On Sat, 10 Feb 2001, Steve Schear wrote:
Not entirely true. If watermarking become ubiquitous then their presence is no longer suspicious. If the marks contain encrypted content then almost no one will know or care as they are passed and published and only the intended recipients will receive the messages.
If stego is meant to be used between individuals, it's unlikely that a watermark would be present in the content naturally - after all, the marks are meant for CRM applications and individuals rarely take such good care of their private communications. And as for watermarks on commercial content, anyone caring about the presence of hidden communications can obtain a licence so that the watermarks can be completely detected. If the eavestropper is capable of full detection (not just statistical guesses), commercial watermarks fail to provide a meaningful hidden channel. (I.e. one would expect databases of valid marks to be available to an adversary of means.) In fact, many of the meaningful adversaries can perform a removal attack on commercial watermarks, since the licences are available to corporations and governments and, in the absence of workable asymmetric watermarks, detection equals capability to remove. This means that one cannot necessarily even use an existing watermark to hide another carrying your message. I think covert communication has very different needs from CRM. E.g. requiring non-detectability means that you have to model the channel statistics very closely, leading to a low bandwidth covert channel. CRM does not suffer from this, since a watermark only needs to be perceptually insignificant. Sampo Syreeni <decoy@iki.fi>, aka decoy, student/math/Helsinki university