Research On The Design Of Efficient Steganographic Schemes

Steganography is an important branch of information hiding research. It embeds secret data into innocent cover and transmits on the public channels, so as to achive covert communication. It overcomes the problem that encryption algorithms make the messages unreadable and suspicious enough to attract eavesdroppers’attention. Steganography mainly focuses on embedding capacity, embedding distortion and security. In order to promote the above performances and achieve covert communication better, the main contributions of this dissertation are on the design of efficient steganographic schemes. Steganographic schemes for digital images with pixel value differencing achieve high embedding capacity and low embedding distortion, and quantum steganographic schemes with quantum information technique obtain high security.Steganographic schemes for digital images with pixel value differencing are mostly based on the differencing of two consecutive pixel values. This dissertation first analyzes two steganographic schemes for digital images with two-pixel value differencing, and point out that the recipient cannot extract secret data exactly in the first scheme and the choices of readjusting pixels are few in the second one. Then two improved steganographic schemes for digital images with two-pixel value differencing are proposed, so as to ensure the exact extraction and reduce embedding distortion when concealing with the same embedding capacity.Steganographic schemes for digital images with two-pixel value differencing seem not to consider the features of edge sufficiently, and their performances need to be improved. Steganographic schemes for digital images with four-pixel value differencing can solve the above problem. A steganographic scheme for digital images with four-pixel value differencing and modulus function is proposed, and its performance is better than the existing steganographic schemes for digital images with four-pixel value differencing. However, further analysis shows that these steganographic schemes for digital images with four-pixel value differencing are essentially based on the differencing of two consecutive pixel values. Therefore, a new definition named "four-pixel value average differencing" is presented. Pixel value differencing is extended from one dimension to two dimensions, and the features of edge are considered sufficiently. Two novel steganographic schemes for digital images with four-pixel value average differencing are proposed, obtaining high embedding capacity and low embedding distortion.Quantum steganography achieves covert communication of quantum or classical information over quantum channels. It can detect the eavesdropper’s presence, and its security is assured by quantum physical principles. Two quantum steganographic schemes with quantum information technique are proposed, providing good performances on embedding capacity, key consumption rate and application environment.1. A steganographic scheme for digital images with two-pixel value differencing and modulus function was proposed by Wang et al., and we point out that it has a loophole. The original scheme performs mistakenly under some conditions, and the recipient cannot extract secret data exactly. By enlarging the modification range of two consecutive pixels, an improved scheme is proposed so as to ensure the exact extraction.2. A steganographic scheme for digital images with two-pixel value differencing and the readjusting phase was proposed by Yang et al., and we point out that the original readjusting phase has limitations. The original readjusting phase is just executed for one pixel in the pixel pairs whose difference values belong to different levels, before and after embedding. By enlarging the choices of readjusting pixels, an improved scheme is proposed, providing better image quality when concealing with the same embedding capacity.3. A novle steganographic scheme for digital images with four-pixel value differencing and modulus function is proposed. We process a block of2x2four neighboring pixels, and form three two-pixel groups. Using modulus function, two pixels in each group will be modified so that the sum of the remainders of them is equal to secret data. Four pixel values in the block are modified synchronously, and an optimization problem with the constraints is formulated to minimize the embedding distortion. A theoretical proof is given to ensure the solvability of the optimization problem.4. A novel steganographic scheme for digital images with four-pixel value average differencing and modified least significant bit (LSB) substitution is proposed. For the2×2four-pixel block, secret data are embedded into each pixel by the k-bit modified LSB substitution method, where k is decided by the four-pixel value average differencing. Readjustment will be executed to extract secret data exactly and to minimize the embedding distortion. A detailed theoretical proof is given to justify the proposed scheme succeeded in embedding and extracting.5. A novel steganographic scheme for digital images with four-pixel value average differencing and coding technique is proposed. For the2×2four-pixel block, a coding function about four pixel-value modifications is designed, and its parameters are decided by the four-pixel value average differencing. Thus, four pixel values are modified and secret data are embedded adaptively.6. A novel quantum steganographic scheme with noisy depolarizing channels and quantum teleportation is proposed. By using Pauli operations, secret data are disguised as the code errors of quantum error-correcting code, which seem to be caused by the noise of depolarizing channels. The choice of Pauli operations is completely random, which can be exploited for accommodating additional secret data by adding quantum teleportation. A theoretical analysis shows that the proposed scheme can achieve higher embedding capacity with lower key consumption rate, promoting its actual implementation in further development.7. Tradition steganographic schemes are focus on one-to-one application environment. In order to improve the security of multi-party communication, a new definition named "multi-party covert communication" is presented, which can be applied to one-to-multi application environment. A novel quantum steganographic scheme based on a channel hidden within quantum secret sharing is proposed to achieve three-party covert communication. A theoretical analysis shows that the proposed scheme can mainly satisfy these requirements of three-party covert communication.