A Retrospective and a Look Forward: Fifteen Years of Physical Unclonable Function Advancement

Severe security threats and alerts associated with the use of smart devices have drawn increasing public attentions since the inception of Internet of Things (IoT) in late 1990s. IoT devices pose a unique and challenging scenario for hardware security because of their ubiquity and area-power cost constraints. Traditional software techniques and established cryptographic methods are either inadequate or impractical due to the computational capacity and permanent storage required to process and maintain the privacy of the secret key. In this light, Physical Unclonable Function (PUF), a burgeoning technology rooted in 2002, comes in handy as an inexpensive and yet effective security primitive to overcome the forgery tagging problem by its radically different way of generating and processing secret keys in security hardware. PUFs are hardware structures or functions designed to utilize the physical disorder of random nanoscale phenomena for the derivation of keys without having to keep any security-critical information explicitly in hardware. As we usher PUF into its 15th anniversary in 2017, it is timely to review the advancements of PUF over the past decade. Specifically, this survey addresses three fundamental questions which are at all times relevant in the security arms race. These questions are: how secure can a PUF be? what differences have PUFs brought to security applications and how do these differences impact existing security protocols? how is hardware implementation research influenced by the opportunities of nanotechnologies and new discoveries of disorder-based physical phenomena? It is hoped that this retrospective study of problems and solutions encountered in the journey of developing PUF to its current state will foreshadow the challenges and opportunities for future sustainable activities in the field.