Research On Design And Application Of A Multi-bit Stream Cipher Algorithm

The development of computer technology and Internet technology has changed people's way of life.While bringing convenience to people,they have also brought some security risks.Since digital information is easily stolen and attacked by criminals during storage and transmission,how to effectively protect the security of information has become a concern of people.It is known that cryptography is an effective means to protect information security.As an important branch,stream cipher has the advantages of mature theory,wide application range and simple encryption and decryption operations.One of the key issues in stream cipher design is the construction of the key stream generator.Chaotic systems are naturally complex,difficult to predict,extremely sensitive to initial values and parameters.They can produce chaotic sequences with excellent cryptography.Therefore,this thesis will use chaotic system and Latin square transform to construct a new multi-bit stream cipher algorithm.Then use simulation experiments to compare and analyze the encryption effect and security of the new algorithm,and apply the new algorithm to the design of mobile phone encryption software.The innovations studied in this thesis mainly include the following aspects:1)The Devaney chaos of a three-dimensional time-varying symbol dynamic system is proved.Combining with the system and shift register,a keystream generator is proposed.The binary sequence generated has been detected by the monobit test,runs test,poker test and NIST statistical test.The simulation results show that the sequence generated by the new keystream generator has good random performance.It is suitable for constructing stream cipher algorithms with the new keystream generator.2)The modulo 8 basic cryptosystem has been designed by using the Latin squares of orders 8.And we have given the algebraic expressions of the basic cryptosystem.By combining the new keystream generator and the multi-bit basic cryptosystem,a new multi-bit stream cipher algorithm is obtained.The multi-bit stream cipher algorithm reads the plaintext data 3 bits a time.Under the control of the keystream,the plain text is processed according to the transformation rules of the basic system.3)We implement encryption and decryption of image through using the multi-bit stream cipher algorithm.The security of these algorithms are analyzed in terms of gray level histogram,adjacent pixels correlation,information entropy,key space,and key sensitivity.Experiments shows that the three multi-bit algorithms have high security.Then compared with the Logistic chaotic image encryption algorithm,it shows that the algorithm proposed in this paper has a larger key space,stronger anti-statistical attack capability and higher security.Further,in order to verify the practicability of the multi-bit stream cipher algorithm,we use this algorithm to design a mobile phone encryption software which is easy to operate and safe.