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Most of these were in use in the 1940s and 1950s, and have been wonderfully reproduced by Dirk Rijmenants. Photos of the actual hardware can be seen in the Crypto Museum site. This page doesn’t reveal information about current cryptographic systems or key settings that might have been used in the past, and refers strictly to publicly-available information on machines that were used across many countries and have long been decommissioned.

Perhaps one of the main reasons they were largely declassified is they are all based on Enigma, the workings of which are well-known and outlined in any decent book on the subject. All these systems worked on the same principle – the main components were rotors with two sets of pins representing characters. Internal wiring inside each rotor substituted each character with another. Messages encrypted by post-Enigma machines are unlikely to ever be decrypted because of the unimaginable number of possible wheel and pin settings.

The following simulations were created by D. Rijmenants back in 2006 to run on Microsoft Windows XP, but they also run perfectly in WINE, if you’re installing them on Linux. Both simulations and the original machines themselves are works of genius, which is why I’ve devoted a post to these.

ATOMIX

Little is known about this system, and there isn’t information readily available on it, except that it was used in the later years of the Cold War. Pocket-sized crypto devices were in circulation by the late 1980s, so ATOMIX was in service prior to that, perhaps as early as 1965.
As the simulation shows, the device was an electromechanical device with eight wheels, the settings of which formed the message key. There was most likely another mechanism, hidden under the casing to the right of the wheels, used to generate the cipher.

Enigma

This is perhaps the best known of the cipher machines, which the history of Bletchley Park and the first ever digital computer, Colossus, was based around. Enigma was also the first cryptosystem of this kind, and the basis for future crypto devices in this article.
There were several models in use up to 1945. The common model had three wheels, and was used for general communications. Another version, used when a higher level of security was needed, had up to eight wheels.
Usually, a codebook was issued to all the units, and from this, a new key was selected each day. The codebook told the operators which rotors, ringsettings and plug connections to use.

Each wheel had two sets of 26 pins, to represent the characters of the aplhabet. The wiring inside the wheel itself matched each pin to another pin representing a different letter. On its own, this provided a substitution cipher system, which is easy to break, so wiring was changed on a plugboard to further scramble the signals.
To make the code harder to break, the first wheel moved one position each time a character occured more than once in a message. When the first wheel completed one revolution, the second wheel moved a position.

When a key was pressed, and electrical current passed through the wheels, and the wiring inside them, to a reflector. The return wire from the reflector passed the current through the plugboard to one of the lamps in the panel above the keypad. The illuminated letter on the panel was written down. The process repeated for each letter in the message.

The receivers, with identical wheel and plugboard settings on their Enigma machines, entered the coded message. As each letter was typed in, the deciphered letter lighted up on the panel.

Different sections of the German army also used their own characters to represent abbreviations and punctuation, making it harder for third-parties to analyse their messages. Codewords were used if more than one character was repeated sequentially.

Hagelin BC-52

Manufactured by Hagelin Cryptos, this device was the successor to the M-209 used for encrypting high-level messages from the early 1950s. Some of the M-209’s features were also found in the BC-52 and variations of this system. It was particularly secure when the key settings were very carefully chosen.

The user selects six pinwheels from a set of 12, each with 32 pins. Each wheel also had a different sequence of letters and numbers. The start position of these wheels forms the message key, which should only be used for that message.
The printer wheel offset could also be adjusted to further obscure the messages.

KL-7

Based almost directly on Enigma, the KL-7 was compromised a number of times while it was in operation. Introduced by the NSA in 1952-1953, the KL-7 was loaned by the NSA to NATO until 1983, when it was discovered information about the device was passed on to the Soviets. The NSA immediately recalled the devices and related materials, and the KL-7 was decommissioned.

The wiring inside each rotor was kept secret and changed annually. After the machines were recalled, the wiring inside the rotors, and other parts of the machine, was removed altogether to prevent past messages being deciphered. Because of this, the exact workings are still unknown. Rijmenants’ KL-7 simulation is generally accepted as the most accurate model available.

Although it was intended to be vehicle-mounted field kit, the KL-7 was unreliable and suffered a number of mechanical problems.

M-209

Also used as field equipment by the US Army. The M-209 worked in roughly the same way as a typewriter, but to make the device as small and lightweight as possible, a wheel was used to select characters instead of a keypad. Each character, after being selected, was printed onto paper tape (stored under the casing) when the user pushed the large lever to the right of the device.

To set the device for encryption, the user switches the small tab on the left to ‘C’ and sets the message key by rotating the large wheels on the front of the device.
To enter a message, the user rotates a small wheel on the left to select the character, then uses the large tab on the right as a enter key. The encrypted text was printed onto the tape.
To decrypt a message, the small tab on the left was switched to ‘D’, sets the large wheels to match the encryption key, then enters the encrypted message. The plaintext was printed on the tape.

The M-209 was also expendable. If there was risk of capture, the key settings were reset and the machine destroyed.

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