Provided are an arithmetic method and apparatus for supporting Advanced Encryption Standard (AES) and Academy, Research Institute and Agency (ARIA) encryption/decryption functions. The apparatus includes: a key scheduler for generating a round key using an input key; and a round function calculator for generating encrypted/decrypted data using input data and the round key. Here, the round function calculator includes an integrated substitution layer and an integrated diffusion layer capable of performing both AES and ARIA algorithms.