add outcome determination plus test

- also fix bug in smc_sum()

1 files changed, 33 insertions, 2 deletions

diff --git a/crypto.c b/crypto.c
index f46c5df..099d3dd 100644
--- a/crypto.c
+++ b/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.