ACRO-PUF: A Low-power, Reliable and Aging-Resilient Current Starved Inverter-Based Ring Oscillator Physical Unclonable Function

Ring oscillator (RO)-based physical unclonable function (PUF) is an emerging hardware security primitive but its response reproducibility is susceptible to changes in operating conditions and device aging. Present solutions to increase RO PUF reliability either incur large hardware overhead or require sophisticated RO selection algorithm. This paper exploits the optimal biasing of current starved (CS) inverter for the design of RO PUF with very high reliability against both temperature and voltage variations. With two additional transistors, the CS inverter can be adaptively biased at idle time and in active mode to significantly reduce the overall stress, making the proposed CS RO PUF robust against both environmental condition variations and aging. Without using error correction code, the reliability is further improved by a low-cost proximity detector circuit with a small sacrifice on challenge-response pair space. The correlation between successive RO pairs of different input challenges is also broken by an irregular clocking of the linear feedback shift register used to encipher the input challenges. Based on Monte Carlo simulation in TSMC 40-nm CMOS process, the reliability of native PUF responses has been raised substantially from 89.78% for the regular RO PUF to 95.88% for the proposed CS RO PUF over a broad temperature range of -40 degrees C to 120 degrees C and +/- 20% supply variation. With the proximity detector, the proposed Aging-resistant Current-starved RO (ACRO) PUF can attain 100% reliability statistically by discarding 34.47% fewer challenge-response pairs than the regular RO PUF. It is also similar to 3.7x more aging resilient than existing aging-resilient RO PUFs with similar to 2.38x lower power dissipation.