Virtual U.S. Army Cipher Device, Model M-94

Version 1.1.1
Copyright 1997-2003 by Wilhelm M. Plotz (aka CipherClerk)


J U T H G   F F H J T   E U O N G   W Z L I Z   A G O P I
I L L G Z   W C Y P Q   N D Z N I   C S W E I   L Y S U A
L Y R M E   G K B U P   U Z C O S   B C P I M   S M R D W
Y W O Y R   I O S G Z   W H F H L   O U M J T   D L X M H
Y O U U C   J N H S S   Z S F O A   Y D M A B   V Z Z Q W
O Q K C J   N T T R I   V O S A W   V C G H X   B U F P J
V N Y P F   S V H P E   T K D P K   P Q K L F   F C M M P
V C H N X   X X T W L   A K X C H   R R B B W   C N M H S
Q L T K V   T L Y H L   O J C M Y   Z R R G Q   W G S V C
K D J U Z   D S E J P   J Z C G C   A S Q E B   J W Z W Y
B Z V B N   J N U Q Y   E C Z N S   B I A S L   Y A B V W
G C Q U Q   Y K D J X   T V I M J   R G F S U   X Q N W G
I H M R W   J B A W X   I M I N L   L G E Q H   Q U G B X


Introduction

This device was used widely by the U.S. Army from 1923 until 1942. It basically consists of 25 alphabet discs and a shaft. The disks can be mounted on the shaft in any order, they may be rotated relative to each other or may be fixed. On the rim of each alphabet disk there is stamped a different, disarranged alphabet. At it's inside or cup surface each alphabet disk is marked with a number. The numbers run from 1 to 25.

The underlying principle cryptographic - revolving, exchangeable alphabet wheels - was invented by Leo Battista Alberti during the fifteenth century. It has been reinvented by different people over the time: Thomas Jefferson, Major Bazeries (~1901), Colonel Parker Hitt (1914), and may be others. The US-Navy used the device as CSP-488. Have a close look at wheel number seventeen, it will reveal the origin of the device!

Please note that this cipher is not secure. Do not use it to protect vital or valuable information!


Enciphering A Message

At first, the alphabet disks are mounted on the shaft according to a pre-agreed arrangement. Since a series of 25 numbers would be hard to remember, such a series is derived from a key word or key phrase: First, this key is repeated until it's length is 25 letters. Starting at one, numbers are assigned to these letters according to there position in the alphabet and the key word. For example, using the phrase CHINESE LAUNDRY, we obtain:

We assign numbers starting with one at the first letter of the alphabet found in the key phrase - in this case an A:
 

 C 
 H 
 I 
 N 
 E 
 S 
 E 
 L 
 A 
 U 
 N 
 D 
 R 
 Y 
 C 
 H 
 I 
 N 
 E 
 S 
 E 
 L 
 A 
 U 
 N 
 
 
 
 
 
 
 
 
1
 
 
 
 
 
 
 
 
 
 
 
 
 
2
 
 

We continue with the second letter of the alphabet present in the key phrase - since there are no B's in our example, this it the letter C:
 

 C 
 H 
 I 
 N 
 E 
 S 
 E 
 L 
 A 
 U 
 N 
 D 
 R 
 Y 
 C 
 H 
 I 
 N 
 E 
 S 
 E 
 L 
 A 
 U 
 N 
3
 
 
 
 
 
 
 
1
 
 
 
 
 
4
 
 
 
 
 
 
 
2
 
 

This procedure is repeated until we've got all 25 numbers:
 

 C 
 H 
 I 
 N 
 E 
 S 
 E 
 L 
 A 
 U 
 N 
 D 
 R 
 Y 
 C 
 H 
 I 
 N 
 E 
 S 
 E 
 L 
 A 
 U 
 N 
3
10
12
16
6
21
7
14
1
23
17
5
20
25
4
11
13
18
8
22
9
15
2
24
19

We find the order in which the alphabet discs must be put on the shaft as: 3, 10, 12, ... 19.

Now the alphabet disks are rotated so that the first 25 letters of the message to be enciphered are found in a row. Then the discs are fixed so that unintended rotations are avoided.

Finally, a line is chosen at random. It's letters form the enciphered text. It is not needed to remember the position of the chosen line relative to the plain text.

The rest of the message is processed the same way.


Deciphering A Message

The discs are arranged as described above. Then the alphabet disks are rotated so that the first 25 letters of the cipher text are found in a row, the the discs are fixed so that unintended rotations are avoided. Now all other lines are examined, one of them must contain intelligible text. It is extremely improbable - if not impossible - that there are two or more lines containing intelligible text.

For example, you may try to decipher the following message using the key as given above:


The Virtual Cipher Device

This simulation of the U.S. Army cipher device M-94 is based on the alphabet disks as described in Military Cryptanalytics, Part II.


Using The Simulator

  1. To change the order of the alphabet discs, enter a key word or phrase and press the Change Key button
  2. A disc may be rotated by using the mouse by click & drag.
  3. To select a disc, click on it. The selected disc is marked by a red label below it.
  4. You may rotate the selected disc pressing arrow up, arrow down, page up, or page down.
  5. To rotate all discs, press the Up or Down buttons. Hold down the control key while pressing arrow up, arrow down, page up, or page down will rotate all discs as well.
  6. Press the Grab button or F10 to copy the line between the markers into a text area for further processing. If you hold down the shift key, all characters up to the last modified disc are copied. Without a shift key disk, all 25 characters are copied.
  7. The Switch bottom toggles between the view of the cipher discs and the text display.
  8. Finally, by typing a letter the selected disk will be rotated to show this letter and the select the next disc, if any.
Please note that the program's actual reaction to user actions may be influenced by the JavaVM. For this reason, not all the features described above may apply for your system.
Note that the simulator is able to simulate Major Bazeries device as well!


Compatibility

Virtual US Army Cipher Device, Model M-94 should run as applet or application in any JavaVM. I've tested the simulator using SUNs Java Development Kit v. 1.1.6, Netscape's Navigator 4.0x, and SUNs HotJava Browser, all on Windows NT 4.0.
However, I have experienced some problems concerning the display of the wheels using M$ Internet Explorer V3 when running in 256 color mode.


Legal Stuff

Major Bazeries Cipher Device Simulator, and Virtual US Army Cipher Device, Model M-94, Version 1.1.1 are copyrighted 1997-2001 by Wilhelm M. Plotz. Altough this software is copyrighted it may be used and distributed freely.

For off-line use, you may download WheelCipher.zip. You need a system capable of using long filenames, e.g. more than 8+3 characters.

I DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL I BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.


References

Advanced Military Cryptography by William F. Friedman, Aegean Park Press (C-8), 1976, or Buckmaster Publishing.

Military Cryptanalytics, Part II, Volume 1 by Lambros D. Callimahos and William F. Friedman, Aegean Park Press (C-44), 1985.

The Codebreakers, David Khan, Scribner, 1967, 1996.

Decrypted Secrets : Methods and Maxims of Cryptology by Friedrich L. Bauer, Springer Verlag

National Maritime Museum Association: http://www.maritime.org/csp488.htm (includes pictures of the device)

Khan's book is the book on the history of cryptography. Bauer's book is pretty good as well: It's much shorter, but more mathemathical and technical. Nevertheless it should be readable to almost everyone. I strongly recommend both! (Provided that you're interested in crypto, offcourse!)


If you are interested in classical cryptography, you might want to have a look my CipherClerk's Applet at members.aon.at/cipherclerk . This applet / application implements some historic cipher schemes and cipher machines.