Analysis of Voltage Drop and Temperature Effects on Harmonic Errors Under EMFI on ROs

Physical Unclonable Functions (PUFs) and True Random Number Generators (TRNGs) have emerged as effective solutions for enhancing local security in digital devices, offering secure IC authentication and random cryptographic keys. Among the components used to implement these primitives, Ring Oscillators (ROs) play a pivotal role due to their simplicity, scalability, and ability to exploit process variability. However, the effectiveness of ROs is challenged by their susceptibility to various fault attacks that tamper with the working conditions. Among these attacks, ElectroMagnetic Fault Injection (EMFI) was underscored as a real threat to the RO frequency through harmonic locking. Therefore, this paper aims to explore the impact of voltage drop and temperature rise on the harmonic susceptibility of a RO under EMFI. Experiments involved deploying a grid of 4600 ROs across different FPGAs to highlight the increased intensity of harmonic errors due to the major effect of voltage fluctuations. Further EMFI campaigns with X-ray irradiation provided additional insights into the critical relationship between the RO frequency and its harmonic susceptibility to EMFI.