S-Box Design And Image Encryption Based On Hyperchaos

In today’s world,there is an ever increasing need for new techniques of maintaining and protecting privacy and integrity of information of mass communication and private information.Chaos theory and cryptography overlap some features which can lead to developing secure chaos-based cryptosystem for secure communication of texts and images.Some of the basic features of chaotic systems such as sensitivity to initial conditions,ergodicity,and pseudorandom behavior,fulfill the analogous requirements for a good cryptosystem.This thesis focuses on the chaos theory,chaotic systems and its types,design of cryptographically strong S-boxes based on hyperchaotic system and image encryption based on the hyperchaotic system.The proposed research work conducted in two parts based on hyperchaos.The first part contains a design of cryptographically strong S-box via the 4D hyperchaotic multi-wing system.At a fundamental level,the security of symmetric key cryptosystems ties back to Shannon’s properties of diffusion and confusion.In constructions of a symmetric key cryptosystem,diffusion and confusion are commonly realized with the application of linear and nonlinear operations,respectively.The Substitution boxes(S-boxes)are the only nonlinear part in a Substitution-Permutation cryptosystem.Without these nonlinear components,the adversaries would easily compromise the system.Therefore,S-box plays an imperative role in designing a cryptographically strong block cipher.Designing S-box based on chaos has attracted lots of attentions because of its distinct characteristics relevant to cryptography.In the proposed work,a batch generation of cryptographically strong S-boxes based on the 4-D 4-wing hyperchaotic system is presented.The sophisticated nonlinear behaviors of suggested hyperchaotic system are used to generate two pseudorandom 8-bit integer sequence,which further drives iterative two-position swap on the identical map on GF(28).According to the indicator of typical evaluation criteria including nonlinearity,differential uniformity,SAC,output bits independence criterion and bijective property,the preferred S-box is obtained from all those patch-generated ones.The comparison with the state-of-the-art chaos-based schemes shows that the obtained S-box achieves better cryptographical performance.Secondly,the presented work focuses on permutation-substitution image encryption based on 4D four-wing hyperchaotic system.In the field of cryptography,a huge research is undergoing on image ciphering to assure security vulnerabilities in confidential images.Multi-dimensional Hyperchaos is emerging area to enhance the security requirement in real-time image encryption instead of the one-dimensional chaotic system due to large key space and complex unpredictable nature.A 4D 4-wing hyperchaotic system is employed to encrypt an image with two independent core procedures i.e.permutation and substitution.A permutation is executed in both column-wise and row-wise by permutation index matrix to spread the influence of a single pixel over others.Moreover,the permuted image is completely confused twice in substitution process.Firstly,each previous ciphered pixel value is XORed with next plain image pixel in the forward direction.Secondly,a key image is produced from a cryptographically strong S-box based on the 4D 4-wing hyperchaotic system.A key image is used for pixel by pixel masking to complete the encryption process.The proposed method is simple,easy to implement,with large key space and capable of encrypting different type of grayscale images with perfect scrambling nature.Histogram analysis,correlation of adjacent pixels analysis,information entropy analysis,key space analysis,key sensitivity analysis,NPCR,and UACI analysis quantify the security level and efficiency of the suggested method.Security analysis shows that the proposed algorithm has high security and abilities to resist statistical attacks,brute-force attacks and differential attacks,which provides enough security for real-time image encryption and transmission.Finally,the whole conclusion is drawn,and the further directions are prospected.