_ Git - BearSSL/blob - src/symcipher/poly1305_ctmulq.c

   1 /*
   2  * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #include "inner.h"
  26
  27 #if BR_INT128 || BR_UMUL128
  28
  29 #if BR_INT128
  30
  31 #define MUL128(hi, lo, x, y)   do { \
  32                 unsigned __int128 mul128tmp; \
  33                 mul128tmp = (unsigned __int128)(x) * (unsigned __int128)(y); \
  34                 (hi) = (uint64_t)(mul128tmp >> 64); \
  35                 (lo) = (uint64_t)mul128tmp; \
  36         } while (0)
  37
  38 #elif BR_UMUL128
  39
  40 #include <intrin.h>
  41
  42 #define MUL128(hi, lo, x, y)   do { \
  43                 (lo) = _umul128((x), (y), &(hi)); \
  44         } while (0)
  45
  46 #endif
  47
  48 #define MASK42   ((uint64_t)0x000003FFFFFFFFFF)
  49 #define MASK44   ((uint64_t)0x00000FFFFFFFFFFF)
  50
  51 /*
  52  * The "accumulator" word is nominally a 130-bit value. We split it into
  53  * words of 44 bits, each held in a 64-bit variable.
  54  *
  55  * If the current accumulator is a = a0 + a1*W + a2*W^2 (where W = 2^44)
  56  * and r = r0 + r1*W + r2*W^2, then:
  57  *
  58  *   a*r = (a0*r0)
  59  *       + (a0*r1 + a1*r0) * W
  60  *       + (a0*r2 + a1*r1 + a2*r0) * W^2
  61  *       + (a1*r2 + a2*r1) * W^3
  62  *       + (a2*r2) * W^4
  63  *
  64  * We want to reduce that value modulo p = 2^130-5, so W^3 = 20 mod p,
  65  * and W^4 = 20*W mod p. Thus, if we define u1 = 20*r1 and u2 = 20*r2,
  66  * then the equations above become:
  67  *
  68  *  b0 = a0*r0 + a1*u2 + a2*u1
  69  *  b1 = a0*r1 + a1*r0 + a2*u2
  70  *  b2 = a0*r2 + a1*r1 + a2*r0
  71  *
  72  * In order to make u1 fit in 44 bits, we can change these equations
  73  * into:
  74  *
  75  *  b0 = a0*r0 + a1*u2 + a2*t1
  76  *  b1 = a0*r1 + a1*r0 + a2*t2
  77  *  b2 = a0*r2 + a1*r1 + a2*r0
  78  *
  79  * Where t1 is u1 truncated to 44 bits, and t2 is u2 added to the extra
  80  * bits of u1. Note that since r is clamped down to a 124-bit value, the
  81  * values u2 and t2 fit on 44 bits too.
  82  *
  83  * The bx values are larger than 44 bits, so we may split them into a
  84  * lower half (cx, 44 bits) and an upper half (dx). The new values for
  85  * the accumulator are then:
  86  *
  87  *  e0 = c0 + 20*d2
  88  *  e1 = c1 + d0
  89  *  e2 = c2 + d1
  90  *
  91  * The equations allow for some room, i.e. the ax values may be larger
  92  * than 44 bits. Similarly, the ex values will usually be larger than
  93  * the ax. Thus, some sort of carry propagation must be done regularly,
  94  * though not necessarily at each iteration. In particular, we do not
  95  * need to compute the additions (for the bx values) over 128-bit
  96  * quantities; we can stick to 64-bit computations.
  97  *
  98  *
  99  * Since the 128-bit result of a 64x64 multiplication is actually
 100  * represented over two 64-bit registers, it is cheaper to arrange for
 101  * any split that happens between the "high" and "low" halves to be on
 102  * that 64-bit boundary. This is done by left shifting the rx, ux and tx
 103  * by 20 bits (since they all fit on 44 bits each, this shift is
 104  * always possible).
