CapPUF: A Tamper-Resistant PUF Utilizing I/O Capacitances for IoT Nodes

We introduce CapPUF, a Physical Unclonable Function (PUF) that utilizes parasitic capacitances of I/O pins to generate unique identifiers (IDs) for Integrated Circuits (ICs) and the IoT nodes encompassing them. CapPUF is based on the observation that the I/O capacitance of each IC is unique and varies from one IC to another. It utilizes the capacitive sensing hardware commonly found in modern microcontroller ICs with touch-sensing capabilities, to measure I/O capacitances and generate the PUF ID. CapPUF also offers tamper resistance. It is thus challenging to reverse-engineer the PUF ID through physical probing of the I/Os. We evaluated CapPUF using 30 different PSoC-5 microcontroller ICs from Infineon Technologies. By measuring the parasitic capacitances of 18 I/Os, CapPUF generated a 153-bit PUF ID for each IC. Performance evaluation based on standard PUF metrics yielded promising results, including a reliability of 99.79%, uniqueness of 43.11%, and uniformity of 44.64%. Testing across various temperature and voltage settings demonstrated the PUF’s stability. Additionally, we demonstrated CapPUF’s resistance to probing attacks.