diff --git a/ChangeLog b/ChangeLog
index c7ee8017f..24d9badcf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,2 +1,7 @@
+Tue Jun  7 15:13:46 CEST 2016
+	Adding public key of the exchange that was used to sign replies
+	to applicable callbacks of libtalerexchange. (This will eventually
+	be needed by the merchant's backend.) -CG
+
 Wed Jun  1 17:27:36 CEST 2016
 	Releasing taler-exchange 0.0.0. -CG
diff --git a/src/benchmark/taler-exchange-benchmark.c b/src/benchmark/taler-exchange-benchmark.c
index 7e19d8318..53c49df80 100644
--- a/src/benchmark/taler-exchange-benchmark.c
+++ b/src/benchmark/taler-exchange-benchmark.c
@@ -222,12 +222,14 @@ fail (const char *msg)
  * @param cls closure with the interpreter state
  * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful deposit;
  *                    0 if the exchange's reply is bogus (fails to follow the protocol)
+ * @param exchange_pub public key used by the exchange for signing
  * @param obj the received JSON reply, should be kept as proof (and, in case of errors,
  *            be forwarded to the customer)
  */
 static void
 deposit_cb (void *cls,
             unsigned int http_status,
+            const struct TALER_ExchangePublicKeyP *exchange_pub,
             const json_t *obj)
 {
   unsigned int coin_index = (unsigned int) (long) cls;
diff --git a/src/exchange-lib/exchange_api_deposit.c b/src/exchange-lib/exchange_api_deposit.c
index 4d13febf4..e65684acf 100644
--- a/src/exchange-lib/exchange_api_deposit.c
+++ b/src/exchange-lib/exchange_api_deposit.c
@@ -94,18 +94,20 @@ struct TALER_EXCHANGE_DepositHandle
  *
  * @param dh deposit handle
  * @param json json reply with the signature
+ * @param exchange_pub set to the exchange's public key
  * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
  */
 static int
 verify_deposit_signature_ok (const struct TALER_EXCHANGE_DepositHandle *dh,
-                             const json_t *json)
+                             const json_t *json,
+                             struct TALER_ExchangePublicKeyP *exchange_pub)
 {
   struct TALER_ExchangeSignatureP exchange_sig;
-  struct TALER_ExchangePublicKeyP exchange_pub;
+
   const struct TALER_EXCHANGE_Keys *key_state;
   struct GNUNET_JSON_Specification spec[] = {
     GNUNET_JSON_spec_fixed_auto ("sig", &exchange_sig),
-    GNUNET_JSON_spec_fixed_auto ("pub", &exchange_pub),
+    GNUNET_JSON_spec_fixed_auto ("pub", exchange_pub),
     GNUNET_JSON_spec_end()
   };
 
@@ -120,7 +122,7 @@ verify_deposit_signature_ok (const struct TALER_EXCHANGE_DepositHandle *dh,
   key_state = TALER_EXCHANGE_get_keys (dh->exchange);
   if (GNUNET_OK !=
       TALER_EXCHANGE_test_signing_key (key_state,
-                                   &exchange_pub))
+                                       exchange_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -129,7 +131,7 @@ verify_deposit_signature_ok (const struct TALER_EXCHANGE_DepositHandle *dh,
       GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_CONFIRM_DEPOSIT,
                                   &dh->depconf.purpose,
                                   &exchange_sig.eddsa_signature,
-                                  &exchange_pub.eddsa_pub))
+                                  &exchange_pub->eddsa_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -200,6 +202,8 @@ handle_deposit_finished (void *cls,
                          const json_t *json)
 {
   struct TALER_EXCHANGE_DepositHandle *dh = cls;
+  struct TALER_ExchangePublicKeyP exchange_pub;
+  struct TALER_ExchangePublicKeyP *ep = NULL;
 
   dh->job = NULL;
   switch (response_code)
@@ -209,11 +213,16 @@ handle_deposit_finished (void *cls,
   case MHD_HTTP_OK:
     if (GNUNET_OK !=
         verify_deposit_signature_ok (dh,
-                                     json))
