Research On The Information Encryption Technology Based On Chaos Theory

The chaotic system has the desirable properties of pseudo randomness,unpredictability, broadband spectrum, ergodicity and high sensitivity to theinitial value and system parameters, so the research of chaotic theory and itsapplication has attracted more attention. Different from text, image has itsintrinsic properties, such as bulk data capacity and strong correlation amongpixels, so that some traditional data encryption technologies are unfit fordigital image encryption. The development of chaotic cryptology provides a newway for digital image encryption. Beside this, the research of chaotic controland chaotic synchronization has developed greatly and has some potentialapplications in secure communication.The research of the paper contains two aspects, the chaos based imageencryption technology and chaotic synchronization based secure communicationtechnology, and the content can be summarized as follows:Firstly, an integer wavelet transform (IWT) based chaos image encryptionscheme is proposed. The integer wavelet transform can be implemented with lowercomputational complexity and less memory requirement. It is more important thatthis transform is much suitable in applications with integer operations.Therefore, this paper presents a chaos image encryption algorithm based on IWT.After the plain image is decomposed with the integer wavelet, the scramblingand diffusion transforms are applied to lower frequency subband and thescrambling transform is applied to higher frequency subbands. Then, the ciperimage is obtained after integer wavelet reconstruction. The experimental resultsshow that the algorithm has large key space and high key sensitivity, and canresist statistical and other typical attacks, such as noise attack, croppingattack and compression attack. The peak signal to noise ratio (PSNR) is usedto measure the decrypted image quality.Secondly, this paper constructs a new spatiotemporal chaotic system bydefining the local nonlinear map in the coupled map lattices (CML) with the nonlinear chaotic algorithm (NCA) chaotic map, and proposes an image encryptionscheme with the permutation-diffusion mechanism based on these chaotic maps.The encryption algorithm diffuses the plain image with the bitwise XOR operationbetween itself pixels, and uses the chaotic sequence generated by the NCA mapto permute the pixels of the resulting image. Finally, the constructedspatiotemporal chaotic sequence is employed to diffuse the shuffled image.Statistical properties of the algorithm are tested by histogram analysis,information entropy analysis, correlation analysis and differential analysis,etc. The safety of the algorithm is tested by sensitivity analysis and key spaceanalysis.In addition, a bit-level permutation-based selective color image encryptionscheme is presented. Logistic map and spatiotemporal chaos are included in thescheme, and the chaotic series generated by logistic map is adopted as the initialvalue of spatiotemporal chaotic system. Because the lower computationalcomplexity of permutation process and the bit-level permutaion has the effectsof both confusion and diffusion, the encryption scheme only contains permutationprocesses. This algorithm forms a binary image by assembling some higher bitsof each pixel from different color channels. Then permute each row of the binaryimage following by permuting each column with the position matrixes generatedfrom the spatiotemporal chaos. In order to resist the chosen-plaintext attackand known-plaintext attack, it should be guaranteed that a secure cryptosystemshould be sensitive to the plaintext. That is to say, a slight change of a pixelof the plain image can cause great change in the cipher image, so the plain-imageis included in the encryption scheme and the key should be dependent on the plainimage.Finally, the chaotic synchronization system driven by chaotic signal outsideis investigated, and which is applied to secure communication scheme. Accordingto the principle that two chaotic systems with different initial values drivenby the same noise can achieve synchronization, continuous and discrete chaoticvariables are adopted to drive two Lorenz chaotic systems, and then thesynchronization effects are compared. In addition, the influencing factor of the chaotic synchronization scheme driven by intermittent signal is discussed.Finally apply the chaotic synchronization driven by discrete chaotic signal tosecure communication. Then test the quality of recovered signal and robustnessof the system.