The Cryptanalysis And Design Of The Chaos Based Image Encryption Scheme

With the rapid development of the Internet technologies and communication tools,the privacy protection of multimedia data such as images and videos has attracted extensive attention.The traditional encryption algorithm may cannot use to protect the content of the multimedia data due to the inherent characteristics of the multimedia data such as massive data,real-time and strong correlation between adjacent elements.In addition,it is difficult for traditional encryption algorithms to achieve real-time encryption.To solve the above-mentioned security problems of the multimedia information,combining chaos theory with traditional encryption algorithms,researchers in the field of non-linearity and computer science have designed a variety of different types of chaotic multimedia encryption algorithms.Particularly,chaos-based image ciphers account for an ever-increasing proportion of chaotic multimedia encryption algorithms.Like traditional ciphers,chaos-based image schemes must be comprehensively tested before they are applied in the real world.However,the existing literature analyses had shown that the cryptanalysis works of chaosbased image encryption schemes are insufficient and the experiences for designers of chaotic image encryption schemes are not enough.It leads that(1)the security deficiencies of chaos-based image encryption schemes have not been fully explored,(2)constructing an encryption scheme which achieve a good trade off between security and efficiency would be a hard work.Based on the aforementioned background,this thesis first gives a cryptanalysis for a classical chaotic image encryption scheme.Specifically,a medical image cipher using high-speed scrambling and pixel adaptive diffusion has been proposed recently by Hua et al.It mainly consists of random data insertion,high-speed scrambling and pixel adaptive diffusion.Before performing the permutation-diffusion process,the external random pixels are inserted to the surrounding of the plain image.Then the high-speed scrambling and the pixel adaptive diffusion process are used to randomly shuffle adjacent pixels and spread them to the entire cipher image,respectively.This scheme can achieve both high efficiency and strong robustness.Unfortunately,we have found that the cipher image can be completely recovered by using a chosen plain image attack without any knowledge about the secret key.To resist this attack,we propose an improved encryption scheme which is extremely sensitive to plain image based on the original algorithm.Experimental results and security analysis show that our improved encryption algorithm can not only resist the chosen plain image attack but also maintain the merits of the original one.Secondly,to increase the security,this thesis proposes a novel image encryption scheme based on the piece wise linear chaotic map(PWLCM)and the standard map.To the best of our knowledge,it is the first chaos-based image encryption scheme combing the PWLCM with the standard map,which adopts permutation-diffusion structure.Not like the traditional scrambling way,a hierarchical diffusion strategy,which not only change the pixel position but also modify the value,is employed in permutation phase.The operation model of row-by-row and column-by-column is further used to enhance the efficiency in the diffusion process.Consequently,a good trade off efficiency and security can be achieved.Furthermore,the numerical simulations and performance analyses illustrate that the proposed encryption scheme can be used in practical application scenarios required lightweight security.Another research topic of chaos-based cryptography is secure communication based on chaotic synchronization.Therefore,this thesis finally proposes a new medical image encryption scheme based on the synchronization control of a fractional-order chaotic system.More concretely,a model-free adaptive sliding mode control(ASMC)methodology is firstly proposed for synchronization of chaotic fractional-order systems(FOSs)with input saturation.Based on the frequency distributed model and the non-integer version of the Lyapunov stability theorem,a model-free ASMC method is designed to overcome the chaotic behavior of the FOSs.The control inputs are free from the nonlinear-linear dynamical terms of the system because of utilizing the boundedness feature of the states of chaotic FOSs.Moreover,a new medical image encryption scheme is tentatively proposed according to our synchronization method,and its effectiveness is verified by numerical simulations.Furthermore,the performance and security analyses are given to confirm the superiority of the proposed encryption scheme,including statistical analysis,key space analysis,key sensitivity analysis,differential attack analysis,encryption quality analysis,and time performance analysis.Based on the cryptanalysis of the image encryption algorithm,this paper designs two different image ciphers with the discrete chaotic system and the continuous chaotic system respectively.As a result,the cryptanalysis work of this paper provides an important reference to find the vulnerability of chaotic image encryption algorithm,and it is of great significance to further summarize the security evaluation criteria of the chaotic image cipher.In addition,for lightweight security requirements application scenarios,two chaotic image ciphers are tentatively designed based on different chaotic systems.It provides an empirical reference for exploring and designing secure and efficient encryption algorithms,and thus provides literature for further condensing the design principles of more general chaotic encryption algorithms.To sum up,this paper studies the cryptanalysis and the design of chaotic image cipher which has a certain meaning to further promote the development of chaos-based cryptography.