Basic operation M-209

basic operation of m-209 relatively straightforward. 6 adjustable key wheels on top of box each display letter of alphabet. these 6 wheels comprise external key machine, providing initial state, similar initialization vector, enciphering process.

to encipher message, operator sets key wheels random sequence of letters. enciphering-deciphering knob on left side of machine set encipher . dial known indicator disk, on left side, turned first letter in message. letter encoded turning hand crank or power handle on right side of machine; @ end of cycle, ciphertext letter printed onto paper tape, key wheels each advance 1 letter, , machine ready entry of next character in message. indicate spaces between words in message, letter z enciphered. repeating process remainder of message gives complete ciphertext, can transmitted using morse code or method. since initial key wheel setting random, necessary send settings receiving party; these may encrypted using daily key or transmitted in clear.

printed ciphertext automatically spaced groups of 5 m-209 ease of readability. letter counter on top of machine indicated total number of encoded letters, , used point of reference if mistake made in enciphering or deciphering.

the deciphering procedure same enciphering; operator sets enciphering-deciphering knob decipher , , aligns key wheels same sequence used in enciphering. first letter of ciphertext entered via indicator disk, , power handle operated, advancing key wheels , printing decoded letter on paper tape. when letter z encountered, cam causes blank space appear in message, reconstituting original message spaces. absent z s can typically interpreted operator, based on context.

an experienced m-209 operator might spend 2 4 seconds enciphering or deciphering each letter.