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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
*
* All curves taken from NIST recommendation paper of July 1999
* Available at http://csrc.nist.gov/cryptval/dss.htm
*/
#include "ecc.h"
/**
@file ltc_ecc_mulmod_timing.c
ECC Crypto, Tom St Denis
*/
#ifdef LTC_MECC
/**
Perform a point multiplication (timing resistant)
@param k The scalar to multiply by
@param G The base point
@param R [out] Destination for kG
@param modulus The modulus of the field the ECC curve is in
@param map Boolean whether to map back to affine or not (1==map, 0 == leave in projective)
@return 0 on success
*/
int ltc_ecc_mulmod(mpz_t k, ecc_point *G, ecc_point *R, mpz_t modulus, int map)
{
ecc_point *tG, *M[3];
int i, j, err;
unsigned long buf;
int first, bitbuf, bitcpy, bitcnt, mode, digidx;
assert(k != NULL);
assert(G != NULL);
assert(R != NULL);
assert(modulus != NULL);
/* alloc ram for window temps */
for (i = 0; i < 3; i++) {
M[i] = ltc_ecc_new_point();
if (M[i] == NULL) {
for (j = 0; j < i; j++) {
ltc_ecc_del_point(M[j]);
}
return -1;
}
}
/* make a copy of G incase R==G */
tG = ltc_ecc_new_point();
if (tG == NULL) { err = -1; goto done; }
/* tG = G and convert to montgomery */
mpz_set(tG->x, G->x);
mpz_set(tG->y, G->y);
mpz_set(tG->z, G->z);
/* calc the M tab */
/* M[0] == G */
mpz_set(M[0]->x, tG->x);
mpz_set(M[0]->y, tG->y);
mpz_set(M[0]->z, tG->z);
/* M[1] == 2G */
if ((err = ltc_ecc_projective_dbl_point(tG, M[1], modulus)) != 0) { goto done; }
/* setup sliding window */
mode = 0;
bitcnt = 1;
buf = 0;
digidx = mpz_size(k) - 1;
bitcpy = bitbuf = 0;
first = 1;
/* perform ops */
for (;;) {
/* grab next digit as required */
if (--bitcnt == 0) {
if (digidx == -1) {
break;
}
buf = mpz_getlimbn(k, digidx);
bitcnt = (int) MP_DIGIT_BIT;
--digidx;
}
/* grab the next msb from the ltiplicand */
i = (buf >> (MP_DIGIT_BIT - 1)) & 1;
buf <<= 1;
if (mode == 0 && i == 0) {
/* dummy operations */
if ((err = ltc_ecc_projective_add_point(M[0], M[1], M[2], modulus)) != 0) { goto done; }
if ((err = ltc_ecc_projective_dbl_point(M[1], M[2], modulus)) != 0) { goto done; }
continue;
}
if (mode == 0 && i == 1) {
mode = 1;
/* dummy operations */
if ((err = ltc_ecc_projective_add_point(M[0], M[1], M[2], modulus)) != 0) { goto done; }
if ((err = ltc_ecc_projective_dbl_point(M[1], M[2], modulus)) != 0) { goto done; }
continue;
}
if ((err = ltc_ecc_projective_add_point(M[0], M[1], M[i^1], modulus)) != 0) { goto done; }
if ((err = ltc_ecc_projective_dbl_point(M[i], M[i], modulus)) != 0) { goto done; }
}
/* copy result out */
mpz_set(R->x, M[0]->x);
mpz_set(R->y, M[0]->y);
mpz_set(R->z, M[0]->z);
/* map R back from projective space */
if (map) {
err = ltc_ecc_map(R, modulus);
} else {
err = 0;
}
done:
ltc_ecc_del_point(tG);
for (i = 0; i < 3; i++) {
ltc_ecc_del_point(M[i]);
}
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_mulmod_timing.c,v $ */
/* $Revision: 1.13 $ */
/* $Date: 2007/05/12 14:32:35 $ */
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