An expanded set of design criteria for substitution boxes and their use in strengthening DES-like cryptosystems

The security of DES-like cryptosystems depends heavily on the strength of the substitution boxes (S-boxes) used. The design of new S-boxes is therefore an important concern in the creation of new and more secure cryptosystems. The full set of design criteria for the S-boxes of DES has never been released and a complete set has yet to be proposed in the open literature. A unified S-box design framework is introduced based on information theory and illustrates how it can be used to strengthen and design the S-boxes used in DES-like cryptosystems