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add additional proof on encrypt_bid for M+1st price auctions

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This is needed to ensure bidders are only chosing bids from the subset which is
allowed to them. This prevents ties and keeps the protocol way more simple for
M+1st price auctions.
This commit is contained in:
Markus Teich 2016-10-09 14:16:53 +02:00
parent d4932019ad
commit ebd955858f
1 changed files with 54 additions and 1 deletions
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55
crypto.c
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@ -705,6 +705,7 @@ smc_encrypt_bid (struct BRANDT_Auction *ad, size_t *buflen)
struct msg_head *head;
struct proof_0og *proof3;
gcry_mpi_t r_sum;
gcry_mpi_t r_sum2;
gcry_mpi_t r_part;
brandt_assert (ad && buflen);
@ -721,6 +722,7 @@ smc_encrypt_bid (struct BRANDT_Auction *ad, size_t *buflen)
cur = ret + sizeof (*head);
r_sum = gcry_mpi_new (256);
r_sum2 = gcry_mpi_new (256);
r_part = gcry_mpi_new (256);
for (uint16_t j = 0; j < ad->k; j++)
@ -735,11 +737,29 @@ smc_encrypt_bid (struct BRANDT_Auction *ad, size_t *buflen)
ec_point_serialize ((struct ec_mpi *)cur, ad->alpha[ad->i][j]);
ec_point_serialize (&((struct ec_mpi *)cur)[1], ad->beta[ad->i][j]);
gcry_mpi_addm (r_sum, r_sum, r_part, ec_n);
/* prepare sum for additional M+1st price auction proof (see below) */
if (0 < ad->m && j >= ad->i && 0 == (j - ad->i) % ad->n)
gcry_mpi_addm (r_sum2, r_sum2, r_part, ec_n);
cur += 2 * sizeof (struct ec_mpi) + sizeof (struct proof_0og);
}
smc_zkp_2dle (NULL, NULL, ad->Y, ec_gen, r_sum, (struct proof_2dle *)cur);
/* in M+1st price auctions we need to prove that our bid is from the valid
* subset of bids as well */
if (0 < ad->m)
{
struct proof_2dle *proof2;
*buflen += sizeof (struct proof_2dle);
ret = GNUNET_realloc (ret, *buflen);
proof2 = (struct proof_2dle *)(ret + *buflen -
sizeof (struct proof_2dle));
smc_zkp_2dle (NULL, NULL, ad->Y, ec_gen, r_sum2, proof2);
}
gcry_mpi_release (r_sum);
gcry_mpi_release (r_sum2);
gcry_mpi_release (r_part);
return ret;
@ -758,11 +778,13 @@ smc_recv_encrypted_bid (struct BRANDT_Auction *ad,
gcry_mpi_point_t **ct; /* ciphertexts */
gcry_mpi_point_t alpha_sum = gcry_mpi_point_new (0);
gcry_mpi_point_t beta_sum = gcry_mpi_point_new (0);
gcry_mpi_point_t alpha_sum2 = gcry_mpi_point_new (0);
gcry_mpi_point_t beta_sum2 = gcry_mpi_point_new (0);
brandt_assert (ad && buf);
if (buflen != (ad->k * (sizeof (struct ec_mpi) * 2 + sizeof (*proof3)) +
sizeof (struct proof_2dle)) ||
(0 < ad->m ? 2 : 1) * sizeof (struct proof_2dle)) ||
NULL == (ct = smc_init2 (2, ad->k)))
{
weprintf ("wrong size of received encrypted bid");
@ -771,6 +793,8 @@ smc_recv_encrypted_bid (struct BRANDT_Auction *ad,
ec_point_copy (alpha_sum, ec_zero);
ec_point_copy (beta_sum, ec_zero);
ec_point_copy (alpha_sum2, ec_zero);
ec_point_copy (beta_sum2, ec_zero);
for (uint16_t j = 0; j < ad->k; j++)
{
@ -784,6 +808,15 @@ smc_recv_encrypted_bid (struct BRANDT_Auction *ad,
}
gcry_mpi_ec_add (alpha_sum, alpha_sum, ct[0][j], ec_ctx);
gcry_mpi_ec_add (beta_sum, beta_sum, ct[1][j], ec_ctx);
/* precalculate ciphertext sums for second 2dle proof needed in M+1st
* price auctions */
if (0 < ad->m && j >= ad->i && 0 == (j - ad->i) % ad->n)
{
gcry_mpi_ec_add (alpha_sum2, alpha_sum2, ct[0][j], ec_ctx);
gcry_mpi_ec_add (beta_sum2, beta_sum2, ct[1][j], ec_ctx);
}
cur += 2 * sizeof (struct ec_mpi) + sizeof (struct proof_0og);
}
@ -798,6 +831,24 @@ smc_recv_encrypted_bid (struct BRANDT_Auction *ad,
goto quit;
}
/* On M+1st price auctions check with the second 2dle proof if the bidder
* only bid on one of his allowed indizes */
if (0 < ad->m)
{
cur += sizeof (struct proof_2dle);
gcry_mpi_ec_sub (alpha_sum2, alpha_sum2, ec_gen, ec_ctx);
if (smc_zkp_2dle_check (alpha_sum2,
beta_sum2,
ad->Y,
ec_gen,
(struct proof_2dle *)cur))
{
weprintf ("wrong second zkp2 for alpha, beta received. "
"bid not allowed for this user in M+1st price auctions.");
goto quit;
}
}
for (uint16_t j = 0; j < ad->k; j++)
{
ec_point_copy (ad->alpha[sender][j], ct[0][j]);
@ -809,6 +860,8 @@ smc_recv_encrypted_bid (struct BRANDT_Auction *ad,
quit:
gcry_mpi_point_release (alpha_sum);
gcry_mpi_point_release (beta_sum);
gcry_mpi_point_release (alpha_sum2);
gcry_mpi_point_release (beta_sum2);
return ret;
}