Weak Physycally Unclonable Functions in CMOS Technology: A Review

Physically unclonable functions (PUFs) represent emerging cryptographic primitives that exploit the uncertainty of the CMOS manufacturing process as an entropy source for generating unique, random and stable keys. These devices can be potentially used in a wide variety of applications ranging from secret key generation, anti-counterfeiting, and low-cost authentications to advanced protocols such as oblivious transfer and key exchange. Unfortunately, guaranteeing adequate PUF stability is still challenging, thus often requiring post-silicon stability enhancement techniques. The latter help to contrast the raw sensitivity to on-chip noise and variations in the environmental conditions (i.e., voltage and temperature variations), but their area and energy costs are not always feasible for IoT devices that operate with constrained budgets. This pushes the demand for ever more stable, area- and energy-efficient solutions at design time. This review aims to provide an overview of several weak PUF solutions implemented in CMOS technology, discussing their performance and suitability for being employed in security applications.