Suitability of Generalized GAROs on FPGAs as PUFs or TRNGs Considering Spatial Correlations

Abstract

In the last years, guaranteeing the security in IoT communications has become an essential task. In this paper, the bias of a wide set of oscillators has been studied to determine their suitability as both True Random Number Generators (TRNGs) and Physically Unclonable Functions (PUFs). For this purpose, a generic configurable structure has been proposed and implemented in an FPGA. With this implementation, by introducing some external signals it is possible to configure the system in different oscillator topologies. This way, we have managed to analyze 2730 oscillators composed by 7 Lookup Tables (LUTs) without having to resynthesize the code each time. The performed analysis has included conventional ring oscillators, Galois ring oscillators and newly proposed oscillator topologies. From this analysis we have concluded that none of these oscillators behave as an ideal TRNG but ring oscillators present the closest to an ideal behavior. Regarding their suitability as PUFs, some of the newly proposed oscillators in this paper present a high reproducibility, higher than that of conventional ring oscillator PUF (RO-PUF) and a high uniqueness. Furthermore, we have noticed that both their reproducibility and their uniqueness tend to improve when increasing the length of the oscillators, which opens the possibility of finding new oscillators with even better properties by studying oscillators of bigger lengths. Finally, by studying the spatial correlation of the bias of these oscillators, we have observed that they present a much lower spatial correlation compared to the ring oscillators, which opens the possibility of using these oscillators in PUF architectures that use more comparisons than typical RO-PUFs.