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209 lines
6.3 KiB
209 lines
6.3 KiB
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
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*/
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/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
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*
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* All curves taken from NIST recommendation paper of July 1999
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* Available at http://csrc.nist.gov/cryptval/dss.htm
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*/
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#define LTC_SOURCE 1
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#include "tomcrypt.h"
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/**
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@file ltc_ecc_mul2add.c
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ECC Crypto, Shamir's Trick, Tom St Denis
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*/
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#ifdef MECC
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#ifdef LTC_ECC_SHAMIR
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/** Computes kA*A + kB*B = C using Shamir's Trick
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@param A First point to multiply
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@param kA What to multiple A by
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@param B Second point to multiply
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@param kB What to multiple B by
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@param C [out] Destination point (can overlap with A or B
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@param modulus Modulus for curve
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@return CRYPT_OK on success
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*/
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int ltc_ecc_mul2add(ecc_point *A, void *kA,
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ecc_point *B, void *kB,
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ecc_point *C,
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void *modulus)
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{
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ecc_point *precomp[16];
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unsigned bitbufA, bitbufB, lenA, lenB, len, x, y, nA, nB, nibble;
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unsigned char *tA, *tB;
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int err, first;
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void *mp, *mu;
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/* argchks */
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LTC_ARGCHK(A != NULL);
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LTC_ARGCHK(B != NULL);
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LTC_ARGCHK(C != NULL);
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LTC_ARGCHK(kA != NULL);
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LTC_ARGCHK(kB != NULL);
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LTC_ARGCHK(modulus != NULL);
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/* allocate memory */
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tA = XCALLOC(1, ECC_BUF_SIZE);
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if (tA == NULL) {
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return CRYPT_MEM;
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}
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tB = XCALLOC(1, ECC_BUF_SIZE);
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if (tB == NULL) {
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XFREE(tA);
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return CRYPT_MEM;
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}
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/* get sizes */
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lenA = mp_unsigned_bin_size(kA);
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lenB = mp_unsigned_bin_size(kB);
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len = MAX(lenA, lenB);
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/* sanity check */
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if ((lenA > ECC_BUF_SIZE) || (lenB > ECC_BUF_SIZE)) {
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err = CRYPT_INVALID_ARG;
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goto ERR_T;
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}
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/* extract and justify kA */
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mp_to_unsigned_bin(kA, (len - lenA) + tA);
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/* extract and justify kB */
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mp_to_unsigned_bin(kB, (len - lenB) + tB);
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/* allocate the table */
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for (x = 0; x < 16; x++) {
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precomp[x] = ltc_ecc_new_point();
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if (precomp[x] == NULL) {
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for (y = 0; y < x; ++y) {
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ltc_ecc_del_point(precomp[y]);
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}
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err = CRYPT_MEM;
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goto ERR_T;
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}
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}
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/* init montgomery reduction */
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if ((err = mp_montgomery_setup(modulus, &mp)) != CRYPT_OK) {
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goto ERR_P;
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}
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if ((err = mp_init(&mu)) != CRYPT_OK) {
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goto ERR_MP;
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}
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if ((err = mp_montgomery_normalization(mu, modulus)) != CRYPT_OK) {
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goto ERR_MU;
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}
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/* copy ones ... */
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if ((err = mp_mulmod(A->x, mu, modulus, precomp[1]->x)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = mp_mulmod(A->y, mu, modulus, precomp[1]->y)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = mp_mulmod(A->z, mu, modulus, precomp[1]->z)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = mp_mulmod(B->x, mu, modulus, precomp[1<<2]->x)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = mp_mulmod(B->y, mu, modulus, precomp[1<<2]->y)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = mp_mulmod(B->z, mu, modulus, precomp[1<<2]->z)) != CRYPT_OK) { goto ERR_MU; }
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/* precomp [i,0](A + B) table */
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if ((err = ltc_mp.ecc_ptdbl(precomp[1], precomp[2], modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = ltc_mp.ecc_ptadd(precomp[1], precomp[2], precomp[3], modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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/* precomp [0,i](A + B) table */
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if ((err = ltc_mp.ecc_ptdbl(precomp[1<<2], precomp[2<<2], modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = ltc_mp.ecc_ptadd(precomp[1<<2], precomp[2<<2], precomp[3<<2], modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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/* precomp [i,j](A + B) table (i != 0, j != 0) */
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for (x = 1; x < 4; x++) {
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for (y = 1; y < 4; y++) {
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if ((err = ltc_mp.ecc_ptadd(precomp[x], precomp[(y<<2)], precomp[x+(y<<2)], modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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}
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}
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nibble = 3;
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first = 1;
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bitbufA = tA[0];
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bitbufB = tB[0];
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/* for every byte of the multiplicands */
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for (x = -1;; ) {
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/* grab a nibble */
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if (++nibble == 4) {
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++x; if (x == len) break;
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bitbufA = tA[x];
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bitbufB = tB[x];
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nibble = 0;
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}
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/* extract two bits from both, shift/update */
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nA = (bitbufA >> 6) & 0x03;
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nB = (bitbufB >> 6) & 0x03;
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bitbufA = (bitbufA << 2) & 0xFF;
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bitbufB = (bitbufB << 2) & 0xFF;
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/* if both zero, if first, continue */
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if ((nA == 0) && (nB == 0) && (first == 1)) {
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continue;
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}
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/* double twice, only if this isn't the first */
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if (first == 0) {
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/* double twice */
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if ((err = ltc_mp.ecc_ptdbl(C, C, modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = ltc_mp.ecc_ptdbl(C, C, modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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}
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/* if not both zero */
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if ((nA != 0) || (nB != 0)) {
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if (first == 1) {
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/* if first, copy from table */
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first = 0;
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if ((err = mp_copy(precomp[nA + (nB<<2)]->x, C->x)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = mp_copy(precomp[nA + (nB<<2)]->y, C->y)) != CRYPT_OK) { goto ERR_MU; }
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if ((err = mp_copy(precomp[nA + (nB<<2)]->z, C->z)) != CRYPT_OK) { goto ERR_MU; }
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} else {
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/* if not first, add from table */
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if ((err = ltc_mp.ecc_ptadd(C, precomp[nA + (nB<<2)], C, modulus, mp)) != CRYPT_OK) { goto ERR_MU; }
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}
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}
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}
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/* reduce to affine */
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err = ltc_ecc_map(C, modulus, mp);
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/* clean up */
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ERR_MU:
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mp_clear(mu);
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ERR_MP:
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mp_montgomery_free(mp);
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ERR_P:
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for (x = 0; x < 16; x++) {
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ltc_ecc_del_point(precomp[x]);
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}
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ERR_T:
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#ifdef LTC_CLEAN_STACK
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zeromem(tA, ECC_BUF_SIZE);
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zeromem(tB, ECC_BUF_SIZE);
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#endif
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XFREE(tA);
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XFREE(tB);
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return err;
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}
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#endif
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#endif
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/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_mul2add.c,v $ */
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/* $Revision: 1.6 $ */
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/* $Date: 2006/12/04 05:07:59 $ */
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