ElGamal's proof assumes the Diffie–Hellman assumptions, which are quite strong. Actually every modern asymmetric key encryption algorithm's security would imply the existence of one-way functions, which in turn would imply P!=NP - as far as my outdated information goes, we don't have a proof of that yet. But even if I'd trust P!=NP, there's a lot of other ways the strongers assumptions could fail, e.g. maybe your particular key is one of those 10% that's easy to revert.

I'm not sure why you say "there's no crypto" and call it quantum signaling - BB84 is obviously an encryption protocol. Maybe you were thinking about entangled states communication, which also is provably secure (assuming basic quantum information principles and some things about the physical detectors), but as a protocol is simple and relies almost solely on sending entangled pairs.

A 1024 qbit quantum computer _will_ give you an exponential advantage in RSA-breaking (compared to classical algorithms we know) even if the key is longer - the algorithm might get more complicated, but there obviously are things a QC can do (in a reasonable time) while a classical can't. Regardless of that - if your encryption protocol assumes nobody will have 5000 qbit quantum computer in fifty years, then it has a weakness. When Enigmas were being used, do you think anyone thought the Bombes - massive electromechanical devices capable of doing a massive analytical job - were possible? One more thing - a 5000 qbit computer is most probably easy to do, once you know how to do a 1024 one - it's not exponential in difficulty, the only problem is to find a solution to decoherence that will scale, that doesn't have an inherent limitation.

The BB84 quantum encryption protocol (invented in 1984) is already provably secure, assuming basic quantum information principles and some detector reliability (we don't assume they're perfect, BB84 takes into account all kinds of noises on detectors and emitters; noises are always assumed to be caused by a breaking attempt, we take into account the possibility of the enemy having parts more perfect than anything we could produce). The "basic QI principles" is basically the non-cloning principle (a bit more precisely - the principle that all observations are describable by unitary positive matrices) - which is something I'd trust a lot more than even P!=NP. Saying it could be wishful thinking is like saying Newton's motion is wishful thinking. A mechanical lock still works just as advertised, quantum mechanics or general relativity won't help you break it. Maybe particles do clone when you go outside QM, e.g. the universe's growth may create particles, but making that an exploit would require you to control the universe's growth :)

Those quantum exploits you see are caused by attempts at making the protocols more practical - of course there's a ton of problems with the theory going into practice. But saying "quantum information theory is shaky" is more crazy than saying "P=NP", and way more crazy than saying "there might be a fast algo for the discrete logarithm for certain primes we don't know of yet".