The increasing demand in the VLSI technology is also proportionately increasing the threats to these ICs. Hardware Trojan is one such threat that once inserted into the chip can cause malfunctioning of the chip or degradation in performance of the chip. A physical unclonable function (PUF) is one feature that can be a preventive shield against the Trojans. The PUF provides each device with a distinct identity, and in higher-level security architecture, this identity serves as a trust anchor. This chapter uses cellular automata (CA) paradigm implemented in nano-crossbar circuits to impart these unique features. Attacks are designed on the implemented architecture, and the obtained results immediately reflect the presence of some attacks. The results prove that CA-based design can be a competitive and encouraging contender for PUF primitives.