On-Line Method to Limit Unreliability and Bit-Aliasing in RO-PUF

Physical Unclonable Functions (PUFs) allow generating an intrinsic signature in electronic device thanks to process variability. One of the most researched solutions for PUF implementation is the Ring Oscillator PUF (RO-PUF). This solution is based on the comparison of the frequency of 2 identically designed ROs in an IC. Ideally these 2 ROs would have the same frequency, however this in not the case in reality due to fabrication-induced process variability. By measuring and comparing their actual frequency, a 1-bit PUF response is generated. The RO-PUF has been demonstrated to satisfy the principal randomness requirements (uniformity and uniqueness) but it suffers from problems such as bitaliasing and unrepeatability (i.e. low reliability). In this paper we perform a thorough analysis of RO-PUF bitaliasing and reliability and propose a methodology for its analytical estimation based on the variability profile of the underling technology.