Abstract: An aspect of the present invention is a cryptographic processing apparatus including a division unit that divides input data into multiple partial data items, the input data being one of plaintext and a round processing result; multiple data holding units that hold the partial data items, respectively; and a combining unit that combines the partial data items held in the multiple data holding units into a single round processing target data item to be subjected to round processing. The division unit selects a storage destination of each partial data item from among the data holding units, and stores each of the partial data items into the storage destination selected. The combining unit combines the partial data items into a round processing target item to reconstruct the input data according to the storage destination of each partial data item selected by the division unit.

Abstract: A cryptography processing device has: a round processing unit configured to obtain a processing-object data and generate an intermediate data by applying round processing to the processing-object data; a random number generation unit configured to generate a random number data; a memory circuit in which the intermediate data or the random number data is stored; and a selection control unit configured to select which one of the intermediate data and the random number data is to be stored in the memory circuit. The selection control unit selects the data to be stored in the memory circuit such that the random number data is stored after the intermediate data is stored.