200 lines
6.4 KiB
C
200 lines
6.4 KiB
C
#include "amplify_tommath_private.h"
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#ifdef AMPLIFY_BN_S_MP_EXPTMOD_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/* Modifications Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved. */
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#ifdef AMPLIFY_MP_LOW_MEM
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# define TAB_SIZE 32
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# define MAX_WINSIZE 5
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#else
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# define TAB_SIZE 256
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# define MAX_WINSIZE 0
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#endif
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amplify_mp_err amplify_s_mp_exptmod(const amplify_mp_int *G, const amplify_mp_int *X, const amplify_mp_int *P, amplify_mp_int *Y, int redmode)
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{
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amplify_mp_int M[TAB_SIZE], res, mu;
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amplify_mp_digit buf;
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amplify_mp_err err;
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int bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;
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amplify_mp_err(*redux)(amplify_mp_int *x, const amplify_mp_int *m, const amplify_mp_int *mu);
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/* find window size */
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x = amplify_mp_count_bits(X);
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if (x <= 7) {
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winsize = 2;
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} else if (x <= 36) {
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winsize = 3;
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} else if (x <= 140) {
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winsize = 4;
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} else if (x <= 450) {
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winsize = 5;
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} else if (x <= 1303) {
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winsize = 6;
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} else if (x <= 3529) {
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winsize = 7;
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} else {
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winsize = 8;
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}
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winsize = MAX_WINSIZE ? AMPLIFY_MP_MIN(MAX_WINSIZE, winsize) : winsize;
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/* init M array */
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/* init first cell */
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if ((err = amplify_mp_init(&M[1])) != AMPLIFY_MP_OKAY) {
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return err;
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}
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/* now init the second half of the array */
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for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
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if ((err = amplify_mp_init(&M[x])) != AMPLIFY_MP_OKAY) {
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for (y = 1<<(winsize-1); y < x; y++) {
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amplify_mp_clear(&M[y]);
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}
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amplify_mp_clear(&M[1]);
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return err;
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}
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}
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/* create mu, used for Barrett reduction */
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if ((err = amplify_mp_init(&mu)) != AMPLIFY_MP_OKAY) goto LBL_M;
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if (redmode == 0) {
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if ((err = amplify_mp_reduce_setup(&mu, P)) != AMPLIFY_MP_OKAY) goto LBL_MU;
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redux = amplify_mp_reduce;
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} else {
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if ((err = amplify_mp_reduce_2k_setup_l(P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_MU;
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redux = amplify_mp_reduce_2k_l;
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}
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/* create M table
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*
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* The M table contains powers of the base,
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* e.g. M[x] = G**x mod P
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*
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* The first half of the table is not
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* computed though accept for M[0] and M[1]
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*/
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if ((err = amplify_mp_mod(G, P, &M[1])) != AMPLIFY_MP_OKAY) goto LBL_MU;
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/* compute the value at M[1<<(winsize-1)] by squaring
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* M[1] (winsize-1) times
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*/
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if ((err = amplify_mp_copy(&M[1], &M[(size_t)1 << (winsize - 1)])) != AMPLIFY_MP_OKAY) goto LBL_MU;
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for (x = 0; x < (winsize - 1); x++) {
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/* square it */
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if ((err = amplify_mp_sqr(&M[(size_t)1 << (winsize - 1)],
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&M[(size_t)1 << (winsize - 1)])) != AMPLIFY_MP_OKAY) goto LBL_MU;
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/* reduce modulo P */
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if ((err = redux(&M[(size_t)1 << (winsize - 1)], P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_MU;
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}
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/* create upper table, that is M[x] = M[x-1] * M[1] (mod P)
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* for x = (2**(winsize - 1) + 1) to (2**winsize - 1)
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*/
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for (x = (1 << (winsize - 1)) + 1; x < (1 << winsize); x++) {
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if ((err = amplify_mp_mul(&M[x - 1], &M[1], &M[x])) != AMPLIFY_MP_OKAY) goto LBL_MU;
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if ((err = redux(&M[x], P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_MU;
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}
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/* setup result */
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if ((err = amplify_mp_init(&res)) != AMPLIFY_MP_OKAY) goto LBL_MU;
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amplify_mp_set(&res, 1uL);
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/* set initial mode and bit cnt */
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mode = 0;
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bitcnt = 1;
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buf = 0;
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digidx = X->used - 1;
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bitcpy = 0;
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bitbuf = 0;
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for (;;) {
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/* grab next digit as required */
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if (--bitcnt == 0) {
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/* if digidx == -1 we are out of digits */
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if (digidx == -1) {
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break;
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}
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/* read next digit and reset the bitcnt */
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buf = X->dp[digidx--];
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bitcnt = (int)AMPLIFY_MP_DIGIT_BIT;
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}
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/* grab the next msb from the exponent */
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y = (buf >> (amplify_mp_digit)(AMPLIFY_MP_DIGIT_BIT - 1)) & 1uL;
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buf <<= (amplify_mp_digit)1;
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/* if the bit is zero and mode == 0 then we ignore it
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* These represent the leading zero bits before the first 1 bit
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* in the exponent. Technically this opt is not required but it
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* does lower the # of trivial squaring/reductions used
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*/
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if ((mode == 0) && (y == 0)) {
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continue;
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}
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/* if the bit is zero and mode == 1 then we square */
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if ((mode == 1) && (y == 0)) {
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if ((err = amplify_mp_sqr(&res, &res)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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if ((err = redux(&res, P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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continue;
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}
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/* else we add it to the window */
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bitbuf |= (y << (winsize - ++bitcpy));
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mode = 2;
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if (bitcpy == winsize) {
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/* ok window is filled so square as required and multiply */
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/* square first */
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for (x = 0; x < winsize; x++) {
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if ((err = amplify_mp_sqr(&res, &res)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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if ((err = redux(&res, P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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}
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/* then multiply */
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if ((err = amplify_mp_mul(&res, &M[bitbuf], &res)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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if ((err = redux(&res, P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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/* empty window and reset */
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bitcpy = 0;
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bitbuf = 0;
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mode = 1;
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}
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}
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/* if bits remain then square/multiply */
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if ((mode == 2) && (bitcpy > 0)) {
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/* square then multiply if the bit is set */
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for (x = 0; x < bitcpy; x++) {
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if ((err = amplify_mp_sqr(&res, &res)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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if ((err = redux(&res, P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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bitbuf <<= 1;
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if ((bitbuf & (1 << winsize)) != 0) {
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/* then multiply */
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if ((err = amplify_mp_mul(&res, &M[1], &res)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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if ((err = redux(&res, P, &mu)) != AMPLIFY_MP_OKAY) goto LBL_RES;
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}
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}
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}
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amplify_mp_exch(&res, Y);
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err = AMPLIFY_MP_OKAY;
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LBL_RES:
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amplify_mp_clear(&res);
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LBL_MU:
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amplify_mp_clear(&mu);
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LBL_M:
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amplify_mp_clear(&M[1]);
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for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
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amplify_mp_clear(&M[x]);
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}
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return err;
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}
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#endif
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