Analysis and Enhancement of Ring Oscillators Based Physical Unclonable Functions in FPGAs

The paper analyzes and proposes some enhancements of Ring Oscillator based Physical Unclonable Functions (PUFs) that are used to extract a unique signature of an integrated circuit in order to be used for device authentication purposes and/or key generation. We analyze in more details the concept developed by Suh et al. in 2007. Contrary to what authors claim, we show that the designer of the Ring Oscillator PUFs implemented in FPGAs needs precise control of placement and routing in order to get unique responses and repeatable results for each individual device, especially when the rest of the reconfigurable device should remain up gradable. One main disadvantage of the original design is its high power consumption. We propose a simple improvement that reduces the consumption of the PUF published by Suh et al. by up to 96.6%. Last but not least, we point out that ring oscillators significantly influence one another and can even be locked. This questions the reliability of the PUF and should be taken into account during the design.