79 lines
3.3 KiB
C
79 lines
3.3 KiB
C
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/***********************************************************************
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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_PREC_IMPL_H
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#define SECP256K1_ECMULT_GEN_PREC_IMPL_H
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#include "ecmult_gen_prec.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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static void secp256k1_ecmult_gen_create_prec_table(secp256k1_ecmult_gen_context *ctx, void **prealloc) {
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secp256k1_ge prec[ECMULT_GEN_PREC_N * ECMULT_GEN_PREC_G];
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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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size_t const prealloc_size = ECMULT_GEN_PREC_TABLE_SIZE;
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void* const base = *prealloc;
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ctx->prec = (secp256k1_ge_storage (*)[ECMULT_GEN_PREC_N][ECMULT_GEN_PREC_G])manual_alloc(prealloc, prealloc_size, base, prealloc_size);
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/* get the generator */
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secp256k1_gej_set_ge(&gj, &secp256k1_ge_const_g);
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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, &secp256k1_ge_const_g, NULL);
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}
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/* compute prec. */
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{
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secp256k1_gej precj[ECMULT_GEN_PREC_N * ECMULT_GEN_PREC_G]; /* Jacobian versions of prec. */
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secp256k1_gej gbase;
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secp256k1_gej numsbase;
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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 < ECMULT_GEN_PREC_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*ECMULT_GEN_PREC_G] = numsbase;
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for (i = 1; i < ECMULT_GEN_PREC_G; i++) {
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secp256k1_gej_add_var(&precj[j*ECMULT_GEN_PREC_G + i], &precj[j*ECMULT_GEN_PREC_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 < ECMULT_GEN_PREC_B; 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 == ECMULT_GEN_PREC_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, ECMULT_GEN_PREC_N * ECMULT_GEN_PREC_G);
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}
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for (j = 0; j < ECMULT_GEN_PREC_N; j++) {
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for (i = 0; i < ECMULT_GEN_PREC_G; i++) {
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secp256k1_ge_to_storage(&(*ctx->prec)[j][i], &prec[j*ECMULT_GEN_PREC_G + i]);
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}
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}
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}
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#endif /* SECP256K1_ECMULT_GEN_PREC_IMPL_H */
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