From: eli+@gs160.sp.cs.cmu.edu
Date: Tue, 22 Oct 1996 15:37:56 -0700 (PDT)
To: cypherpunks@toad.com
Subject: Re: [DES] Criteria for Key Recovery target.
In-Reply-To: <+cmu.andrew.internet.computing.coderpunks+YmPCtHi00UfAI10Mcw@andrew.cmu.edu>
Message-ID: <199610222237.PAA04951@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


Russell Holt writes:
>BTW, does anyone have references to statistical comparisons of key
>searches in "real world" settings? Eg, random starting locations
>versus random keys .. etc..

E(time) with all trial keys distinct: 
        1/N Sigma^N i = N/2 = 2^55.
E(time) for random trials:
        1/N + (N-1)/N (1 + E(time))
        so E(time) = N = 2^56.

Centralized keyspace handling is a clear lose, IMO.  The RC4-40
project had server problems; scaling up by another 2^16 would be
non-trivial.  Then there are problems with malicious searchers,
corrupt servers, flaky networks... all this for a factor of two?
(And, admittedly, the reduction in variance.)

To rain on the parade a bit, what this discussion says to me is that
most applications of DES are safe from net cracking for a few years
yet...

-- 
   Eli Brandt
   eli+@cs.cmu.edu