The present disclosure relates to an electronic device comprising: a debug port (112) providing a communications interface for debugging purposes; one or more processing unit access ports (AP1, APn); an authentication interface circuit (110) configured to authenticate the external device (200); and a further access port (APO) coupled between the debug port (112) and the authentication interface circuit (110), the further access port (APO) being configured to be in an open state in which communications are relayed between the debug port and the authentication interface circuit (110), the authentication interface circuit (110) comprising registers (202) including a status register (302) capable of being read by the external device (200) via the debug port (112) and the further access port (APO), the status register being configured to store an indication of the open or closed state of each of the processing unit access ports (AP1, APn) .