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Hagelin CD-57
Portable mechanical cipher machine

The CD-57 was a hand-held mechanical cipher machine, developed by Boris Hagelin and manufactured by Crypto AG in Zug (Switzerland) around 1957. The device is compatible with the Hagelin CX-52 desktop cipher machine and was small enough to fit in the pocket of, say, a coat.
 
The device measures only 137 x 80 x 40 mm and weights about 1 kg. It consists of a two-part die-cast aluminium enclosure in which all mechanical parts are mounted at the bottom. The upper half is a hinged lid that is opened by pressing a small button at the top of the device.

The CD-57 was available in several civil and military versions, all of which were fully compatible. It was available in grey (green) hammerite and olive (green). The latter was often issued to the military and is shown in the image on the right, together with the manual.
  

The CD-57 was introduced around 1957 and remained in service until the mid-1970s. In some countries it was used even longer. Due to its small size and the fact that it was compatible with the larger CX-52, the machine became popular with a number of Armies in Europe and elsewhere. The Austrian and the Swiss Army used it for tactical messages for many years.

As the CD-57 could easily be concealed, for example in the pocket of a coat, it became a popular encryption device with a number of intelligence agencies, such as the French Secret Service, during the Cold War. A special version of the CD-57 was produced for the Vatican. Rather than aluminium and steel, it was layed out in gold and ivory. The manufacturer, Crypto AG, used this 'limited edition' also as a gift to special foreign visitors. In the late 1950s and the early 1960s, the CD-57 was also built under licence, as the STG-61, by the German Manufacturer Rudolf Hell.
 

 
Wheels
In order to obtain the maximum cipher period (i.e. the number of steps before the machine repeats itself), each coding wheel (or disc) has a different number of divisions and pins. Each pin can be placed in an active or inactive position. The following 12 wheels are known:

25 26 29 31 34 37 38 41 42 43 46 47


Of these 12 wheels, only 6 are present in the device at any time. Quite often, the machines were supplied with just 6 cipher wheels, e.g.:

29 31 37 41 43 47


In some situations, two identical wheels sets were issued with a machine. It allowed the operator to prepair the alternate wheel set for a new key, whilst the old key was still in use. When the key was changed, e.g. at 12 o'clock midnight, all the operator had to do was swap the wheels sets. The 'old' wheelset could then be used to set the key for the following day.
 
Removing the wheels
In order to removed the wheels, it is important that the operating lever is in the locked position (i.e. fully pressed-in and locked). Next, open the case and swing the wheel locking spring to the side. The wheels can now be lifted from their axle. Alternatively, turn the device over with one hand and let the wheels drop into the other hand.
 
Setting up the key
Setting of the cryptographic key, involves the following settings:
 
  • Order of the coding discs
  • Setting of the pins on each disc
  • Start position of the wheels
Civil version
Although there is no functional difference between the civil version and the military version of the CD-57, i.e. both variants are compatible and interoperable, the device was available in two design variants: one painted in grey hammerite and one with a typical military green (olive) finish.
 
The grey hammerite version is generally identified as the civil version, although it was also issued to some military customers, such as the Austrian Army (see below). The image on the right shows a typical civil version of the CD-57.

The device can be opened by pressing the small push-button at the top, after which the hinged top half of the case can be swung away. The crank for manually moving the coding discs is stored inside the top lid. This version is usually supplied with 6 different wheels.
  
Civil version of the CD-57

 
Military version
The military version of the CD-57 is operational identical to the civil version (i.e. the two are fully compatible and interoperable). In line with other army equipment, the machine is finished in non-shiny green olive paint.
 
To prevent accidental opening of the device in a tactical environment, most military machines have a different type of lock, whereby the push button on top of the device is replaced by a curdled knob. In order to open the device, the knob should be rotated clockwise.
 
Austrian Army version
The Austrian Army used the civil version of the CD-57. In their case, the units were painted in a grey-green hammerite finish. The color was sligtly more green-ish than the standard civil (grey) variant. Whether this subtle difference in colour was deliveratly choosen for the Amry is not known. It is also possible that it was just a variation in paint colours.
 
The image on the right shows a typical CD-57 that was issued to the Austrian Army. Judging from the large circular scratch on the top surface of the device, it has seen quite some action. The scratch is caused by operating the manual crank.

The interior of this machine is still in excellent condition, which proves that it has been maintained well during its operational life.
  

 

 
Random tape version
Each CD-57 can easily be converted from an algorithm-based cipher machine into a one-time pad cipher machine, simply be replacing the coding discs by the so-called RT unit. RT stands for Random Tape. Using a properly generated random tape, makes the machine truely unbreakable.
 
...   
Close-up of the tape exit path

 
Box containing the RT/CD-57 Contents of the box. At the bottom right the RT option. Bare CD-57 machine The interior of the CD-57 with 6 cipher wheels The RT option aside the CD-57 Locking he RT option in place CD-57 with RT unit in place of the coding discs Close-up of the tape exit path

 
HELL STG-61
The CD-57 was also built under licence by the German manufacturer HELL, who designated the machine STG-61. Although the STG-61 pricipally is a straight copy of the CD-57, the Germans managed to squeeze-in a few modifications and improvements.

 More information
  
Typical view of the STB-61 with the handle in the extended position

 
Documentation
  1. Crypto AG, Pocket Cryptographer Type CD-57, Technical Description
    No. 3088-b. English. Oskar Stürzinger. August 1966. 21 pages.

  2. Crypto AG, Taschenchiffriergeraet Typ CD-57, Technische Beschreibung
    No. I 1088-b. Technical description (German). Oskar Stürzinger. December 1963. 23 pages.

  3. Crypto AG, Technical images (photographs) of CD-57
    Appendix to the above manuals. 2 Feb 1958. 12 pages.

  4. Crypto AG, Serviceanleitung fuer Taschenchiffriergeraet Typ CD-57
    No. A-1153. Service Manual (German). Oskar Stürzinger. November 1964. 13 pages.

  5. Michael Topf, Taschenchiffriergerät CD-57
    Übung zu Angewandter Systemtheorie: Kryptographie. Theoretical backgrounds on CD-57 (German). Johannes Kepler Universität Linz (Austria). 1977. 14 pages.

References
  1. Crypto AG, Pocket Cryptographer CD-57
    Short operation instructions in English, French, German and Spanish. Date unkown.

  2. US Patent 2,851,794, Cryptogrammic coding and decoding apparatus
    Filed 23 May 1956 by Boris Caesar Wilhelm Hagelin.

Further information

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