Since chaotic cryptography has a long-term problem of dynamic degradation, this paper presents proof that chaotic systems resist dynamic degradation through theoretical analysis. Based on this proof, a novel one-dimensional two-parameter with a wide-range system mixed coupled map lattice model (TWMCML) is given. The evaluation of TWMCML shows that the system has the characteristics of strong chaos, high sensitivity, broader parameter ranges and wider chaos range, which helps to enhance the security of chaotic sequences. Based on the excellent performance of TWMCML, it is applied to the newly proposed encryption algorithm. The algorithm realizes double protection of private images under the premise of ensuring efficiency and safety. First, the important information of the image is extracted by edge detection technology. Then the important area is scrambled by the three-dimensional bit-level coupled XOR method. Finally, the global image is more fully confused by the dynamic index diffusion formula. The simulation experiment verified the effectiveness of the algorithm for grayscale and color images. Security tests show that the application of TWMCML makes the encryption algorithm have a better ability to overcome conventional attacks.

This paper proposes a new chaotic image encryption scheme, which employs Josephus traversing and mixed chaotic map. The scheme consists of three processes: key stream generation process; three-round scrambling process; and one-round diffusion process. The proposed mathematical model is applied for the key stream generator in the first process. The initial values and parameters are sensitive to both the secret keys in the new scheme and plain images. The second process employs the Josephus traversing in scrambling; then the rows and columns of pixels are exchanged. The third process can modify the pixel gray-level values and crack the strong correlations between adjacent pixels simultaneously. The initial conditions for chaotic systems are derived using external secret keys by applying some algebraic transformations to the key. Security analysis indicates that the new scheme is effective, which can resist common attacks.