Depends whether you are aiming to conceal the fact that a signal is being transmitted or whether you "merely" wish to conceal the contents of those signals. The

Depends whether you are aiming to conceal the fact that a signal is being transmitted or whether you "merely" wish to conceal the contents of those signals. The latter is (as I am sure any NH reader knows all too well) achieved my means of encryption, at least some of which, paranoia aside, is widely regarded to be pretty solidly robust to just about anything known (even most of the NSA-quantum-computer speculation is focussed on public key cryptography being attacked by factorisation attacks... lattice algorithms and lots of stream ciphers are not directly attackable by this means if the session key is not exchanged by "potentially vulnerable" public key cryptographic means).