I'm not a cryptographer. That said: the PDF you link to seems to show that provably secure steganography (as defined by this paper) exists if, and only if, one

I'm not a cryptographer. That said: the PDF you link to seems to show that provably secure steganography (as defined by this paper) exists if, and only if, one-way functions exist. (See section 5.3) It so happens that if one-way functions exist then, as a corollary, P != NP. In other words: if steganography is provably secure, P != NP. So let's not get ahead of ourselves. ;-)