Re: Double Encryption Illegal?

On Mon, 18 Sep 2000 10:13:01 -0400, "root_at_localhost <spamthis>" <osiris_at_deltaville.net> wrote, in part:

>He said that applying Ceaser cipher twice does not enhance security. He
>was correct in that statement.

That may be, but that was not the statement quoted and contradicted.

Essentially, the case where multiple encryption would do nothing is if the cipher were a *group*: that is, there existed a key k3 such that for any keys k1 and k2, E(E(x,k1),k2) = E(x,k3); that is, there would exist a key, even if it was hard to find, for any two other keys such that encrypting with that key would be the same as encrypting twice, with those two other keys in order.

That's true for the Caesar cipher, but it certainly isn't true for the AES candidates.

John Savard
http://home.ecn.ab.ca/~jsavard/crypto.htm Received on Tue Sep 19 2000 - 01:37:26 CEST