The Research Of AES Key Expansion's Improvement And Randomness Analysis

The information is something that used to eliminate the uncertainty. The primary purpose of the cryptography is to hide the meaning of information, not the existence of information. So, how to change meaning to meaningless? Randomness meets the requirements. In the modern information security system, the random plays an important role. Almost all security system related to the cryptography will use random number. For example: handshake protocol, session key, the production of key in RSA algorithm. However, the true random number is very hard to obtain. Most of the the random number that used in cryptographic algorithms currently is generated by programming. This kind of method can only gain numbers called pseudo-random numbers. On the pseudo-random numbers, it is impossible to achieve its strict mathematical randomness in theory, and it's unnecessary in practical application. For most of the random number system, the system's security objectives is dependent on the randomness of the random number. The quality requirement of the random number in various application areas is different. The investigation showed that in a large number of the security systems that has been attacked, one of the most important reasons is that they are not random keys, which are very easy to be "speculation" or "analysis" by attackers. On the basic concept of randomness, the general method to determine the randomness is disscussed in this paper, and take out the randomness of random sequences in security for examples to explain the estimate of randomness.As the next generation of symmetric cipher algorithm standard, AES attract people's attention for its outstanding safety and effectiveness. And at the same time, the reaseach and the attack on AES is aroused because of its wideness and foundation in practial application. In the second part of the AES's basic tenets, the focus is put on its Key expansion and its improvement. With the comparison to the Hash method that get the cipher key, we analyse the pros and cons of each programme from theperspective of randomness.