In this chapter, we report a novel hardware method for generating authentication keys by utilizing a physically unclonable function (PUF) of a perimeter-gated single-photon avalanche diode (pg-SPAD) imager. We tested three 64 \(\times \) 64 pg-SPAD imagers over a wide temperature range above the room temperature, and demonstrated that temperature-resilient authentication keys can be generated with quantifiable difference. To achieve that, we used the imager’s spatial dark count variation as a PUF, i.e., as a means to generate unique hardware fingerprints on which the keys are based. Without applying any complex key generation algorithm or any temperature compensation technique, we obtained approximately \(0.1\) in average normalized Normalized Hamming distance (NHD) Hamming distance (nHD) between intra-chip keys generated from the same challenge. Average nHD between intra-chip keys generated from different challenges and inter-chip keys generated with the same challenge also showed sufficient differentiation, i.e., an average nHD of approximately \(0.5\) , close to the ideal value. Leveraging the active noise modulation capability of pg-SPADs, we have also demonstrated a technique to increase the number of challenge-response pairs (CRPs). We also explored pg-SPADs as random binary sequence generators, which find application as hardware security primitives. This chapter is largely based on its related publications (Sajal et al., all in 2023) (Sajal and Dandin (2023) Concealable physically unclonable functions and key generation using a geiger mode imager. In: 2023 IEEE International Symposium on Circuits and Systems (ISCAS). IEEE, pp 1–5; Sajal and Dandin (2023) Challenge-response pair space enhancement for imager-based physically unclonable functions. In: 2023 IEEE 66th International Midwest Symposium on Circuits and Systems (MWSCAS), pp 217–221; Sajal and Dandin (2024) IEEE Trans Circuits Syst II: Express Briefs 71(3):1586–1590), Copyright, IEEE.