From: Alan Bostick <abostick@netcom.com>
Date: Mon, 13 Jan 1997 17:59:30 -0800 (PST)
To: Ed Falk <ed.falk@Eng.Sun.COM>
Subject: Re: encryption program
In-Reply-To: <199701132023.MAA22372@peregrine.eng.sun.com>
Message-ID: <Pine.3.89.9701131715.A13546-0100000@netcom4>
MIME-Version: 1.0
Content-Type: text/plain




On Mon, 13 Jan 1997, Ed Falk wrote:

> > what do you mean, polyalphabetic substitution?
> 
> Someone can correct me if I'm wrong, but I believe it refers to a cipher
> where each character is encrypted individually, using a different
> monoalphabetic cipher for each one.  The ciphers repeat after
> a certain period, usually the key length.
> 
> Vigenere is the simplest polyalphabetic cipher of them all, with
> the individual ciphers simply being ROT-n.
> 

I'm convinced that the message in question is a polyalphabetic 
substitution.  Among other things, did people notice quite how much known 
(or *very easily guessable*) plaintext there was in the message sample,
above and beyond the free giveaway of the first line?  Things like 
"CONFIG.SYS", "FILES=20", BUFFERS=20", and so on.  There's enough
stuff there to make serious inroads into the message without cracking
the cipher; and with their help I'm pretty sure the back of the cipher
itself can be broken.  In the half-hour I played with it I got to the
point where I could make some educated guesses about the repetition
length of the substitution, and start filling in the various alphabets.

No doubt a *real* cryptanalyst could do even better.


Alan Bostick               | To achieve harmony in bad taste is the height
mailto:abostick@netcom.com | of elegance.
news:alt.grelb             |      Jean Genet
http://www.alumni.caltech.edu/~abostick