Complex Cryptographic and User‐Centric Physically Unclonable Functions Enabled by Strain‐Sensitive Nanocrystals via Selective Ligand Exchange

Abstract Physically unclonable functions (PUFs) harness the device‐intrinsic randomness to generate secure cryptographic keys. Conventional electrical PUFs exhibit limited entropy and are susceptible to machine‐learning attacks, while optical and magnetic PUFs require bulky or impractical readout systems. This study designed electromechanically responsive, strain‐sensitive, nanocrystal‐based PUFs. These PUFs allow secure and efficient key extraction through resistance measurements with practical readability. The surface chemistry of the nanocrystals is designed by a selective ligand exchange strategy based on hard‐soft acid‐base theory and steric hindrance, leading to chemical randomness‐enhanced percolation networks of Ag/ZnO mixtures with stochastic effective interparticle distances. By tuning the mixture ratio and leveraging the strain‐responsive electrical behavior, the designed system is used to encode robust binary keys via a ranking mechanism. The random distribution of nanocrystals induced unique electrical paths, and percolation thresholds are engineered to optimize sensitivity. The morphological and electrical characteristics confirm that the strain‐induced resistance has high entropy as well as high uniqueness and repeatability. These multiple key generations offer low‐cost fabrication, low power consumption, mechanical flexibility, and hinge joint bending motion driven security. The results enhance resistance to modeling attacks and enable dynamic key generation on flexible substrates, opening new directions for adaptive encryption techniques in smart devices.