82 lines
3.1 KiB
C
82 lines
3.1 KiB
C
/***********************************************************************
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* Copyright (c) 2013, 2014, 2015 Pieter Wuille, Gregory Maxwell *
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* Distributed under the MIT software license, see the accompanying *
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* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
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***********************************************************************/
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#ifndef SECP256K1_ECMULT_GEN_COMPUTE_TABLE_IMPL_H
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#define SECP256K1_ECMULT_GEN_COMPUTE_TABLE_IMPL_H
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#include "ecmult_gen_compute_table.h"
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#include "group_impl.h"
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#include "field_impl.h"
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#include "ecmult_gen.h"
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#include "util.h"
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static void secp256k1_ecmult_gen_compute_table(secp256k1_ge_storage* table, const secp256k1_ge* gen, int bits) {
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int g = ECMULT_GEN_PREC_G(bits);
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int n = ECMULT_GEN_PREC_N(bits);
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secp256k1_ge* prec = checked_malloc(&default_error_callback, n * g * sizeof(*prec));
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secp256k1_gej gj;
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secp256k1_gej nums_gej;
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int i, j;
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/* get the generator */
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secp256k1_gej_set_ge(&gj, gen);
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/* Construct a group element with no known corresponding scalar (nothing up my sleeve). */
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{
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static const unsigned char nums_b32[33] = "The scalar for this x is unknown";
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secp256k1_fe nums_x;
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secp256k1_ge nums_ge;
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int r;
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r = secp256k1_fe_set_b32(&nums_x, nums_b32);
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(void)r;
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VERIFY_CHECK(r);
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r = secp256k1_ge_set_xo_var(&nums_ge, &nums_x, 0);
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(void)r;
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VERIFY_CHECK(r);
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secp256k1_gej_set_ge(&nums_gej, &nums_ge);
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/* Add G to make the bits in x uniformly distributed. */
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secp256k1_gej_add_ge_var(&nums_gej, &nums_gej, gen, NULL);
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}
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/* compute prec. */
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{
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secp256k1_gej gbase;
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secp256k1_gej numsbase;
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secp256k1_gej* precj = checked_malloc(&default_error_callback, n * g * sizeof(*precj)); /* Jacobian versions of prec. */
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gbase = gj; /* PREC_G^j * G */
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numsbase = nums_gej; /* 2^j * nums. */
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for (j = 0; j < n; j++) {
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/* Set precj[j*PREC_G .. j*PREC_G+(PREC_G-1)] to (numsbase, numsbase + gbase, ..., numsbase + (PREC_G-1)*gbase). */
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precj[j*g] = numsbase;
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for (i = 1; i < g; i++) {
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secp256k1_gej_add_var(&precj[j*g + i], &precj[j*g + i - 1], &gbase, NULL);
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}
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/* Multiply gbase by PREC_G. */
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for (i = 0; i < bits; i++) {
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secp256k1_gej_double_var(&gbase, &gbase, NULL);
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}
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/* Multiply numbase by 2. */
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secp256k1_gej_double_var(&numsbase, &numsbase, NULL);
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if (j == n - 2) {
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/* In the last iteration, numsbase is (1 - 2^j) * nums instead. */
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secp256k1_gej_neg(&numsbase, &numsbase);
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secp256k1_gej_add_var(&numsbase, &numsbase, &nums_gej, NULL);
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}
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}
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secp256k1_ge_set_all_gej_var(prec, precj, n * g);
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free(precj);
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}
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for (j = 0; j < n; j++) {
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for (i = 0; i < g; i++) {
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secp256k1_ge_to_storage(&table[j*g + i], &prec[j*g + i]);
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}
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}
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free(prec);
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}
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#endif /* SECP256K1_ECMULT_GEN_COMPUTE_TABLE_IMPL_H */
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