To make it difficult to estimate processing or cryptographic key from the waveform of consumed current by processing data to be processed and normal processing data according to the same instruction while using the result of inverting the bit values of both the data.
When an output state changes from '1' to '0' or changes reverse, a CMOS composing a chip for IC card consumes a current and at the time of this output state change, the consumed current flows to a data bus 203. By observing this condition, which is operated in the chip can be discriminated. A co-processor 202 enables long remainder operation for 512 bits, for example, parallel with a central arithmetic unit 201 and can observe a consumed current waveform different from the consumed current of the central arithmetic unit 201 for a long time and the cryptographic key can be estimated by measuring how many times the co-processor 202 is operated. Then, it is made difficult to reproduce the current waveform of hardware consumption of a chip for IC card by random operation or useless dummy processing addition without constantly executing a program 205 at all the time.
FUKUZAWA YASUKO
OKUHARA SUSUMU
KAMINAGA MASAHIRO
