The Design Principles Of AES Algorithm And The Improvement Of Its Key Expanding Algorithm

With the continuous expansion of the network applications, the security of the network system as the cornerstone of these applications is becoming an important research area and has a wide range of applications in military, political, financial, business and other departments, In the field of network information transmission, AES algorithm as the current or even in the next 10 years core data encryption algorithm has an important value in theoretical research and practical application. Reviewing the development process of AES, the blockcipher cryptography initials from classical cryptography which rely on the wisdom of one person, and develops to many scientists combining their efforts. Cryptography is no longer a mere "art", the crack is no longer a mere intuition as well, but rely on the strict inference and advanced computer. Accordingly, the design of new encryption algorithm must also fit an assumption that the cracker has a strong computing ability. During the three-year selection process of AES algorithm,15 candidates from around the world participated in the race. Finally, Rijndael, which designed by two scientists from Belgium, named Joan Daemen and Vincent Rijmen, win and is confirmed by the U.S. government standard, the National Institute of Standards and Technology (NIST) of U.S. gives the comment that "Rijndael brings together security, performance, efficiency, ease of use and flexibility advantages, making it the most suitable option AES, Rijndael in particular, with or without a feedback mode in the computing environment of the hardware and software that can show its very good performance. It is a key installation time well, also has a good sensitivity. The low memory requirements of Rijndael also make it very suitable for constrained environments. The simple, can withstand strong and real-time attacks. In addition, it is not many with special emphasis on the defensive performance." In the assessment process of Rijndael, the only way to crack the algorithm is from the energy analysis to the realization on smart card. The goal of this paper is to overcome this threat faced by AES.To overcome this threat, this paper firstly describes the encryption algorithm, decryption algorithm, the key expansion algorithm, and the working mode of AES. Then, I make a systematic analysis of the design principles which the designers used in AES. Next, I give some methods that can attack AES in detail. Finally, I propose my suggestions to the AES algorithm. There are 3 concrete improvements in all. Improvement 1 is a reference to the key expansion algorithm of Mars which another candidate algorithm of AES algorithm. Through the wheel key for the various wheels to reduce the correlation between the wheel keys, but the improvement 1 lost some flexibility close to the original key expansion algorithm. In order to adapt to practical needs, this paper presents design strategy called "one-way" strategy, and proposes to improve the algorithm 2 and improved algorithm 3 under the guidance of such a strategy. The basic idea is, in the key expansion algorithm, that the wheels are still the key from the previous one by changing a wheel after the keys are derived. The difference lies in the derivation of the relationship is one-way and not reversible, that is, if the attacker AES algorithm is obtained by energy analysis of all the AES algorithm is a 1 or a particular sub-key in parts of sub-rounds key, and even a few rounds of all the sub-keys can not be obtained through the forward derivation of the user's initial seed key. This perspective from the principles of the realization of algorithms to provide strong support, so that attackers can not energy analysis method for crack AES algorithm, thus enhancing the security of AES implementation extends the AES algorithm applications. Improved algorithm proposed in each one, I have given a detailed safety analysis of the algorithm, obtained the algorithm improved security strength. The security strength of improved algorithm 2 is enough to resist power analysis attacks after 4 round, but each round of Algorithm 2 more than the original algorithm of running a complex operation, its theoretical efficiency is only about half of the original algorithm. The final improved algorithm not only the safety of three to two after the can resist power analysis attacks, and its operational efficiency of the theory itself, with the AES algorithm is the same as the key expansion algorithm, through my own Intel T5200 processor, the concrete test The results slightly faster than the original key expansion algorithm. So I improve and not undermine this highly efficient AES own character, but also realize the unity of safety and efficient.The results of this are original. I propose the concept of "one way" in the first time in the field of research in AES algorithm and apply it to the design of the key expansion algorithm. As the aim of the key expansion algorithm is to supply subkeys for add round key steps of encryption and decryption algorithm, but not participate in other steps. So, such a change to the encryption algorithm does not have other unknown effects, but only change the key principle to expand the sub-module in accordance with AES principle. In the application of this algorithm, you don't need for more security for AES analysis, which makes this algorithm has a highly practical value. The significance of this paper is not only to extend the security of implementation of AES in theoretically, but also provides a new way of thinking for design and evaluation in other block cipher and provides a reference model for the future design of new block cipher. In the next research, how to enhance the security of block cipher and reduce the algorithm to run the required time and space is still the subject of our research, but more important thing is how to unify such a high safety and efficiency. This result provides a feasible solution and the process writing this article also reflects the idea of such a research question. That is, to meet the security conditions and to constantly pursuit efficiency. This is very important in block cipher areas.