Efficient attacks on robust ring oscillator PUF with enhanced challenge-response set

Physically Unclonable Function (PUF) circuits are an important class of hardware security primitives that promise a paradigm shift in applied cryptography. Ring Oscillator PUF (ROPUF) is an important PUF variant, but it suffers from hardware overhead limitations, which in turn restricts the size of its challenge space. To overcome this fundamental shortcoming, improved ROPUF variants based on the subset selection concept have been proposed, which significantly “expand” the challenge space of a ROPUF at acceptable hardware overhead. In this paper, we develop cryptanalytic attacks on a previously proposed low-overhead and robust ROPUF variant. The proposed attacks are practical as they have quadratic time and data complexities in the worst case. We demonstrate the effectiveness of the proposed attack by successfully attacking a public domain dataset acquired from FPGA implementations.