working on cleaning up /refresh/melt logic

9 files changed, 367 insertions, 269 deletions

diff --git a/src/include/taler_signatures.h b/src/include/taler_signatures.h
index 84968582e..0518af3f0 100644
--- a/src/include/taler_signatures.h
+++ b/src/include/taler_signatures.h
@@ -234,6 +234,36 @@ struct TALER_DepositConfirmation
 
 
 /**
+ * Format of the block signed by the Mint in response to
+ * a successful "/refresh/melt" request.  Hereby the mint
+ * affirms that all of the coins were successfully melted.
+ */
+struct RefreshMeltResponseSignatureBody
+{
+  /**
+   * Purpose is #TALER_SIGNATURE_REFRESH_MELT_RESPONSE.
+   */
+  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
+
+  /**
+   * Signature of the client over the melt request (thereby
+   * indirectly including all of the information the client
+   * sent).
+   */
+  struct GNUNET_CRYPTO_EddsaSignature melt_client_signature;
+
+  /**
+   * Public key of the refresh session for which
+   * @e melt_client_signature must be a valid signature.
+   */
+  struct GNUNET_CRYPTO_EddsaPublicKey session_key;
+};
+
+
+
+
+
+/**
  * FIXME
  */
 struct TALER_MINT_SignKeyIssue
@@ -296,15 +326,6 @@ struct RefreshCommitResponseSignatureBody
 };
 
 
-/**
- * FIXME
- */
-struct RefreshMeltResponseSignatureBody
-{
-  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
-  struct GNUNET_HashCode melt_response_hash;
-};
-
 
 /**
  * FIXME
diff --git a/src/mint/mint.h b/src/mint/mint.h
index 1e1221157..e2d559701 100644
--- a/src/mint/mint.h
+++ b/src/mint/mint.h
@@ -36,54 +36,6 @@
 
 
 
-/**
- * Global information for a refreshing session.
- */
-struct RefreshSession
-{
-  /**
-   * Signature over the commitments by the client.
-   */
-  struct GNUNET_CRYPTO_EddsaSignature commit_sig;
-
-  /**
-   * Public key of the refreshing session, used to sign
-   * the client's commit message.
-   */
-  struct GNUNET_CRYPTO_EddsaPublicKey session_pub;
-
-  /**
-   * Number of coins we are melting.
-   */
-  uint16_t num_oldcoins;
-
-  /**
-   * Number of new coins we are creating.
-   */
-  uint16_t num_newcoins;
-
-  /**
-   * Number of parallel operations we perform for the cut and choose.
-   * (must be greater or equal to three for security).
-   */
-  uint16_t kappa;
-
-  /**
-   * Index (smaller @e kappa) which the mint has chosen to not
-   * have revealed during cut and choose.
-   */
-  uint16_t noreveal_index;
-
-  /**
-   * FIXME.
-   */
-  int has_commit_sig;
-
-  /**
-   * FIXME.
-   */
-  uint8_t reveal_ok;
-};
 
 
 
diff --git a/src/mint/mint_db.c b/src/mint/mint_db.c
index 5c52948e6..67cf4b352 100644
--- a/src/mint/mint_db.c
+++ b/src/mint/mint_db.c
@@ -582,76 +582,6 @@ TALER_MINT_DB_insert_refresh_order (PGconn *db_conn,
 
