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From: krs@amdahl.UUCP
Newsgroups: sci.crypt
Subject: Re: Completely Secure Encryption
Message-ID: <6924@amdahl.amdahl.com>
Date: Fri, 22-May-87 13:22:04 EDT
Article-I.D.: amdahl.6924
Posted: Fri May 22 13:22:04 1987
Date-Received: Sat, 23-May-87 10:48:51 EDT
References: <581@gec-mi-at.co.uk>
Reply-To: krs@amdahl.UUCP (Kris Stephens)
Organization: Amdahl Corp, Sunnyvale CA
Lines: 32

In article <581@gec-mi-at.co.uk> adam@gec-mi-at.co.uk (Adam Quantrill) writes:
>
>	I have been thinking about the one really secure encryption technique,
>where the text is exclusive-ored with a random string used once only.
>[...]
>for a less secure method, I propose to generate the random string by exclusive-
>oring any combination of n text and binary files held on computer:
>[...]
>               The other caveat is that the sender's and receiver's machines
>share identical files (which is reasonably common between machines of the same 
>make running the same o.s.).
>
>Does anyone have any comments as to the security of this method? It would
>obviously be more secure using a common but unique random file owned by the two
>parties, in combination with the standard system files.

Bad news, I'm afraid.  Even standard Un*x executables change when .h's are
altered in a system.  We ran a couple of sysgens from the *same* tapes, on
the *same* system, and the kernels were different because the configuration
data had been altered (add a new type of device to the configuration, and
even the *contents* of the kernel will change).  I wouldn't even count on
the "standard" commands in machines of identical hardware running the same
levels of the O/S release matching -- add a configuration change here and
a local mod there and you have *no* *idea* what the binaries will look
like.

...Kris
-- 
Kristopher Stephens, | (408-746-6047) |          {whatever}!amdahl!krs
Amdahl Corporation   |                |    -or-  krs@amdahl.amdahl.com
     [The opinions expressed above are mine, solely, and do not    ]
     [necessarily reflect the opinions or policies of Amdahl Corp. ]