Research On Chaos Based Image Encryption And Compression Algorithm

Digital image has become an important information carrier in modern communication field because it can transmit information vividly and widely exists in people's life.However,the image data is large and redundant,and it easy to leak information in storage and transmission.In order to improve storage efficiency,transmission efficiency and security of image data,it is very necessary to compress and encrypt image.Combining image encryption with image compression synchronously can result in the design flexibility and computational simplification.Moreover,encryption and compression are mixed together to ensure better security.However,since encryption is diffusion and confusion of image,the correlation between pixels can be destroyed,and image compression needs to use the correlation of images to eliminate redundancy.Therefore,there is a clear contradiction between the encryption and compression.Reducing the conflict,guaranting both good compression performance and good encryption effect to combine image encryption with image compression synchronously is a very meaningful topic.As a nonlinear dynamic system with high degree of freedom,the good cryptography properties of chaos enable the chaos-based cryptographic systems to possess excellent randomness in ciphers.At the same time,the determinacy of chaotic motion make it easy to realize for applying chaos to cryptography.The computation cost of chaotic cryptography is far less than that of other traditional cryptography method.Therefore,it is very suitable for image encryption processing with large amount of data.Based on the chaos theory,joint image compression and encryption is studied in this paper.The main research contents of this paper are as follows:?1?Hyperchaos system and pseudo-random sequence generation algorithm.The theoretical study on chaotic system is the premise to guarantee the security of chaotic encryption algorithm.The limitation of computer precision makes the low dimensional chaotic system prone to performance degradation,which affects the encryption security.This paper first studies the theory of hyperchaotic system.Then a five-dimensional hyperchaotic system is constructed by adding a linear and nonlinear state feedback controllers and its dynamic characteristics is analyzed.Generating chaos system,namely chaos anti-control or chaotization,used in the field of cryptography is an important subject.The dynamic behavior of hyperchaotic system is more complicated,which has obvious advantages over low dimensional chaos.The generated chaotic sequence by hyperchaotic system relies on more parameters and initial values and its dynamic behavior is difficult to predict.The maximum Lyapunov exponent of the constructed five-dimensional hyperchaotic system is larger than that of many classical hyperchaotic systems,which has more significant chaotic behavior and is more suitable for application to image encryption.Secondly,in the guarantee of hyperchaos sequence character such as nonlinearity,randomness,use long cycle characteristics of linear feedback shift register to disturb hyperchaos sequence to construct pseudo-random sequence generator with good performance.That effectively solves the cycle degradation of discretized chaotic sequence.Finally,the designed hyperchaos cipher is applied to image encryption for several image formats.The algorithm adopts the bidirectional diffusion and scrambling using three dimensional baker with dynamic block based on hyperchaos to ensure security and efficiency.?2?Joint image lossy compression and encryption algorithm.In terms of lossy compression and encryption,this paper first studies the joint image compression and encryption scheme based on discrete cosine transform.Discrete cosine transform is fast,and it is widely used in image processing.Based on the feature of discrete cosine transform and the hyperchaotic system,a joint image encryption and compression scheme which can deal with two images simultaneously is proposed.The quantified coefficients are divided into groups,so as to full encryption is realized and the influence on compression performance is reduced.The scheme can effectively give consideration to both security performance and compression performance on joint compression and encryption schemes based on discrete cosine transform.Secondly,the algorithm of image encryption and compression based on the curvelet transform is studied.As a multi-scale transform,curvelet transform has a good orientation characteristic compared with wavelet transform,and is more suitable for the characteristic of image curve detail.However,at present,the compression processing based on the curvelet transform does not consider the security or the compression and encryption are dealt with separately.Based on the characteristics of curvelet transform,quantization matrix is designed.Then according to the quantization matrix,curvelet coefficients of different scales and different directions are dealt with threshold processing,run-length coding,hyperchaos based encryption and Huffman coding.Encryption and compression are combined,full and secure image compression based on curvelet transform is realized.?3?Joint image lossless compression and encryption algorithm based on on interpolating the biorthogonal integer wavelet transform?IB-IWT?and set partitioning in hierarchical trees?SPIHT?.In terms of lossless compression and encryption,for there is no good joint image lossless compression and encryption algorithm,this paper studies the joint image encryption and compression scheme based on IB-IWT and SPIHT.Compared with other integer wavelet transforms based on the lifting method,IB-IWT has only two lifting steps,which reduces the number of floating-point operations.So it is very suitable for real-time image lossless compression.Hyperchaos based encryption is performed on wavelet coefficient,SPIHT coding and bit stream.The proposed Secure SPIHT?SSPIHT?integrates encryption into the SPIHT sorting process.SSPIHT does not affect the compression performance while increases the security.In the encryption algorithm,the nonlinear operation based on the inverse operation of the finite domain Z₆₅₅₃₇5537 is introduced into the diffusion process to resist the attack.The method is effective in the joint processing of image encryption and lossless compression.?4?Joint image lossless compression and encryption algorithm based on CALIC with predictive model.In terms of lossless compression and encryption and high correlation between image pixels,joint image encryption and CALIC compression scheme is studied.CALIC is easy to implement and has good lossless compression performance without considering security.This paper first studies the CALIC coding principle,discusses and evaluates four parts that can be encrypted:gradient-adjusted prediction?GAP?,final residual,two lines of pixels needed by prediction mode,and entropy coding bit stream.Then according to four parts,encryption methods are designed based on the hyperchaotic system.Secure image compression based on CALIC is realized,the security is added in the case of minor reduction of compression ratio.