Research Of Encryption Algorithm On Digital Image Based On Chaotic Theory And Optimal Design Of The System

As a kind of information security technologies with a long history, cryptography haspassed the test of time, and proved that it is the most effective means to protect theinformation. Due to the natural contact and structural similarity between chaos andcryptography, this dissertation is mainly on the fields of category of chaoticcryptography research. By modeling the chaotic systems and anglicizing theircharacteristics, this dissertation gradually reveals research on the designing andrealization of chaotic cryptographic algorithm, and does research on problems arisingfrom realization during practical process.First of all, as encryption systems which are based on low dimensional chaotic systemshave small key space, which could be easily influenced by the limited hardwareprecision that could lead to the degradation of chaotic characteristic(i.e. degradation ofrandom characteristic), and decrease the safety of the key lastly. In this dissertation,high dimension chaotic systems were studied to construct encryption/decryptionsystem. Models were built to simulate the generation of chaotic signals and the chaoticcharacteristic were analyzed;Secondly, by studying encryption algorithms based on "confusion" and "diffusion"principles, an improved encryption/decryption algorithm was designed. Anincensement was attained on the performance of working speed and safety. A series oftests were done to verify the correctness of the results;What’s more, in view of the fact that the processing object of some classical imagescrambling algorithms is the standard square image, while in the practical situation,images are mostly rectangular with unequal width and height even irregular shapes,utilizing classical algorithms to do the processing of these irregular shapes does not have cycle characteristics. In this degree thesis, an image scrambling method whichused image interpolation algorithms to do preprocessing was proposed. Compared withsome of the isometric image scrambling methods concerned, there is improvement onthe efficiency. In addition, quality of processed images is proved to be good after aseries of tests.Finally, the hardware resources of the whole encryption/decryption system areimportant factors, which mean a large chip area would lead to the rise of the cost and asmall area to achieve the same function would result in a low working speed of thesystem. In this dissertation, an optimal scheme which uses the thought of time divisionmultiplexing for reference to design the double-precision chaotic signal generator. Bytiming control and adopts parallel structure rationally, the balance at both sides of chiparea and working speed was achieved; experiments show the aim of this theme isattained.