Research On Digital Image Encryption Algorithm Based On Chaos Theory

With the rapid development of the Internet, multimedia and cloud computing technologies, a greatdeal of multimedia information, such as audio, video, images etc, can be transmitted conveniently throughnetwork. But the problem of security in storage and transmission of confidential multimedia data isgrowing in importance. Many conventional text ciphers such as DES, AES, RSA, are no longer suitable forthe digital image encryption in real time due to some intrinsic properties of images such as bulky datacapacity, high redundancy and strong correlation etc. In order to protect the digital image informationefficiently, many digital image encryption algorithms have been designed based on the feature of theimages. In particular, introducing chaos theory to image encryption has attracted widely attentions for manyresearchers.Chaotic systems have demonstrated great potential for information especially image encryption due tothe desirable properties of high sensitivity to initial conditions and parameters, pseudo-randomness,unpredictability and so forth. In recent years, many image encryption algorithms are proposed based onchaotic systems. However, most existing chaotic cryptosystems still suffer from fundamental drawbackssuch as small key space, weak security function and only using integer-order chaotic systems. Furtherstudies reveal that the fractional-order chaotic systems has more complex dynamical behavior than theinteger-order ones, which can reflect the history information of the systems and has a strong ability inmemory. Therefore, the studies on digital image encryption algorithms based on fractional-order chaoshave great theoretical significance and practical value.Combining the algorithm design and numerical simulations, this paper proposes several fast andsecure digital image encryption algorithms using the hyperchaotic systems and the fractional-order chaoticsystems via the techniques of image blocking, the permutation of the image pixel positions and thecross-diffusion of the cipher-text. Furthermore, the detailed analysis on the security and efficiency of thepresented image encryption algorithms are given. The main achievements contained in this paper are asfollows:Based on a hyperchaotic system and a fractional-order chaotic one, a digital image encryption schemeis proposed. Firstly, a hyperchaotic system is used to generate the permutation matrix, which is then appliedto scramble the image pixel positions. Secondly, the chaotic key generated from a fractional-order chaoticsystem is employed to modify the image pixel values by introducing the crisscross diffusion of thecipher-text between the color components. The presented encryption algorithm can not only effectivelyreduce the correlation coefficients of adjacent pixels in the plain-image, but resist a statistical attack.By using the fractional-order chaotic systems and the parity crisscross diffusion technologies, a digitalimage encryption algorithm is designed. According to some mapping function, the pixel positions of theplain-image are scrambled. Each color component is diffused applying both the alternate back and forth andthe parity crisscross method with two rounds. The experimental results show that the designed algorithm has good encryption effect, high safety performance etc, and can well resist against a ciphertext-only attack,a differential attack and so forth.A new chaotic encryption algorithm is presented based on the permutation and diffusion of the imageblocks. Firstly, the plain-image is divided into several sub-images and the blocks are shuffled according tothe random integer sequences generated from the Logistic system. Secondly, each color component of thescrambling image is decomposed into two blocks. Then the image pixel values of both two blocks aremodified and diffused simultaneously in a parallel manner with two rounds. The simulation resultsdemonstrate that the designed algorithm has good encryption effect, high security, fast speed etc.