Reconfigurable Physical Unclonable Functions - Enabling technology for tamper-resistant storage

A PUF or physical unclonable function is a function that is embodied in a physical structure that consists of many random uncontrollable components which originate from process variations during manufacturing. Due to this random structure a physical stimulus or challenge generates unpredictable responses. Because of their physical properties PUFs are unclonable and very promising primitives for the purpose of authentication and storage of cryptographic keys. Previous work on PUFs considers mainly static challenge-response PUFs. In many applications, however, a dynamic PUF would be desirable, e.g., in order to allow the key derived from the PUF to be updated. We define a new primitive, the reconfigurable PUF (rPUF) which is a PUF with a mechanism to transform it into a new PUF with a new unpredictable and uncontrollable challenge response behavior, even if the challenge-response behavior of the original PUF is already known. We present two practical instantiations of a reconfigurable PUF. One is a new variant of the optical PUF, and the other is based on phase change memory. We also illustrate how an rPUF can be used to protect nonvolatile storage against invasive physical attacks.