Chaotic Image Cryptosystem Based On Wavelet Transform And Genetic Algorithm

In recent years,due to the rapid development of communication technology(5G,etc.),digital images occupy a significant portion of network communication,so the security of image transmission has become particularly important.Due to the large amount of data and strong correlation of images,text based encryption schemes such as AES,SM4,DES,RSA,etc.cannot be directly used for digital image encryption.With the development of chaos theory and unified encryption theory,digital image encryption technology has become an important component of information security.Aiming at the shortcomings of classical chaotic encryption algorithms such as large demand for random numbers and poor security performance,this thesis proposes two chaotic image encryption systems.One is a chaotic encryption system based on improved wavelet transform and STL mapping.The STL chaotic system with continuous control coefficients and large phase space is used as a pseudorandom number generator,and the generated pseudorandom numbers have good randomness.An improved wavelet transform structure is used to divide the image into two columns for encryption,which reduces the use of pseudo random numbers and ensures encryption efficiency and strength.According to the simulation structure and performance analysis,it is shown that the image encryption system can effectively resist common attacks such as exhaustive key attacks,ciphertext statistical analysis,and selective plaintext attacks.The second is a unified image encryption system based on dynamic S-box and wavelet transform.Firstly,a genetic algorithm is used to generate S-boxes with high nonlinearity,which meet strict avalanche standards and output bit independence standards.This replaces the prediction and update functions in the lifting wavelet structure,improving the encryption strength of the system.Secondly,the system is constructed based on unified encryption theory,which can use the same algorithm for encryption and decryption,making the software and hardware implementation of this algorithm very convenient and greatly reducing costs.By comparing and analyzing with other existing encryption schemes,it can be seen that this algorithm has the advantages of high running speed,large key space,good statistical characteristics of ciphertext,and high sensitivity.