An efficient and stable composed entropy extraction method for FPGA-based RO PUF

Abstract

The physical unclonable function (PUF) of the ring oscillator (RO) is applied to key generation and other fields due to its excellent physical characteristics and simple implementation on FPGA. However, the traditional frequency comparison method uses the sign bit of two ROs’ frequency difference which can only extract one bit of entropy, and the bit error rate (BER) of the response always exceeds 1% without error correction schemes. In this paper, we designed RO based on FPGA LUT unit in a single CLB, and proposed a method of getting difference after summing the first-order frequency difference, which we called Difference on Summed Difference (DSD) method. According to experimental measurement results, the DSD method can achieve the BER of 0.39%, and the uniqueness of 50.30%. In order to obtain more entropy, we proposed a composed entropy extraction method which combined the DSD method with the existing higher-order difference method. Experimental results demonstrated that the composed method totally obtained 32-bit response with the BER of 0.84% and the uniqueness of 49.15% while the BER of the existing higher-order difference method is 1.85%.