Physically unclonable functions based on small delay defects in QCA

Abstract

Physically unclonable functions (PUFs) as a physical security entity are widely used in conventional CMOS technology. The specific structure of circuits in quantum dot cellular automata (QCA) technology does not allow the use of the same techniques of CMOS to effectively applied for implementation of PUF in QCA. However, the QCA technology is much susceptible to various random fabrication defects. A large group of these defects is small delay defects (SDDs) that cannot cause a fault at the nominal conditions. In this paper, we propose a PUF construction based on SDDs as a physical feature of QCA technology. For simulation, we randomly inject defects in a circuit, particularly the majority voter gates in an arithmetic unit. A set of picked challenges is applied to the circuit to excite SDDs. The existence of SDDs is disclosed using a new delay-based model that also converts the size of defect to a bit string. Finally a collection of bit strings corresponding to the size of SDDs forms the PUF response or the signature of the entity. The results of simulations exhibit the benefit of SDDs for the realization of PUF in QCA. The extracted signatures satisfy the required robustness and security measures for the PUF objectives such as identification.