Research On Image Encryption Algorithm Based On Hyperchaotic System

With the development of the progress of network information technology,the digital image has become one of the important ways for people to obtain information.Although the digital image has the characteristics of intuitiveness,convenient,and fast,it has gradually gained people’s favor,however its security problems can not be ignored.How to ensure the safe transmission of an image through image encryption technology has become one of the hot spots of current research.A digital image has the characteristics of high redundancy,a large amount of data,and strong pixel correlation,which are different from the one-dimensional data stream.Therefore,traditional encryption algorithms designed for the one-dimensional data stream,such as DES and AES,cannot be applied to image encryption.We need to design a new encryption algorithm to meet the requirements of image encryption.A chaotic system has the characteristics of initial value sensitivity,ergodicity,inherent randomness,which is very consistent with the basic requirements of cryptography,so it has a broad prospect in image encryption.The thesis proposes an image encryption algorithm based on Chen hyperchaotic system.This algorithm utilizes the Arnold scrambling method to scrambling the original image to change the correlation of pixels.Then the chaotic sequence is used to diffuse the scrambled image to get the final encrypted image.Experimental results show that the keyspace of the algorithm is large,the histogram distribution of ciphertext pixels is more uniform,and it has an excellent encryption effect.However,the application scope has some limitations.The algorithm is suitable for square images.Because all parameters in the system are fixed,when the attacker has enough sample data,the encryption algorithm will be cracked.The algorithm can not resist the selective plaintext attack,and the ability to resist the differential attack is not well-built,so it needs further improvement.Based on the above algorithm,the thesis proposes a Chen-hyperchaotic-systembased plaintext associated image encryption scheme.By inputting the original plaintext image into the SHA-512 function,the corresponding hash value is obtained,and then the initial value and system parameters of the chaotic system are calculated.In the scrambling stage,a scrambling method based on a chaotic sequence is adopted in this scheme,which can realize image encryption of any format.In the diffusion stage,the scheme regenerates the initial value and system parameters of the new chaotic system.It uses exclusive or operation to enhance the sensitivity of plaintext to ciphertext.The experimental results show that the scheme can resist the selective plaintext attack and differential attack.After encryption,the pixel histogram is evenly distributed,the keyspace is large,and the sensitivity is strong,which meets the basic requirements of image encryption.