Improvement Of The Advanced Encryption Standard (aes) The Mixcolumns Routine () Function

In recent years, with the rapid development of computer and communication network, information transmission channels have become increasingly dependent on network, especially the Internet. Increasingly security issues closely followed, people need urgent protection of information security, and cryptographic algorithms are the core and foundation of information security, consequently, it has become the key research topic of cryptanalysts. Cryptographic algorithms mainly include the public-key cryptosystem and the block cryptosystem, the block cryptosystem with its concision, swiftness, simply standardization and conveniently for realization of hardware and software, which becomes the preferred method of the information security.The Rijndael algorithm is the Advanced Encryption Standard AES, which is the key iterative block cipher. In the Rijndael algorithm, the time of establishing keys is not only very short, but also performs its capabilities very well in that smaller memory.During the realization process of the Rijndael algorithm, the high speed of implementation, safety and low cost, especially used in some portable electronic devices, which storage space and system are equally limited, such as smart cards and computing speed, certainly, the proportion of speed, space and cost are important. Thus, improving its implementation speed also taking less space will become more and more important research direction.The paper studies along this important research direction, which analyzes the Rijndael algorithm, the main work includes the following,Firstly, On the basis of understanding the limit field, the state matrix and other related concepts, this paper analyzes the design principle of the Rijndael algorithm, the encryption and decryption process, round transformation and key expansion in detail.Secondly, the paper considers comprehensively the speed and space in the realization process of the Rijndael algorithm, analyses the key operation xtime() of the round transformation MixColumns() thoroughly and understands the algorithm of CRC(Cyclical Redundancy Check), on this basis, it proposes the optimized method of the xtime() operation, namely, the newly defined Multi() replaces the operation xtime() in the round transformation and calls its subroutines.Thirdly, through the valid analysis of before and after algorithm, it has been demonstrated the feasibility of this method in theory in advance. Then based on the theory results, simulating the software, namely re-writing codes, with the improved method under the Microsoft Visual C++6.0 development environment, the experimental data show that the application of the new function Multi() and the calling of its subroutines improve the implementation rate of the algorithm.Finally, the paper uses the experience of OpenSSL's thought for reference, adopts a look-up table method, which combines four operations of SubBytes, ShiftRows, MixColumns and AddRoundKey in the round transformation, optimizes the module, and then re-writes corresponding codes under the Microsoft Visual C++6.0 development environment. Through experimental data analysis, it can conclude that not only the efficiency of the AES algorithm is improved significantly, but also the memory space is saved with the operation of looking-up table, thus precisely illustrates the characteristics of lesser space which the AES algorithm could be applied to.