+                                     json,
+                                     &exchange_pub))
     {
       GNUNET_break_op (0);
       response_code = 0;
     }
+    else
+    {
+      ep = &exchange_pub;
+    }
     break;
   case MHD_HTTP_BAD_REQUEST:
     /* This should never happen, either us or the exchange is buggy
@@ -253,6 +262,7 @@ handle_deposit_finished (void *cls,
   }
   dh->cb (dh->cb_cls,
           response_code,
+          ep,
           json);
   TALER_EXCHANGE_deposit_cancel (dh);
 }
diff --git a/src/exchange-lib/exchange_api_deposit_wtid.c b/src/exchange-lib/exchange_api_deposit_wtid.c
index 073ce2b35..66b91413c 100644
--- a/src/exchange-lib/exchange_api_deposit_wtid.c
+++ b/src/exchange-lib/exchange_api_deposit_wtid.c
@@ -84,18 +84,19 @@ struct TALER_EXCHANGE_DepositWtidHandle
  *
  * @param dwh deposit wtid handle
  * @param json json reply with the signature
+ * @param[out] exchange_pub set to the exchange's public key
  * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
  */
 static int
 verify_deposit_wtid_signature_ok (const struct TALER_EXCHANGE_DepositWtidHandle *dwh,
-                                  const json_t *json)
+                                  const json_t *json,
+                                  struct TALER_ExchangePublicKeyP *exchange_pub)
 {
   struct TALER_ExchangeSignatureP exchange_sig;
-  struct TALER_ExchangePublicKeyP exchange_pub;
   const struct TALER_EXCHANGE_Keys *key_state;
   struct GNUNET_JSON_Specification spec[] = {
     GNUNET_JSON_spec_fixed_auto ("exchange_sig", &exchange_sig),
-    GNUNET_JSON_spec_fixed_auto ("exchange_pub", &exchange_pub),
+    GNUNET_JSON_spec_fixed_auto ("exchange_pub", exchange_pub),
     GNUNET_JSON_spec_end()
   };
 
@@ -110,7 +111,7 @@ verify_deposit_wtid_signature_ok (const struct TALER_EXCHANGE_DepositWtidHandle
   key_state = TALER_EXCHANGE_get_keys (dwh->exchange);
   if (GNUNET_OK !=
       TALER_EXCHANGE_test_signing_key (key_state,
-                                       &exchange_pub))
+                                       exchange_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -119,7 +120,7 @@ verify_deposit_wtid_signature_ok (const struct TALER_EXCHANGE_DepositWtidHandle
       GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_CONFIRM_WIRE,
                                   &dwh->depconf.purpose,
                                   &exchange_sig.eddsa_signature,
-                                  &exchange_pub.eddsa_pub))
+                                  &exchange_pub->eddsa_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -146,6 +147,8 @@ handle_deposit_wtid_finished (void *cls,
   struct GNUNET_TIME_Absolute execution_time = GNUNET_TIME_UNIT_FOREVER_ABS;
   const struct TALER_Amount *coin_contribution = NULL;
   struct TALER_Amount coin_contribution_s;
+  struct TALER_ExchangePublicKeyP exchange_pub;
+  struct TALER_ExchangePublicKeyP *ep = NULL;
 
   dwh->job = NULL;
   switch (response_code)
@@ -177,11 +180,16 @@ handle_deposit_wtid_finished (void *cls,
       coin_contribution = &coin_contribution_s;
       if (GNUNET_OK !=
           verify_deposit_wtid_signature_ok (dwh,
-                                            json))
+                                            json,
+                                            &exchange_pub))
       {
         GNUNET_break_op (0);
         response_code = 0;
       }
+      else
+      {
+        ep = &exchange_pub;
+      }
     }
     break;
   case MHD_HTTP_ACCEPTED:
@@ -231,6 +239,7 @@ handle_deposit_wtid_finished (void *cls,
   }
   dwh->cb (dwh->cb_cls,
            response_code,
+           ep,
            json,
            wtid,
            execution_time,
diff --git a/src/exchange-lib/exchange_api_refresh.c b/src/exchange-lib/exchange_api_refresh.c
