Abstract: The apparatus for generating a secure substitution-box immune to differential and linear cryptanalysises comprises a preprocessor for exchanging a location by the unit of bit while passing the input of 64 bits data to be protected; a parity checker for obtaining 56 bits key information by passing the input of the 64 bits key by byte unit; a key expander for repetitive operation for generating 48 bits information upon receiving the key information; a first to sixteenth operating portion for performing the 16 times of operation for one data from the preprocessor while mixing the data with an expanding key information from the key expander; and a postprocessor for generating an output signal of 64 bits data upon receiving an operated result from the first to sixteenth operating portion.