Research On Image Encryption Algorithm Based On Hyper-Chaos

With the rapid development of computer network technology, more and moreinformation needs to be exchanged and transmitted over the network, so theprotective treatment of important or sensitive information is very necessary. Digitalimage as an important information carrier has features of intuition, less error-proneand easily accepted, and so on. And digital image data has unique features itself, suchas information-rich of data bits, strong correlation between pixels, having lots ofredundancy, etc, so as that the traditional encryption methods can’t meet theencryption requirements.Chaotic systems have excellent pseudo-randomness and ergodic property. It issensitive to the initial value and parameter. In addition, chaotic systems show theoverall stability with regional instability. These are well matched with the basicrequirements of cryptography. However, many current image encryption methods arelow-dimensional chaotic systems. The low-dimensional chaotic encryptiontechnology suffers to the exhaustion attack, phase space reconstruction and otherseasily, which has been proved to be unsafe. The high dimensional chaotic system withcomplex structure, multi-parameters, and more unpredictability of motion behavior,will improve the safety of image encryption undoubtedly.First of all, the background and significance of research are described, withcurrent situation at home and abroad. Then the relevant knowledge of chaos theory,cryptography, and chaotic cryptography was introduced. After that, the chaotic imageencryption technology and the pretreatment methods of hyper-chaos sequence werehighlighted.Second, security analyses were carried out for a hyper-chaotic image encryptionalgorithm. Results show that the intermediate key sequence of this algorithm hadnothing to do with the plain-text with its encryption formula can be of anti-pushoperation, and the pixels which to be encrypted were only adopted the method ofXOR. These made the intermediate key sequence be decoded, so as to all thecipher-text. Based on this research, a kind of improved image encryption algorithm based on hyper-chaotic system was put forward with simulation analyses of it. Testsshowed that the improved algorithm had large key space with the equilibriumdistribution of cipher-text gray. Compared with the original algorithm, the improvedalgorithm is more sensitive with key and stronger to resist differential attack.Finally, the image encryption algorithm of bit-plane based on hyper-chaossystem was studied. Plain-text image was decomposed into bit-planes according topixel bits, and plain-text information was got to generate keys through iteration ofhyper-chaotic system. Then, binary key sequence, which was obtained after thepretreatment of the hyper-chaos sequence, was used to perform separation ofscrambling operations among high four bit-planes. After that, adaptive encryptionoperation was carried out among high four bit-planes and low four bit-planes to getthe cipher-text. The results of several analyses, such as histogram, relevant of pixel,information entropy with key sensitivity and key space of the cipher-text, showed thatthe encrypted image was very sensitive with plain-text and keys. And it also caneffectively resist the statistic, brute-force and differential attacks, etc, which verifiedthe security of algorithm.