From: kentborg@world.std.com (Kent Borg)
Date: Wed, 6 Jul 94 22:43:35 PDT
To: cypherpunks@toad.com
Subject: Schneier Claims on Multiple Encryption
Message-ID: <199407070543.AA14055@world.std.com>
MIME-Version: 1.0
Content-Type: text/plain


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!