An information-theoretic model for steganography with passive adversaries is proposed. The adversary's task of distinguishing between an innocent cover message C and a modified message S containing a secret part is interpreted as a hypothesis testing problem. The security of a steganographic system is quantified in terms of the relative entropy (or discrimination) between P_C and P_S. It is shown that secure steganographic schemes exist in this model provided the covertext distribution satisfies certain conditions. A universal stegosystem is presented in this model for which the participants do not have to know the covertext distribution except that it consists of a series of independent experiments.
By: Christian Cachin
Published in: RZ3256 in 2000
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