A data carrier that communicates confidential data is configured to mask process-dependent power consumption by using power stored in an internal capacitor. The capacitor is initially charged to the voltage of an external power source, and then decoupled from the external power source. The capacitor provides power to an internal processor, and consequently discharges gradually. At the end of a given time interval, the capacitor is discharged to a fixed voltage, then charged to the supply voltage. In this manner the power consumed by charging of the capacitor is decoupled from the power consumed by the processor. If the capacitor drops below a threshold voltage before processing is completed, the processor is halted. To optimize the available processing time, the time interval before discharging the capacitor to the fixed voltage is dynamically adjusted to reduce the time that the processor is halted.