M-209
To encipher a message, the operator sets the key wheels to a random sequence of letters.
Repeating the process for the remainder of the message gives a complete ciphertext, which can then be transmitted using Morse code or another method.
Each key wheel is associated with a slanted metal guide arm that is activated by any pins in the "effective" position.
An effective pin causes its guide arm to tilt forward, contacting the drum.
When the operator turns the power handle, the cylindrical drum makes a complete revolution through all 27 bars.
A set of intermediate gears advances the key wheels by one position, and a locking arm latches into the drum to prevent a second encoding until the indicator disk is adjusted for the next letter.
This configuration includes the settings for each pin on all six of the key wheels, and the position of each lug on the rotating drum; these were typically specified by tables in a secret system publication given to both sender and receiver.
The rotational alignment of the key wheels could be chosen by the sender at random, and provided to the receiver via a secure channel of communication.
The resulting ciphertext is then compared with a long check string to verify that all of the internal settings have been performed properly.
The check string for this particular configuration is: Key wheel pins come into play when they reach the lower part of the key wheel during rotation; it is here that they may contact or release the guide arm that deflects the lugs to the left.
A new set of guide arms will interact with the drum, resulting in a different shift for the next encoding operation, and so on.
As with the Lorenz Electric teletypewriter cipher machine (codenamed Tunny by the Allies), if a codebreaker got hold of two overlapping sequences, he would have a fingerhold into the M-209 settings, and its operation had some distinctive quirks that could be exploited.
As of early 1943, German code breaking in World War II was able to read 10–30 percent of M-209 messages.
US researcher Dennis Ritchie has described a 1970s collaboration with James Reeds and Robert Morris on a ciphertext-only attack on the M-209 that could solve messages of at least 2,000–2,500 letters.
[3] Ritchie relates that, after discussions with the National Security Agency (NSA), the authors decided not to publish it, as they were told the principle was applicable to machines then still in use by foreign governments.
[4] The U.S. M-209s were produced at a rate of 400 units per day by Smith Corona Typewriter Company in Groton, NY, starting in 1942.
Had the Menzer devices been put into service, they would have certainly caused trouble for Allied cryptanalysts, though they were no more uncrackable than the M-209.
The C-52 featured a period of up to 2,756,205,443; wheels that could be removed and reinserted in a different order; and a printwheel with a mixed alphabet.
