SecNFC: Securing inductively-coupled Near Field Communication at physical layer

Near Field Communication (NFC) is widely used today in many useful applications, such as contactless payment, identification, and file exchange. Due to the limitations on computation, power, and cost of NFC devices, NFC systems are often lack of encryption or weakly encrypted, leaving them exposed to security attacks. One solution for this problem is to install strong cryptographic protocols on NFC devices. However, it involves upgrading and revoking deployed NFC devices, which is costly and impractical. Moreover, encryption algorithms are usually considered expensive for resource constrained NFC devices in terms of computation overhead and energy consumption. In this paper, aiming at securing NFC from eavesdropping at physical layer, we propose SecNFC, a solution that changes the signals on the initiators to hide the communications, but does not require any changes to the targets. In this work, for the first time, we address a practical problem of synchronization offset between two NFC terminals, which can be exploited by an eavesdropper to compromise the transmitted bits. SecNFC takes into consideration the synchronization offset and solves the challenge by introducing blocking signals around the transition point when the target switches load between on and off. With this solution, even with the existence of synchronization offset, eavesdroppers cannot extract any bit information from eavesdropping. We conduct extensive simulations to evaluate the performance of SecNFC. We also build a testbed based on USRP software defined radio and off-the-shelf NFC tags to evaluate SecNFC in a real-world environment. Both simulation and experimental results show that SecNFC can efficiently prevent NFC from eavesdropping with a slight and tolerable decoding performance degradation at the initiator.