Typex

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. The cipher machine (and its many revisions) was used until the mid-1950s when other more modern military encryption systems came into use.

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 (but without the weakness of being reciprocal), 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 the 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 a speed of 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.

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.

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 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 Oswyn G. W. G. Lywood to adapt the commercial Enigma by adding a printing unit but the committee decided against pursuing Lywood's proposal.

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Wikipedia