
| 256 | mp *dd; |
| 257 | if (MP_BIT(&sc)) { |
| 258 | while (sq) { |
| 259 | dd = mpmont_mul(mm, spare, ar, ar); |
| 260 | spare = ar; ar = dd; |
| 261 | sq--; |
| 262 | } |
| 263 | dd = mpmont_mul(mm, spare, d, ar); |
| 264 | spare = d; d = dd; |
| 265 | } |
| 266 | sq++; |
| 267 | if (!MP_STEP(&sc)) |
| 268 | break; |
| 269 | } |
| 270 | } |
| 271 | MP_DROP(ar); |
| 272 | if (spare != MP_NEW) |
| 273 | MP_DROP(spare); |
| 274 | return (d); |
| 275 | } |
| 276 | |
| 277 | /* --- @mpmont_exp@ --- * |
| 278 | * |
| 279 | * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context |
| 280 | * @const mp *a@ = base |
| 281 | * @const mp *e@ = exponent |
| 282 | * |
| 283 | * Returns: Result, %$a^e \bmod m$%. |
| 284 | */ |
| 285 | |
| 286 | mp *mpmont_exp(mpmont *mm, const mp *a, const mp *e) |
| 287 | { |
| 288 | mp *d = mpmont_expr(mm, a, e); |
| 289 | d = mpmont_reduce(mm, d, d); |
| 290 | return (d); |
| 291 | } |
| 292 | |
| 293 | /*----- Test rig ----------------------------------------------------------*/ |
| 294 | |
| 295 | #ifdef TEST_RIG |
| 296 | |
| 297 | static int tcreate(dstr *v) |
| 298 | { |
| 299 | mp *m = *(mp **)v[0].buf; |
| 300 | mp *mi = *(mp **)v[1].buf; |
| 301 | mp *r = *(mp **)v[2].buf; |
| 302 | mp *r2 = *(mp **)v[3].buf; |
| 303 | |
| 304 | mpmont mm; |
| 305 | int ok = 1; |
| 306 | |
| 307 | mpmont_create(&mm, m); |
| 308 | |
| 309 | if (mm.mi != mi->v[0]) { |
| 310 | fprintf(stderr, "\n*** bad mi: found %lu, expected %lu", |
| 311 | (unsigned long)mm.mi, (unsigned long)mi->v[0]); |
| 312 | fputs("\nm = ", stderr); mp_writefile(m, stderr, 10); |
| 313 | fputc('\n', stderr); |
| 314 | ok = 0; |
| 315 | } |
| 316 | |
| 317 | if (MP_CMP(mm.r, !=, r)) { |
| 318 | fputs("\n*** bad r", stderr); |
| 319 | fputs("\nm = ", stderr); mp_writefile(m, stderr, 10); |
| 320 | fputs("\nexpected ", stderr); mp_writefile(r, stderr, 10); |
| 321 | fputs("\n found ", stderr); mp_writefile(mm.r, stderr, 10); |
| 322 | fputc('\n', stderr); |
| 323 | ok = 0; |
| 324 | } |
| 325 | |
| 326 | if (MP_CMP(mm.r2, !=, r2)) { |
| 327 | fputs("\n*** bad r2", stderr); |
| 328 | fputs("\nm = ", stderr); mp_writefile(m, stderr, 10); |
| 329 | fputs("\nexpected ", stderr); mp_writefile(r2, stderr, 10); |
| 330 | fputs("\n found ", stderr); mp_writefile(mm.r2, stderr, 10); |
| 331 | fputc('\n', stderr); |
| 332 | ok = 0; |
| 333 | } |
| 334 | |
| 335 | MP_DROP(m); |
| 336 | MP_DROP(mi); |
| 337 | MP_DROP(r); |
| 338 | MP_DROP(r2); |
| 339 | mpmont_destroy(&mm); |
| 340 | return (ok); |
| 341 | } |
| 342 | |
| 343 | static int tmul(dstr *v) |
| 344 | { |
| 345 | mp *m = *(mp **)v[0].buf; |
| 346 | mp *a = *(mp **)v[1].buf; |
| 347 | mp *b = *(mp **)v[2].buf; |
| 348 | mp *r = *(mp **)v[3].buf; |
| 349 | mp *mr, *qr; |
| 350 | int ok = 1; |
| 351 | |
| 352 | mpmont mm; |
| 353 | mpmont_create(&mm, m); |
| 354 | |
| 355 | { |
| 356 | mp *ar = mpmont_mul(&mm, MP_NEW, a, mm.r2); |
| 357 | mp *br = mpmont_mul(&mm, MP_NEW, b, mm.r2); |
| 358 | mr = mpmont_mul(&mm, MP_NEW, ar, br); |
