  The physical unclonable functions (PUF) are used to provide software as well
as hardware security for the cyber-physical systems. They have been used for
performing significant cryptography tasks such as generating keys, device
authentication, securing against IP piracy, and to produce the root of trust as
well. However, they lack in reliability metric. We present a novel approach for
improving the reliability as well as the uniqueness of the field programmable
gated arrays (FPGAs) based ring oscillator PUF and derive a random number,
consuming very small area (< 1%) concerning look-up tables (LUTs). We use
frequency profiling method for distributing frequency variations in ring
oscillators (RO), spatially placed all across the FPGA floor. We are able to
spot suitable locations for RO mapping, which leads to enhanced ROPUF
reliability. We have evaluated the proposed methodology on Xilinx -7 series
FPGAs and tested the robustness against environmental variations, e.g.
temperature and supply voltage variations, simultaneously. The proposed
approach achieves significant improvement (i) in uniqueness value upto 49:90%,
within 0.1% of the theoretical value (ii) in the reliability value upto 99:70%,
which signifies that less than 1 bit flipping has been observed on average, and
(iii) in randomness, signified by passing NIST test suite. The response
generated through the ROPUF passes all the applicable relevant tests of NIST
uniformity statistical test suite.
