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From: ken@argus.UUCP (Kenneth Ng)
Newsgroups: net.crypt
Subject: Re: randomly adding bits/bytes
Message-ID: <454@argus.UUCP>
Date: Tue, 19-Aug-86 17:55:26 EDT
Article-I.D.: argus.454
Posted: Tue Aug 19 17:55:26 1986
Date-Received: Thu, 21-Aug-86 04:02:41 EDT
References: <8608042018.AA04376@ucbjade.Berkeley.Edu>, <437@argus.UUCP> <7035@utzoo.UUCP>
Organization: NJ Inst of Tech., Newark NJ
Lines: 44

In article <7035@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes:
> > ...The scheme is using Lempal Ziv
> > compression to compress the text, resulting in essentially random
> > information, with redundent text removed.  The output of that is then
> > fed through a 256 byte translate table.  Thus both sides must have only
> > the translate table to communicate back and forth.  Does anyone know
> > how resistent to cracking this method would be?  ...
> 
> It depends on how private your L-Z compressor is.  The translate table
> is a monoalphabetic substitution; by itself, any bright 8th-grader could
> break it.  
I don't remember if it was in 8th grade, but I remember doing something
like that quite a few years ago.  The thing is, the method I used
depended on the frequency of different characters being different.
It went something like the most common letter was E, followed by N, T,
S, I don't know what frequency blanks have though, and the order may
be different. I've been told that the output of the L-Z compaction
method is essentially uniformally distributed, which would foul up
my method.

The primary use of this idea was to enable communication across a
finite bandwidth channel and to make the data reasonably secure.
It'll probably never carry national security secrets.  The L-Z
compression combined with the translate table seems to be a reasonably
fast way to both speed up transmission and somewhat encrypt the
information.  Thank you for your advice.

> 				Henry Spencer @ U of Toronto Zoology
> 				{allegra,ihnp4,decvax,pyramid}!utzoo!henry

-- 
Kenneth Ng:
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