An information theoretic model for physical uncloneable functions

A "physical uncloneable function" (PUF) is a function that is realized by a physical system, such that the function is easy to evaluate but the physical system is hard to characterize. PUFs were introduced as a cost-effective way of generating secure keys for cryptographic purposes. A PUF is a physical system designed such that it interacts in a complicated way with stimuli (challenges) and leads to unique but unpredictable responses. A PUF is similar to a keyed hash function. The key is the physical system consisting of many "random" components.