index 7e207d795..b86e58362 100644
--- a/src/exchange-lib/exchange_api_refresh.c
+++ b/src/exchange-lib/exchange_api_refresh.c
@@ -951,20 +951,21 @@ struct TALER_EXCHANGE_RefreshMeltHandle
  *
  * @param rmh melt handle
  * @param json json reply with the signature
+ * @param[out] exchange_pub public key of the exchange used for the signature
  * @param[out] noreveal_index set to the noreveal index selected by the exchange
  * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
  */
 static int
 verify_refresh_melt_signature_ok (struct TALER_EXCHANGE_RefreshMeltHandle *rmh,
                                   const json_t *json,
+                                  struct TALER_ExchangePublicKeyP *exchange_pub,
                                   uint16_t *noreveal_index)
 {
   struct TALER_ExchangeSignatureP exchange_sig;
-  struct TALER_ExchangePublicKeyP exchange_pub;
   const struct TALER_EXCHANGE_Keys *key_state;
   struct GNUNET_JSON_Specification spec[] = {
     GNUNET_JSON_spec_fixed_auto ("exchange_sig", &exchange_sig),
-    GNUNET_JSON_spec_fixed_auto ("exchange_pub", &exchange_pub),
+    GNUNET_JSON_spec_fixed_auto ("exchange_pub", exchange_pub),
     GNUNET_JSON_spec_uint16 ("noreveal_index", noreveal_index),
     GNUNET_JSON_spec_end()
   };
@@ -983,7 +984,7 @@ verify_refresh_melt_signature_ok (struct TALER_EXCHANGE_RefreshMeltHandle *rmh,
   key_state = TALER_EXCHANGE_get_keys (rmh->exchange);
   if (GNUNET_OK !=
       TALER_EXCHANGE_test_signing_key (key_state,
-                                   &exchange_pub))
+                                       exchange_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -1006,7 +1007,7 @@ verify_refresh_melt_signature_ok (struct TALER_EXCHANGE_RefreshMeltHandle *rmh,
       GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_CONFIRM_MELT,
                                   &confirm.purpose,
                                   &exchange_sig.eddsa_signature,
-                                  &exchange_pub.eddsa_pub))
+                                  &exchange_pub->eddsa_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -1126,6 +1127,7 @@ handle_refresh_melt_finished (void *cls,
 {
   struct TALER_EXCHANGE_RefreshMeltHandle *rmh = cls;
   uint16_t noreveal_index = TALER_CNC_KAPPA; /* invalid value */
+  struct TALER_ExchangePublicKeyP exchange_pub;
 
   rmh->job = NULL;
   switch (response_code)
@@ -1136,6 +1138,7 @@ handle_refresh_melt_finished (void *cls,
     if (GNUNET_OK !=
         verify_refresh_melt_signature_ok (rmh,
                                           json,
+                                          &exchange_pub,
                                           &noreveal_index))
     {
       GNUNET_break_op (0);
@@ -1146,6 +1149,7 @@ handle_refresh_melt_finished (void *cls,
       rmh->melt_cb (rmh->melt_cb_cls,
                     response_code,
                     noreveal_index,
+                    (0 == response_code) ? NULL : &exchange_pub,
                     json);
       rmh->melt_cb = NULL;
     }
@@ -1190,6 +1194,7 @@ handle_refresh_melt_finished (void *cls,
     rmh->melt_cb (rmh->melt_cb_cls,
                   response_code,
                   UINT16_MAX,
+                  NULL,
                   json);
   TALER_EXCHANGE_refresh_melt_cancel (rmh);
 }
@@ -1731,7 +1736,7 @@ TALER_EXCHANGE_refresh_reveal (struct TALER_EXCHANGE_Handle *exchange,
   struct GNUNET_CURL_Context *ctx;
   struct MeltData *md;
   unsigned int j;
-  
+
   GNUNET_assert (GNUNET_YES ==
 		 MAH_handle_is_ready (exchange));
   md = deserialize_melt_data (refresh_data,
diff --git a/src/exchange-lib/exchange_api_refund.c b/src/exchange-lib/exchange_api_refund.c
index d622ddc75..fff03acf9 100644
--- a/src/exchange-lib/exchange_api_refund.c
+++ b/src/exchange-lib/exchange_api_refund.c
