libbrandt/fp_pub.c

/* 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 fp_pub.c
 * @brief Implementation of the first price public outcome algorithm.
 * @author Markus Teich
 */

#include "platform.h"

#include <gcrypt.h>

#include "crypto.h"
#include "internals.h"
#include "util.h"


void
fp_pub_prep_outcome (struct BRANDT_Auction *ad)
{
  gcry_mpi_t coeff = gcry_mpi_copy (GCRYMPI_CONST_ONE);
  gcry_mpi_point_t tmp = 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;

  ad->gamma2 = smc_init2 (ad->n, ad->k);
  brandt_assert (ad->gamma2);

  ad->delta2 = smc_init2 (ad->n, ad->k);
  brandt_assert (ad->delta2);

  ad->tmpa1 = smc_init1 (ad->k);
  brandt_assert (ad->tmpa1);

  ad->tmpb1 = smc_init1 (ad->k);
  brandt_assert (ad->tmpb1);

  /* 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);

  /* temporary lookup table for sum of bid vectors */
  for (uint16_t i = 0; i < ad->n; i++)
  {
    smc_sums_partial (tlta2[i], ad->alpha[i], ad->k, 1, 1);
    smc_sums_partial (tltb2[i], ad->beta[i], ad->k, 1, 1);
    for (uint16_t j = 0; j < ad->k; j++)
    {
      gcry_mpi_ec_sub (tlta2[i][j],
                       tlta2[i][ad->k - 1],
                       tlta2[i][j],
                       ec_ctx);
      gcry_mpi_ec_sub (tltb2[i][j],
                       tltb2[i][ad->k - 1],
                       tltb2[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++)
  {
    smc_sum (tlta1[j], &tlta2[0][j], ad->n, ad->k);
    smc_sum (tltb1[j], &tltb2[0][j], ad->n, ad->k);
  }
  smc_free2 (tlta2, ad->n, ad->k);
  smc_free2 (tltb2, ad->n, ad->k);
  brandt_assert (! ec_point_cmp (ec_zero, tlta1[ad->k - 1]));
  brandt_assert (! ec_point_cmp (ec_zero, tltb1[ad->k - 1]));

  /* initialize tmp array with zeroes, since we are calculating a sum */
  for (uint16_t j = 0; j < ad->k; j++)
  {
    ec_point_copy (ad->tmpa1[j], ec_zero);
    ec_point_copy (ad->tmpb1[j], ec_zero);
  }
  /* store the \sum_{i=1}^n2^{i-1}b_i in tmp1 until outcome determination,
   * since it is needed each time a gamma,delta pair is received from another
   * bidder */
  for (uint16_t i = 0; i < ad->n; i++)
  {
    for (uint16_t j = 0; j < ad->k; j++)
    {
      gcry_mpi_ec_mul (tmp, coeff, ad->alpha[i][j], ec_ctx);
      gcry_mpi_ec_add (ad->tmpa1[j], ad->tmpa1[j], tmp, ec_ctx);
      gcry_mpi_ec_mul (tmp, coeff, ad->beta[i][j], ec_ctx);
      gcry_mpi_ec_add (ad->tmpb1[j], ad->tmpb1[j], tmp, ec_ctx);
    }
    gcry_mpi_lshift (coeff, coeff, 1);
  }

  for (uint16_t j = 0; j < ad->k; j++)
  {
    /* 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->gamma2[a][j], tlta1[j]);
      ec_point_copy (ad->delta2[a][j], tltb1[j]);
    }
  }

  gcry_mpi_release (coeff);
  gcry_mpi_point_release (tmp);
  smc_free1 (tlta1, ad->k);
  smc_free1 (tltb1, ad->k);
}


/**
 * fp_pub_compute_outcome computes the outcome for first price auctions with a
 * public outcome and packs it into a message buffer together with proofs of
 * correctnes.
 *
 * @param[in] ad Pointer to the BRANDT_Auction struct to operate on
 * @param[out] buflen Size of the returned message buffer in byte
 * @return A buffer containing the encrypted outcome vectors
 * which needs to be broadcast
 */
unsigned char *
fp_pub_compute_outcome (struct BRANDT_Auction *ad, size_t *buflen)
{
  unsigned char     *ret;
  unsigned char     *cur;
  gcry_mpi_point_t tmpa = gcry_mpi_point_new (0);
  gcry_mpi_point_t tmpb = gcry_mpi_point_new (0);
  struct msg_head   *head;
  struct ec_mpi     *gamma;
  struct ec_mpi     *delta;
  struct proof_2dle *proof2;

  brandt_assert (ad && buflen);

