Re: pseudo one time pad...

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Article #1862

#1862

From: Leonard Erickson
Date: Wed, 18 Nov 1992 13:31

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butzerd@blanc.eng.ohio-state.edu (Dane C. Butzer) writes:

>Nope.  I was just using DES as an example, since its output in CFM is
>unpredictable as well as statisctally random.  The real question was: If
>you have a good enough PRNG (or try URNG - unpredictable random number
>generator), why is a pseudo one time pad bad?

Because your key depends *totally* on the starting value. If the
"enemy" knows the *system* (which they will, sooner or later), then
once they crack *any* message they can read them all. 

Output from *any* "generator" depends on input/starting values. So
*those* are the "key". And for a "brute force" attack *they* become the
"key space" that needs to be searched. So I just feed all the 
starting conditions in and see which ones give reasonable messages.

-- 
Leonard Erickson		      leonard@qiclab.scn.rain.com
CIS: [70465,203]			 70465.203@compuserve.com
FIDO:   1:105/51	 Leonard.Erickson@f51.n105.z1.fidonet.org
(The CIS & Fido addresses are preferred)

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<1992Nov11.173642.29608@ee.eng.ohio-state.edu> <1992Nov11.144908.4035@memstvx1.memst.edu> <1992Nov12.000152.316@ee.eng.ohio-state.edu>

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Path: arc1-ca.pugleaf.net!sparky!uunet!haven.umd.edu!darwin.sura.net!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!uwm.edu!ogicse!qiclab!leonard
From: leonard@qiclab.scn.rain.com (Leonard Erickson)
Newsgroups: sci.crypt
Subject: Re: pseudo one time pad...
Message-ID: <1992Nov18.133121.23563@qiclab.scn.rain.com>
Date: 18 Nov 92 13:31:21 GMT
Article-I.D.: qiclab.1992Nov18.133121.23563
References: <1992Nov11.173642.29608@ee.eng.ohio-state.edu> <1992Nov11.144908.4035@memstvx1.memst.edu> <1992Nov12.000152.316@ee.eng.ohio-state.edu>
Reply-To: Leonard.Erickson@f51.n105.z1.fidonet.org
Organization: SCN Research/Qic Laboratories of Tigard, Oregon.
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