 
 int
-TALER_MINT_DB_get_refresh_session (PGconn *db_conn,
-                                   const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
-                                   struct RefreshSession *session)
-{
-  int res;
-  struct TALER_DB_QueryParam params[] = {
-    TALER_DB_QUERY_PARAM_PTR(refresh_session_pub),
-    TALER_DB_QUERY_PARAM_END
-  };
-
-  PGresult *result = TALER_DB_exec_prepared (db_conn, "get_refresh_session", params);
-
-  if (PGRES_TUPLES_OK != PQresultStatus (result))
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Query failed: %s\n",
-                PQresultErrorMessage (result));
-    PQclear (result);
-    return GNUNET_SYSERR;
-  }
-
-  if (0 == PQntuples (result))
-    return GNUNET_NO;
-
-  GNUNET_assert (1 == PQntuples (result));
-
-  /* We're done if the caller is only interested in
-   * whether the session exists or not */
-
-  if (NULL == session)
-    return GNUNET_YES;
-
-  memset (session, 0, sizeof (struct RefreshSession));
-
-  session->session_pub = *refresh_session_pub;
-
-  struct TALER_DB_ResultSpec rs[] = {
-    TALER_DB_RESULT_SPEC("num_oldcoins", &session->num_oldcoins),
-    TALER_DB_RESULT_SPEC("num_newcoins", &session->num_newcoins),
-    TALER_DB_RESULT_SPEC("kappa", &session->kappa),
-    TALER_DB_RESULT_SPEC("noreveal_index", &session->noreveal_index),
-    TALER_DB_RESULT_SPEC("reveal_ok", &session->reveal_ok),
-    TALER_DB_RESULT_SPEC_END
-  };
-
-  res = TALER_DB_extract_result (result, rs, 0);
-
-  if (GNUNET_OK != res)
-  {
-    GNUNET_break (0);
-    PQclear (result);
-    return GNUNET_SYSERR;
-  }
-
-  if (TALER_DB_field_isnull (result, 0, "session_commit_sig"))
-    session->has_commit_sig = GNUNET_NO;
-  else
-    session->has_commit_sig = GNUNET_YES;
-
-  session->num_oldcoins = ntohs (session->num_oldcoins);
-  session->num_newcoins = ntohs (session->num_newcoins);
-  session->kappa = ntohs (session->kappa);
-  session->noreveal_index = ntohs (session->noreveal_index);
-
-  PQclear (result);
-  return GNUNET_YES;
-}
-
-
-int
 TALER_MINT_DB_get_known_coin (PGconn *db_conn,
                               const struct GNUNET_CRYPTO_EcdsaPublicKey *coin_pub,
                               struct KnownCoin *known_coin)
@@ -744,34 +674,6 @@ TALER_MINT_DB_get_known_coin (PGconn *db_conn,
 
 
 int
-TALER_MINT_DB_create_refresh_session (PGconn *db_conn,
-                                      const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub)
-{
-  uint16_t noreveal_index;
-  struct TALER_DB_QueryParam params[] = {
-    TALER_DB_QUERY_PARAM_PTR(session_pub),
-    TALER_DB_QUERY_PARAM_PTR(&noreveal_index),
-    TALER_DB_QUERY_PARAM_END
-  };
-
-  noreveal_index = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 1<<15);
-  noreveal_index = htonl (noreveal_index);
-
-  PGresult *result = TALER_DB_exec_prepared (db_conn, "insert_refresh_session", params);
-
-  if (PGRES_COMMAND_OK != PQresultStatus (result))
-  {
-    break_db_err (result);
-    PQclear (result);
-    return GNUNET_SYSERR;
-  }
-
-  PQclear (result);
-  return GNUNET_OK;
-}
-
-
-int
 TALER_MINT_DB_set_commit_signature (PGconn *db_conn,
                                     const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub,
                                     const struct GNUNET_CRYPTO_EddsaSignature *commit_sig)
@@ -1882,6 +1784,145 @@ TALER_MINT_DB_insert_deposit (PGconn *db_conn,
 
