Analysis And Design Of Cipher Based On Prefix Codes

With the rapid development of Internet, the sharing of resources on the network are more and more strengthen. Attendant, the problem of network security has become prominent increasingly. Network brings a lot of convenience to people; however, it also became the targets of many criminals. They use the computer as a tool, and used the computer as the targets at the same time. They delete and modify the information on computer data on the network maliciously. In order to guarantee the confidentiality of information transmission, authenticity, integrity and non-repudiation of communication, cryptography has become a major area of computer security research. Thus a wide range of encryption algorithm research has great theoretical significance and practical value.The paper researches the non-symmetric encryption system and symmetric encryption system mainly, and it analysises the procedure of digital signature and makes improvements, in the end it implements the hybrid encryption system, and completes the hybrid encryption.Firstly, for the non-symmetric encryption system, the paper introduces the RSA algorithm for comprehensive detail, and then analysis the efficiency and security of RSA algorithm. RSA algorithm based on of large numbers, and its operating efficiency determines the performance of RSA public key cryptography, the papers introduces a variety of fast implementation methods of modular exponentiation multiplication, and then does comparative analysis.Secondly, for the symmetric encryption system, it takes the DES (Data Encryption Standard) algorithm and Rijndael algorithm as the focus, firstly introduces the encryption principle of the DES and Rijndael encryption algorithm and find their deficiencies though the depth analysis of the algorithm, such that DES encryption algorithm is vulnerable to chosen-plaintext attack method, while the Square attacks is the most effective method to Rijndael algorithm. Their principles of attacks are based on the invariance of encryption systems, so the paper puts forward to a solution which is based on prefix codes, because prefix codes have a very good decoding characteristics, through the introduction of the prefix codes, it could decodes the plaintext to change the sequence of sub-key of the algorithm, and makes the encryption system be not invariance, but be variable with the different plaintext. This method makes the algorithm have good resistance to some attacks.Finally, the paper analysises the procedure of the digital signature, MD5 algorithm has been cracked, so the digital signature has the hidden danger to be forged. In this paper, it puts forword to a solution of digital signature which is based on prefix codes, through the decoding characteristics of the prefix codes, it decodes and transformed the summary which is generated by the MD5 algorithm, and then transmitted over the network, so it could eliminat the hidden danger that the digital signature may be forged. After that the paper completes the hybrid encryption system which is based on improved Rijndael algorithm and RSA algorithm and applies the improved digital signature procedure to the system to make the hybrid encryption system has more higher efficiency and security.