Information Transmission and Steganography

Recently there has been strong interest in developing models of steganography based on information theory. Previous work has considered under what conditions the security of the stegosystem can be guaranteed and the number of bits that can then be embedded in a cover Work. This work implicitly assumes that the hidden message is uncorrelated with the cover Work, the latter simply being used to conceal the hidden message. Here, we consider the case in which the cover Work is chosen such that it is correlated with the covert message. In this situation, the number of bits needed to encode the hidden message can be considerably reduced. We discuss the information that can then be transmitted and show that it is substantially greater than simply the number of embedded bits. We also note that the security of the system as defined by Cachin need not be compromised. However, the Shannon security may be compromised, but it remains unclear to what extent. Experimental results are presented that demonstrate the fundamental concepts.