 105  */
 106
 107 static void
 108 poly1305_inner_big(uint64_t *acc, uint64_t *r, const void *data, size_t len)
 109 {
 110
 111 #define MX(hi, lo, m0, m1, m2)   do { \
 112                 uint64_t mxhi, mxlo; \
 113                 MUL128(mxhi, mxlo, a0, m0); \
 114                 (hi) = mxhi; \
 115                 (lo) = mxlo >> 20; \
 116                 MUL128(mxhi, mxlo, a1, m1); \
 117                 (hi) += mxhi; \
 118                 (lo) += mxlo >> 20; \
 119                 MUL128(mxhi, mxlo, a2, m2); \
 120                 (hi) += mxhi; \
 121                 (lo) += mxlo >> 20; \
 122         } while (0)
 123
 124         const unsigned char *buf;
 125         uint64_t a0, a1, a2;
 126         uint64_t r0, r1, r2, t1, t2, u2;
 127
 128         r0 = r[0];
 129         r1 = r[1];
 130         r2 = r[2];
 131         t1 = r[3];
 132         t2 = r[4];
 133         u2 = r[5];
 134         a0 = acc[0];
 135         a1 = acc[1];
 136         a2 = acc[2];
 137         buf = data;
 138
 139         while (len > 0) {
 140                 uint64_t v0, v1, v2;
 141                 uint64_t c0, c1, c2, d0, d1, d2;
 142
 143                 v0 = br_dec64le(buf + 0);
 144                 v1 = br_dec64le(buf + 8);
 145                 v2 = v1 >> 24;
 146                 v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
 147                 v0 &= MASK44;
 148                 a0 += v0;
 149                 a1 += v1;
 150                 a2 += v2 + ((uint64_t)1 << 40);
 151                 MX(d0, c0, r0, u2, t1);
 152                 MX(d1, c1, r1, r0, t2);
 153                 MX(d2, c2, r2, r1, r0);
 154                 a0 = c0 + 20 * d2;
 155                 a1 = c1 + d0;
 156                 a2 = c2 + d1;
 157
 158                 v0 = br_dec64le(buf + 16);
 159                 v1 = br_dec64le(buf + 24);
 160                 v2 = v1 >> 24;
 161                 v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
 162                 v0 &= MASK44;
 163                 a0 += v0;
 164                 a1 += v1;
 165                 a2 += v2 + ((uint64_t)1 << 40);
 166                 MX(d0, c0, r0, u2, t1);
 167                 MX(d1, c1, r1, r0, t2);
 168                 MX(d2, c2, r2, r1, r0);
 169                 a0 = c0 + 20 * d2;
 170                 a1 = c1 + d0;
 171                 a2 = c2 + d1;
 172
 173                 v0 = br_dec64le(buf + 32);
 174                 v1 = br_dec64le(buf + 40);
 175                 v2 = v1 >> 24;
 176                 v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
 177                 v0 &= MASK44;
 178                 a0 += v0;
 179                 a1 += v1;
 180                 a2 += v2 + ((uint64_t)1 << 40);
 181                 MX(d0, c0, r0, u2, t1);
 182                 MX(d1, c1, r1, r0, t2);
 183                 MX(d2, c2, r2, r1, r0);
 184                 a0 = c0 + 20 * d2;
 185                 a1 = c1 + d0;
 186                 a2 = c2 + d1;
 187
 188                 v0 = br_dec64le(buf + 48);
 189                 v1 = br_dec64le(buf + 56);
 190                 v2 = v1 >> 24;
 191                 v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
 192                 v0 &= MASK44;
 193                 a0 += v0;
 194                 a1 += v1;
 195                 a2 += v2 + ((uint64_t)1 << 40);
 196                 MX(d0, c0, r0, u2, t1);
 197                 MX(d1, c1, r1, r0, t2);
 198                 MX(d2, c2, r2, r1, r0);
 199                 a0 = c0 + 20 * d2;
 200                 a1 = c1 + d0;
 201                 a2 = c2 + d1;
 202
 203                 a1 += a0 >> 44;
 204                 a0 &= MASK44;
 205                 a2 += a1 >> 44;
 206                 a1 &= MASK44;
 207                 a0 += 20 * (a2 >> 44);
 208                 a2 &= MASK44;
 209
 210                 buf += 64;
 211                 len -= 64;
 212         }
 213         acc[0] = a0;
 214         acc[1] = a1;
 215         acc[2] = a2;
 216
 217 #undef MX
 218 }
 219
 220 static void
 221 poly1305_inner_small(uint64_t *acc, uint64_t *r, const void *data, size_t len)
 222 {
 223         const unsigned char *buf;
 224         uint64_t a0, a1, a2;
 225         uint64_t r0, r1, r2, t1, t2, u2;
 226
 227         r0 = r[0];
 228         r1 = r[1];
 229         r2 = r[2];
 230         t1 = r[3];
 231         t2 = r[4];
 232         u2 = r[5];
 233         a0 = acc[0];
 234         a1 = acc[1];
 235         a2 = acc[2];
 236         buf = data;
 237
 238         while (len > 0) {
 239                 uint64_t v0, v1, v2;
 240                 uint64_t c0, c1, c2, d0, d1, d2;
