Ring oscillators based physical unclonable functions (RO PUF) is a classical FPGA-friendly Weak PUF structure with better performance, but it can only produce limited challenge-response pairs (CRPs) with lack reliability. This paper proposes a new Strong RO PUF structure with highly reliability and enhanced challenge response pairs resilient to modeling attacks. It divides 2 RO rings into two groups and compares their cumulative frequency under the control of the -bit challenge to generate 2

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... s. The reliability of each bit PUF responses is tested and marked in real time, and a highly reliable anti-fuse PUF structure is introduced to fuzzify the CRPs. FPGA verification results show that this bit self-test RO PUF (BST-RPUF) has a uniformity of 46.78% and a uniqueness of 48.64%, and the bit error rate of the marked reliable responses can be less than 10 −9 . In order to extend the challenge response space of RO PUF, a new RO PUF structure is proposed in this paper, which is shown in Fig. 1 . This Strong PUF generates 2 challenge response pairs by dividing the frequencies of 2 RO rings into two groups and then compare the accumulated