| 359 | mr = mpmont_reduce(&mm, mr, mr); |
| 360 | MP_DROP(ar); MP_DROP(br); |
| 361 | } |
| 362 | |
| 363 | qr = mp_mul(MP_NEW, a, b); |
| 364 | mp_div(0, &qr, qr, m); |
| 365 | |
| 366 | if (MP_CMP(qr, !=, r)) { |
| 367 | fputs("\n*** classical modmul failed", stderr); |
| 368 | fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); |
| 369 | fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); |
| 370 | fputs("\n b = ", stderr); mp_writefile(b, stderr, 10); |
| 371 | fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); |
| 372 | fputs("\nqr = ", stderr); mp_writefile(qr, stderr, 10); |
| 373 | fputc('\n', stderr); |
| 374 | ok = 0; |
| 375 | } |
| 376 | |
| 377 | if (MP_CMP(mr, !=, r)) { |
| 378 | fputs("\n*** montgomery modmul failed", stderr); |
| 379 | fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); |
| 380 | fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); |
| 381 | fputs("\n b = ", stderr); mp_writefile(b, stderr, 10); |
| 382 | fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); |
| 383 | fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10); |
| 384 | fputc('\n', stderr); |
| 385 | ok = 0; |
| 386 | } |
| 387 | |
| 388 | MP_DROP(m); |
| 389 | MP_DROP(a); |
| 390 | MP_DROP(b); |
| 391 | MP_DROP(r); |
| 392 | MP_DROP(mr); |
| 393 | MP_DROP(qr); |
| 394 | mpmont_destroy(&mm); |
| 395 | return ok; |
| 396 | } |
| 397 | |
| 398 | static int texp(dstr *v) |
| 399 | { |
| 400 | mp *m = *(mp **)v[0].buf; |
| 401 | mp *a = *(mp **)v[1].buf; |
| 402 | mp *b = *(mp **)v[2].buf; |
| 403 | mp *r = *(mp **)v[3].buf; |
| 404 | mp *mr; |
| 405 | int ok = 1; |
| 406 | |
| 407 | mpmont mm; |
| 408 | mpmont_create(&mm, m); |
| 409 | |
| 410 | mr = mpmont_exp(&mm, a, b); |
| 411 | |
| 412 | if (MP_CMP(mr, !=, r)) { |
| 413 | fputs("\n*** montgomery modexp failed", stderr); |
| 414 | fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); |
| 415 | fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); |
| 416 | fputs("\n e = ", stderr); mp_writefile(b, stderr, 10); |
| 417 | fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); |
| 418 | fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10); |
| 419 | fputc('\n', stderr); |
| 420 | ok = 0; |
| 421 | } |
| 422 | |
| 423 | MP_DROP(m); |
| 424 | MP_DROP(a); |
| 425 | MP_DROP(b); |
| 426 | MP_DROP(r); |
| 427 | MP_DROP(mr); |
| 428 | mpmont_destroy(&mm); |
| 429 | return ok; |
| 430 | } |
| 431 | |
| 432 | |
| 433 | static test_chunk tests[] = { |
| 434 | { "create", tcreate, { &type_mp, &type_mp, &type_mp, &type_mp } }, |
| 435 | { "mul", tmul, { &type_mp, &type_mp, &type_mp, &type_mp } }, |
| 436 | { "exp", texp, { &type_mp, &type_mp, &type_mp, &type_mp } }, |
| 437 | { 0, 0, { 0 } }, |
| 438 | }; |
| 439 | |
| 440 | int main(int argc, char *argv[]) |
| 441 | { |
| 442 | sub_init(); |
| 443 | test_run(argc, argv, tests, SRCDIR "/tests/mpmont"); |
| 444 | return (0); |
| 445 | } |
| 446 | |
| 447 | #endif |
| 448 | |
| 449 | /*----- That's all, folks -------------------------------------------------*/ |