In Applied Cryptography (at 8.2.5) Bruce Schneier says: "What about encrypting a block once with algorithm A and key K-a, and then again with algorythm B and key K-b? Aside from being susceptable to ... meet-in-the-middle attacks, there is no guarantee that the two algorythms will work together to increase security. There may be subtle interactions between the two algorithms which actually *decrease* security." Wait. If applying a different algorithm with an unrelated key might decrease security, then the TLAs could themselves apply another algorithm with their own unrelated key as an analysis technique, no? Kent's Hypothosis: Superencrypting different algorithms with unrelated keys can never weaken non-trivial algorithms. Stacking DES on top of IDEA on top of Ceasar can be no worse than the strongest of the the set--assuming the keys are unrelated and the attempted security is not through obscurity and the algorithms are not so confused as to be each other's analysis. -kb -- Kent Borg +1 (617) 776-6899 kentborg@world.std.com kentborg@aol.com Proud to claim 31:15 hours of TV viewing so far in 1994!