The cryptographic strength of DES-like cryptosystem based on Substitution-Permutation network (SP-network) depends crucially on the strength of its substitution boxes (S-boxes). The design of good S-boxes is therefore an important part of designing a DES-like cryptosystem. In this thesis, we investigate the design of DES-like S-box.
Using Walsh transform, we derive a set of conditions under which the information leakage of S-box reduces to zero in particular cases. And then we observe that it is desirable for the information leakage criterion to discard the S-boxes which have significant information leakage and to be used with other S-box design criteria considering the structure of DES and the cryptanalysis of DES. We set up the S-box design criteria considering the structure of DES, the cryptanalysis of DES, and the information leakage. Our S-box design criteria can produce S-boxes which strengthen the security of DES.
