mirror of
https://github.com/rn10950/RetroZilla.git
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138 lines
3.6 KiB
C
138 lines
3.6 KiB
C
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include "ecp.h"
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#include "mpi.h"
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#include "mplogic.h"
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#include "mpi-priv.h"
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#define ECP521_DIGITS ECL_CURVE_DIGITS(521)
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/* Fast modular reduction for p521 = 2^521 - 1. a can be r. Uses
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* algorithm 2.31 from Hankerson, Menezes, Vanstone. Guide to
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* Elliptic Curve Cryptography. */
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static mp_err
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ec_GFp_nistp521_mod(const mp_int *a, mp_int *r, const GFMethod *meth)
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{
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mp_err res = MP_OKAY;
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int a_bits = mpl_significant_bits(a);
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int i;
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/* m1, m2 are statically-allocated mp_int of exactly the size we need */
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mp_int m1;
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mp_digit s1[ECP521_DIGITS] = { 0 };
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MP_SIGN(&m1) = MP_ZPOS;
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MP_ALLOC(&m1) = ECP521_DIGITS;
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MP_USED(&m1) = ECP521_DIGITS;
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MP_DIGITS(&m1) = s1;
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if (a_bits < 521) {
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if (a==r) return MP_OKAY;
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return mp_copy(a, r);
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}
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/* for polynomials larger than twice the field size or polynomials
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* not using all words, use regular reduction */
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if (a_bits > (521*2)) {
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MP_CHECKOK(mp_mod(a, &meth->irr, r));
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} else {
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#define FIRST_DIGIT (ECP521_DIGITS-1)
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for (i = FIRST_DIGIT; i < MP_USED(a)-1; i++) {
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s1[i-FIRST_DIGIT] = (MP_DIGIT(a, i) >> 9)
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| (MP_DIGIT(a, 1+i) << (MP_DIGIT_BIT-9));
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}
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s1[i-FIRST_DIGIT] = MP_DIGIT(a, i) >> 9;
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if ( a != r ) {
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MP_CHECKOK(s_mp_pad(r,ECP521_DIGITS));
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for (i = 0; i < ECP521_DIGITS; i++) {
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MP_DIGIT(r,i) = MP_DIGIT(a, i);
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}
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}
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MP_USED(r) = ECP521_DIGITS;
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MP_DIGIT(r,FIRST_DIGIT) &= 0x1FF;
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MP_CHECKOK(s_mp_add(r, &m1));
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if (MP_DIGIT(r, FIRST_DIGIT) & 0x200) {
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MP_CHECKOK(s_mp_add_d(r,1));
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MP_DIGIT(r,FIRST_DIGIT) &= 0x1FF;
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} else if (s_mp_cmp(r, &meth->irr) == 0) {
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mp_zero(r);
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}
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s_mp_clamp(r);
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}
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CLEANUP:
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return res;
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}
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/* Compute the square of polynomial a, reduce modulo p521. Store the
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* result in r. r could be a. Uses optimized modular reduction for p521.
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*/
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static mp_err
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ec_GFp_nistp521_sqr(const mp_int *a, mp_int *r, const GFMethod *meth)
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{
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mp_err res = MP_OKAY;
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MP_CHECKOK(mp_sqr(a, r));
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MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
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CLEANUP:
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return res;
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}
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/* Compute the product of two polynomials a and b, reduce modulo p521.
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* Store the result in r. r could be a or b; a could be b. Uses
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* optimized modular reduction for p521. */
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static mp_err
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ec_GFp_nistp521_mul(const mp_int *a, const mp_int *b, mp_int *r,
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const GFMethod *meth)
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{
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mp_err res = MP_OKAY;
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MP_CHECKOK(mp_mul(a, b, r));
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MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
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CLEANUP:
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return res;
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}
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/* Divides two field elements. If a is NULL, then returns the inverse of
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* b. */
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static mp_err
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ec_GFp_nistp521_div(const mp_int *a, const mp_int *b, mp_int *r,
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const GFMethod *meth)
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{
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mp_err res = MP_OKAY;
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mp_int t;
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/* If a is NULL, then return the inverse of b, otherwise return a/b. */
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if (a == NULL) {
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return mp_invmod(b, &meth->irr, r);
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} else {
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/* MPI doesn't support divmod, so we implement it using invmod and
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* mulmod. */
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MP_CHECKOK(mp_init(&t));
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MP_CHECKOK(mp_invmod(b, &meth->irr, &t));
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MP_CHECKOK(mp_mul(a, &t, r));
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MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
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CLEANUP:
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mp_clear(&t);
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return res;
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}
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}
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/* Wire in fast field arithmetic and precomputation of base point for
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* named curves. */
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mp_err
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ec_group_set_gfp521(ECGroup *group, ECCurveName name)
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{
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if (name == ECCurve_NIST_P521) {
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group->meth->field_mod = &ec_GFp_nistp521_mod;
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group->meth->field_mul = &ec_GFp_nistp521_mul;
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group->meth->field_sqr = &ec_GFp_nistp521_sqr;
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group->meth->field_div = &ec_GFp_nistp521_div;
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}
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return MP_OKAY;
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}
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