To ensure security while reducing an update frequency of a mask value in a data converter.

A data converter can independently update mask values M1 and M2 relating to S layer conversion (SubBytes) and a mask value M3 relating to P layer conversion (ShiftRows and MixColumns). For instance, the data converter uses the mask value M3 as a mask value M4 XORed with the mask value M2, and updates the mask value M3 more frequently than the mask values M1 and M2. Although it retrieves more pieces of identical data (SubBytes S0 to S15) in the P layer conversion than in the S layer conversion, the data converter can ensure security in communications by frequently updating the mask value M3. And, by determining only the mask value M3 to be updatable, the data converter can reduce an update frequency of the mask values M1 and M2, and can reduce consumption power required for the updating.