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.
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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]
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]
Typex Mark III was a more portable variant, using the same drums as the Mark II machines, but powered by turning a handle (it was also possible to attach a motor drive). The maximum operating speed is around 60 letters a minute, significantly slower than the 300 achievable with the Mark II.
Typex Mark VI was another handle-operated variant, measuring 20"×12"×9", weighing 30 pounds, and consisting of over 700 components.
Plugboards for the reflector were added to the machine from November 1941.
For inter-Allied communications during World War II, the Combined Cipher Machine (CCM) was developed, used in the Royal Navy from November 1943. The CCM was implemented by making modifications to Typex and the United States ECM Mark II machine so that they would be interoperable.
Typex Mark VIII was a Mark II fitted with a morse perforator.
Typex 22 (BID/08/2) and Typex 23 (BID/08/3) were late models that incorporated plugboards for improved security. Mark 23 was a Mark 22 modified for use with the CCM. In New Zealand, Typex Mark II and Mark III were superseded by Mark 22 and Mark 23 on 1 January 1950.
Erskine (2002) estimates that around 12,000 Typex machines had been constructed by the end of World War II.
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 agreed upon a Combined Cipher Machine (CCM). The British Typex and American ECM Mark II could be adapted to become interoperable. While the British showed Typex to the Americans, the Americans never permitted the British to see the ECM, which was a more advanced design. Instead, 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 as against the Enigma, due to the increased complexity of the system and the low levels of traffic. A Typex machine without rotors was captured by German forces during the Battle of France and more than one German cryptanalytic section proposed attempting to crack Typex; however, the B-Dienst codebreaking organization gave up on it after 6 weeks, when further time and personnel for such attempts was refused. One German cryptanalyst stated that the Typex was more secure than the Enigma since it had seven rotors and therefore no major effort was made to crack Typex messages as they believed that the Enigma's messages were unbreakable.[3]
Typex machines continued in use after the war up until the 1970s (the New Zealand government disposed of its last machine about 1973.[4])
Several Internet Typex articles say that only Vaseline was used to lubricate Typex machines and that no other lubricant was used. Vaseline was used to lubricate the rotor disc contacts. Without this there was a risk of arcing which would burn the insulation between the contacts. For the rest of the machine two grades of oil (Spindle Oils 1 and 2) were used. Regular cleaning and maintenance was essential. In particular, the letters/figures cam-cluster balata discs had to be kept lubricated.
All the versions of the Typex had advantages over the German military versions of the Engima machine. The German equivalent teleprinter machines in World War II used by higher-level but not field units were the Lorenz SZ 40 and Siemens and Halske T52 using Fish cyphers.
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