  *buflen = (sizeof (*head)
             + ad->k * (sizeof (*gamma)
                        + sizeof (*delta)
                        + sizeof (*proof2)));
  ret = GNUNET_new_array (*buflen, unsigned char);

  head = (struct msg_head *) ret;
  head->prot_version = htonl (0);
  head->msg_type = htonl (msg_outcome);
  cur = ret + sizeof (*head);

  for (uint16_t j = 0; j < ad->k; j++)
  {
    gamma = (struct ec_mpi *) cur;
    delta = &((struct ec_mpi *) cur)[1];
    proof2 = (struct proof_2dle *) (cur + 2 * sizeof (struct ec_mpi));

    ec_point_copy (tmpa, ad->gamma2[ad->i][j]);
    ec_point_copy (tmpb, ad->delta2[ad->i][j]);

    /* apply random masking to first summand */
    smc_zkp_2dle (ad->gamma2[ad->i][j],
                  ad->delta2[ad->i][j],
                  tmpa,
                  tmpb,
                  NULL,
                  proof2);

    ec_point_serialize (gamma, ad->gamma2[ad->i][j]);
    ec_point_serialize (delta, ad->delta2[ad->i][j]);

    /* add winner determination for own gamma,delta */
    gcry_mpi_ec_add (ad->gamma2[ad->i][j],
                     ad->gamma2[ad->i][j],
                     ad->tmpa1[j],
                     ec_ctx);
    gcry_mpi_ec_add (ad->delta2[ad->i][j],
                     ad->delta2[ad->i][j],
                     ad->tmpb1[j],
                     ec_ctx);

    cur += sizeof (*gamma) + sizeof (*delta) + sizeof (*proof2);
  }

  gcry_mpi_point_release (tmpa);
  gcry_mpi_point_release (tmpb);
  return ret;
}


int
fp_pub_recv_outcome (struct BRANDT_Auction *ad,
                     const unsigned char   *buf,
                     size_t buflen,
                     uint16_t sender)
{
  int ret = 0;
  const unsigned char *cur = buf;
  struct proof_2dle   *proof2;
  gcry_mpi_point_t gamma = gcry_mpi_point_new (0);
  gcry_mpi_point_t delta = gcry_mpi_point_new (0);

  brandt_assert (ad && buf);

  if (buflen != (ad->k * (2 * sizeof (struct ec_mpi) + sizeof (*proof2))))
  {
    GNUNET_log_from (GNUNET_ERROR_TYPE_WARNING,
                     "libbrandt",
                     "wrong size of received outcome\n");
    goto quit;
  }

  for (uint16_t j = 0; j < ad->k; j++)
  {
    ec_point_parse (gamma, (struct ec_mpi *) cur);
    ec_point_parse (delta, &((struct ec_mpi *) cur)[1]);
    proof2 = (struct proof_2dle *) (cur + 2 * sizeof (struct ec_mpi));
    if (smc_zkp_2dle_check (gamma,
                            delta,
                            ad->gamma2[sender][j],
                            ad->delta2[sender][j],
                            proof2))
    {
      GNUNET_log_from (GNUNET_ERROR_TYPE_WARNING,
                       "libbrandt",
                       "wrong zkp2 for gamma, delta received\n");
      goto quit;
    }
    ec_point_copy (ad->gamma2[sender][j], gamma);
    ec_point_copy (ad->delta2[sender][j], delta);

    /* add winner determination summand */
    gcry_mpi_ec_add (ad->gamma2[sender][j],
                     ad->gamma2[sender][j],
                     ad->tmpa1[j],
                     ec_ctx);
    gcry_mpi_ec_add (ad->delta2[sender][j],
                     ad->delta2[sender][j],
                     ad->tmpb1[j],
                     ec_ctx);

    cur += 2 * sizeof (struct ec_mpi) + sizeof (*proof2);
  }

  ret = 1;
quit:
  gcry_mpi_point_release (gamma);
  gcry_mpi_point_release (delta);
  return ret;
}


void
fp_pub_prep_decryption (struct BRANDT_Auction *ad)
{
  gcry_mpi_point_t tmp = gcry_mpi_point_new (0);

  ad->phi2 = smc_init2 (ad->n, ad->k);
  brandt_assert (ad->phi2);

  for (uint16_t j = 0; j < ad->k; j++)
  {
    smc_sum (tmp, &ad->delta2[0][j], ad->n, ad->k);

    /* copy still encrypted 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 decryption messages */
    for (uint16_t a = 0; a < ad->n; a++)
      ec_point_copy (ad->phi2[a][j], tmp);
  }

  gcry_mpi_point_release (tmp);
}


/**
 * fp_pub_decrypt_outcome decrypts part of the outcome and packs it into a
 * message buffer together with proofs of correctnes.
 *
 * @param[in] ad Pointer to the BRANDT_Auction struct to operate on
 * @param[out] buflen Size of the returned message buffer in byte
 * @return A buffer containing the own share of the decrypted outcome
 * which needs to be broadcast
 */
unsigned char *
fp_pub_decrypt_outcome (struct BRANDT_Auction *ad, size_t *buflen)
{
  unsigned char     *ret;
  unsigned char     *cur;
  gcry_mpi_point_t tmp = gcry_mpi_point_new (0);
  struct msg_head   *head;
  struct ec_mpi     *phi;
  struct proof_2dle *proof2;

  brandt_assert (ad && buflen);

