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From: mat@mtx5a.UUCP (m.terribile)
Newsgroups: sci.crypt
Subject: Re: Re: Completely Secure Encryption
Message-ID: <1802@mtx5a.UUCP>
Date: Sun, 31-May-87 18:59:46 EDT
Article-I.D.: mtx5a.1802
Posted: Sun May 31 18:59:46 1987
Date-Received: Tue, 2-Jun-87 03:09:13 EDT
References: <581@gec-mi-at.co.uk> <1171@mit-amt.MEDIA.MIT.EDU> <5892@brl-smoke.ARPA>
Organization: AT&T Information Systems, Middletown, NJ 07748-4801.
Lines: 32

>  ...
> Note that the XOR stream you use is no better than simply taking
> yay many (truly) random bits and putting them in a protected
> file, so the added complexity of combining non-random files is
> rather pointless.  (Send your recipient a copy of the file on
> a couriered magtape.)
> 
> I highly recommend working your way through the first two
> volumes of Military Cryptanalytics (Callimahos & Friedman),
> including working all the problem sets AND ESPECIALLY heeding
> their advice for proposers of new cryptosystems, before trying
> to design a new cryptosystem. ...

I've not read the books in question, but for a less imposing and more
interesting introduction, there's the classic *The Code Breakers* by David
Kahn.  Interspersed with all of the history is enough material on breaking
encryption to show why a lot of obvious schemes are very weak, along with
notes on the consequences of refusing to believe how weak they are.  The
black chambers were breaking polyalphabetics two and three centuries ago,
(and simple formal methods of attack were developed in the 19th century) but
even in 1917, Scientific American claimed that running-key polyalphabetics
were unbreakable.  Ouch!

For a would-be code maker, *The Code-Breakers* is highly recommended.
-- 

	from Mole End			Mark Terribile
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