The Researches Of Several Key Techniques In Steganography Domain

Steganography and steganalysis are two important embranchments of information security domain and have been developing swiftly recent years. The aim of steganography is to embedded secret information imperceptibly into cover files (can be images, audios, videos or other mediums) so that the presence of hidden data can not be detected. On the contrary, steganalysis is to try finding the probability of the secret information's presence and exposing the hidden data. People usually design diverse steganographic arithmetic based on cover fires'types, transformation domains and other characters in order to obtain low perceptibility, sufficient payload, and high robust. Steganography and steganalysis are two subjects which can accelerate each other. So steganalysis have to face on a large number of doubtful objects and changeful steganographic methods in practice. Therefore, if analyst can implement a steganalytic method against certain steganographic method in condition of private cover images, the method can be considered as a valuable steganalytic method.This dissertation bases on the researches of several key techniques in steganography domain and puts forward two new steganographic methods: improved LSB matching steganographic method with histogram characters reserved, and writing on wet paper based on wavelet transformation. The purposes of our reseaches are: to design the steganographic method whose invisibility, embedding rate and robust can be a balance point and to provide algorithmic supporting for developing information security techniques. The major innovations achieved in the dissertation are as follows:1. The limitations of LSB matching steganographic method are affirmed through frequency analyzing and experiments. The conception of steganographic information table is put forward. Steganographic information table records the transformations of each pixel value during embedding. The direction of increasing or decreasing is affirmed based on the data in steganographic information table. A new LSB matching steganographic method which can reserve histogram characters is put forward. This method can hold the characters of images'histogram as well as hold images'statistical characters. Almost all steganalysis methods which work on the images'histogram are inefficacy in front of the new method.2. Through entropy H, coding gain G, product of peak-peak ratio PPR and coding gain G, PSNR of restruction image in the lowest pass band, character of energy focus and character of energy distributing, we implement the experiments of performance evaluating for 6 wavelet functions. And we choose Daubechies9/7 wavelet to be the one which we use during algorithm design according the results of experiment. We put forward the lifting scheme of wavelet transformation, including the theory and the process of implmenting. We also compare the performance of lifting algorithm with convolution algorithm through the aspects of the algorithm complexity and PSNR.3. The selection channel in wavelet transformation is designed. And the solution existence of a key linear system of equations in wavelet transformation domain is proved. A new steganographic method of writing on wet paper based on wavelet transformation is put forward. This method integrates the advantages of steganographic methods in wavelet domain and wet paper, and can provide the steganographic signals with high robustness and invisibility. This method is propitious to covert communications and it is a highly applied steganographic method.