@@ -83,18 +83,19 @@ struct TALER_EXCHANGE_RefundHandle
  *
  * @param rh refund handle
  * @param json json reply with the signature
+ * @param[out] exchange_pub set to the exchange's public key
  * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
  */
 static int
 verify_refund_signature_ok (const struct TALER_EXCHANGE_RefundHandle *rh,
-                             const json_t *json)
+                            const json_t *json,
+                            struct TALER_ExchangePublicKeyP *exchange_pub)
 {
   struct TALER_ExchangeSignatureP exchange_sig;
-  struct TALER_ExchangePublicKeyP exchange_pub;
   const struct TALER_EXCHANGE_Keys *key_state;
   struct GNUNET_JSON_Specification spec[] = {
     GNUNET_JSON_spec_fixed_auto ("sig", &exchange_sig),
-    GNUNET_JSON_spec_fixed_auto ("pub", &exchange_pub),
+    GNUNET_JSON_spec_fixed_auto ("pub", exchange_pub),
     GNUNET_JSON_spec_end()
   };
 
@@ -109,7 +110,7 @@ verify_refund_signature_ok (const struct TALER_EXCHANGE_RefundHandle *rh,
   key_state = TALER_EXCHANGE_get_keys (rh->exchange);
   if (GNUNET_OK !=
       TALER_EXCHANGE_test_signing_key (key_state,
-				       &exchange_pub))
+				       exchange_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -118,7 +119,7 @@ verify_refund_signature_ok (const struct TALER_EXCHANGE_RefundHandle *rh,
       GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND,
                                   &rh->depconf.purpose,
                                   &exchange_sig.eddsa_signature,
-                                  &exchange_pub.eddsa_pub))
+                                  &exchange_pub->eddsa_pub))
   {
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
@@ -141,6 +142,8 @@ handle_refund_finished (void *cls,
                         const json_t *json)
 {
   struct TALER_EXCHANGE_RefundHandle *rh = cls;
+  struct TALER_ExchangePublicKeyP exchange_pub;
+  struct TALER_ExchangePublicKeyP *ep = NULL;
 
   rh->job = NULL;
   switch (response_code)
@@ -150,11 +153,16 @@ handle_refund_finished (void *cls,
   case MHD_HTTP_OK:
     if (GNUNET_OK !=
         verify_refund_signature_ok (rh,
-				    json))
+				    json,
+                                    &exchange_pub))
     {
       GNUNET_break_op (0);
       response_code = 0;
     }
+    else
+    {
+      ep = &exchange_pub;
+    }
     break;
   case MHD_HTTP_BAD_REQUEST:
     /* This should never happen, either us or the exchange is buggy
@@ -188,6 +196,7 @@ handle_refund_finished (void *cls,
   }
   rh->cb (rh->cb_cls,
           response_code,
+          ep,
           json);
   TALER_EXCHANGE_refund_cancel (rh);
 }
diff --git a/src/exchange-lib/exchange_api_wire_deposits.c b/src/exchange-lib/exchange_api_wire_deposits.c
index 0601f9b4a..91e2aef7b 100644
--- a/src/exchange-lib/exchange_api_wire_deposits.c
+++ b/src/exchange-lib/exchange_api_wire_deposits.c
@@ -186,6 +186,7 @@ handle_wire_deposits_finished (void *cls,
           break;
         wdh->cb (wdh->cb_cls,
                  response_code,
+                 &exchange_pub,
                  json,
                  &h_wire,
                  &total_amount,
@@ -224,6 +225,7 @@ handle_wire_deposits_finished (void *cls,
   }
   wdh->cb (wdh->cb_cls,
            response_code,
+           NULL,
            json,
            NULL, NULL, 0, NULL);
   TALER_EXCHANGE_wire_deposits_cancel (wdh);
diff --git a/src/exchange-lib/test_exchange_api.c b/src/exchange-lib/test_exchange_api.c
index 75a9cfbd9..83fb0eb32 100644
--- a/src/exchange-lib/test_exchange_api.c
+++ b/src/exchange-lib/test_exchange_api.c
@@ -1028,12 +1028,14 @@ reserve_withdraw_cb (void *cls,
  * @param cls closure with the interpreter state
  * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful deposit;
  *                    0 if the exchange's reply is bogus (fails to follow the protocol)
