Break IC, Recover MCU, Microcontroller Reverse Engineering

We made some improvements to the existing power analysis setup. This is a new approach and we have not seen any reference to it before. Instead of using a resistor in the power or ground line we used a ferrite core transformer. That brought some changes to the waveform because the DC component of the signal was lost. At the same time it has some advantages, there is almost no limitation DC current flow where with a 10 resistor a transient increase in the consumption current to 100 mA will cause a 1 V drop, which could disrupt the normal operation of the device. Reducing the resistor value will solve the problem but make it harder to recognise small changes in the power consumption, as needed to perform reliable analysis. With the transformer, there is no need to use an expensive active probe, as the standard passive probe gives almost the same result (Figure 40). If the signal is too small, extra turns in the secondary coil will increase the amplitude. Also the transformer acts as a passive filter itself. As it can be seen from the waveforms in Figures 37 and 40, the same CPU instructions have different influence on the waveform for resister and transformer measurements. That can be used as a form of post-processing of the acquired signal.