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From: aptr@ur-tut.UUCP (The Wumpus)
Newsgroups: net.crypt
Subject: Re: randomly adding bits/bytes
Message-ID: <588@ur-tut.UUCP>
Date: Sat, 9-Aug-86 18:08:23 EDT
Article-I.D.: ur-tut.588
Posted: Sat Aug  9 18:08:23 1986
Date-Received: Mon, 11-Aug-86 04:27:20 EDT
References: <8608042018.AA04376@ucbjade.Berkeley.Edu> <437@argus.UUCP>
Reply-To: aptr@ur-tut.UUCP (The Wumpus)
Organization: U. of Rochester Computing Center
Lines: 27

In article <437@argus.UUCP> ken@argus.UUCP (Kenneth Ng) writes:
>In article <8608042018.AA04376@ucbjade.Berkeley.Edu>, simsong@wisdom.bitnet (Simson L. Garfinkel) writes:
>> 
>> There are other ways of making a message difficult to decrypt. Perhaps
>> the best is to use a space-compression program on it first....
>
>...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.

The problem I can see with the system is that it is possible for a person to
both decode and encode a message from both sides.  This means that all that
is really needed to find out how the translation table works is for someone
to feed a know set of text into the translator, then look at the output.
Once the translation is broken, it would probably be easy to break the
(de)compression system by using the same technique as the above.

My favorite system for any set up is still adding a random number to each
letter in the message.  This also will break up most of the common character
occurence methods of breaking.  Of course a repeatable sequence of randoms
is needed.  A random number generator that does not repeat for >10,000 loops
would work fairly well as long as the key is changed often.
-- 
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