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File:Typex nocase.jpg
Typex was based on the commercial Enigma machine, but incorporated a number of additional features to improve the security. This model, a Typex 23, was a late variant, incorporating two plugboards.

In the history of cryptography, Typex (alternatively, Type X or TypeX) machines were British cipher machines used from 1937. It was an adaptation of the commercial German Enigma with a number of enhancements that greatly increased its security.

History and development

By the 1920s, the British Government were seeking a replacement for their book code systems, which had been shown to be insecure, and which, with superencipherment, proved to be slow and awkward to use in practice. In 1926, an inter-departmental committee was formed to consider whether they could be replaced with cipher machines. Over a period of several years and at large expense, the committee investigated a number of options but no proposal was decided upon. One suggestion was put forward by Wing Commander O. G. W. G. Lywood to adapt the commercial Enigma, adding a printing unit, but the committee decided against pursuing Lywood's proposal.

In August 1934, Lywood began work on a machine regardless, authorised by the RAF. Lywood worked with J. C. Coulson, A. P. Lemmon, and W. E. Smith at Kidbrooke in Oxfordshire, with the printing unit provided by Creed & Company. The first prototype was delivered to the Air Ministry on 30 April 1935. In early 1937, around 30 Typex Mk I machines were supplied to the RAF. The machine was initially termed the "RAF Enigma with Type X attachments".

The design of its successor had begun by February 1937. In June 1938, Typex Mk II was demonstrated to the cipher-machine committee, who approved an order of 350 machines. After some initial trials, the machine was soon adopted by the Army and other governmental departments. During World War II, a large number of Typex machines were manufactured by Powers-Samas (Campbell-Kelly, 1990).

Description of Typex

Typex Mk III was a portable version powered by a handle.

Like Enigma, Typex was a rotor machine. Typex came in a number of variations, but were five-rotor machines (as opposed to three or four in the Enigma) with a non-rotating reflector. In most versions, the first two rotors were stationary during encipherment, although they could be set by hand. These additional stationary rotors provided a similar sort of protection to that of the Enigma's plugboard, which the Typex lacked.

Another improvement the Typex had over the commercial Enigma machine was that each rotor in the machine contained multiple notches that would turn its neighbouring rotor.

Some Typex rotors came in two parts — a slug containing the wiring was inserted into a metal casing. Different casings contained different numbers of notches around the rim, such as 5, 7 or 9 notches. Each slug could be inserted into a casing in two different ways by turning it over. In use, all the rotors of the machine would use casings with the same number of notches. Normally five slugs were chosen from a set of ten.

On some models, operators could achieve 20 words a minute, and the output ciphertext or plaintext was printed on paper tape. For some portable versions, such as the Mark III, a message was typed with the left hand while the right hand turned a handle (Devours and Kruh, 1985).

Security and usage

Typex was used by the British armed forces and was also used in Commonwealth countries such as Canada and New Zealand.

From 1943 the Americans and the British signed the Holden Agreement and BRUSA to develop a Combined Cipher Machine (CCM). The American SIGABA (M-134-C) was another rotor machine, although the Americans never permitted the British to see it. Attachments were built for both that allowed them to read messages created on the other.

Although a British test cryptanalytic attack made considerable progress, the results were not as significant than against the Enigma, due to the increased complexity of the system and the low levels of traffic. A Typex machine was captured by German forces, but it was without rotors. Their inability to use the machine in order to crack Typex messages may have convinced some of them even more of the security of Enigma.

Typex machines continued in use after the war up until the 1970s (the New Zealand government disposed of its last machine in 1973 [1]). This was one of the reasons the British kept the Ultra secret for so long; another was that they continued to read the traffic from other nations using Enigma and Typex, while their users continued to consider them secure.

External links


  • Martin Campbell-Kelly, ICL: A Business and Technical History, Oxford University Press, 1990.
  • Cipher A. Deavours and Louis Kruh, "Machine Cryptography and Modern Cryptanalysis", Artech House, 1985, pp144–145; 148–150.
  • Ralph Erskine, "The Admiralty and Cipher Machines During the Second World War: Not So Stupid after All." Journal of Intelligence History 2(2) (Winter 2002).
  • Ralph Erskine, "The Development of Typex", The Enigma Bulletin 2 (1997): pp69–86
  • Kruh and Deavours, "The Typex Cryptograph" Cryptologia 7(2), pp145–167, 1983

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