Research On The Security And Optimization Of Steganography Algorithm

The transparency of the steganographic algorithm and capability of resisting steganalysis are the key requirements for the security of the steganographic algorithm. The steganographic algorithm hides the secret messages into the cover image in terms of keeping the statistical properties of the host images, so that the presence of the hidden data is statistically undetectable. Generally, the steganographic algorithm is considered as a more secure algorithm if the secret messages insertions make fewer modifications to the cover image. However, pursuing fewer modifications to the cover object is always at the expense of occupying more available bits of the cover image, leading to the less capacity of the secret information.While numerous progresses are being made in steganography against steganalysis, the latter is also striving to advice their attack strategies in order to defeat the effort of information hider. The thesis summarizes the results obtained from the research on the security problem for the steganography, which has been carried out in view of the information warfare with the data hider on one side, and the steganalyst on the other. The achievements of this research on the security and transparency problem for the steganographic algorithm are classified into the following four categories:(1) A new approach of fast coding is proposed to improve steganographic efficiency, in which the amount of bit alterations introduced into a cover medium is significantly reduced, leading to less distortion and enhanced security against steganalysis. Dynamical running coding was previously proposed as a method for construction of steganographic schemes in digital steganography. Original embedding method is discussed in two cases of constructing different generating matrix; however, the proposed method generalizes the problem to only one case by changing the construction method from the original method. Therefore, the complexity of the proposed method is less than the original method. Meanwhile, both theoretical analysis and experiment results show better performance in terms of distortions and alterations of the cover objects when the same amount of information data bits is embedded, which proves a better resistance against steganalysis.(2) A generalization of the fast coding method for efficient data hiding has been proposed. In this way, each secret digit in a prime-base notational system is represented by a series of cover values. Modification on one cover value can be used to embed several secret digits, so that distortion is observably reduced. The original fast coding method can be viewed as a special case of the generalized scheme with a prime base p= 2. And theoretical analysis shows that the generalized running coding with p= 3 can provide the best performance.(3) EMD steganographic method by exploiting modification direction in the host images to send secret messages was proposed by Zhang, which highlights the high embedding efficiency, compared with other steganographic algorithms. A new novel method of steganography based on the idea of EMD embedding has been proposed, which builds up the multi-level for the secret messages and decreases the redundancy of the cover image's transparency for better embedding rate. In order to obtain better transparency of images and conveniency of algorithm, embedding modification does not happen on LSB of the pixels but frequency coefficients in new improved EMD method. The results of experiments show that the proposed method has better performances on the embedding efficiency and better embedding rate than the EMD steganography.(4) A generalized method of analyzing the security of JEPG steganography has been proposed based on Benford's Law. A series of simulation experiments and research on the relationship between the Benford's law and statistical properties of the jpeg image files have been made. We have found that the generalized Benford's law can be applied to the detection of double compressed JPEG images. So the generalized Benford's law has been used to analyze the security of some steganographic algorithm and the capability of resisting steganalysis. As the conclusion for the research and experiments, some valuable suggestions have been given for the improvements of the security of the algorithm...