An encryption apparatus divides input original data into one or more data blocks. The size of each data block is an integer multiple of the bank size of a non-volatile memory equipped in a decryption apparatus. The encryption apparatus generates authentication data from this data block. The encryption apparatus generates encrypted data after it combines the authentication data to the data block. On the other hand, a decryption apparatus executes reverse processes to decrypt original data, and writes it in a non-volatile memory.