🚀 go-pugleaf

In article <1eg516INNrrq@uniwa.uwa.edu.au>, markd@uniwa.uwa.edu.au (Mark Diamond) writes:
|> The question arose in a previous reply to this posting of whether
|> triple, double or any other repeated DES encryption was stronger than a
|> single encryption.  The previous reply indicated that the question was
|> still open.  It is not open ... it has been settled and the results
|> presented at CRYPTO 92.
|> 
|> Essentially the question about the strength of double encryption is the
|> same as the question about whether DES is or is not a group.
|> 
|> If DES were a group then for two keys K1 and K2
|> 
|>        DES( DES(Plaintext, K1), K2) == DES(Plaintext, K3) for some
|> 
|> K3 which presumably the eavesdropper is trying to discover ... the point
|> being that they would not have to find K1 and K2, but only a kind of
|> "combination" K3.
|> 
|> The recently demonstrated fact that DES is *not* a group indicates that
|> a double encryption *is* stronger than single encryption.

    Excuse me, for I am really an amateur in this subject, but I
don't see the chain of reasoning here.  If I am just being particularly
dense, please keeps the flames low, and I'll shut up.

    What has been shown is that iteration of DES with different keys 
results, in general, in encryption which is different from DES.  I 
believe that that is different from showing that iteration results
in something _stronger_.  As far as I can see, it is consistent
with someone discovering that two applications of DES could result
in a encryption which is in fact easier to break -- for example,
there could be some interaction between keys, that would result in
an easy cipher to break, so that there would have to be some care
in choosing keys.  It is also consistent with it being discovered
that iterations of DES are _equally_ difficult to break as single 
uses, perhaps just a different method has to be used.

-- 
Tom Scharle                |cm65n6@irishmvs(Bitnet)
Room G003 Computing Center |scharle@lukasiewicz.cc.nd.edu(Internet)
University of Notre Dame  Notre Dame, IN 46556-0539 USA