Research On And Cryptanalysis Of Chaos-based Image Encryption Technologies

With the dramatic developments of computer and communication technologies,multimedia contents such as image,video have become the widest and most important information of networks,owing to their clearity,lifelikeness and vividness.As the image always involes the commercial,military,economical,medical,scientific and political sensitive affaris,how to secure their transmission and storage over public networks has drawn much more attention than ever before in cryptographic and information security fields.Encryption is the simplest whereas the most effective approach for information security.However,recent research achievements have shown that traditional block ciphers such as DES,AES are poorly suited for imag encryption.For ciphering images,one should pay attention to their intrinsic features such as large volume and high pixel correlation etc.,which are distinc from textual contents.Chaos theory has paved a novel perspective and approach for image encryption.The fundamental characteristics of chaotic systems,such as ergodicity,sensitivity to initial condition and control parameters,have attracted researchers' attention as such features can be considered analogous to the desired cryptographic properties.In the past decades,chaos-based ciphers has drawn much attention,and become an important branch of modern cryptography.In this paper,we summarize the recent achievements on chaos-based image encryption,and then investigate six characteristic image cryptosystems.The main innovations of these cryptosystems lie in three aspects:permutation approach with diffusion effect embedded,reuse of the chaotic state variables and Gray-code based permutation strategy.Besides,we have made cryptanalysis on a recently developed image permutation-then double random phase encoding cryptosystem.We propose and experimentally verify an effective chosen-plaintext attack,and then we improve this scheme with no extra complexity and equipment required.The innovations of the present paper can be summarized as follows:(1)Aiming to accelerate the diffusion process of traditional chaos-based image ciphers,two kinds of permutation approaches that can contribute certain diffusion effect have been developed.Based on these novel permutation techniques,two complete image cryptosytems have been subsequently built.As effective image permutation approaches,the proposed algorithms firstly ensure the image permutation effects,which should be qualified and comparable with traditional image permutation techniques.As the primary novelty,the algorithms should also contribute image diffusion performance simultaneously.The subtle difference between the plaintext has spread out to larger scale in the ciphertexts.Therefore,the achievement can effectively overcome the drawback of the traditional ciphers that the image diffusion effects are merely contributed by the diffusion module.The required cipher counts can be therefore reduced,and the encryption speed is thus accelerated.(2)In most of the permutation-diffusion type image ciphers,permutation and diffusion are two independent procedures.And hence,at least two chaotic state variables are required for encrypting one plain pixel,in the permutation and diffusion stages respectively.Chaotic state variables produced with high computational complexity are not sufficiently used.Regarding this,three kinds of technologies that can reuse the chaotic state variables in the permutation and diffusion procedures have been proposed.In these mechanisms,the chaotic state variables are independently produced,and are subsequently reused in the permutation and diffusion procedures to produce the required key stream elements.In this scenario,the required chaotic iteration and quantization can be double reduced,and the encryption efficiency is consequently promoted.(3)A novel Gray-code based image permutation approach is proposd.In traditional chaos-based image ciphers,the primary computational complexity derives from the floating point arthmatic in the chaotic iteration and quantization.Regarding this,a novel permutation strategy based on the intrinsic and nonlinear features of(n,k,p)-Gray-code achievement is proposed.As the Gray code convertion just requires limited XOR and right shift operations,which are primitive commands of CPU and are high efficiently implemented,the proposed permutation approach is also with high operation efficiency.Collaborating with an image diffusion module with an orbit perturbing mechanism,a complete image cryptosystem is subsequently constructed.(4)An effective chosen-plaintext attack is investigated for image permutation-then double random phase encoding cryptosystems.Such cryptosystems synthesize the advanteges of chaos and optical techniques,and have been always considered secure.However,cryptanalysis reveals that the original combined structure does little contribution to address the flaws in DRPE and image permutation themselves.An effective chosen-plaintext attack is then proposed,and its effectiveness has been experimentally verified.Corresponding improvement is subsequently proposed,without any extra optical equipment and computational complexity required.