ReaderPrint: A Universal Method for RFID Readers Authentication Based on Impedance Mismatch

Unauthorized access attack has always been a critical problem in RFID systems since any illegitimate reader can conduct access commands on tags without authorization and leave no trace. Past solutions for reader authentication require either modifications on EPC-global Gen2 protocol, which are inapplicable to existing infrastructures, or numerous extra customized devices as communication monitors, which incur high overhead. In this paper, we present a universal, low-cost and effective system to authenticate RFID readers, namely ReaderPrint, which only requires an extra passive tag array and is fully compatible with Gen2 protocol. The key insight behind ReaderPrint is that the impedance mismatch degrees (IMD) of different reader antennas across channels are distinguishable. We verify this mechanism through empirical studies using vector network analyzer and further propose two brand-new forms of hardware fingerprints, i.e., IMD-induced transmission power attenuation (ITPA) and phase shifts (IPS) across channels to quantify the IMD. Besides, to address the negative impacts of environmental changes, well-refined fingerprint matching algorithms are designed accordingly. We implement a prototype of ReaderPrint and evaluate it on 96 different readers in three indoor scenarios. Experimental results show that ReaderPrint can achieve fairly high authentication accuracy of up to 97.2%, regardless of environmental or device conditions.