1. A data transformation apparatus for transforming two arbitrary pieces of data of A input data ( 101 ) and B input data ( 102 ) comprising: a configuration for performing a first nonlinear transformation of the A input data using a first key parameter ( 111 ), outputting a transformed result, performing an XOR operation of the transformed result and B input data to output an XORed result as B intermediate data, and outputting B input data as A intermediate data without any transformation, a configuration for operating a second nonlinear transformation of the A intermediate data using a second key parameter, outputting a transformed result, performing an XOR operation of the transformed result and the B intermediate data to output an XORed result as next B intermediate data, and outputting the B intermediate data as A intermediate data without any transformation, and wherein the above two configurations are connected in a cascade to output last A intermediate data and B intermediate data as output data ( 103 and 104 ) after transformation.