diff --git a/src/knx/device_object.cpp b/src/knx/device_object.cpp
index 2930b8e..e033f7f 100644
--- a/src/knx/device_object.cpp
+++ b/src/knx/device_object.cpp
@@ -9,7 +9,9 @@
 
 DeviceObject::DeviceObject()
 {
-    //Default to KNXA (0xFA)
+    // Default to KNXA (0xFA)
+    // Note: ETS does not accept a SN 00FA00000000 in data secure mode.
+    //       ETS says that 00FA00000000 looks "suspicious" in the log file.
     uint8_t serialNumber[] = {0x00, 0xFA, 0x01, 0x02, 0x03, 0x04};
     uint8_t hardwareType[] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
 
diff --git a/src/knx/secure_application_layer.cpp b/src/knx/secure_application_layer.cpp
index 4211ef8..bc33538 100644
--- a/src/knx/secure_application_layer.cpp
+++ b/src/knx/secure_application_layer.cpp
@@ -8,8 +8,12 @@
 #include "bau.h"
 #include "string.h"
 #include "bits.h"
+
+// Select what cipher modes to include. We need AES128-CBC and AES128-CTR modes.
+#define CBC 1
+#define CTR 1
+#define ECB 0
 #include "aes.hpp"
-#include <stdio.h>
 
 const uint8_t SecureDataPdu = 0;
 const uint8_t SecureSyncRequest = 2;