+ * @param exchange_pub public key the exchange used for signing
  * @param obj the received JSON reply, should be kept as proof (and, in case of errors,
  *            be forwarded to the customer)
  */
 static void
 deposit_cb (void *cls,
             unsigned int http_status,
+            const struct TALER_ExchangePublicKeyP *exchange_pub,
             const json_t *obj)
 {
   struct InterpreterState *is = cls;
@@ -1062,12 +1064,14 @@ deposit_cb (void *cls,
  *                    0 if the exchange's reply is bogus (fails to follow the protocol)
  * @param noreveal_index choice by the exchange in the cut-and-choose protocol,
  *                    UINT16_MAX on error
+ * @param exchange_pub public key the exchange used for signing
  * @param full_response full response from the exchange (for logging, in case of errors)
  */
 static void
 melt_cb (void *cls,
          unsigned int http_status,
          uint16_t noreveal_index,
+         const struct TALER_ExchangePublicKeyP *exchange_pub,
          const json_t *full_response)
 {
   struct InterpreterState *is = cls;
@@ -1388,6 +1392,7 @@ wire_cb (void *cls,
  *
  * @param cls closure
  * @param http_status HTTP status code we got, 0 on exchange protocol violation
+ * @param exchange_pub public key the exchange used for signing
  * @param json original json reply (may include signatures, those have then been
  *        validated already)
  * @param wtid extracted wire transfer identifier, or NULL if the exchange could
@@ -1400,6 +1405,7 @@ wire_cb (void *cls,
 static void
 wire_deposits_cb (void *cls,
                   unsigned int http_status,
+                  const struct TALER_ExchangePublicKeyP *exchange_pub,
                   const json_t *json,
                   const struct GNUNET_HashCode *h_wire,
                   const struct TALER_Amount *total_amount,
@@ -1515,6 +1521,7 @@ wire_deposits_cb (void *cls,
  *
  * @param cls closure
  * @param http_status HTTP status code we got, 0 on exchange protocol violation
+ * @param exchange_pub public key the exchange used for signing
  * @param json original json reply (may include signatures, those have then been
  *        validated already)
  * @param wtid wire transfer identifier used by the exchange, NULL if exchange did not
@@ -1527,6 +1534,7 @@ wire_deposits_cb (void *cls,
 static void
 deposit_wtid_cb (void *cls,
                  unsigned int http_status,
+                 const struct TALER_ExchangePublicKeyP *exchange_pub,
                  const json_t *json,
                  const struct TALER_WireTransferIdentifierRawP *wtid,
                  struct GNUNET_TIME_Absolute execution_time,
@@ -1580,12 +1588,14 @@ deposit_wtid_cb (void *cls,
  * @param cls closure
  * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful deposit;
  *                    0 if the exchange's reply is bogus (fails to follow the protocol)
+ * @param exchange_pub public key the exchange used for signing @a obj
  * @param obj the received JSON reply, should be kept as proof (and, in particular,
  *            be forwarded to the customer)
  */
 static void
 refund_cb (void *cls,
            unsigned int http_status,
+           const struct TALER_ExchangePublicKeyP *exchange_pub,
            const json_t *obj)
 {
   struct InterpreterState *is = cls;
diff --git a/src/include/taler_exchange_service.h b/src/include/taler_exchange_service.h
index e65a9faee..5f79b9bee 100644
--- a/src/include/taler_exchange_service.h
+++ b/src/include/taler_exchange_service.h
@@ -416,12 +416,14 @@ struct TALER_EXCHANGE_DepositHandle;
  * @param cls closure
  * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful deposit;
  *                    0 if the exchange's reply is bogus (fails to follow the protocol)
