M-209 Workings

M-209 Home Page

Overview

 This page describes the M-209 and its different parts. You will learn the vocabulary usefull to understand the explanations about M-209 working.

Using

 This page describes M-209 using, i.e. how to cipher a plain message or decipher a ciphered message.

Inner Setting

 Before ciphering a message (or deciphering one), the code clerk needs to set the internal setting of the M-209 according to a key chart. This page describes all these elements.

M-209 Working

The working of M-209 is described from different points of view :
  • From a mechanical point of view : what are the parts of the machine which act during ciphering.
  • From a mathematical point of view : given a special configuration, what will be the resulting encryption.
  • From a computer point of view : an example of program which emulates the M-209.
    Note: It is assumed that you have read the mathematical page.
  • A paper analog : we show an example of a paper analog of the M-209 for the key used in all examples.
    Note: It is assumed that you have read the mathematical page.

General material

In the explanations we use texts (plain and encrypted) and keys (external and internal) as follows: 

Plain text:  Attack at dawn
Plain text, by 5 letters group after replacing each space by letter Z:   
             ATTAC KZATZ DAWN 
Cipher text: WUHDU AJRJQ TLRG 

External key:  PEOPLE

Internal key: (from TM 11-380 Manual 1944), 
cipher-key Indicator:  "LP"

Position of key wheels pins
Wheel 1 (26):   AB_D___HI_K_MN____ST_VW___
Wheel 2 (25):   A__DE_G__JKL__O__RS_U_X__
Wheel 3 (23):   AB____GH_J_LMN___RSTU_X
Wheel 4 (21):   __C_EF_HI___MN_P__STU
Wheel 5 (19):   _B_DEF_HI___MN_P__S
Wheel 6 (17):   AB_D___H__K__NO_Q

Position of drum bar lugs
1.  3-6		10.  2-0		19.  2-0
2.  0-6		11.  2-0		20.  2-5
3.  1-6		12.  2-0		21.  2-5
4.  1-5		13.  2-0		22.  0-5
5.  4-5		14.  2-0		23.  0-5
6.  0-4		15.  2-0		24.  0-5
7.  0-4		16.  2-0		25.  0-5
8.  0-4		17.  2-0		26.  0-5
9.  0-4		18.  2-0		27.  0-5

References