Using Polynomial Interpolation for Reproducing Multi-Valued Responses of Physical Unclonable Functions on FPGAs

A well-known problem when using Physical Unclonable Functions for secret key generation and storage, is the instability of PUF responses due to environmental conditions like temperature variations. Using Ring Oscillator PUFs (RO-PUFs), a response bit is usually derived based on the comparison of a RO frequency with either a threshold or another RO frequency. Especially for multi-valued PUFs it is of importance to decrease RO frequency errors before digitization. Otherwise, these errors can result in a huge amount of bit-flips. To counteract environmental influence in the reproduction phase, we propose to map a frequency, which might be remeasured under a temperature condition different from initialization, closer to the initial frequency by using a method based on polynomial interpolation. This paper presents how such an approach can decrease errors in multi-valued responses and evaluates the error based on the used polynomial order and thus complexity.