Patent ID: 8209765

Claim:
An electronic circuit device for executing operations dependent on secret information, the electronic circuit device, comprising: power supply connections; a processing unit comprising a plurality of processing circuits for use in execution of respective parts of the operations dependent on the secret information, the processing circuits being fed from the power supply connections; an activity monitor circuit, coupled to receive pairs of processing signals, each of the pairs of processing signals including an input signal and an output signal of one of the processing circuits, the activity monitor circuit being arranged to derive activity information from each pair of processing signals, the activity information indicative of whether each of the processing circuits generates a logic level transition, and to derive from the activity information a combined activity signal indicative of a sum of power supply currents that will be consumed by the processing circuits dependent on the processing signals; a current drawing circuit connected to the power supply connections and controlled by the activity monitor circuit to draw a cloaking current controlled by the combined activity signal, so that power supply current variations dependent on the secret information are cloaked in a combination of the cloaking current and current drawn by the processing circuits; characterized in that the activity monitor circuit is coupled to receive a pair of processing signals for each of the processing circuits, coming into and out of the processing circuit respectively, the activity monitor circuit being configured to derive the activity information from each pair of processing signals and to derive from the activity information for said processing circuits the combined activity signal dependent on the processing signals indicative of the sum of power supply currents that will be consumed by said processing circuits in combination; the activity monitor circuit being coupled to the current drawing circuit to control generation of the cloaking current under control of the combined activity signal.