A Ring Oscillator-Based Physical Unclonable Function with Enhanced Challenge–Response Pairs to Improve the Security of Internet of Things Devices

Portable and wearable sensor systems implemented in the paradigm of the Internet of Things (IoT) are part of our daily activities as well as commercial and industrial products. The connection of measurement devices has led to not only a sharp increase in information sharing, but also to the frequency of cyber-attacks, in which system vulnerabilities are exploited to steal confidential information, corrupt data, or even make the system unavailable. Physical unclonable function (PUF)-based devices exploit the inherent randomness introduced during device manufacturing to create a unique fingerprint. They are widely used to generate passwords and cryptographic keys to mitigate security issues in IoT applications. Among the existing different PUF structures, ring oscillator (RO)-based PUF devices are very popular due to their simple structure and their potential easy integration onto chips. In this paper, the possibility of increasing the number of challenge–response pairs (CRPs) of RO-based PUF devices by measuring two different parameters (the oscillation frequency and the duty cycle) is investigated. The results achieved by the performed circuit level simulations and experimental measurements show that these two parameters feature a weak correlation. The proposed PUF device can be used to increase the number of CRPs to improve device security while achieving a high uniqueness value (49.77%).