Liquid-metal physical unclonable functions resistant to both physical and digital cloning

Physical unclonable functions (PUFs) leverage device-specific randomness for hardware security, yet their static, persistently accessible responses allow attackers to collect sufficient data for digital cloning. We present a liquid-metal PUF (LM-PUF) that integrates physical unclonability with material-driven resistance to digital attacks. Randomly mixed, visually indistinguishable LM particles form thermally unique microstructures, ensuring physical unclonability. Digital protection arises from two concealment mechanisms: time-limited accessibility restricts meaningful data collection, while decoy obscuration prevents reliable key identification. At equilibrium, the device remains cryptographically silent, but heating through a transient non-equilibrium window reveals thermal patterns convertible to cryptographic keys. Outside the predefined temperature range, misleading thermal patterns conceal the authentic key among decoys. LM-PUF supports scalable patterning, demonstrated in secure labels and QR codes, highlighting its potential for secure supply chains and physical unclonable authentication. Physical unclonable functions (PUFs) secure hardware identity but can be digitally cloned by machine-learning attacks. Here, authors report a liquid-metal PUF whose thermal keys appear only briefly during heating and are hidden among decoys, resisting both physical and digital cloning.