diff --git a/app/services/scanner.py b/app/services/scanner.py
index 3c7df49..58be59a 100644
--- a/app/services/scanner.py
+++ b/app/services/scanner.py
@@ -49,7 +49,7 @@ def getCardService(timeout: int = 10):
         cardservice = cardrequest.waitforcard()
     except CardRequestTimeoutException:
         logger.error("No tag detected within the timeout.")
-        raise Exception
+        raise Exception("No tag detected within the timeout.")
     return cardservice
 
 def DeleteCard():
@@ -95,26 +95,14 @@ def WriteNewCard():
         from app.main import scanner as scannerThread
         scannerThread.stop()
 
-        cardtype = AnyCardType()
-        cardrequest = CardRequest(timeout=10, cardType=cardtype)
-        print("Please present DESfire tag...")
-        try:
-            cardservice = cardrequest.waitforcard()
-        except CardRequestTimeoutException:
-            logger.error("No tag detected within the timeout.")
-            return None
-
+        cardservice = getCardService(20)
         cardservice.connection.connect()
 
-        # Create Desfire object
         desfire = DESFire(PCSCDevice(cardservice.connection.component))
 
         # Create Key objects
-        AES_NULL_KEY_DATA = "00" * 16
-        aes_keysettings = KeySettings(
-            key_type=DESFireKeyType.DF_KEY_AES,
-        )
-        aes_null_key = DESFireKey(aes_keysettings, AES_NULL_KEY_DATA)
+        aes_keysettings = KeySettings(key_type=DESFireKeyType.DF_KEY_AES)
+        aes_null_key = DESFireKey(aes_keysettings, "00" * 16)
         aes_master_key = DESFireKey(aes_keysettings, MIFARE_APP_MASTER_KEY)
         keysetting = desfire.get_key_setting()
         desKey = DESFireKey(keysetting, "00" * 8)
@@ -151,15 +139,15 @@ def WriteNewCard():
 
         # Select application
         desfire.select_application(MIFARE_APP_ID)
-        #Auth again as 0key
-        aes_null_auth_key = DESFireKey(aes_keysettings, AES_NULL_KEY_DATA)
-        desfire.authenticate(0x0, aes_null_auth_key)
-        # Authenticate with AES key, as this has been set as the default key
-        aes_app_mk = DESFireKey(aes_keysettings, MIFARE_APP_MASTER_KEY)
-        desfire.change_key(0x0, aes_null_key, aes_app_mk, 0x1)
+
+        #recreate key object
+        desfire.authenticate(0x0, aes_null_key)
+        desfire.change_key(0x0, aes_null_key, aes_master_key, 0x1)
 
         print("new key auth")
-        desfire.authenticate(0x0, aes_app_mk)
+        desfire.authenticate(0x0, aes_master_key)
+
+        aes_null_key = DESFireKey(aes_keysettings, "00" * 16)
 
         #generate div data
         diversification_data = [0x01] + uid + get_list(MIFARE_APP_ID) + get_list(MIFARE_SYS_ID)