From: peter.allan@aeat.co.uk (Peter M Allan)
Date: Thu, 22 Aug 1996 22:06:09 +0800
To: cypherpunks@toad.com
Subject: Re: cryptoanalysis 002
Message-ID: <9608221149.AA13676@clare.risley.aeat.co.uk>
MIME-Version: 1.0
Content-Type: text/plain



> From: Scottauge@aol.com
> Date: Tue, 20 Aug 1996 18:36:45 -0400
> Subject: cryptoanalysis 002

> For example, if the crypto-alphabet for e is 23, 45, 190, 200, etc, one can
> remove some of the frequency for a letter.  This definately makes it harder
> to attack with the frequency analysis method because the "resolution" of the
> distribution for the letter is lessened to a near randomness.  (So it looks,
> there are still clues, eh?)

I think (from memory) this is called "homoalphabetic".

Encyclopaedia Brittanica (Cryptology - article by Gus Simmons)
says that it is still vulnerable to frequencies of digraphs, trigraphs
etc.  But even Gauss was keen on it once.

I guess it might have value as a part of another system, making a known plaintext
into one of many.  Whether it's worth the increased cyphertext size in a system
you'd hope to be immune to known plaintext attacks anyway is another question.

PA