As a kind of special nonlinear phenomenon, chaos has a series of excellent features such as pseudorandomness, orbit unpredictability, the extreme sensitivity to initial conditions and system parameters, non-repetition of iteration, and so on. Because an increasing number of widely used image and multimedia information has characteristics such as large amount of data and high redundancy, it has become a challenge to the traditional encryption technology. Having natural randomness and concealment, chaotic signal is well fit for secrecy communication.