Method of protecting electronic circuit against eavesdropping by power analysis and electronic circuit using the same

An electronic circuit with protection against eavesdropping by power analysis, comprising:

• a storage element, configured to store a set of bits;
• a random bit generator, configured to generate random bits corresponding to the stored set of bits respectively;
• a selector, coupled to the storage element and the random bit generator, configured to output at least one replaced bit by replacing at least one bit of the stored set of bits with a random value or an opposite value according to the random bits;
• a combinatorial logic unit, coupled to the selector, configured to perform logic calculations in at least two cycles and provide a next state set of bits after the at least two cycles to the storage element, wherein the combinatorial logic unit is configured to perform a first logic calculation on the output of the selector including the at least one replaced bit under a first distribution of power consumption in a first cycle, and is configured to perform a last logic calculation on all of the stored set of bits under a second distribution of power consumption in a last cycle, and wherein the combinatorial logic unit is configured to obtain some of the stored initial set of bits from the storage element in the first cycle and replacing the rest of the bits which have been replaced by the random values in the first cycle with the corresponding bits of the stored initial set of bits after the first cycle and before the last cycle.