...
(provided back door attacks, fundamental breakthroughs in cryptography, etc. are not made...a bet I'm forced to make, even though I don't like it)
You can tilt the odds in your favor some at the cost of speed; use more rounds for the block ciphers and base your public-key security on two hard problems, not one (i.e., encrypt randomness with one public-key cryptosystem and encrypt the key XORed with this randomness with an algorithm based on an unrelated hard problem). That means much more work, but the insurance against improvements in math/crypto is worth it, I'd think. ...
Actually, Eternity is no different than emailing a file, given a SIGINT capability at the attacker which allows all internet traffic to be monitored. If the data is still relevant and worth breaking in 50 years, they could just intercept the encrypted email, store it in a government vault for 50 years, then attack it...
It *is* a little different, actually; confidential messages are rarely relevant in 50 years (and even when they are, NSA doesn't know which messages are relevant and which aren't), whereas authors must remain anonymous until they're sufficiently dead that they can't be hurt (and NSA *does* have more of an idea of which documents need to be looked into, since they know their contents). ...
- -- Ryan Lackey rdl@mit.edu http://mit.edu/rdl/
--------------------------------------------------------------------------- Randall Farmer rfarmer@hiwaay.net http://hiwaay.net/~rfarmer