Typex

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The British key rotor machine Typex (here: Model Mk III) (2011)

The Typex (also: TypeX , TYPEX , Type X or Type – X ), British BID device designation BID / 08/02 for the Typex Mk 22 and BID / 08/03 for the Typex Mk 23, is a rotor key machine that The British armed forces not only used it for their own secret communications during World War II , but also used it as an aid to deciphering the communications of the German Wehrmacht encrypted with the German Enigma .

history

After the First World War , the British armed forces - like the German military - looked for a replacement for the now outdated, cumbersome and insecure manual encryption methods (for example code books ) that had been used until then. For this purpose, machine procedures came into consideration because they promised easier handling and improved cryptographic security. Based on technologies that emerged at the beginning of the 20th century , such as the electric typewriter and the teleprinter , four inventors, independently of one another and almost simultaneously, came up with the idea of ​​the rotor principle for encrypting texts. These are the American Edward Hugh Hebern in 1917, the German Arthur Scherbius in 1918 and the Dutch Hugo Alexander Koch and the Swede Arvid Gerhard Damm in 1919, all of whom registered patents for their ideas for rotor cipher machines.

In the mid-1920s, a British government commission, the so-called Inter-Departmental Cypher Committee , examined the commercial rotor key machines that are now freely available on the market, such as the German Enigma machine, with regard to their usefulness for secret military communications . An important aspect was the assessment of the security of the encryption against unauthorized decipherment. After an intensive examination of the machine and the Scherbius patents, this aspect was denied by the government commission and the development of an own, better machine was suggested. The development lasted nine years from 1926 to 1935 and culminated in Typex. It was used successfully by the authorities and services for many years.

principle

Typex in the Royal Signals Museum in Blandford

At first glance, the Typex looks like a typewriter, just like other Rotor key machines. You can see a keyboard , a set of rollers made up of five interchangeable rotors and a printing device for outputting the text. The set of rollers is the heart of the encryption. The rotors are rotatably arranged and have electrical contacts on both sides for the 26 capital letters of the Latin alphabet , which are irregularly connected to one another in pairs by insulated wires . If you press a letter key , electrical current flows from a battery in the Typex via the pressed key through the set of rollers and results in a letter being printed on a strip of paper. The printed letter corresponds to the encryption of the pressed letter key. Since the rotors continue to turn each time a button is pressed, similar to a mechanical odometer , the secret key alphabet changes after each letter.

It is important and cryptographically strong that each letter is encrypted in a different way due to the rotation. The cryptographer speaks of many different (secret) "alphabets" that are used for encryption and describes this as polyalphabetic substitution . In contrast, with a simple monoalphabetic substitution, only a single ciphertext alphabet is used and a plaintext letter is always converted to the same ciphertext letter. If the rotors of the Typex did not turn, you would only get a simple monoalphabetic encryption.

Cryptographic strengths

Box with Typex rotors

The cryptanalytical inspection of all available machines, especially the German Enigma, carried out professionally by the British government commission, revealed weaknesses in the existing cryptographic concepts, for example the fixed point-free permutations and the involutive plug board, which were specifically avoided during the construction of Typex. The Typex uses in contrast to the Enigma

  • two additional (discontinued) input / output stators, each of which can be rotated by hand, so that the permutation caused by their combination is not inverse to itself like the plug connections of the Enigma
  • more than one, namely five, seven or nine indexing notches per rotor
  • Rotors that can be used in two orientations,
  • whose internal wiring can be changed without much effort.
  • An assortment of initially ten, then 120, later 240 different rotors,
  • five of which are inserted into the machine, and
  • no involutor plug board.

Due to these astonishingly simple, but cryptographically very effective measures, the security of Typex against unauthorized decipherment could be significantly strengthened. In particular, one could rightly assume that a conceivable breach in the encryption would not compromise the entire system in the long term, since the effective combinatorial complexity of the Typex is considerably greater due to the above-mentioned design features, especially the extensive range of rotors and its easy changeability is as for example the Enigma.

Models

In 1937, production began with the first model in the series, the Typex Mk I. A year later, the government commission was presented with a further improved variant, the Typex Mk II, which checked and approved it. It was released for military service use and used in the British Army , the Royal Navy and later in Winston Churchill's Cabinet War Rooms .

Typex with external patch panels

The British specialists achieved a further strengthening of the encryption with the Typex Mk IV by adding an external device that looks a bit bulky, but with which the combinatorial complexity of the machine could be increased considerably in an easily manageable way. These were two external patch panels which, however, were non-invulatory , i.e. structured differently from the Enigma's involutive "connector board", and are therefore more comparable in their cryptographic effectiveness with the freely wirable reversing roller D introduced by the German Air Force in 1944 . A special modification made the Typex the Mark 23 model , which was used as a combined cipher machine for the secret exchange of messages with the American allies .

The abundance of cryptologically sound measures that the British introduced in good time resulted in the fact that German code crackers did not succeed in breaking the Typex encryption and, after several unsuccessful attempts, they completely gave up deciphering the British Typex message traffic, although some machines could be captured during the war, for example in 1940 after the British withdrew from the Battle of Dunkirk .

Deciphering the German Enigma

Since Typex is based on principles that it has in common with the German Enigma - despite all the important differences - including involutorics (encryption = decryption), the cryptanalysts in Bletchley Park, England, were also able to use it as an aid against the German machine. After the keys of the German Enigma radio messages had been "cracked" using other methods, such as the Turing bomb , and were thus available, the Typex was used to mechanically decrypt these radio messages using the known key, similar to that of the authorized recipient . For this purpose, the rotors of the Typex were set identically to the known wiring of the German key rollers. The Typex was not only used by the British for their own encryption, but also helped decipher the Enigma as a clone .

Cinematic reception

Typex made a short cinematic appearance in Enigma - The Secret , a British fictional film based on the novel Enigma , which deals with the deciphering work of the British codebreakers at Bletchley Park. During a short flashback, several Typex machines can be seen, which are used by " Wrens " (the female assistants) to decipher German radio messages after the code breakers have cracked the associated keys. Notable in the film are the many authentic props that are original showpieces from the Bletchley Park Museum. The various radio messages have been realistically generated and encrypted especially for the film according to the original rules and procedures.

literature

Web links

Commons : Typex  - album with pictures, videos and audio files

Individual evidence

  1. ^ Crypto Museum UK Cipher Machines. Retrieved July 7, 2017.
  2. ^ Typex modified as an Enigma . Retrieved July 1, 2008
  3. ↑ Robert Harris: Enigma . Novel. Weltbild, Augsburg 2005. ISBN 3-89897-119-8
  4. ^ Tony Sale: Making the Enigma ciphers for the film "Enigma" . Retrieved March 26, 2008.