A lot of crypto algorithm's are theoretically secure for thousands of years (or longer) assuming an eavesdropper has access to existing algorithms and classical hardware with Moore's law scaling. Unfortunately, it's currently non-existing attack algorithms you really need to worry about. Advances are relentless. Then there are things on the horizon like quantum computing...
While Shor's algorithm demonstrates that integer factorization is in BQP, there are very good reasons to believe that many other problems are not; a large enough quantum computer may break RSA, but it won't break everything.
(Downplaying Quantum Computing ostrich-style is very popular in classical crypto circles for some reason, but that's a topic for another day!)
A floppy disk worth of IRC chat is actually quite a lot but it also had a 'degraded mode' which used the last chunk of the random data as a symmetric cypher key. That would keep things going until the next disk arrived in the post.
This just goes to show that if you are stupid enough to tell a geek what the best answer is then there is a pretty good chance that they will confuse it with the right answer.
My only hope is that our inane chats about movies are, even now, causing cycles to be burned on a NSA supercomputer somewhere :-)