Image Compression-encryption Algorithms Combining Hyper-chaotic System With Discrete Cosine Transform

The hyper-chaotic system,compressive sensing and discrete fractional random transform are combined for image security in this dissertation.Two image compression-encryption algorithms are designed,and their high security and good compression performance is verified by a large number of simulation experiments.The main research results of this dissertation are as follows:An efficient image compression-encryption algorithm based on hyper-chaotic system and 2D compressive sensing is proposed.The discrete cosine transformation is used to sparse the original image,and the measurement matrices controlled by Logistic map is utilized to measure the original image in two directions to achieve compression and encryption simultaneously.Then the resulting image is re-encrypted by the cycle shift operation controlled by a hyper-chaotic system.Cycle shift operation can change the values of the pixels efficiently.The proposed nonlinear cryptosystem decreases the volume of data to be transmitted and reduces the keys for distribution simultaneously.The decryption process includes the inverse process of the cycle shift operation and the reconstruction process with the ANSL0 algorithm.Simulation results indicate that the proposed image compression and encryption algorithm is effective,robust and secure with good compression performance and is also able to stand statistical analysis,brute force attack and noise attack due to its considerably large key space.An image compression-encryption algorithm based on hyper-chaotic system and discrete fractional random transform is designed.The discrete cosine transform is first performed to transform the original image into a spectrum,and then the resulting image is compressed according to the method of spectrum cutting.The chaotic sequence originated from the high dimensional hyper-chaotic system is used to control the random matrix of the discrete fractional random transform,and the compressed image is encrypted in the discrete fractional random transform domain.The order of DFRT and the parameters of the hyper-chaotic system are the main keys of this image encryption algorithm,which enlarges the key space.The algorithm can not only be applicable for compressing and encrypting single image,but also for encrypting multiple images once.As for multiple images,the original images are necessarily transformed into spectra by the discrete cosine transform before the encryption,and then the spectra are incised and spliced by Zigzag scanning into a composite spectrum to achieve the compression of multiple images.Simulation results demonstrate that the proposed image compression and encryption algorithm is of high security and good compression performance.In addition,it also could resist some common attacks.