A chaos-based image encryption algorithm with its hardware implementation

In this thesis, a chaos-based symmetric image encryption algorithm is designed for color and gray images. The proposed algorithm contains permutation (confusion) and modification (diffusion) processes related to the image pixels. In confusion part, Arnold Cat map is used to change the pixel positions of the plain image and then improved Logistic map for the generation of encryption key is used to modify the pixel values in diffusion part. Firstly, an improved chaotic map is designed to exhibit better performance than the standard Logistic map in terms of key space range, complexity, uniformity and chaotic substantiality. Generated encryption codes are not only sensitive to the control parameter and initial condition of the improved map but also strongly depend on the plain image characteristic. Hence, the proposed scheme can resist statistical attacks, differential attacks, known-plaintext and chosen-plaintext attacks. Furthermore, to get higher encryption strength of the cryptosystem, both confusion and diffusion processes are repeated one more time and different encryption codes are used in each iteration in diffusion part. All statistical and differential analyses about the proposed cryptosystem are studied in detail. Compared to the results of the some conventional encryption algorithms, the proposed scheme shows superior performance according to the speed and security of the algorithm. The practical applications including key generator, encryption and decryption parts of the proposed cryptosystem are successfully synthesized and implemented into the FPGA (Field Programmable Gate Array) as a hardware environment. Theoretical analyses and simulation results confirm that the proposed image encryption system has high level of security and effectively encrypts and decrypts the square images with different sizes as well. Experimental results also demonstrate the feasibility of the proposed cryptosystem in practical applications.