An Autonomous Clock Frequency Supervision Circuit

Abstract

An important class of attacks is based on manipulating the victim’s hardware clock to gain control over the system. We propose a circuit that can be added to an IP module to detect and hence mitigate such attacks. It employs a ring oscillator as a tamper-proof internal time reference. We embed this oscillator into a complete circuit whose design carefully takes metastability issues at the boundary between supervised clock and reference clock into account. Furthermore, we analyze the attainable accuracy considering the frequency ratio between these clocks, as well as ring oscillator frequency tolerances. Finally, we give guidelines to parameterize our circuit for given requirements and present a demo implementation as a proof of concept. Index Terms—clock supervision, cycle counting, metastability, autonomous, ring oscillator