Study And Application Of The Stream Cipher Based On Chaos

Much attention is devoted, firstly, to the theory of modem cryptography,to the mathematical model, the secure measure and the classification of the cryptography systems, to the basic concept and principle of stream cipher, together with chaotic development history, present status and feature. Then probe into the excellent attribute of secret codes in nonlinear chaotic system; introduce stream cipher based on the chaotic system, with the conclusion that both the process of encryption and decryption is the iterative process of a same chaotic system.Based on the research of chaotic sequence code generation system, a few key technological points are solved in this paper as the fol lowing: First, pre-treatment of variables creates consequently output sequences with good autocorrelation features so to improve the system' s phenomenon of short period in limited accuracy; introduction of a way of system variables feedback quickens the non- correlation process in order to meet the needs of quick response to very small difference of initial status and parameter in the Lorenz system; a new method designed by sharing out equally space once creates many bits of binary system so to quicken the secret key process. This chaotic encryption method based on Lorenz system, is of reliable security, time effective and space complex; therefore it is with high anti-broken capability. Second, combining practical application, this 3DES model and dynamic 3DES algorithm, set up by utilization of Multi-dimension chaos is with high security, extensive applicability. Under the condition that calculating complexity is not increased, it fully uses the system resource. Third, the approaches are presented to stream cipher utilizing a peculiar dynamical system called double chaotic discrete dynamical system, which consists of two chaotic dynamical systems. The secret keys are in the initial state of the chaotic dynamical systems, and the plaintext is used as its double chaotic sequence that decides the choice of iterating function in the iterating process. The algorithm is also provided with uniform distributing cipher text. These peculiarities prevent cipher text from leaking information of plaintext and secret key and make the security of the algorithms not depend on the complexity of the cipher text. Fourth, combining practical application, the paper presents the digital watermarking algorithm, which has characteristics of easy realization , little calculating quantity , good robustness, strong anti-attack ability, good imperceptivity, good invertibility. It will have practical use value.