1. An encryption apparatus, comprising: an encryption processing unit configured to iterate a specified operation in order to encrypt data and to externally output the encrypted data, said encryption processing unit, including: a non-linear transformation circuit configured to non-linearly transform an input first data block based on input key information and configured to output the non-linearly transformed result value, a logical operation circuit configured to logically operate on the non-linearly transformed result value and an input second data block and configured to output the logical operated result value, and a substitution module configured to substitute said second data block with said first data block and said first data block with the logical operated result value; and a changing module configured to change said key information input into said non-linear transformation circuit into a value unrelated to said key information, wherein said changing module begins execution after said encrypted data is output from said encryption processing unit.