smc_zkp_dl: make v an output parameter

1 files changed, 7 insertions, 4 deletions

diff --git a/crypto.c b/crypto.c
index d7d2e0f..3619f3c 100644
--- a/crypto.c
+++ b/crypto.c
@@ -616,15 +616,15 @@ smc_compute_outcome (struct AuctionData *ad)
  * 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.
  *
- * @param[in] v input point. Must be known to the verifier.
+ * @param[out] v output point. Must be known to the verifier.
  * @param[in] x private key. Knowledge of this number is certified in the proof
  * @param[out] proof pointer where to save the output proof structure. Must be
  * shared with the verifier.
  */
 void
-smc_zkp_dl (const gcry_mpi_point_t v,
-            const gcry_mpi_t       x,
-            struct proof_dl        *proof)
+smc_zkp_dl (gcry_mpi_point_t v,
+            const gcry_mpi_t x,
+            struct proof_dl  *proof)
 {
         struct zkp_challenge_dl challenge;
         struct brandt_hash_code challhash;
@@ -633,6 +633,9 @@ smc_zkp_dl (const gcry_mpi_point_t v,
         gcry_mpi_t              c = gcry_mpi_new (0);
         gcry_mpi_t              z = gcry_mpi_new (0);
 
+        /* v = xg */
+        gcry_mpi_ec_mul (v, x, ec_gen, ec_ctx);
+
         /* a = zg */
         ec_keypair_create (a, z);