 
 /**
+ * Lookup refresh session data under the given public key.
+ *
+ * @param db_conn database handle to use
+ * @param refresh_session_pub public key to use for the lookup
+ * @param session[OUT] where to store the result
+ * @return #GNUNET_YES on success,
+ *         #GNUNET_NO if not found,
+ *         #GNUNET_SYSERR on DB failure
+ */
+int
+TALER_MINT_DB_get_refresh_session (PGconn *db_conn,
+                                   const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
+                                   struct RefreshSession *session)
+{
+  // FIXME: check logic!
+  int res;
+  struct TALER_DB_QueryParam params[] = {
+    TALER_DB_QUERY_PARAM_PTR(refresh_session_pub),
+    TALER_DB_QUERY_PARAM_END
+  };
+
+  PGresult *result = TALER_DB_exec_prepared (db_conn, "get_refresh_session", params);
+
+  if (PGRES_TUPLES_OK != PQresultStatus (result))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Query failed: %s\n",
+                PQresultErrorMessage (result));
+    PQclear (result);
+    return GNUNET_SYSERR;
+  }
+
+  if (0 == PQntuples (result))
+    return GNUNET_NO;
+
+  GNUNET_assert (1 == PQntuples (result));
+
+  /* We're done if the caller is only interested in
+   * whether the session exists or not */
+
+  if (NULL == session)
+    return GNUNET_YES;
+
+  memset (session, 0, sizeof (struct RefreshSession));
+
+  struct TALER_DB_ResultSpec rs[] = {
+    TALER_DB_RESULT_SPEC("num_oldcoins", &session->num_oldcoins),
+    TALER_DB_RESULT_SPEC("num_newcoins", &session->num_newcoins),
+    TALER_DB_RESULT_SPEC("kappa", &session->kappa),
+    TALER_DB_RESULT_SPEC("noreveal_index", &session->noreveal_index),
+    TALER_DB_RESULT_SPEC_END
+  };
+
+  res = TALER_DB_extract_result (result, rs, 0);
+
+  if (GNUNET_OK != res)
+  {
+    GNUNET_break (0);
+    PQclear (result);
+    return GNUNET_SYSERR;
+  }
+
+  if (TALER_DB_field_isnull (result, 0, "session_commit_sig"))
+    session->has_commit_sig = GNUNET_NO;
+  else
+    session->has_commit_sig = GNUNET_YES;
+
+  session->num_oldcoins = ntohs (session->num_oldcoins);
+  session->num_newcoins = ntohs (session->num_newcoins);
+  session->kappa = ntohs (session->kappa);
+  session->noreveal_index = ntohs (session->noreveal_index);
+
+  PQclear (result);
+  return GNUNET_YES;
+}
+
+
+/**
+ * Store new refresh session data under the given public key.
+ *
+ * @param db_conn database handle to use
+ * @param refresh_session_pub public key to use to locate the session
+ * @param session session data to store
+ * @return #GNUNET_YES on success,
+ *         #GNUNET_SYSERR on DB failure
+ */
+int
+TALER_MINT_DB_create_refresh_session (PGconn *db_conn,
+                                      const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub,
+                                      const struct RefreshSession *session)
+{
+  // FIXME: actually store session data!
+  uint16_t noreveal_index;
+  struct TALER_DB_QueryParam params[] = {
+    TALER_DB_QUERY_PARAM_PTR(session_pub),
+    TALER_DB_QUERY_PARAM_PTR(&noreveal_index),
+    TALER_DB_QUERY_PARAM_END
+  };
+
+  noreveal_index = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 1<<15);
+  noreveal_index = htonl (noreveal_index);
+
+  PGresult *result = TALER_DB_exec_prepared (db_conn, "insert_refresh_session", params);
+
+  if (PGRES_COMMAND_OK != PQresultStatus (result))
+  {
+    break_db_err (result);
+    PQclear (result);
+    return GNUNET_SYSERR;
+  }
+
+  PQclear (result);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Update new refresh session with the new state after the
+ * /refresh/commit operation.
+ *
+ * @param db_conn database handle to use
+ * @param refresh_session_pub public key to use to locate the session
+ * @param noreveal_index index chosen for the client to not reveal
+ * @param commit_client_sig signature of the client over its commitment
+ * @return #GNUNET_YES on success,
+ *         #GNUNET_SYSERR on DB failure
+ */
+int
+TALER_MINT_DB_update_refresh_session (PGconn *db_conn,
+                                      const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub,
+                                      uint16_t noreveal_index,
+                                      const struct GNUNET_CRYPTO_EddsaSignature *commit_client_sig)
+{
+  // FIXME: implement!
+  return GNUNET_SYSERR;
+}
+
+
+/**
  * Test if the given /refresh/melt request is known to us.
  *
  * @param db_conn database connection
diff --git a/src/mint/mint_db.h b/src/mint/mint_db.h
index 57b74f46e..e53df8ac2 100644
--- a/src/mint/mint_db.h
+++ b/src/mint/mint_db.h
@@ -44,10 +44,9 @@ TALER_MINT_DB_insert_refresh_order (PGconn *db_conn,
                                     const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub,
                                     const struct GNUNET_CRYPTO_rsa_PublicKey *denom_pub);
 
-int
-TALER_MINT_DB_get_refresh_session (PGconn *db_conn,
-                                   const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
-                                   struct RefreshSession *r_session);
+
+
+
 
