1. A cryptographic processing apparatus that executes cryptographic processing to which an extended Feistel structure in which the number of data lines d is set to an integer satisfying d≧3 is applied, characterized by comprising: a data processing unit that executes data processing including a common swapping process which is common to encryption processing and decryption processing, wherein the data processing unit is configured to modify applied round keys in the encryption processing and the decryption processing to execute data processing including the common swapping process in both the encryption processing and the decryption processing.