From: C445585@mizzou1.missouri.edu (John Kelsey)
Subject: Re: How large are commercial keys?
Nntp-Posting-Host: mizzou1.missouri.edu
Organization: University of Missouri
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In article <1993Apr20.182038.12009@ee.eng.ohio-state.edu>
butzerd@maumee.eng.ohio-state.edu (Dane C. Butzer) writes:
 
>Finally, can anyone even concieve of a time/place where 128 bit keys aren't
>sufficient?  (I certainly can't - even at a trillion keys a second, it
>would take about 10 billion years to search just one billionth of that keys
>space.)
 
   It depends on the attack.  Adding a bit to the key doubles the amount of
work to be done in a straight brute-force attack, where you try every single
possible key until one works.  Processing and storage requirements for this
kind of attack on a 128-bit key seem like they ought to make it effectively
impossible.  However, there may be other attacks whose difficulty is (for
example) proportional to, say, 2**sqrt(n), or some such.  Also, a long
key does you little good if there is a way to incrementally guess a little
of the key at a time....
 
>Thanks,
>Dane
   --John
