Q&A #13134

Teachers' Lounge Discussion: Code breaking - History

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To: Teacher2Teacher Public Discussion
Date: 2006122009:40:28

From: Xtian Simon <xtian@christiansimon.com>
To: Teacher2Teacher Public Discussion
Date: 2006120123:25:53
Subject: Code Breaking

While waiting for responses to my post for reading reccomendations on
x-over books in geometry. I read this post and thought to myself, "You
got to give to get?" Right?

Dulles, Allen (editor). Great true spy stories. New York, NY: Harper &
Row. 1968

I read this book as a young man. It has one of the best basic
encription stories ever told. The basic plot:

A soviet spy is caught in the US. Among his posessions is a
hollow-quarter. Inside is a micro dot with, what is called in the
encription lingo, a one time cypher. This is a matrix of numbers that
is used to make a code unbreakable in transit.

It goes like this. The spy writes their message. Using a
pre-determined code phrase, they create a basic matrix (am I using
this term right?) that begins with this word and continues on the next
line with the remaining letters not used in the code phrase forming a
5x6 grid. Then, the X-axis and Y-axis are numbered. Encoding a letter
will result in the same coordinate code. This is a basic code and very
vunerable to decription.

What the one time cyper does is change the coded number sequence. The
one time cyper pad is composed of random numbers. A second duplicate
pad with the same numbers is at the receiving end. Along with the
pre-determined code phrase is a predetermined cypher pad page. The
encoder looks up that page, and here is the fun math trick, uses
modular addition to change the number sequence and eliminate the
repeting patterns. 

The theory being the only way to break the code is to have both the
same set of random numbers, and the same pre-determined code phrase. 

As far as my knowledge extends in cyphers, every modern code system
uses some form of random number mathematics to disrupt the pattern of
repeating letters to make a code unbreakable.

Good Luck. Email me directly if you don't find the book and I will see
if I can track down the story.

Christian Simon

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