Challenge-Response Pair Space Enhancement for Imager-Based Physically Unclonable Functions.

We report a novel method for increasing the number of challenge-response pairs (CRPs) of a physically unclonable function (PUF) implemented using a 64 × 64 perimeter-gated single-photon avalanche diode (pg-SPAD) imager fabricated in a 0.35 µm CMOS process. We found that reconfiguring the PUF using perimeter gating enhanced the CRP space while maintaining temperature resiliency. We used the imagers' spatial dark count variation as the PUF and pixel addresses as an explicit challenge. Further, we used a set of perimeter gate voltages as an implicit challenge to alter the pixels' dark count response depending on their positions in the explicit challenge vector. The resulting variation in dark count response for different permutations of the same set of pixels yielded an increase in the size of the space of possible CRPs that can be used with the PUF.