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/* This file is part of libbrandt.
* Copyright (C) 2016 GNUnet e.V.
*
* libbrandt is free software: you can redistribute it and/or modify it under
* the terms of the GNU General Public License as published by the Free Software
* Foundation, either version 3 of the License, or (at your option) any later
* version.
*
* libbrandt is distributed in the hope that it will be useful, but WITHOUT ANY
* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
* A PARTICULAR PURPOSE. See the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along with
* libbrandt. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* @file mp_priv.c
* @brief Implementation of the m+1st price private outcome algorithm.
* @author Markus Teich
*/
#include "platform.h"
#include <gcrypt.h>
#include "crypto.h"
#include "internals.h"
#include "util.h"
void
mp_priv_prep_outcome (struct BRANDT_Auction *ad)
{
gcry_mpi_t factor = gcry_mpi_new (256);
gcry_mpi_point_t subtr = gcry_mpi_point_new (0);
gcry_mpi_point_t tmpa = gcry_mpi_point_new (0);
gcry_mpi_point_t tmpb = gcry_mpi_point_new (0);
gcry_mpi_point_t *tlta1;
gcry_mpi_point_t *tltb1;
gcry_mpi_point_t **tlta2;
gcry_mpi_point_t **tltb2;
gcry_mpi_point_t **tlta3;
gcry_mpi_point_t **tltb3;
ad->gamma3 = smc_init3 (ad->n, ad->n, ad->k);
brandt_assert (ad->gamma3);
ad->delta3 = smc_init3 (ad->n, ad->n, ad->k);
brandt_assert (ad->delta3);
/* create temporary lookup tables with partial sums */
tlta1 = smc_init1 (ad->k);
tltb1 = smc_init1 (ad->k);
tlta2 = smc_init2 (ad->n, ad->k);
tltb2 = smc_init2 (ad->n, ad->k);
tlta3 = smc_init2 (ad->n, ad->k);
tltb3 = smc_init2 (ad->n, ad->k);
/* temporary lookup table for first summand (building ladder of bids) */
for (uint16_t i = 0; i < ad->n; i++)
{
smc_sums_partial (tlta3[i], ad->alpha[i], ad->k, 1, 1);
smc_sums_partial (tltb3[i], ad->beta[i], ad->k, 1, 1);
for (uint16_t j = 0; j < ad->k; j++)
{
gcry_mpi_ec_sub (tlta2[i][j],
tlta3[i][ad->k - 1],
tlta3[i][j],
ec_ctx);
gcry_mpi_ec_sub (tltb2[i][j],
tltb3[i][ad->k - 1],
tltb3[i][j],
ec_ctx);
}
brandt_assert (!ec_point_cmp (ec_zero, tlta2[i][ad->k - 1]));
brandt_assert (!ec_point_cmp (ec_zero, tltb2[i][ad->k - 1]));
}
for (uint16_t j = 0; j < ad->k; j++)
{
/* 2L - 2I */
smc_sum (tmpa, &tlta2[0][j], ad->n, ad->k);
smc_sum (tmpb, &tltb2[0][j], ad->n, ad->k);
gcry_mpi_ec_mul (tlta1[j], GCRYMPI_CONST_TWO, tmpa, ec_ctx);
gcry_mpi_ec_mul (tltb1[j], GCRYMPI_CONST_TWO, tmpb, ec_ctx);
/* I */
smc_sum (tmpa, &ad->alpha[0][j], ad->n, ad->k);
smc_sum (tmpb, &ad->beta[0][j], ad->n, ad->k);
/* 2L - 2I + I = 2L - I */
gcry_mpi_ec_add (tlta1[j], tlta1[j], tmpa, ec_ctx);
gcry_mpi_ec_add (tltb1[j], tltb1[j], tmpb, ec_ctx);
}
/* This check only works directly after the loop when tmpa/tmpb are still
* the sum of the last row */
brandt_assert (!ec_point_cmp (tmpa, tlta1[ad->k - 1]));
brandt_assert (!ec_point_cmp (tmpb, tltb1[ad->k - 1]));
/* temporary lookup table for second summand (hide outcome from losers) */
