Research On An Mixed Cryptology Algorithm

With the development of the global information, the information technique has already become a strategic technique which has the largest application and the strongest permeation. Increasingly popularization of Internet greatly boosts the pace of national information. At the same time, it brings rare development opportunities with us. However, it also gave a series of security problems. On the other hand, because information is a kind of important strategic resources, conflict round information's obtaining, using and controlling played more and more strongly throughout the world. Cryptology is the core technique of the information security. Therefore, facing the urgent situation, it has important theoretic meaning and practical values to strengthen research and improve on cryptology.Modern cryptograph can be divided into symmetrical key system (public key system) and dissymmetrical key system (private key system). They have different characteristics: I) the key management: Dissymmetrical key system is better than symmetrical key system. II) The speed of encrypting and decrypting: symmetrical key system is faster than dissymmetrical key system. III) Data signature: symmetrical key system can't be used for data signature and identity authentication in principle, but dissymmetrical key system is easy for data signature and to identity authentication. In this thesis we emphasize on these aspects as below.First, the function ShiftRows(State) of Round() in symmetrical key system AES is a operation of Bytes shifting. It makes the bytes on row i column j shift to row i column (j-C_i) mod N_b. So we can combine ShiftRows(State) withMixColumns(State) as a function in implementing AES. The improved algorithm is implemented with VC++6.0 and is proved faster than the traditional AES.Using a single cryptology in information encryption has certain disadvantages. Considering speed and security demand, a mixed cryptology consists of symmetrical key system and dissymmetrical key system is proposed. In this cryptology, the improved AES algorithm is used for encrypting data and the dissymmetrical encrypting algorithm RSA is used for encrypting the AES key. The amount of total data equals to the amount of the real data adding with the AES key. So the main task is to encrypt the real data, therefore the speed of encrypting total data approximates to the speed of AES; RSA algorithm is used for encrypting AES key and the receiver doesn't need to save the AES key. So, like RSA algorithm, the mixed cryptology is more facility to key management.At the same time, this mixed cryptology also has the function of data signature. This cryptology use MD5 algorithm in computing the digest of the original data and use RSA algorithm in data signature and authentication, the integrality of data is ensured consequently.