add outcome determination plus test

- also fix bug in smc_sum()

crypto.c

@@ -594,7 +594,7 @@ smc_sum (gcry_mpi_point_t out,
 	brandt_assert (NULL != out);
 	/**\todo: how to copy a point more efficiently? */
 	gcry_mpi_ec_add (out, ec_zero, ec_zero, ec_ctx);
-	for (uint16_t i = 0; i < len; i += step)
+	for (uint16_t i = 0; i < len * step; i += step)
 		gcry_mpi_ec_add (out, out, in[i], ec_ctx);
 }
 
@@ -616,7 +616,7 @@ smc_gen_keyshare (struct AuctionData *ad, size_t *buflen)
 	brandt_assert (ad && buflen);
 	*buflen = (sizeof (struct ec_mpi) + sizeof (*proof1));
 	if (NULL == (ret = calloc (1, *buflen)) ||
-	    NULL == (ad->y = calloc (ad->n, sizeof (*ad->y))))
+	    NULL == (ad->y = smc_init1 (ad->n)))
 	{
 		weprintf ("unable to alloc memory for key shares");
 		return NULL;
@@ -1103,6 +1103,37 @@ quit:
 }
 
 
+int32_t
+smc_determine_outcome (struct AuctionData *ad)
+{
+	int32_t          ret = -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 = 0; j < ad->k; j++)
+	{
+		smc_sum (sum_gamma, &ad->gamma[0][ad->i][j], ad->n, ad->n * ad->k);
+		smc_sum (sum_phi, &ad->phi[0][ad->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 != ret)
+			{
+				weprintf ("multiple winning prices detected");
+				return -1;
+			}
+			ret = j;
+		}
+	}
+
+	gcry_mpi_point_release (sum_gamma);
+	gcry_mpi_point_release (sum_phi);
+	return ret;
+}
+
+
 /**
  * smc_zkp_dl creates a proof of knowledge of @a x with \f$v = xg\f$ where
  * \f$g\f$ is the base point on Ed25519.

crypto.h

@@ -135,4 +135,6 @@ int smc_recv_decryption (struct AuctionData *ad,
                          size_t             buflen,
                          uint16_t           sender);
 
+int32_t smc_determine_outcome (struct AuctionData *ad);
+
 #endif /* ifndef _BRANDT_CRYPTO_H */

test_crypto.c

@@ -317,19 +317,38 @@ test_round3 ()
 }
 
 
+int
+test_outcome ()
+{
+	int32_t ret = -1;
+
+	for (uint16_t i = 0; i < ad->n; i++)
+	{
+		if (-1 != smc_determine_outcome (&ad[i]))
+		{
+			check (-1 == ret, "multiple winners detected");
+			ret = i;
+		}
+	}
+	check (-1 != ret, "no winner detected");
+	fputs ("winner detected", stderr);
+	return 1;
+}
+
+
 void
 cleanup_auction_data ()
 {
 	for (uint16_t i = 0; i < bidders; i++)
 	{
-		for (uint16_t h = 0; h < bidders; h++)
-			gcry_mpi_point_release (ad[i].y[h]);
-
 		gcry_mpi_point_release (ad[i].Y);
 		gcry_mpi_release (ad[i].x);
-		free (ad[i].y);
+		smc_free1 (ad[i].y, ad[i].n);
 		smc_free2 (ad[i].alpha, ad[i].n, ad[i].k);
 		smc_free2 (ad[i].beta, ad[i].n, ad[i].k);
+		smc_free3 (ad[i].gamma, ad[i].n, ad[i].n, ad[i].k);
+		smc_free3 (ad[i].delta, ad[i].n, ad[i].n, ad[i].k);
+		smc_free3 (ad[i].phi, ad[i].n, ad[i].n, ad[i].k);
 	}
 	free (ad);
 }
@@ -361,6 +380,7 @@ main (int argc, char *argv[])
 		run (test_round1);
 		run (test_round2);
 		run (test_round3);
+		run (test_outcome);
 		cleanup_auction_data ();
 	}