Coding Theorems for General Stegosystems

In this paper we discuss coding theorems for extensions of the information-theoretic stegosystem proposed by Cachin. We consider a stegosystem in which a covertext is generated from a general source. The variational distance between the probability distributions of a covertext and a stegotext is required to be negligible for ensuring validity as a stegosystem. We determine the maximum rate at which a sender can transmit a message to a receiver securely in the presence of an opponent under the assumption on an oracle at the decoder. In addition, we show that the assumption on the oracle is not needed when side information of a covertext is available at a decoder.