 
 /**
@@ -86,10 +85,6 @@ TALER_MINT_DB_insert_known_coin (PGconn *db_conn,
                                  const struct KnownCoin *known_coin);
 
 
-int
-TALER_MINT_DB_create_refresh_session (PGconn *db_conn,
-                                      const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub);
-
 
 /**
  * Store the commitment to the given (encrypted) refresh link data
@@ -521,10 +516,111 @@ TALER_MINT_DB_insert_deposit (PGconn *db_conn,
                               const struct Deposit *deposit);
 
 
+
+/**
+ * Global information for a refreshing session.  Includes
+ * dimensions of the operation, security parameters and
+ * client signatures from "/refresh/melt" and "/refresh/commit".
+ */
+struct RefreshSession
+{
+  /**
+   * Signature over the commitments by the client,
+   * only valid if @e has_commit_sig is set.
+   */
+  struct GNUNET_CRYPTO_EddsaSignature commit_sig;
+
+    /**
+   * Signature over the melt by the client.
+   */
+  struct GNUNET_CRYPTO_EddsaSignature melt_sig;
+
+  /**
+   * Number of coins we are melting.
+   */
+  uint16_t num_oldcoins;
+
+  /**
+   * Number of new coins we are creating.
+   */
+  uint16_t num_newcoins;
+
+  /**
+   * Number of parallel operations we perform for the cut and choose.
+   * (must be greater or equal to three for security).  0 if not yet
+   * known.
+   */
+  uint16_t kappa;
+
+  /**
+   * Index (smaller @e kappa) which the mint has chosen to not
+   * have revealed during cut and choose.  Only valid if
+   * @e has_commit_sig is set to #GNUNET_YES.
+   */
+  uint16_t noreveal_index;
+
+  /**
+   * #GNUNET_YES if we have accepted the /refresh/commit and
+   * thus the @e commit_sig is valid.
+   */
+  int has_commit_sig;
+
+};
+
+
+/**
+ * Lookup refresh session data under the given public key.
+ *
+ * @param db_conn database handle to use
+ * @param refresh_session_pub public key to use for the lookup
+ * @param session[OUT] where to store the result
+ * @return #GNUNET_YES on success,
+ *         #GNUNET_NO if not found,
+ *         #GNUNET_SYSERR on DB failure
+ */
+int
+TALER_MINT_DB_get_refresh_session (PGconn *db_conn,
+                                   const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
+                                   struct RefreshSession *session);
+
+
+/**
+ * Store new refresh session data under the given public key.
+ *
+ * @param db_conn database handle to use
+ * @param refresh_session_pub public key to use to locate the session
+ * @param session session data to store
+ * @return #GNUNET_YES on success,
+ *         #GNUNET_SYSERR on DB failure
+ */
+int
+TALER_MINT_DB_create_refresh_session (PGconn *db_conn,
+                                      const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub,
+                                      const struct RefreshSession *session);
+
+
+/**
+ * Update new refresh session with the new state after the
+ * /refresh/commit operation.
+ *
+ * @param db_conn database handle to use
+ * @param refresh_session_pub public key to use to locate the session
+ * @param noreveal_index index chosen for the client to not reveal
+ * @param commit_client_sig signature of the client over its commitment
+ * @return #GNUNET_YES on success,
+ *         #GNUNET_SYSERR on DB failure
+ */
+int
+TALER_MINT_DB_update_refresh_session (PGconn *db_conn,
+                                      const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub,
+                                      uint16_t noreveal_index,
+                                      const struct GNUNET_CRYPTO_EddsaSignature *commit_client_sig);
+
+
 /**
- * Specification for a /refresh/melt operation.
+ * Specification for coin in a /refresh/melt operation.
  */
-struct RefreshMelt
+struct RefreshMelt /* FIXME: name to make it clearer this is about ONE coin! */
 {
   /**
    * Information about the coin that is being melted.
diff --git a/src/mint/taler-mint-httpd_db.c b/src/mint/taler-mint-httpd_db.c
index eae37199b..2f6ca0137 100644
--- a/src/mint/taler-mint-httpd_db.c
+++ b/src/mint/taler-mint-httpd_db.c
@@ -602,6 +602,8 @@ refresh_accept_melts (struct MHD_Connection *connection,
  *
  * @param connection the MHD connection to handle
  * @param refresh_session_pub public key of the refresh session
+ * @param client_signature signature of the client (matching @a refresh_session_pub)
+ *         over the melting request
  * @param num_new_denoms number of entries in @a denom_pubs
  * @param denum_pubs public keys of the coins we want to withdraw in the end
  * @param coin_count number of entries in @a coin_public_infos
@@ -611,6 +613,7 @@ refresh_accept_melts (struct MHD_Connection *connection,
 int
 TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
                                     const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
+                                    const struct GNUNET_CRYPTO_EddsaSignature *client_signature,
                                     unsigned int num_new_denoms,
                                     struct GNUNET_CRYPTO_rsa_PublicKey *const*denom_pubs,
                                     unsigned int coin_count,
@@ -622,57 +625,48 @@ TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
   PGconn *db_conn;
   int res;
 
