Robust RO-PUFs with enhanced challenge-response set

Ring Oscillator (RO) Physical Unclonable Functions (PUFs) are one of the best performing PUF types among various structures presented in the literature. The robustness problem of conventional RO-PUFs, that arises due to the noisy nature of ROs, is overcome with the Ordering-Based RO-PUFs presented recently. However, the shortage of usable Challenge-Response Pairs (CRPs) still limits the use of RO-PUFs, especially for authentication protocols in security systems. For a fully secure authentication based on PUF circuits, CRPs should be independent from each other and a full read-out of all CRPs should be infeasible. In conventional RO-PUFs, the number of possible CRPs is very limited and in ordering based RO-PUFs, the CRP concept is not defined at all. In this work, two methods based on RO selection is proposed for generating enhanced CRP set in ordering based RO-PUFs and their performance is analyzed in terms of area efficiency and uniqueness. With the proposed methods, robust, area and power efficient RO-PUFs with a very high number of CRPs are available for use in many security applications.