Study And Application Of Streams Ciphers Based On Components Of Block Ciphers And LFSR

Stream cipher is a very important symmetric cryptosystem which encrypts the plaintext with the keystrem bit by bit. Now, the stream cipher is widely used and especially suitable for encrypting the mass data.In this thesis, the components of AES, such as S-Box, MixCoLumns are analysed. The merits of designing these components are poited out. Then, the LFSR which has good psedurandom property is introduced from one dimensional Logistic function. The corresponding theory of generating pseudorandom number is explained and the applications of LFSR are briefly introduced. After that, a kind of stream cipher with LFSR is presented. Based on the analysis above, the merits of constructing stream cipher using the components of AES and LFSR are pointed out. At the same time, snow2.0 is utilized to verify the above merits.Secondly, the sixteen statistical tests of NIST (National Institute of Standards and Technology) for random and pseunorandon number generators are studied. Parts of the statistical test theories are analysed. Although statistical test cannot serve as a substitute for cryptanalysis, these tests may be regarded as a way to determine whether a pseudorandom number generator is good or not.Finally, a selective encryption algorithm based on spatial domain with no lose is proposed in this paper. In order to cut down the data which need to be encrypted, the following ways are employed: Firstly, partition the image on the bit planes. Then the selected bit planes are processed by run-length encoding. After that, data amount is further reduced by using the technology of image morphology. At last, security of the algorithm is analysed. Theroetical analysis and simulation show that this algorithm is secure as well as fast.In a word, this thesis fouses on two aspects—the test and design of stream cipher based on LFSR and a selective encryption algorithm based on spatial domain.