-  /* We incrementally update the db with other parameters in a transaction.
-   * The transaction is aborted if some parameter does not validate. */
-
-  /* Send response immediately if we already know the session.
-   * Do _not_ care about fields other than session_pub in this case. */
-
   if (NULL == (db_conn = TALER_MINT_DB_get_connection ()))
   {
     GNUNET_break (0);
     return TALER_MINT_reply_internal_db_error (connection);
   }
+  if (GNUNET_OK !=
+      TALER_MINT_DB_transaction (db_conn))
+  {
+    GNUNET_break (0);
+    return TALER_MINT_reply_internal_db_error (connection);
+  }
   res = TALER_MINT_DB_get_refresh_session (db_conn,
                                            refresh_session_pub,
-                                           NULL);
+                                           &session);
   if (GNUNET_YES == res)
   {
-    if (GNUNET_OK !=
-        (res = TALER_MINT_DB_get_refresh_session (db_conn,
-                                                  refresh_session_pub,
-                                                  &session)))
-      {
-        // FIXME: send internal error
-        GNUNET_break (0);
-        return MHD_NO;
-      }
+    TALER_MINT_DB_rollback (db_conn);
     return TALER_MINT_reply_refresh_melt_success (connection,
-                                                  &session,
+                                                  &session.melt_sig,
                                                   refresh_session_pub);
   }
   if (GNUNET_SYSERR == res)
   {
-    // FIXME: return 'internal error'?
-    GNUNET_break (0);
-    return MHD_NO;
+    TALER_MINT_DB_rollback (db_conn);
+    return TALER_MINT_reply_internal_db_error (connection);
   }
 
 
-  if (GNUNET_OK !=
-      TALER_MINT_DB_transaction (db_conn))
-  {
-    GNUNET_break (0);
-    return TALER_MINT_reply_internal_db_error (connection);
-  }
 
-  if (GNUNET_OK != TALER_MINT_DB_create_refresh_session (db_conn,
-                                                         refresh_session_pub))
+  session.melt_sig = *client_signature;
+  session.num_oldcoins = coin_count;
+  session.num_newcoins = num_new_denoms;
+  session.kappa = 0; /* FIXME: should be chosen by mint per config! */
+  session.noreveal_index = UINT16_MAX;
+  session.has_commit_sig = GNUNET_NO;
+  if (GNUNET_OK !=
+      (res = TALER_MINT_DB_create_refresh_session (db_conn,
+                                                   refresh_session_pub,
+                                                   &session)))
   {
-    // FIXME: return 'internal error'?
-    GNUNET_break (0);
     TALER_MINT_DB_rollback (db_conn);
-    return MHD_NO;
+    return TALER_MINT_reply_internal_db_error (connection);
   }
 
   /* The next two operations must see the same key state,
@@ -725,7 +719,7 @@ TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
       return MHD_NO;
     }
   return TALER_MINT_reply_refresh_melt_success (connection,
-                                                &session,
+                                                client_signature,
                                                 refresh_session_pub);
 
