Improving the Quality of Ring Oscillator PUFs on FPGAs

Physical Unclonable Functions (PUFs) based on Ring Oscillators (ROs) are a promising primitive for FPGA security. However, the quality of their implementation depends on several design parameters. In this paper, we show that ring oscillator frequencies strongly depend on surrounding logic. Based on these findings, we propose a strategy for improving the quality of RO PUF designs by placing and comparing ROs in a chain-like structure. We also show that an increased RO runtime and RO disabling has a clear positive effect on the quality of a RO PUF. We implemented a RO PUF key generation system on an FPGA using our design strategy. Our results clearly indicate that our proposed design strategy can significantly improve the quality of a RO PUF implementation.