libbrandt/fp_priv.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_priv.c
 * @brief Implementation of the first price private outcome algorithm.
 * @author Markus Teich
 */

#include "platform.h"

#include <gcrypt.h>

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


void
fp_priv_prep_outcome (struct BRANDT_Auction *ad)
{
	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 (no one has a higher bid) */
	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 (tlta3[i][j],
			                 tlta2[i][ad->k - 1],
			                 tlta2[i][j],
			                 ec_ctx);
			gcry_mpi_ec_sub (tltb3[i][j],
			                 tltb2[i][ad->k - 1],
			                 tltb2[i][j],
			                 ec_ctx);
		}
		brandt_assert (!ec_point_cmp (ec_zero, tlta3[i][ad->k - 1]));
		brandt_assert (!ec_point_cmp (ec_zero, tltb3[i][ad->k - 1]));
	}
	for (uint16_t j = 0; j < ad->k; j++)
	{
		smc_sum (tlta1[j], &tlta3[0][j], ad->n, ad->k);
		smc_sum (tltb1[j], &tltb3[0][j], 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]));
	/* \todo: merge into one nested i,j loop and one nested j,i loop? */

	/* temporary lookup table for second summand (my bid is not lower) */
	for (uint16_t i = 0; i < ad->n; i++)
	{
		for (uint16_t j = 0; j < ad->k; j++)
		{
			gcry_mpi_ec_sub (tlta2[i][j], tlta2[i][j], ad->alpha[i][j], ec_ctx);
			gcry_mpi_ec_sub (tltb2[i][j], tltb2[i][j], ad->beta[i][j], ec_ctx);
		}
		brandt_assert (!ec_point_cmp (ec_zero, tlta2[i][0]));
		brandt_assert (!ec_point_cmp (ec_zero, tltb2[i][0]));
	}

	/* temporary lookup table for third summand (no one with a lower index has
	 * the same bid) */
	for (uint16_t j = 0; j < ad->k; j++)
	{
		smc_sums_partial (&tlta3[0][j], &ad->alpha[0][j], ad->n, ad->k, ad->k);
		smc_sums_partial (&tltb3[0][j], &ad->beta[0][j], ad->n, ad->k, ad->k);
		for (uint16_t i = 0; i < ad->n; i++)
		{
			gcry_mpi_ec_sub (tlta3[i][j], tlta3[i][j], ad->alpha[i][j], ec_ctx);
			gcry_mpi_ec_sub (tltb3[i][j], tltb3[i][j], ad->beta[i][j], ec_ctx);
		}
		brandt_assert (!ec_point_cmp (ec_zero, tlta3[0][j]));
		brandt_assert (!ec_point_cmp (ec_zero, tltb3[0][j]));
	}

	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_add (tmpa, tmpa, tlta3[i][j], ec_ctx);

			/* compute inner delta */
			gcry_mpi_ec_add (tmpb, tltb1[j], tltb2[i][j], ec_ctx);
			gcry_mpi_ec_add (tmpb, tmpb, tltb3[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_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);
}


/**
 * fp_priv_compute_outcome computes encrypted outcome shares and packs them 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 bytes
 * @return A buffer containing the encrypted outcome vectors
 * which needs to be broadcast
 */
unsigned char *
fp_priv_compute_outcome (struct BRANDT_Auction *ad, size_t *buflen)
{
	unsigned char     *ret;
	unsigned char     *cur;
	struct msg_head   *head;
	gcry_mpi_point_t  tmpa = gcry_mpi_point_new (0);
	gcry_mpi_point_t  tmpb = gcry_mpi_point_new (0);
	struct ec_mpi     *gamma;
	struct ec_mpi     *delta;
	struct proof_2dle *proof2;

	brandt_assert (ad && buflen);