 241                 unsigned char tmp[16];
 242
 243                 if (len < 16) {
 244                         memcpy(tmp, buf, len);
 245                         memset(tmp + len, 0, (sizeof tmp) - len);
 246                         buf = tmp;
 247                         len = 16;
 248                 }
 249                 v0 = br_dec64le(buf + 0);
 250                 v1 = br_dec64le(buf + 8);
 251
 252                 v2 = v1 >> 24;
 253                 v1 = ((v0 >> 44) | (v1 << 20)) & MASK44;
 254                 v0 &= MASK44;
 255
 256                 a0 += v0;
 257                 a1 += v1;
 258                 a2 += v2 + ((uint64_t)1 << 40);
 259
 260 #define MX(hi, lo, m0, m1, m2)   do { \
 261                 uint64_t mxhi, mxlo; \
 262                 MUL128(mxhi, mxlo, a0, m0); \
 263                 (hi) = mxhi; \
 264                 (lo) = mxlo >> 20; \
 265                 MUL128(mxhi, mxlo, a1, m1); \
 266                 (hi) += mxhi; \
 267                 (lo) += mxlo >> 20; \
 268                 MUL128(mxhi, mxlo, a2, m2); \
 269                 (hi) += mxhi; \
 270                 (lo) += mxlo >> 20; \
 271         } while (0)
 272
 273                 MX(d0, c0, r0, u2, t1);
 274                 MX(d1, c1, r1, r0, t2);
 275                 MX(d2, c2, r2, r1, r0);
 276
 277 #undef MX
 278
 279                 a0 = c0 + 20 * d2;
 280                 a1 = c1 + d0;
 281                 a2 = c2 + d1;
 282
 283                 a1 += a0 >> 44;
 284                 a0 &= MASK44;
 285                 a2 += a1 >> 44;
 286                 a1 &= MASK44;
 287                 a0 += 20 * (a2 >> 44);
 288                 a2 &= MASK44;
 289
 290                 buf += 16;
 291                 len -= 16;
 292         }
 293         acc[0] = a0;
 294         acc[1] = a1;
 295         acc[2] = a2;
 296 }
 297
 298 static inline void
 299 poly1305_inner(uint64_t *acc, uint64_t *r, const void *data, size_t len)
 300 {
 301         if (len >= 64) {
 302                 size_t len2;
 303
 304                 len2 = len & ~(size_t)63;
 305                 poly1305_inner_big(acc, r, data, len2);
 306                 data = (const unsigned char *)data + len2;
 307                 len -= len2;
 308         }
 309         if (len > 0) {
 310                 poly1305_inner_small(acc, r, data, len);
 311         }
 312 }
 313
 314 /* see bearssl_block.h */
 315 void
 316 br_poly1305_ctmulq_run(const void *key, const void *iv,
 317         void *data, size_t len, const void *aad, size_t aad_len,
 318         void *tag, br_chacha20_run ichacha, int encrypt)
 319 {
 320         unsigned char pkey[32], foot[16];
 321         uint64_t r[6], acc[3], r0, r1;
 322         uint32_t v0, v1, v2, v3, v4;
 323         uint64_t w0, w1, w2, w3;
 324         uint32_t ctl;
 325
 326         /*
 327          * Compute the MAC key. The 'r' value is the first 16 bytes of
 328          * pkey[].
 329          */
 330         memset(pkey, 0, sizeof pkey);
 331         ichacha(key, iv, 0, pkey, sizeof pkey);
 332
 333         /*
 334          * If encrypting, ChaCha20 must run first, followed by Poly1305.
 335          * When decrypting, the operations are reversed.
 336          */
 337         if (encrypt) {
 338                 ichacha(key, iv, 1, data, len);
 339         }
 340
 341         /*
 342          * Run Poly1305. We must process the AAD, then ciphertext, then
 343          * the footer (with the lengths). Note that the AAD and ciphertext
 344          * are meant to be padded with zeros up to the next multiple of 16,
 345          * and the length of the footer is 16 bytes as well.
 346          */
 347
 348         /*
 349          * Apply the "clamping" on r.
 350          */
 351         pkey[ 3] &= 0x0F;
 352         pkey[ 4] &= 0xFC;
 353         pkey[ 7] &= 0x0F;
 354         pkey[ 8] &= 0xFC;
 355         pkey[11] &= 0x0F;
 356         pkey[12] &= 0xFC;
 357         pkey[15] &= 0x0F;
 358
 359         /*
 360          * Decode the 'r' value into 44-bit words, left-shifted by 20 bits.
 361          * Also compute the u1 and u2 values.
 362          */
 363         r0 = br_dec64le(pkey +  0);
 364         r1 = br_dec64le(pkey +  8);
 365         r[0] = r0 << 20;
 366         r[1] = ((r0 >> 24) | (r1 << 40)) & ~(uint64_t)0xFFFFF;
 367         r[2] = (r1 >> 4) & ~(uint64_t)0xFFFFF;
 368         r1 = 20 * (r[1] >> 20);
 369         r[3] = r1 << 20;
 370         r[5] = 20 * r[2];
 371         r[4] = (r[5] + (r1 >> 24)) & ~(uint64_t)0xFFFFF;
 372
 373         /*
 374          * Accumulator is 0.
