Physical unclonable function with tristate buffers

The lack of robust tamper-proofing techniques in security applications has provided attackers the ability to virtually circumvent mathematically strong cryptographic primitives by directly attacking the hardware. Consequently, physical tamper-proofing has emerged as an essential element in secure system design. To this end, physical unclonable functions (PUF) have been proposed to build tamper proof hardware and thereby create secure data storages. A delay based PUF scheme was proposed which uses the intrinsic process variations to randomize switches and thereby implement a pseudorandom function family. When tampered with, the device experiences a change in its internal physical parameters. This will alter the pseudorandom function family. Therefore, rendering an attack unsuccessful. In this paper, we propose a delay based PUF circuit that is constructed from tristate buffers. The proposed PUF circuit consumes less power and requires less area. Furthermore, we develop a linear delay model which turns out to be identical to that of switch based PUFs. Hence, the nonlinearization techniques proposed to secure switch based PUFs can directly be applied to secure tristate PUFs as well.