 
@@ -741,6 +735,8 @@ TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
  * @a kappa sets of private transfer keys should not be revealed.
  *
  * @param connection the MHD connection to handle
+ * @param refresh_session public key of the session
+ * @param commit_client_sig signature of the client over this commitment
  * @param kappa size of x-dimension of @commit_coin and @commit_link arrays
  * @param num_oldcoins size of y-dimension of @commit_link array
  * @param num_newcoins size of y-dimension of @commit_coin array
@@ -754,6 +750,7 @@ TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
 int
 TALER_MINT_db_execute_refresh_commit (struct MHD_Connection *connection,
                                       const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
+                                      const struct GNUNET_CRYPTO_EddsaSignature *commit_client_sig,
                                       unsigned int kappa,
                                       unsigned int num_oldcoins,
                                       unsigned int num_newcoins,
@@ -773,12 +770,35 @@ TALER_MINT_db_execute_refresh_commit (struct MHD_Connection *connection,
     return TALER_MINT_reply_internal_db_error (connection);
   }
 
-  /* Send response immediately if we already know the session.
-   * Do _not_ care about fields other than session_pub in this case. */
-
+  if (GNUNET_OK !=
+      TALER_MINT_DB_transaction (db_conn))
+  {
+    GNUNET_break (0);
+    return TALER_MINT_reply_internal_db_error (connection);
+  }
   res = TALER_MINT_DB_get_refresh_session (db_conn,
                                            refresh_session_pub,
                                            &refresh_session);
+  if (GNUNET_SYSERR == res)
+  {
+    TALER_MINT_DB_rollback (db_conn);
+    return TALER_MINT_reply_internal_db_error (connection);
+  }
+  if (GNUNET_NO == res)
+  {
+    TALER_MINT_DB_rollback (db_conn);
+    return TALER_MINT_reply_arg_invalid (connection,
+                                         "session_pub");
+  }
+  if (GNUNET_YES == refresh_session.has_commit_sig)
+  {
+    TALER_MINT_DB_rollback (db_conn);
+    res = TALER_MINT_reply_refresh_commit_success (connection,
+                                                   &refresh_session);
+    return (GNUNET_SYSERR == res) ? MHD_NO : MHD_YES;
+  }
+
+
   // FIXME: this should check that kappa and num_newcoins match
   // our expectations from refresh_session!
 
@@ -814,47 +834,20 @@ TALER_MINT_db_execute_refresh_commit (struct MHD_Connection *connection,
     }
   }
 
-
-
-
-
-  if ( (GNUNET_YES == res) &&
-       (GNUNET_YES == refresh_session.has_commit_sig) )
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                "sending cached commit response\n");
-    res = TALER_MINT_reply_refresh_commit_success (connection,
-                                                   &refresh_session);
-    GNUNET_break (res != GNUNET_SYSERR);
-    return (GNUNET_SYSERR == res) ? MHD_NO : MHD_YES;
-  }
-  if (GNUNET_SYSERR == res)
-  {
-    // FIXME: return 'internal error'?
-    GNUNET_break (0);
-    return MHD_NO;
-  }
+  refresh_session.noreveal_index
+    = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                refresh_session.kappa);
 
   if (GNUNET_OK !=
-      TALER_MINT_DB_transaction (db_conn))
+      (res = TALER_MINT_DB_update_refresh_session (db_conn,
+                                                   refresh_session_pub,
+                                                   refresh_session.noreveal_index,
+                                                   commit_client_sig)))
   {
-    GNUNET_break (0);
+    TALER_MINT_DB_rollback (db_conn);
     return TALER_MINT_reply_internal_db_error (connection);
   }
 
-  /* Re-fetch the session information from the database,
-   * in case a concurrent transaction modified it. */
-
-  res = TALER_MINT_DB_get_refresh_session (db_conn,
-                                           refresh_session_pub,
-                                           &refresh_session);
-  if (GNUNET_OK != res)
-  {
-    // FIXME: return 'internal error'?
-    GNUNET_break (GNUNET_SYSERR != res);
-    TALER_MINT_DB_rollback (db_conn);
-    return MHD_NO;
-  }
 
   if (GNUNET_OK !=
       TALER_MINT_DB_commit (db_conn))
@@ -943,24 +936,14 @@ TALER_MINT_db_execute_refresh_reveal (struct MHD_Connection *connection,
     return TALER_MINT_reply_internal_db_error (connection);
   }
 
