Circuits for Autonomous Clock Frequency Supervision

An important class of attacks is based on manipulating the victim’s hardware clock to make it misbehave in a targeted way and ultimately gain control over the system. We propose two types of circuits that can be added to an IP module to detect and hence mitigate such attacks. They both employ a ring oscillator as a tamper-proof internal time reference but differ in their measurement principle. We embed this oscillator into complete circuits whose design carefully takes metastability issues at the boundary between supervised clock and reference clock into account. Furthermore, for both variants, we analyze and compare the attainable accuracy considering the frequency ratio between these clocks, as well as ring oscillator frequency tolerances. Finally, we give guidelines to parameterize our circuits for given requirements and present demo implementations as a proof of concept.