Aging resilient ring oscillators for reliable Physically Unclonable Functions (PUFs)

Physically Unclonable Functions (PUFs) are a promising low-cost solution for authentication and key generation in cryptosystems. However, it has been shown in the literature that, due to aging mechanisms such as Bias Temperature Instability (BTI), PUFs may no longer be able to generate correct outputs after a certain lifetime, thus becoming unreliable. In order to mitigate this problem, we present a novel ring oscillator (RO) based PUF design that is highly robust against BTI degradation. It will be hereinafter referred to as Highly BTI Resilient RO – HBTIRRO. In particular, we present two possible implementations for our HBTIRRO, each one corresponding to a different tradeoff among robustness against BTI, power consumption and area occupation. We compare the effectiveness and costs of the two proposed HBTIRRO implementations to those of a standard RO, and of the most recent alternative solution presented in the literature. We show that, one of our HBTIRRO implementation features the highest robustness against BTI, enabling a reduction in frequency degradation of 57.2 % and 34.6 % with respect to the standard RO and the recent alternate solution, respectively, while requiring a similar area and some increase in power consumption. The other implementation of our HBTIRRO features a very low cost in terms of area occupation, while featuring a robustness against BTI that is comparable to the most recent alternative solution presented in the literature. Moreover, we show that, compared to both the considered alternative solutions, our two HBTIRRO implementations present similar or higher (i.e., better) values in the three classical PUF figures of merit (namely, uniqueness, reliability and randomness), and the highest standard deviation in the statistical distribution of the oscillation frequency resulting from process variation. Therefore, our two proposed HBTIRRO offer also a more secure implementation for RO-based PUF than the compared solutions.