-  /* Send response immediately if we already know the session,
-   * and the session commited already.
-   * Do _not_ care about fields other than session_pub in this case. */
-
   res = TALER_MINT_DB_get_refresh_session (db_conn,
                                            refresh_session_pub,
                                            &refresh_session);
-  if (GNUNET_YES == res && 0 != refresh_session.reveal_ok)
-    return helper_refresh_reveal_send_response (connection,
-                                                db_conn,
-                                                &refresh_session,
-                                                refresh_session_pub);
+  if (GNUNET_NO == res)
+    return TALER_MINT_reply_arg_invalid (connection,
+                                         "session_pub");
   if (GNUNET_SYSERR == res)
-  {
-    GNUNET_break (0);
-    // FIXME: return 'internal error'?
-    return MHD_NO;
-  }
+    return TALER_MINT_reply_internal_db_error (connection);
 
   /* Check that the transfer private keys match their commitments.
    * Then derive the shared secret for each kappa, and check that they match. */
diff --git a/src/mint/taler-mint-httpd_db.h b/src/mint/taler-mint-httpd_db.h
index e53d1b8ef..4b9aa1fe0 100644
--- a/src/mint/taler-mint-httpd_db.h
+++ b/src/mint/taler-mint-httpd_db.h
@@ -91,6 +91,8 @@ TALER_MINT_db_execute_withdraw_sign (struct MHD_Connection *connection,
  *
  * @param connection the MHD connection to handle
  * @param refresh_session_pub public key of the refresh session
+ * @param client_signature signature of the client (matching @a refresh_session_pub)
+ *         over the melting request
  * @param num_new_denoms number of entries in @a denom_pubs
  * @param denum_pubs array of public denomination keys for the refresh (?)
  * @param coin_count number of entries in @a coin_public_infos
@@ -100,6 +102,7 @@ TALER_MINT_db_execute_withdraw_sign (struct MHD_Connection *connection,
 int
 TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
                                     const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
+                                    const struct GNUNET_CRYPTO_EddsaSignature *client_signature,
                                     unsigned int num_new_denoms,
                                     struct GNUNET_CRYPTO_rsa_PublicKey *const*denom_pubs,
                                     unsigned int coin_count,
@@ -115,6 +118,8 @@ TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
  * @a kappa sets of private transfer keys should not be revealed.
  *
  * @param connection the MHD connection to handle
+ * @param refresh_session public key of the session
+ * @param commit_client_sig signature of the client over this commitment
  * @param kappa size of x-dimension of @commit_coin and @commit_link arrays
  * @param num_oldcoins size of y-dimension of @commit_coin array
  * @param num_newcoins size of y-dimension of @commit_link array
@@ -129,6 +134,7 @@ TALER_MINT_db_execute_refresh_melt (struct MHD_Connection *connection,
 int
 TALER_MINT_db_execute_refresh_commit (struct MHD_Connection *connection,
                                       const struct GNUNET_CRYPTO_EddsaPublicKey *refresh_session_pub,
+                                      const struct GNUNET_CRYPTO_EddsaSignature *commit_client_sig,
                                       unsigned int kappa,
                                       unsigned int num_oldcoins,
                                       unsigned int num_newcoins,
diff --git a/src/mint/taler-mint-httpd_refresh.c b/src/mint/taler-mint-httpd_refresh.c
index e7497327b..1267ca48b 100644
--- a/src/mint/taler-mint-httpd_refresh.c
+++ b/src/mint/taler-mint-httpd_refresh.c
@@ -242,8 +242,10 @@ handle_refresh_melt_binary (struct MHD_Connection *connection,
                                        "error", "value mismatch");
   }
 
+  /* FIXME: we must also store the signature over the melt! (#3635) */
   return TALER_MINT_db_execute_refresh_melt (connection,
                                              refresh_session_pub,
+                                             NULL, /* FIXME: #3635! */
                                              num_new_denoms,
                                              denom_pubs,
                                              coin_count,
@@ -715,6 +717,7 @@ handle_refresh_commit_json (struct MHD_Connection *connection,
   /* FIXME: we must also store the signature! (#3635) */
   res = TALER_MINT_db_execute_refresh_commit (connection,
                                               refresh_session_pub,
+                                              NULL /* FIXME: 3635! */,
                                               kappa,
                                               num_oldcoins,
                                               num_newcoins,
diff --git a/src/mint/taler-mint-httpd_responses.c b/src/mint/taler-mint-httpd_responses.c
index 892b92ca7..de0736bdc 100644
--- a/src/mint/taler-mint-httpd_responses.c
+++ b/src/mint/taler-mint-httpd_responses.c
@@ -518,43 +518,37 @@ TALER_MINT_reply_withdraw_sign_success (struct MHD_Connection *connection,
 
