Fundamental Study on Electromagnetic Analysis Attack Detection using Oscillation Shift of Ring Oscillator

Electromagnetic analysis attacks that extract secret data from a cryptographic IC by measuring and analyzing changes in electromagnetic (EM) fields have been reported. Against such attacks, it is effective to detect an EM field probe in the measurement stage, which is the preliminary stage of the analysis. A detection method using magnetic field coupling between the sensor coil, which makes up an LC oscillator in the chip and an EM probe has been proposed. However, their detection distance is limited to the inside of the chip, and EM field measurement from outside the chip is not covered by this method. In this paper, we propose a detection method using the capacitance change of a metallic film formed above the chip, which is capacitively coupled to the EM probe. The metallic film, applied externally to cover the entire IC, has the capability to detect an EM probe over a wide range, independent of the EM probe’s orientation. To achieve high-precision detection, a ring oscillator is configured with the metallic film as part of the wiring and its frequency change is used. As a result, we confirm that an EM probe is detectable at distances of up to 6 mm directly above the chip.