	*buflen = (sizeof (*head) +                /* msg header */
	           ad->n * ad->k *                 /* nk * (gamma, delta, proof2) */
	           (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 i = 0; i < ad->n; i++)
	{
		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->gamma3[ad->i][i][j]);
			ec_point_copy (tmpb, ad->delta3[ad->i][i][j]);

			/* apply random masking for losing bidders */
			smc_zkp_2dle (ad->gamma3[ad->i][i][j],
			              ad->delta3[ad->i][i][j],
			              tmpa,
			              tmpb,
			              NULL,
			              proof2);

			ec_point_serialize (gamma, ad->gamma3[ad->i][i][j]);
			ec_point_serialize (delta, ad->delta3[ad->i][i][j]);

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

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


int
fp_priv_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->n * 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 i = 0; i < ad->n; i++)
	{
		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->gamma3[sender][i][j],
			                        ad->delta3[sender][i][j],
			                        proof2))
			{
				GNUNET_log_from (GNUNET_ERROR_TYPE_WARNING,
				                 "libbrandt",
				                 "wrong zkp2 for gamma, delta received\n");
				goto quit;
			}
			ec_point_copy (ad->gamma3[sender][i][j], gamma);
			ec_point_copy (ad->delta3[sender][i][j], delta);
			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_priv_prep_decryption (struct BRANDT_Auction *ad)
{
	gcry_mpi_point_t tmp = gcry_mpi_point_new (0);

	ad->phi3 = smc_init3 (ad->n, ad->n, ad->k);
	brandt_assert (ad->phi3);

	ad->phiproofs3 = GNUNET_new_array_3d (ad->n,
	                                      ad->n,
	                                      ad->k,
	                                      struct proof_2dle);
	brandt_assert (ad->phiproofs3);

	for (uint16_t i = 0; i < ad->n; i++)
	{
		for (uint16_t j = 0; j < ad->k; j++)
		{
			smc_sum (tmp, &ad->delta3[0][i][j], ad->n, 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->phi3[a][i][j], tmp);
		}
	}

	gcry_mpi_point_release (tmp);
}


static unsigned char *
fp_priv_decrypt_outcome_seller (struct BRANDT_Auction *ad, size_t *buflen)
{
	unsigned char     *ret;
	unsigned char     *cur;
	struct msg_head   *head;
	gcry_mpi_point_t  tmp = gcry_mpi_point_new (0);
	struct ec_mpi     *phi;
	struct proof_2dle *proof2;

	*buflen = (sizeof (*head) +
	           (ad->n - 1) * ad->n * 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 h = 0; h < ad->n; h++)
	{
		for (uint16_t i = 0; i < ad->n; i++)
		{
			/* don't reveal outcome to losing bidders */
			if (h == i)
				continue;

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

				ec_point_serialize (phi, ad->phi3[h][i][j]);
				memcpy (proof2, &ad->phiproofs3[h][i][j], sizeof (*proof2));

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

	gcry_mpi_point_release (tmp);
	return ret;
}


static unsigned char *
fp_priv_decrypt_outcome_bidder (struct BRANDT_Auction *ad, size_t *buflen)
{
	unsigned char     *ret;
	unsigned char     *cur;
	struct msg_head   *head;
	gcry_mpi_point_t  tmp = gcry_mpi_point_new (0);
	struct ec_mpi     *phi;
	struct proof_2dle *proof2;

	*buflen = (sizeof (*head) +
	           ad->n * 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 i = 0; i < ad->n; i++)
	{
		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->phi3[ad->i][i][j]);

			/* decrypt outcome component and prove the correct key was used */
			smc_zkp_2dle (ad->phi3[ad->i][i][j],
			              NULL,
			              tmp,
			              ec_gen,
			              ad->x,
			              proof2);

			ec_point_serialize (phi, ad->phi3[ad->i][i][j]);

