Research On Security Of Image Encryption And Watermarking Algorithms Based On Chaos

With the development of computer network and communication technologies,multimedia data represented by images and videos has grown explosively.How to ensure the security of multimedia data has become an important research.In order to protect the security of multimedia data such as images,there exist two techniques:image encryption and digital watermarking.The former can prevent the attacker from getting the content of the image,and the latter illegal copy and propagation.The sensitivity of chaos to initial conditions and system parameters,and the chaotic sequences are non-periodic and pseudo-random are naturally associated with cryptography.In the fields of image encryption and digital watermarking,a large number of image encryption and digital watermarking algorithms based on chaos have been proposed.Compared with traditional cryptography,the security analysis of chaos-based image encryption algorithms has not been thoroughly analyzed.For chaos-based watermarking,the work of security analysis is weak.Algorithm design and algorithm cryptanalysis promote each other in the game of attack and defense,and continue to develop.In this thesis we focus on the security of algorithms and study chaos-based image encryption and chaos-based digital watermarking.On the one hand,we analyze the security of some typical algorithms,and summarize the security flaws of these algorithms.On the other hand,we design more secure algorithms.Through in-depth research and analysis of algorithm security,we have made the following progress:(?)We analyze the security of two multi-round permutation--substitution image encryption algorithms,i.e.,Fu's algorithm and Zhou's algorithm.We propose a double differential cryptanalysis comparison(DDCC)method to break Fu's algorithm with multi-round,which only needs O(L)chosen plain-images,where L is the size of the image.We further propose an improved DDCC method,which can be used to analyze a class of permutation-substitution algorithms with multi-round,such as Fridrich's algorithm,only need O(2Ks· L)chosen plain-image.We use codebook attack method to break Zhou's algorithm,which only needs O(L)chosen cipher-images.This method can also be extended to other multi-round permutation-substitution algorithms with some characteristics.The costs of the above attacks are independent of the encryption rounds.(?)To eliminate the vulnerabilities caused by static permutation matrix and key stream,we design a dynamic encryption system.Basing on this dynamic system,we construct dynamic permutation,dynamic substitution and dynamic permutation-substitution algorithms,which can meet different security requirements.Theoretical and statistical analysis shows that these three algorithms can not only resist the exhaustive attack,but also resist the chosen-plaintext or chosen-ciphertext attacks.(?)The security of two robust blind watermarking algorithms are analyzed and evaluated,and the numbers of signals used in analysis are given.Then we analyze a fragile watermarking algorithm with the function of tamper detection and image recovery,and propose two kinds of effective attacks.To resist the attacks,we give some suggestions.(?)We proposed a secure and robust watermarking scheme based on discrete cosine transform(DCT)domain of the scrambled image.This scheme not only protects watermark information,but also the embedding positions.A sub key generation mechanism is designed.The generation of the sub key depends on both the main key and the feature codes of the original image.Also we design a detection method to resist geometric attacks.Theoretical analysis and simulation demonstrate that the proposed scheme not only has good imperceptibility and robustness,but also achieves a high level of security.