From: "Perry E. Metzger" <perry@piermont.com>
Date: Sun, 10 Mar 1996 06:51:35 +0800
To: Marc North <mnorth@netcom.com>
Subject: Re: Index of Coincidence
In-Reply-To: <Pine.SUN.3.91.960309113033.18346B-100000@netcom12>
Message-ID: <199603092025.PAA16611@jekyll.piermont.com>
MIME-Version: 1.0
Content-Type: text/plain



Marc North writes:
> I'm looking for detailed information on a statistical tool to aid in
> cryptanalysis called an "index of coincidence".  I would appreciate it if
> someone could please explain what this is, how one builds such an index
> against a given ciphertext, and how it is valuable in the cryptanalysis of
> said ciphertext. 

There is a fairly good general description in "The Codebreakers";
there is also a book by Friedman available from Agean Park Press that
covers the topic. I don't know of any public tools to do the work,
but it isn't very hard...

Perry