H-field probe Detection Method under Supply Voltage Fluctuation using Time Series Variation of Oscillation Frequency Difference of Multiple Ring Oscillators

An electromagnetic (EM) analysis attack has been reported to reveal secret keys by measuring and analyzing changes in EM fields generated by the operation of cryptographic circuits.Against such attacks, it is effective to detect the Hfield probe in the measurement stage, which is the preliminary stage of the analysis.In response to this, a method has been proposed to detect H-field probes by forming a metallic film directly above the chip that is capacitively coupled to the H-field probe and capturing the capacitance change as a frequency change of the Ring Oscillator (RO).In this method, the sensitivity of the RO to variations in power supply voltage is an issue, and a method that eliminates only DC variations from the frequency difference of multiple ROs has been considered.Therefore, there is a possibility of false detection for voltage fluctuations that vary over time.In contrast, this paper proposes a method to reduce temporal power supply voltage fluctuations by utilizing the time variation of the frequency difference between multiple ROs.In experiments, it is shown that the effect of power supply voltage fluctuation on the oscillation frequency of ROs for sensors can be reduced in an environment where the power supply voltage fluctuates.As a result, it is shown that it is possible to detect the H-field probe at a distance of 8 mm as stably as in an environment where the power supply does not fluctuate.