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

	gcry_mpi_point_release (tmp);
	return ret;
}


/**
 * fp_priv_decrypt_outcome decrypts the own shares of the outcome and packs them
 * into a message buffer together with proofs of correctnes. When this is called
 * as the seller it will not decrypt anything, but just create the message
 * buffer from all received decryption shares to broadcast back to all bidders.
 *
 * @param[in] ad Pointer to the BRANDT_Auction struct to operate on
 * @param[out] buflen Size of the returned message buffer in bytes
 * @return A buffer containing the share of the decrypted outcome
 * which needs to be broadcast
 */
unsigned char *
fp_priv_decrypt_outcome (struct BRANDT_Auction *ad, size_t *buflen)
{
	brandt_assert (ad && buflen);
	if (ad->seller_mode)
		return fp_priv_decrypt_outcome_seller (ad, buflen);
	else
		return fp_priv_decrypt_outcome_bidder (ad, buflen);
}


static int
fp_priv_recv_decryption_seller (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);

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

	for (uint16_t i = 0; i < ad->n; i++)
	{
		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->phi3[sender][i][j],
			                        ec_gen,
			                        proof2))
			{
				GNUNET_log_from (GNUNET_ERROR_TYPE_WARNING,
				                 "libbrandt",
				                 "wrong zkp2 for phi, y received from bidder\n");
				goto quit;
			}

			/* store proof. we need to rebroadcast it to the other bidders */
			memcpy (&ad->phiproofs3[sender][i][j], proof2, sizeof (*proof2));

			ec_point_copy (ad->phi3[sender][i][j], phi);
			cur += sizeof (struct ec_mpi) + sizeof (*proof2);
		}
	}

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


static int
fp_priv_recv_decryption_bidder (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);

	if (buflen != ((ad->n - 1) * ad->n * ad->k * (sizeof (struct ec_mpi) +
	                                              sizeof (*proof2))))
	{
		GNUNET_log_from (
		    GNUNET_ERROR_TYPE_WARNING,
		    "libbrandt",
		    "wrong size of received outcome decryption from seller\n");
		goto quit;
	}

	for (uint16_t h = 0; h < ad->n; h++)
	{
		for (uint16_t i = 0; i < ad->n; i++)
		{
			/* those combinations are not sent by the seller */
			if (h == i)
				continue;

			/* we already have our own phi values */
			if (h == ad->i)
			{
				cur += ad->k * (sizeof (struct ec_mpi) + sizeof (*proof2));
				continue;
			}

			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[h],
				                        ad->phi3[h][i][j],
				                        ec_gen,
				                        proof2))
				{
					GNUNET_log_from (
					    GNUNET_ERROR_TYPE_WARNING,
					    "libbrandt",
					    "wrong zkp2 for phi, y received from seller\n");
					goto quit;
				}
				ec_point_copy (ad->phi3[h][i][j], phi);
				cur += sizeof (struct ec_mpi) + sizeof (*proof2);
			}
		}
	}

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


int
fp_priv_recv_decryption (struct BRANDT_Auction *ad,
                         const unsigned char   *buf,
                         size_t                buflen,
                         uint16_t              sender)
{
	brandt_assert (ad && buf);
	if (ad->seller_mode)
		return fp_priv_recv_decryption_seller (ad, buf, buflen, sender);
	else
		return fp_priv_recv_decryption_bidder (ad, buf, buflen, sender);
}


struct BRANDT_Result *
fp_priv_determine_outcome (struct BRANDT_Auction *ad,
                           uint16_t              *len)
{
	struct BRANDT_Result *ret;
	int32_t              price = -1;
	int32_t              winner = -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 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 (-1 != price)
				{
					GNUNET_log_from (GNUNET_ERROR_TYPE_ERROR,
					                 "libbrandt",
					                 "multiple winning prices detected\n");
					return NULL;
				}
				if (-1 != winner)
				{
					GNUNET_log_from (GNUNET_ERROR_TYPE_ERROR,
					                 "libbrandt",
					                 "multiple winners detected\n");
					return NULL;
				}
				price = j;
				winner = i;
			}
		}
	}

	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;
}