Although discrete chaotic systems is sensitive to initial conditions and its behavior seems to be random

it is not really stochastic process but determinate.It results in that chaos based encryption schemes are not good as we expect.In order to enhance the performance of the encryption algorithms based on discrete chaotic dynamical system

we present composite discrete chaotic dynamical systems and gives some results about its invariant distribution density and iteration sequence.We present a new approach to stream cipher utilizing a peculiar composite discrete chaotic dynamical system.Because of its sensitivity to initial conditions and randomness of the iteration sequence

the approach mingles secret keys with plaintext by iterating the chaotic system to produce ciphertext.Therefor they hold very complex and sensitive nonlinear relations.It prevents ciphertext to leak the information of plaintext and secret key and makes the security of the algorithm independent of the complexity of the ciphertext.The algorithm is provided with larger secret space and uniform distributing ciphertext.