+ * @param sign_key exchange key used to sign @a obj, or NULL
  * @param obj the received JSON reply, should be kept as proof (and, in case of errors,
  *            be forwarded to the customer)
  */
 typedef void
 (*TALER_EXCHANGE_DepositResultCallback) (void *cls,
                                          unsigned int http_status,
+                                         const struct TALER_ExchangePublicKeyP *sign_key,
                                          const json_t *obj);
 
 
@@ -502,12 +504,14 @@ struct TALER_EXCHANGE_RefundHandle;
  * @param cls closure
  * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful deposit;
  *                    0 if the exchange's reply is bogus (fails to follow the protocol)
+ * @param sign_key exchange key used to sign @a obj, or NULL
  * @param obj the received JSON reply, should be kept as proof (and, in particular,
  *            be forwarded to the customer)
  */
 typedef void
 (*TALER_EXCHANGE_RefundResultCallback) (void *cls,
 					unsigned int http_status,
+                                        const struct TALER_ExchangePublicKeyP *sign_key,
 					const json_t *obj);
 
 
@@ -833,12 +837,14 @@ struct TALER_EXCHANGE_RefreshMeltHandle;
  *                    0 if the exchange's reply is bogus (fails to follow the protocol)
  * @param noreveal_index choice by the exchange in the cut-and-choose protocol,
  *                    UINT16_MAX on error
+ * @param sign_key exchange key used to sign @a full_response, or NULL
  * @param full_response full response from the exchange (for logging, in case of errors)
  */
 typedef void
 (*TALER_EXCHANGE_RefreshMeltCallback) (void *cls,
                                        unsigned int http_status,
                                        uint16_t noreveal_index,
+                                       const struct TALER_ExchangePublicKeyP *sign_key,
                                        const json_t *full_response);
 
 
@@ -1135,6 +1141,7 @@ struct TALER_WireDepositDetails
  *
  * @param cls closure
  * @param http_status HTTP status code we got, 0 on exchange protocol violation
+ * @param sign_key exchange key used to sign @a json, or NULL
  * @param json original json reply (may include signatures, those have then been
  *        validated already)
  * @param wtid extracted wire transfer identifier, or NULL if the exchange could
@@ -1147,6 +1154,7 @@ struct TALER_WireDepositDetails
 typedef void
 (*TALER_EXCHANGE_WireDepositsCallback)(void *cls,
                                        unsigned int http_status,
+                                       const struct TALER_ExchangePublicKeyP *sign_key,
                                        const json_t *json,
                                        const struct GNUNET_HashCode *h_wire,
                                        const struct TALER_Amount *total_amount,
@@ -1195,6 +1203,7 @@ struct TALER_EXCHANGE_DepositWtidHandle;
  *
  * @param cls closure
  * @param http_status HTTP status code we got, 0 on exchange protocol violation
+ * @param sign_key exchange key used to sign @a json, or NULL
  * @param json original json reply (may include signatures, those have then been
  *        validated already)
  * @param wtid wire transfer identifier used by the exchange, NULL if exchange did not
@@ -1205,6 +1214,7 @@ struct TALER_EXCHANGE_DepositWtidHandle;
 typedef void
 (*TALER_EXCHANGE_DepositWtidCallback)(void *cls,
                                       unsigned int http_status,
+                                      const struct TALER_ExchangePublicKeyP *sign_key,
                                       const json_t *json,
                                       const struct TALER_WireTransferIdentifierRawP *wtid,
                                       struct GNUNET_TIME_Absolute execution_time,