 375          */
 376         acc[0] = 0;
 377         acc[1] = 0;
 378         acc[2] = 0;
 379
 380         /*
 381          * Process the additional authenticated data, ciphertext, and
 382          * footer in due order.
 383          */
 384         br_enc64le(foot, (uint64_t)aad_len);
 385         br_enc64le(foot + 8, (uint64_t)len);
 386         poly1305_inner(acc, r, aad, aad_len);
 387         poly1305_inner(acc, r, data, len);
 388         poly1305_inner_small(acc, r, foot, sizeof foot);
 389
 390         /*
 391          * Finalise modular reduction. At that point, the value consists
 392          * in three 44-bit values (the lowest one might be slightly above
 393          * 2^44). Two loops shall be sufficient.
 394          */
 395         acc[1] += (acc[0] >> 44);
 396         acc[0] &= MASK44;
 397         acc[2] += (acc[1] >> 44);
 398         acc[1] &= MASK44;
 399         acc[0] += 5 * (acc[2] >> 42);
 400         acc[2] &= MASK42;
 401         acc[1] += (acc[0] >> 44);
 402         acc[0] &= MASK44;
 403         acc[2] += (acc[1] >> 44);
 404         acc[1] &= MASK44;
 405         acc[0] += 5 * (acc[2] >> 42);
 406         acc[2] &= MASK42;
 407
 408         /*
 409          * The value may still fall in the 2^130-5..2^130-1 range, in
 410          * which case we must reduce it again. The code below selects,
 411          * in constant-time, between 'acc' and 'acc-p'. We encode the
 412          * value over four 32-bit integers to finish the operation.
 413          */
 414         v0 = (uint32_t)acc[0];
 415         v1 = (uint32_t)(acc[0] >> 32) | ((uint32_t)acc[1] << 12);
 416         v2 = (uint32_t)(acc[1] >> 20) | ((uint32_t)acc[2] << 24);
 417         v3 = (uint32_t)(acc[2] >> 8);
 418         v4 = (uint32_t)(acc[2] >> 40);
 419
 420         ctl = GT(v0, 0xFFFFFFFA);
 421         ctl &= EQ(v1, 0xFFFFFFFF);
 422         ctl &= EQ(v2, 0xFFFFFFFF);
 423         ctl &= EQ(v3, 0xFFFFFFFF);
 424         ctl &= EQ(v4, 0x00000003);
 425         v0 = MUX(ctl, v0 + 5, v0);
 426         v1 = MUX(ctl, 0, v1);
 427         v2 = MUX(ctl, 0, v2);
 428         v3 = MUX(ctl, 0, v3);
 429
 430         /*
 431          * Add the "s" value. This is done modulo 2^128. Don't forget
 432          * carry propagation...
 433          */
 434         w0 = (uint64_t)v0 + (uint64_t)br_dec32le(pkey + 16);
 435         w1 = (uint64_t)v1 + (uint64_t)br_dec32le(pkey + 20) + (w0 >> 32);
 436         w2 = (uint64_t)v2 + (uint64_t)br_dec32le(pkey + 24) + (w1 >> 32);
 437         w3 = (uint64_t)v3 + (uint64_t)br_dec32le(pkey + 28) + (w2 >> 32);
 438         v0 = (uint32_t)w0;
 439         v1 = (uint32_t)w1;
 440         v2 = (uint32_t)w2;
 441         v3 = (uint32_t)w3;
 442
 443         /*
 444          * Encode the tag.
 445          */
 446         br_enc32le((unsigned char *)tag +  0, v0);
 447         br_enc32le((unsigned char *)tag +  4, v1);
 448         br_enc32le((unsigned char *)tag +  8, v2);
 449         br_enc32le((unsigned char *)tag + 12, v3);
 450
 451         /*
 452          * If decrypting, then ChaCha20 runs _after_ Poly1305.
 453          */
 454         if (!encrypt) {
 455                 ichacha(key, iv, 1, data, len);
 456         }
 457 }
 458
 459 /* see bearssl_block.h */
 460 br_poly1305_run
 461 br_poly1305_ctmulq_get(void)
 462 {
 463         return &br_poly1305_ctmulq_run;
 464 }
 465
 466 #else
 467
 468 /* see bearssl_block.h */
 469 br_poly1305_run
 470 br_poly1305_ctmulq_get(void)
 471 {
 472         return 0;
 473 }
 474
 475 #endif