An IO-Efficient SC PUF Used for Protecting Chips from PCB-level Attacks

Abstract: This paper proposes a chip–PCB hybrid switched-capacitor (SC) physical unclonable function (PUF) to detect PCB-level attacks using only two, or even a single, sense IO. An on-chip capacitor array is employed to compensate for and balance the capacitances between the two sense IOs (or between one sense IO and one on-chip capacitor). The sense IOs then form a sense SC circuit, while two on-chip capacitors constitute a reference SC circuit to which a small threshold capacitor is further introduced. An unchanged relationship between the output voltages of the sense and reference SC circuits under variation of the threshold capacitor in the reference SC circuit indicates that the capacitance mismatch between the two sense IOs (or between a sense IO and an on-chip capacitor) exceeds a predefined threshold. This reflects a significant change in the capacitance of the sense IO, potentially caused by PCB-level desoldering, resoldering, or probing attacks. Furthermore, the two capacitors in the reference SC circuit are partitioned into multiple sub-capacitors to form multiple sub-reference SC circuits. Together with the sense SC circuit, these structures constitute multiple SC PUF units that generate PUF keys strongly correlated with the parasitic capacitance of the sense IOs. The proposed anti–PCB-level attack scheme is fabricated in a 180nm CMOS process for silicon verification. Measurement results demonstrate that the SC PUF output keys effectively reflect IO capacitance variations caused by PCB-level attacks, thereby providing reliable protection for the chip against such attacks.

Keywords: SC, PUF, PCB-level attack, sense IO, invasive attack

Recommended citation: Zhang M, Song M, Zhang Z, et al. An IO-Efficient SC PUF Used for Protecting Chips From PCB-Level Attacks[J]. IEEE Transactions on Circuits and Systems I: Regular Papers, Early Access.
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