  *buflen = (sizeof (*head) + ad->k * (sizeof (*phi) + sizeof (*proof2)));
  ret = GNUNET_new_array (*buflen, unsigned char);

  head = (struct msg_head *) ret;
  head->prot_version = htonl (0);
  head->msg_type = htonl (msg_decrypt);
  cur = ret + sizeof (*head);

  for (uint16_t j = 0; j < ad->k; j++)
  {
    phi = (struct ec_mpi *) cur;
    proof2 = (struct proof_2dle *) (cur + sizeof (*phi));

    ec_point_copy (tmp, ad->phi2[ad->i][j]);

    /* decrypt outcome component and prove the correct key was used */
    smc_zkp_2dle (ad->phi2[ad->i][j],
                  NULL,
                  tmp,
                  ec_gen,
                  ad->x,
                  proof2);

    ec_point_serialize (phi, ad->phi2[ad->i][j]);

    cur += sizeof (*phi) + sizeof (*proof2);
  }

  gcry_mpi_point_release (tmp);
  return ret;
}


int
fp_pub_recv_decryption (struct BRANDT_Auction *ad,
                        const unsigned char   *buf,
                        size_t buflen,
                        uint16_t sender)
{
  int ret = 0;
  const unsigned char *cur = buf;
  struct proof_2dle   *proof2;
  gcry_mpi_point_t phi = gcry_mpi_point_new (0);

  brandt_assert (ad && buf);

  if (buflen != (ad->k * (sizeof (struct ec_mpi) + sizeof (*proof2))))
  {
    GNUNET_log_from (GNUNET_ERROR_TYPE_WARNING,
                     "libbrandt",
                     "wrong size of received outcome decryption\n");
    goto quit;
  }

  for (uint16_t j = 0; j < ad->k; j++)
  {
    ec_point_parse (phi, (struct ec_mpi *) cur);
    proof2 = (struct proof_2dle *) (cur + sizeof (struct ec_mpi));
    if (smc_zkp_2dle_check (phi,
                            ad->y[sender],
                            ad->phi2[sender][j],
                            ec_gen,
                            proof2))
    {
      GNUNET_log_from (GNUNET_ERROR_TYPE_WARNING,
                       "libbrandt",
                       "wrong zkp2 for phi, y received\n");
      goto quit;
    }
    ec_point_copy (ad->phi2[sender][j], phi);
    cur += sizeof (struct ec_mpi) + sizeof (*proof2);
  }

  ret = 1;
quit:
  gcry_mpi_point_release (phi);
  return ret;
}


struct BRANDT_Result *
fp_pub_determine_outcome (struct BRANDT_Auction *ad,
                          uint16_t              *len)
{
  struct BRANDT_Result *ret;
  int32_t price = -1;
  int32_t winner = -1;
  int dlogi = -1;
  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);

  for (uint16_t j = ad->k - 1; j >= 0; j--)
  {
    smc_sum (sum_gamma, &ad->gamma2[0][j], ad->n, ad->k);
    smc_sum (sum_phi, &ad->phi2[0][j], ad->n, ad->k);
    gcry_mpi_ec_sub (sum_gamma, sum_gamma, sum_phi, ec_ctx);
    /* first non-zero component determines the price */
    if (ec_point_cmp (sum_gamma, ec_zero))
    {
      price = j;
      break;
    }
  }

  {
    struct GNUNET_CRYPTO_EccPoint ec_point = {0};
    gcry_mpi_t q_y;

    GNUNET_assert (0 == gcry_mpi_ec_set_point ("q", sum_gamma, ec_ctx));
    q_y = gcry_mpi_ec_get_mpi ("q@eddsa", ec_ctx, 0);
    GNUNET_assert (q_y);
    GNUNET_CRYPTO_mpi_print_unsigned (ec_point.v,
                                      sizeof(ec_point.v),
                                      q_y);
    dlogi = GNUNET_CRYPTO_ecc_dlog (ad->dlogctx,
                                    &ec_point);
    gcry_mpi_release (q_y);
  }

  brandt_assert (dlogi > 0);

  /* all bidders participated with a multiplicative share */
  dlogi /= ad->n;

  /* can only support up to bits(dlogi) bidders */
  brandt_assert (sizeof (int) * 8 > ad->n);
  for (uint16_t i = 0; i < ad->n; i++)
  {
    /* first set bit determines the winner */
    if (dlogi & (1 << i))
    {
      winner = i;
      break;
    }
  }

  gcry_mpi_point_release (sum_gamma);
  gcry_mpi_point_release (sum_phi);

  if (-1 == winner || -1 == price)
    return NULL;

  ret = GNUNET_new (struct BRANDT_Result);
  ret->bidder = winner;
  ret->price = price;
  ret->status = BRANDT_bidder_won;
  if (len)
    *len = 1;
  return ret;
}