Exploiting Switching of Transistors in Digital Electronics for RFID Tag Design

Existing analog-signal side-channels, such as EM emanations, are a consequence of current-flow changes that are dependent on activity inside electronic circuits. In this paper, we introduce a new class of side-channels that is a consequence of impedance changes in switching circuits, and we refer to it as an impedance-based side-channel. One example of such a side-channel is when digital logic activity causes incoming EM signals to be modulated as they are reflected (backscattered), at frequencies that depend on both the incoming EM signal and the circuit activity. This can cause EM interference or leakage of sensitive information, but it can also be leveraged for radiofrequency identification (RFID) tag design. In this paper, we first introduce a new class of side-channels that is a consequence of impedance differences in switching circuits, and we refer to it as an impedance-based side-channel. Then, we demonstrate that the impedance difference between transistor gates in the high-state and in the low-state changes the radar cross section and modulates the backscattered signal. Furthermore, we have investigated the possibility of implementing the proposed RFID on ASIC for signal enhancement. Finally, we propose a digital circuit that can be used as a semi-passive RFID tag. To illustrate the adaptability of the proposed RFID, we have designed a variety of RFID applications across carrier frequencies at 5.8 GHz, 17.46 GHz, and 26.5 GHz to demonstrate the flexible carrier frequency selection and bit configuration.