Secure and robust steganography using side information at the encoder

Two important classes of data hiding methods are the ones established by watermarking and steganographic applications. Whereas in both cases information is concealed inside a host signal subject to an imperceptibility constraint, some of their fundamental requirements differ. Indeed, the design of watermarking schemes is usually guided by the maximum achievable rate with respect to a given attack power, while the most important constraint for steganographic methods is the undetectability of the hidden communication. In this work we examine the tradeoff between achievable rate and undetectability when watermarking and steganographic constraints are simultaneously imposed to a data hiding scheme. In order to illustrate this tradeoff we focus our attention on two relevant methods which are parallel in their structures, and are, respectively, suitable for the two problems at hand. The first one, distortion-compensated dither modulation, is nearly optimal with respect to the watermarking-like requirements. The second one, stochastic quantisation index modulation, automatically meets the undetectability condition under certain assumptions. Conclusions are drawn as to which scheme is preferable for joint watermarking and steganography constraints, given certain channel characteristics