Placing a capacitor in parallel with the LED should be sufficient to prevent it. That would form a low pass filter when combined with the current limiting resistor for the LED.
The attack is not really practical though. The smart card has to be read for 65 minutes while recording the power LED. The cards are normally only read for a fraction of a second.
Yikes! I wonder how isolated the led has to be to the CPU power supply to prevent this sort of attack!
Placing a capacitor in parallel with the LED should be sufficient to prevent it. That would form a low pass filter when combined with the current limiting resistor for the LED.
The attack is not really practical though. The smart card has to be read for 65 minutes while recording the power LED. The cards are normally only read for a fraction of a second.