Design And Study On Software Package Used In Cryptography

As we all know, cryptanalysis is a very important part of cryptology and its main task is to filch classified information or bilk by breaking cipher or fabricating authentication. We can evaluate the security of cryptographic algorithms by comprehensive analysis of the ability which the algorithms can resist against all attacks. It's dangerous to use a cryptographic algorithm which security is not been proved, but it's also difficult to prove the cryptographic algorithm's security. Usually, our procedure is inspecting the essential condition of cryptographic algorithm's security--whether the algorithm can go through the cryptographic algorithm statistical tests or not, which is the foundation of cryptographic algorithm's security. Moreover, the security of the cipher's component directly affects the cryptographic algorithm's security, and s-box is an important component of block cipher, this requires that the s-box used in a cryptology should have very good cryptographic properties. Therefore, the design criterions and the selection methods of s-box are very important.This thesis studied the statistical tests of cryptographic algorithms and the design of s-box, several principal achievements have been obtained as follows:1) Systematic summarized the statistical tests of various cryptographic algorithms. A major study is programming realized the randomness tests of stream cipher key sequence generator, the randomness tests, diffusion tests, and the effectiveness tests of key changing on block cipher. For stream cipher randomness tests, we compared traditional methods with the tests selected by NIST and then serial test is proved to be superior to the other tests.2) Studied cryptographic properties of s-box and summarized its design methods, then programming realized the computation of s-box's criterions. A major study is the nonlinearity of a bijective s-box. Based on Hill Climbing algorithm, we discuss an improved method which can greatly improve the nonlinearity of bijective s-boxes.