# How to Construct a Cipher Disk

Moshe Rubin (mosher@mountainvistasoft.com)

Recently I scoured the Web for a generic, clean template for creating a 26-letter cipher disk.  Alas, all the templates I found had the standard alphabet already written in, were of poor quality, or were too small.  To solve this, I wrote a PGF/TikZ script to draw N-section disks of any size.

To help people in a similar predicament, I've uploaded a PDF document with three different-sized cipher disks with no letters filled in around the periphery.  Just print it out and cut out as many disk as you need.

For general cipher disk needs I created three PDFs containing templates for 26-letter cipher disks:

Following are pictures I took of two complete cipher disks I built: a standard cipher disk with two concentric disks, and John Savard's rotor-like cipher disk (see the description halfway down the page).

## Constructing a Standard Two-Disk Cipher Disk

1. Print out the unfilled cipher disk template.
2. Using scissors, cut out the two largest disks.

3. Write one alphabet component on each of the disks.  The components can be standard (i.e., A-to-Z), mixed, identical, reversed, or any other desired order.
4. Insert a pin or thumb tack through the centers of the disks, pinning them to a piece of cardboard , cork, wood, etc.

Here's what mine looks like:

## Constructing John Savard's Rotor-Like Cipher Disk

1. Be sure to read John's description on his Web site!

2. Print out the cipher disk template twice.  This is because you'll need two disks of the intermediate size.
3. Cut out one (1) large disk, two (2) intermediate disks, and one (1) small disk.
4. On one of the intermediate disks, cut off half of the outer disk.  You should now have four disks that look like this (I snapped the photo only after filling in the alphabetic and numeric components <g>):

5. Fill in the alphabetic and numeric components similar to the preceding picture (I used the precise components shown on John's Web page).  I highlighted the tow intermediate disks with green and orange highlighters as per John's diagram.  It simplifies telling the two disks apart during encryption/decryption.

6. The orange intermediate disk will reside on top of the large disk:

7. The green intermediate disk will be mounted on the orange one:

8. Mount the smallest disk on top:

Quoting John's description for one way of using the disk:

One way to make use of this construction would be to have layers of cardboard between the disks, so that each rim is individually exposed for a short distance. The 26 possible key letters would be allocated so that seven of them are used to indicate that the lowest disk is to turn counterclockwise from 1 to 7 spaces, another 7 turn the smallest disk clockwise 1 to 7 spaces, and 6 indicate the disk shown with a purple rim is to turn counterclockwise from 1 to 6 spaces, and 6 indicate the disk with half its periphery cut away is to turn clockwise from 1 to 6 spaces.

[Ed. I hope to expand this page and show step-by-step enciphering and deciphering sessions.]

Created: 3 April 2009
Updated: 23 January 2013