gcry_mpi_set_ui (factor, ad->m);
gcry_mpi_lshift (factor, factor, 1);
gcry_mpi_add_ui (factor, factor, 2);
for (uint16_t i = 0; i < ad->n; i++)
{
for (uint16_t j = 0; j < ad->k; j++)
{
gcry_mpi_ec_mul (tlta2[i][j], factor, tlta3[i][j], ec_ctx);
gcry_mpi_ec_mul (tltb2[i][j], factor, tltb3[i][j], ec_ctx);
}
}
/* temporary lookup table for subtrahend (getting M+1st highest bid) */
gcry_mpi_sub_ui (factor, factor, 1);
gcry_mpi_ec_mul (subtr, factor, ec_gen, ec_ctx);
/* compute gamma and delta */
for (uint16_t i = 0; i < ad->n; i++)
{
for (uint16_t j = 0; j < ad->k; j++)
{
/* compute inner gamma */
gcry_mpi_ec_add (tmpa, tlta1[j], tlta2[i][j], ec_ctx);
gcry_mpi_ec_sub (tmpa, tmpa, subtr, ec_ctx);
/* compute inner delta */
gcry_mpi_ec_add (tmpb, tltb1[j], tltb2[i][j], ec_ctx);
/* copy unmasked outcome to all other bidder layers so they don't
* have to be recomputed to check the ZK proof_2dle's from other
* bidders when receiving their outcome messages */
for (uint16_t a = 0; a < ad->n; a++)
{
ec_point_copy (ad->gamma3[a][i][j], tmpa);
ec_point_copy (ad->delta3[a][i][j], tmpb);
}
}
}
gcry_mpi_release (factor);
gcry_mpi_point_release (subtr);
gcry_mpi_point_release (tmpa);
gcry_mpi_point_release (tmpb);
smc_free1 (tlta1, ad->k);
smc_free1 (tltb1, ad->k);
smc_free2 (tlta2, ad->n, ad->k);
smc_free2 (tltb2, ad->n, ad->k);
smc_free2 (tlta3, ad->n, ad->k);
smc_free2 (tltb3, ad->n, ad->k);
}
struct BRANDT_Result *
mp_priv_determine_outcome (struct BRANDT_Auction *ad,
uint16_t *len)
{
struct BRANDT_Result *ret;
int32_t price = -1;
uint16_t winners = 0;
uint16_t max_winners;
gcry_mpi_point_t sum_gamma = gcry_mpi_point_new (0);
gcry_mpi_point_t sum_phi = gcry_mpi_point_new (0);
brandt_assert (ad);
max_winners = ad->seller_mode ? ad->m : 1;
ret = GNUNET_new_array (max_winners, struct BRANDT_Result);
for (uint16_t i = 0; i < ad->n; i++)
{
if (!ad->seller_mode && i != ad->i)
continue;
for (uint16_t j = 0; j < ad->k; j++)
{
smc_sum (sum_gamma, &ad->gamma3[0][i][j], ad->n, ad->n * ad->k);
smc_sum (sum_phi, &ad->phi3[0][i][j], ad->n, ad->n * ad->k);
gcry_mpi_ec_sub (sum_gamma, sum_gamma, sum_phi, ec_ctx);
if (!ec_point_cmp (sum_gamma, ec_zero))
{
if (winners >= max_winners)
{
GNUNET_log_from (GNUNET_ERROR_TYPE_ERROR,
"libbrandt",
"too many winners detected\n");
goto fail;
}
if (-1 != price && j != price)
{
GNUNET_log_from (GNUNET_ERROR_TYPE_ERROR,
"libbrandt",
"multiple winning prices detected\n");
goto fail;
}
price = j;
ret[winners].bidder = i;
ret[winners].price = j / ad->n;
ret[winners].status = BRANDT_bidder_won;
winners++;
}
}
}
gcry_mpi_point_release (sum_gamma);
gcry_mpi_point_release (sum_phi);
if (ad->m <= ad->n && winners < max_winners && -1 != price)
GNUNET_log_from (GNUNET_ERROR_TYPE_ERROR,
"libbrandt",
"too few winners detected\n");
if (0 == winners)
goto fail;
if (len)
*len = winners;
return ret;
fail:
GNUNET_free (ret);
return NULL;
}
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