 
 /**
- * Send a response for "/refresh/melt".
+ * Send a response for "/refresh/melt".  Essentially we sign
+ * over the client's signature and public key, thereby
+ * demonstrating that we accepted all of the client's coins.
  *
  * @param connection the connection to send the response to
- * @param db_conn the database connection to fetch values from
+ * @param signature the client's signature over the melt request
  * @param session_pub the refresh session public key.
  * @return a MHD result code
  */
 int
 TALER_MINT_reply_refresh_melt_success (struct MHD_Connection *connection,
-                                       const struct RefreshSession *session,
+                                       const struct GNUNET_CRYPTO_EddsaSignature *signature,
                                        const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub)
 {
   int ret;
-  json_t *list;
-  struct GNUNET_HashContext *hash_context;
   struct RefreshMeltResponseSignatureBody body;
   struct GNUNET_CRYPTO_EddsaSignature sig;
   json_t *sig_json;
 
-  list = json_array ();
-  hash_context = GNUNET_CRYPTO_hash_context_start ();
   body.purpose.size = htonl (sizeof (struct RefreshMeltResponseSignatureBody));
   body.purpose.purpose = htonl (TALER_SIGNATURE_REFRESH_MELT_RESPONSE);
-  /* FIXME: should we not add something to the hash_context in the meantime? */
-  GNUNET_CRYPTO_hash_context_finish (hash_context,
-                                     &body.melt_response_hash);
+  body.melt_client_signature = *signature;
+  body.session_key = *session_pub;
   TALER_MINT_keys_sign (&body.purpose,
                         &sig);
   sig_json = TALER_JSON_from_sig (&body.purpose, &sig);
-  GNUNET_assert (NULL != sig_json);
   ret = TALER_MINT_reply_json_pack (connection,
                                     MHD_HTTP_OK,
-                                    "{s:o, s:o}",
-                                    "signature", sig_json,
-                                    "blind_session_pubs", list);
+                                    "{s:o}",
+                                    "signature", sig_json);
   json_decref (sig_json);
-  json_decref (list);
   return ret;
 }
 
@@ -570,7 +564,7 @@ TALER_MINT_reply_refresh_melt_success (struct MHD_Connection *connection,
  */
 int
 TALER_MINT_reply_refresh_commit_success (struct MHD_Connection *connection,
-                                         struct RefreshSession *refresh_session)
+                                         const struct RefreshSession *refresh_session)
 {
   struct RefreshCommitResponseSignatureBody body;
   struct GNUNET_CRYPTO_EddsaSignature sig;
diff --git a/src/mint/taler-mint-httpd_responses.h b/src/mint/taler-mint-httpd_responses.h
index ebe1038fd..6cf934094 100644
--- a/src/mint/taler-mint-httpd_responses.h
+++ b/src/mint/taler-mint-httpd_responses.h
@@ -245,20 +245,22 @@ TALER_MINT_reply_withdraw_sign_success (struct MHD_Connection *connection,
  */
 int
 TALER_MINT_reply_refresh_commit_success (struct MHD_Connection *connection,
-                                         struct RefreshSession *refresh_session);
+                                         const struct RefreshSession *refresh_session);
 
 
 /**
- * Send a response for "/refresh/melt".
+ * Send a response for "/refresh/melt". Essentially we sign
+ * over the client's signature and public key, thereby
+ * demonstrating that we accepted all of the client's coins.
  *
  * @param connection the connection to send the response to
- * @param session session data to generate reply from
+ * @param signature the client's signature over the melt request
  * @param session_pub the refresh session public key.
  * @return a MHD result code
  */
 int
 TALER_MINT_reply_refresh_melt_success (struct MHD_Connection *connection,
-                                       const struct RefreshSession *session,
+                                       const struct GNUNET_CRYPTO_EddsaSignature *signature,
                                        const struct GNUNET_CRYPTO_EddsaPublicKey *session_pub);