Detecting Clocking Attack in Contactless Access Control Systems

Contactless access control systems (referred to as CACS) exchange information between contactless smart cards and readers. They have been widely employed in our daily life. To ensure the correctness, both sides of the communication need to be synchronized by embedding synchronization clock into data. However, the clock can be speeded up by attacker to shorten the processing time of demodulating received signals and reply in advance. To address this problem, in this paper, we propose the first general cross-layer scheme to detect clocking attack in CACS by combing data integrity protection and physical layer implementation. Smart cards feed back check-sum of synchronization clock by shifting the response signal's frequency instead of transmitting extra bits. Hence, attacker can't modify the feedback checksum. Reader can use checksum to check whether communication is under clocking attack or not. We show the proposed scheme can be implemented in contactless smart cards and conduct extensive experiments on existing computational radio frequency identification (RFID) tags and reader.