Multiple-Image Encryption Algorithms Based On Fractional Order Transform

Secure information transmission is becoming increasingly important with the fast development of multimedia communication and computer technology.Images play a crucial role in information transmission,since they can carry large amounts of data intuitively.Images are easily stolen by the attacker during transmission or storage,resulting in information leakage,so the secure transmission of image information has attracted great attention.To solve the problems that only a single image can be encrypted and the encryption efficiency is low,the research of secure and efficient multi-image encryption algorithm is of great applications.Two multi-image encryption algoritluns are established based on fractional-order transform and chaotic systems.The main research content of this dissertation is as follows.A nonlinear multi-image encryption algorithm based on chaotic system and 2D linear canonical transform is designed.The low-frequency sub-bands of the four grayscale images are extracted with the contourlet transform,respectively.Then the four sub-bands are synthesized into a ID sequence,which is scrambled with a chaotic sequence produced by the 2D Logistic map.Subsequently,the image converted from the resulting ID sequence is re-encrypted into a white noise-like image by phase truncation and phase reservation in the 2D linear canonical transform domain.Finally,the XOR operation based on the 2D Logistic map is performed on the white noise-like image to yield the final ciphertext image.The parameters of the 2D linear canonical transform and the Logistic map as the main keys enlarge the key space of the proposed multi-image encryption scheme.In addition,the keys regarded as the initial values of the chaotic systems are related to the original images.The phase truncation and the bitwise XOR operation,as nonlinear processes,improve the robustness of the presented multi-image encryption scheme against chosen-plaintext attack.Numerical simulation results verify the validity and the reliability of the proposed multi-image encryption scheme with good performance.A nonlinear multi-image encryption scheme is proposed by combining chaotic system with reality-preserving discrete fractional angular transform.The 2D lifting wavelet transform is performed on the four grayscale images to extract four approximation coefficients,respectively.Then a real-valued image is obtained from the matrix synthesized by the four approximation coefficients with the reality-preserving discrete fractional angular transform.Subsequently,the pixel values are changed with DNA sequence operations.Finally,the resulting image is scrambled with a chaotic sequence produced by the Logistic-Sine system to yield the final ciphertext image.In addition,the initial value of the chaotic system is calculated by the 256-bit binary sequence obtained by taking the statistics information of the original images as the input of SHA-256,which further improves the security of the algorithm.DNA sequence operations,as nonlinear processes,could improve the robustness of the presented multi-image encryption scheme.Simulation results demonstrate the security of the presented multi-image encryption scheme,which can effectively resist common attacks such as noise attacks,chosen-plaintext attacks and statistical analysis attacks.