Enlarging Reliable Pairs via Inter-Distance Offset for a PUF Entropy-Boosting Algorithm

Abstract

Physically Unclonable Functions (PUFs) are emerging hardware security primitives that leverage random variations during chip fabrication to generate unique secrets. The amount of random secrets that can be extracted from a limited number of physical PUF components can be measured by entropy bits. Existing strategies of pairing or grouping N RO-PUF elements have an entropy upper bound limited by log2(N!) or O(N•log2(N)). A recently proposed entropy boosting technique [9] improves the entropy bits to be quadratically large at N(N-1)/2 or O(N^2), significantly improved the RO-PUF hardware utilization efficiency in generating secrets. However, the improved amount of random secrets comes at the cost of discarding a large portion of unreliable bits. In this paper, we propose an "Inter-Distance Offset (IDO)" technique that converts those unreliable pairs to be reliable by adjusting the pair inter-distance to an appropriate range. Theoretical analysis of the ratio of converted unreliable bits is provided along with experimental validations. Experimental evaluations on reliability, Entropy and reliability tradeoffs are given using real RO PUF datasets in [10]. Information leakage is analyzed and evaluated using PUF datasets to identify those offset ranges that leak no information. The proposed technique improves the portion of reliable (quadratically large) entropy bits by 20% and 100% respectively for different offset ranges. Hardware implementation on FPGAs demonstrates that the proposed technique is lightweight in implementation and runtime.