On the Behavior of a Wide Set of Oscillators: PUFs or TRNGs?

Abstract:
In this paper, a generic structure that includes previously studied oscillators (such as ring oscillators) as well as many other new oscillators has been studied to evaluate their suitability as TRNGs or PUFs. The studied structure consists of an array of n combinational logic blocks in a loop where the output of each block is a function of the output of the previous block and the feedback signal. To perform this analysis, a novel implementation has been proposed where, using a single implementation, we can make each block perform any possible 2-input function using some external configuration inputs. By analyzing all possible configurations of size equal or smaller than 7, we have concluded that none of them behave as an ideal TRNG and that ring oscillators present a behavior closest to the ideal one. Regarding their suitability for being used as PUFs, none of the polynomials have shown an ideal behavior but some of them present a higher reproducibility than the classical ring-oscillator PUF. Furthermore, we have noticed that, by increasing the length, we can find configurations with better PUF properties.