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 Internet of Things (IoT) have attracted a significant attention in recent years. The connection of measurement devices has led to a sharp increase in information sharing, but also to the frequency of cyber-attacks, in which system vulnerabilities are exploited to steal confidential information, to corrupt data, or even to 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 existing, different PUF structures, ring oscillator (RO) based PUFs are very popular, due to their simple structure and their possibly being easily implemented on FPGAs. In this paper, the possibility to increase the number of challenge-response pairs (CRPs) of RO based PUFs 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 have shown that these two parameters feature a weak correlation. The proposed PUF can be used to increase the number of CRPs to improve the device security, while achieving a high uniqueness value (49.77 %).