Selective Up‐ and Down‐Conversion Luminescence for Nonlinear Expansion of Unclonable Parameter Space

Abstract Optical physical unclonable functions (PUFs) have attracted considerable attention as an immediately exploitable cryptographic primitive for high‐level hardware security attributed to their potential for implementing a large parameter space through the incorporation of robust optical phenomena. However, previous optical PUFs primarily relied on linear and single‐channel optical processes, requiring an increase in the number of optical inputs (materials or wavelengths) in a monotonous manner to scale up challenge‐response pairs. Herein, an optical PUF capable of nonlinearly expanding the parameter space to enhance the cryptographic strength through the selective adjustment of up‐ and down‐conversion luminescence is introduced. The nonlinearity in the expansion of the parameter space originates from a random distribution of three types of microspheres, with their shells designed to exhibit various positional arrangements of upconversion nanoparticles and perovskite crystals. Because energy and photon interactions depend on their positional proximity and excitation power, adjusting the two excitation inputs into five power steps enables the single PUF to generate 30 unique cryptographic keys, which is 15 times greater than what a linear system can offer. The PUF also demonstrates high stability, maintaining its cryptographic performance when exposed to heat, moisture, and long‐term laser excitation, underscoring its practical applicability in security protocols.