Enhancing SRAM-Based PUF Reliability Through Machine Learning-Aided Calibration Techniques

Abstract

Static random access memory (SRAM)-based physically unclonable functions (PUFs) utilize unpredictable start-up values (SUVs) for key generation, making them widely adopted in cryptographic systems. This unpredictability in SUVs is accompanied by device noise that escalates with process-voltage–temperature (PVT) variations, resulting in significant deviations from the golden response collected at ambient conditions, thereby increasing the bit-error-rate (BER) of the PUF responses. To reduce this high- $(\geq 15\%)$ BER, either an involved error correcting code (ECC) circuitry with significant overhead is required, or more helper information needs to be generated at varying operating conditions, resulting in increased information leakage. We address this issue by proposing the first reported application of machine learning to recalibrate the responses by predicting the golden responses of the SRAM-based PUF (SRAM-PUF) at different operating conditions with high accuracy. Our recalibration technique is based on a novel collective decision that involves observing the neighborhood cells of the SRAM-PUF, as opposed to the traditional single-cell approach. By leveraging a memory map exhibiting a high correlation in ambient reliability amongst neighboring cells, we indirectly use the physical co-location of SRAM cells to assist neighborhood error prediction. It leads to efficient post-processing for SRAM-PUFs by using helper data generated at ambient conditions only while employing a fixed ECC designed for the same. Subsequently, to justify our claims and validate the efficacy of our proposed methodology, we demonstrate extensive experimentation results over multiple SRAM-PUF instances implemented on the Arduino UNO (an 8-bit microcontroller unit) and its scaled-up version, the Arduino Zero (a 32-bit microcontroller unit) boards, by varying supply voltages from 3.8 to 6.2 V and 7 to 12 V, respectively, and temperature from −25° to 70° C in both cases. Our observations show a vast drop in BER from 17.02% to $\approx 1\%$ . Although worst-case conditions with both voltage and temperature variations at play resulted in a BER of 20%, using our proposed approach reduces it to $\approx 1{\text {-}} 2\%$ , in turn demonstrating the high efficacy of our scheme.