🚀 go-pugleaf

In article <1ehqrdINN1f9@iskut.ucs.ubc.ca> unruh@physics.ubc.ca (William Unruh) writes:

   leichter@zodiac.rutgers.edu writes:
   >....  (Actually, "meet in the middle"
   >attacks show that double encryption, done this way, cannot be MUCH stronger
   >than single encryption - though it may be SOMEWHAT stronger.)

   >							-- Jerry
   Since the total number of possible encrypting functions of 64 bits is
   something like (2^64)!, and there are only 2^56 DES encryption
   functions and multiple DES is half the set of all encryptions, I would
   expect (naively) that double encryption would essentially be as strong
   as a key with 2*56=112 bits, unless DES is almost a group ( ie most
   double encryptions yield the same encryption as some single DES). Why is
   this argument wrong, or is DES almost a group in the above sense?



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des^2 could well be a simpler system than des.  as leichter mentioned
in his posting, this would mean that des itself was weak because the
attacker could add a secondary encryption and then attack the
concatenation.  on the other hand, only an attacker who knew that
des^2 was weak would ever think of making such an attack.