In section 126.96.36.199 of Digital Communications: Fundamentals and Applications, Bernard Sklar makes this claim about spread spectrum signals:
Therefore, not only can the spread-spectrum signal be made difficult to jam, but additionally, the signal's very existence may be rendered difficult to perceive. To anyone who does not possess a synchronized replica of the spreading signal, the spread-spectrum signal will seem "buried in the noise."
This seems analogous to symmetric cryptography; there is a symmetric "key" (the spreading signal) that allows one to both transmit and receive messages, and without the key one can neither transmit nor receive a message. Furthermore, without the key one cannot even detect the presence of a message (or, at the very least, it makes it more difficult to do so).
This makes me wonder if there's an asymmetric cryptography analog to direct sequence spread spectrum. I assume there would be a public and private "key" pair, and one could use the public key to transmit a message, but only the private key could be used to receive that message. And without the private key, it would be very difficult to even detect the presence of a coded message (i.e. only the private key could be used to "de-spread" the message).
Does such a technique exist?