Physical layer security sure is hot these days. Its proponents claim provable security, something the cryptographic community hasn't yet been able to provide. Sounds great!
Physical layer security is largely based on the wire-tap channel; here (pdf) is one of the seminal papers on the subject. The great achievement in the wire-tap channel is to allow transmission at capacity on the from source to the legitimate receiver, while the mutual information from source to wire-tapper is zero, even if the wire-tapper knows the code book. Thus, we have "proven" that communication is secure, because the wire-tapper can never accurately guess the message that was sent to the legitimate receiver.
But here's the thing. Look at figures 1 and 2 in the paper I link. Everything relies on the wire-tapper having a physically degraded channel with respect to the legitimate receiver. This makes sense: if, somehow, the situation were reversed and the legitimate receiver were degraded with respect to the wire-tapper, it would obviously be impossible to prevent the wire-tapper from decoding the messages. Put another way, there is no security unless the wire-tapper has a worse channel than the legitimate receiver.
Here is my question: isn't it misleading to call this "secure"? It is unlikely that the wire-tapper would oblige us by providing his channel state information. Thus, we merely exchange one set of uncertainties for another: namely, exchanging uncertainty about the hardness of the factoring problem for uncertainty about the wire-tapper's channel state -- except that factoring is very widely believed to be intractable, whereas it's not hard to imagine a committed adversary being able to find a good channel for a wire-tap.