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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.



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. Typically 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 in early models.

An improvement the Typex had over the standard German Services Enigma was that the rotors 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 a Typex rotor, each electrical contact was doubled to improve reliability.

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.[1]

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 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. 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 Greenwich, 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 Mark 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 Mark II was demonstrated to the cipher-machine committee, who approved an order of 350 machines. The Mark II model was bulky, incorporating two printers: one for plaintext and one for ciphertext. As a result, it was significantly larger than the Enigma, weighing around 120 pounds, and measuring 30" × 22" × 14". After some initial trials, the machine was adopted by the RAF, the Army and other governmental departments. During World War II, a large number of Typex machines were manufactured by Powers-Samas.[2]

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