1. A cryptographic processing apparatus, the cryptographic processing apparatus comprising a data processing unit configured to: modify round keys applied in encryption and decryption processing to execute swapping processes during the encryption and decryption processing; execute cryptographic processing; and perform a round key permutation process in which (i) a sequence of round keys applied in corresponding rounds of the decryption processing is set opposite to a sequence applied during the cryptographic processing, and (ii) round keys input to a plurality of F-functions for even-numbered rounds have an input style different from an input style of the encryption processing.