Probing point for power SCA - CW 305


#1

Hello,
Why is the measuring point for power SCA just a single node - voltage across the crypto block (or with a LNA) or Vcc_int supply?

Is it not better to measure the voltage drop across the shunt resistor (R27)?
Otherwise, what is the purpose of putting the shunt resistor if we don’t measure across it?

Thanks,
Ron


#2

Hi Ron,

The reason the measurement is just a single point is that the capacitance on the high side of the shunt filters out anything you’d pick up with the Chipwhisperer, so the changes in voltage that you measure are what’s dropped across the shunt resistor.