| The rapid development of computer technology has made information transmission faster and more convenient,so that information security has become more complex.As an important component of multimedia files,digital images have the characteristic of image information transmission,and are widely used in social networks,finance,medical and military fields,etc.Protecting digital image security has become a research hotspot.Traditional digital image encryption is the most intuitive of the various protection methods,which can encrypt the image into a meaningless noise-like cipher image,so as to protect the image.However,the noise-like and unseen characteristics of cipher images are likely to attract the attention and thus cause attacks.In order to solve this problem,two different visual encryption algorithms based on chaotic systems have proposed in the thesis.The overall idea is to use chaotic systems to generate pseudo-random sequences for image pixel dislocation and diffusion,and then embed the encrypted cipher image into the carrier image via wavelet transform and obtain a transmitted image that can be transmitted directly over the channel.The thesis first proposed a visual image encryption algorithm based on LSB,which employs a new two-dimensional chaotic model modified by the cascaded coupled model and processes the output of this model by linear operations to obtain the cipher stream.The plain image can be encrypted into a cipher image through Arnold pseudo-random matrix disruption,distribution diffusion and plain associative disruption processes in turn,followed by decomposition of the colour carrier image by RGB three-channel and embedding the cipher image into this carrier image through integer wavelet transform and LSB substitution.Then,a visual image encryption algorithm with high performance is further proposed.This scheme has a cryptographic algorithm with a shared encryption and decryption process.The algorithm’s disruption and diffusion processes are associated with the plaintext and use techniques such as S-boxing,high and low bit separation and merging.In addition,an image disruption algorithm is added to the image embedding process to further ensure the image security.Finally,the two schemes are simulated to analysis their encryption and decryption speed,key space,random properties of chaotic sequences,statistical properties,sensitivity analysis,information entropy and steganography.The security performance of the two chaos-based visual image encryption algorithms in image transmission is verified by comparing them with other schemes in the reference. |
