I'm wondering if there is any particular reason why an encrypted message might not be encrypted with several different keys,within the same message, divided by time.Perhaps synchronized clocks or time stamping might be used to toggle the encryption parameters.This technology might be able to defeat the brute force decryption technologies described in the paper mentioned yesterday.
If you have a system with key exchange you can change the keys on demand in the middle of a stream (provided the protocol you use allows this). This may be done as many times and as often as you please up to the limitations of the (usually) slower key exchange protocol.
Chris Beaumont nutrient cafe wholesale ccat@netcom.com MIME mail graciously accepted ccat@casa.stanford.edu public key available via finger