A Configurable Ring-Oscillator-Based PUF for Xilinx FPGAs

Devadas has first proposed the notion of Silicon Physical Unclonable Function (sPUF), which takes advantage of delay variations of wires and gates. A Ring-Oscillator-Based PUF (RO PUF) is one possible implementation of an sPUF. One disadvantage of RO PUFs is that they require one pair of ring oscillators per bit of output. Therefore, in order to collect enough output bits for a safe security level, a large number of ring oscillators is needed. Configurable PUFs may help solving this problem. In 2009, Maiti introduced a configurable RO PUF to improve RO PUF reliability, where each RO is implemented in one configurable logic block (CLB) by using lookup tables (LUTs) and dedicated multiplexers. In this paper we analyze Maiti's configurable RO PUFs and propose improvements to generate more output bits, by utilizing latches as well as the resource mentioned above. Experimental results demonstrate that our improved method outputs more bits than Maiti's configurable RO PUFs and the original RO PUFs, while using the same amount of area.