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Hagelin
Pin-wheel
  
CX-52 →
← C-446
  
Hagelin C-52
Pin-wheel cipher machine

C-52 was a mechanical pin-and-lug cipher machine introduced around 1952 by the Swede Boris Hagelin and manufactured first by AB Cryptoteknik in Stockholm (Sweden) and later by Crypto AG in Zug (Switzerland). It was intended as a replacement for earlier machines, like the C-446 and M-209, with which it could be made backwards compatible. Like its predecessors, it was readable by the US National Security Agency (NSA). A more secure version was available as the CX-52.

Compared to earlier designs, the machine has a number of advantages. It has 6 removable cipher wheels – the pin-wheels – that can be configured outside of the machine. Furthermore, they can be installed in any order and additional wheels could be ordered. This increased the number of possible KEY settings and hence cipher security.

With the right selection (and order) of the cipher wheels and the settings of the lugs on the slide bars, the C-52 can be backwards compatible with the earlier C-3 and C-4 machines, such as the C-38 (M-209), the BC-38 and the C-446.
  
C-52 with open lid

The machine shares many parts with the more advanced CX-52, such as the enclosure, the printer, the slide bars and the accessories, but is significantly less advanced than the CX-52. It has slightly different pin-wheels, with a regular stepping behaviour, whereas the CX-52 features irregular stepping. The latter is caused by the slide bars. Although the slide bars of the CX-52 can be installed in a C-52, only the last two can advance the wheels. This is explained below.

The machine was offered to existing customers who needed backwards compatibility with C-3 and C-4 machines, but also to customers of non-friendly nations, to which the more advanced CX-52 could not be sold. Such countries were typically on the NSA's and CIA's proscribed list.

Hagelin C-52 ciper machine
C-52 front view
Hagelin C-52
C-52 with open lid
Cipher wheels
Cipher wheels and cage
Right side with serial number tag
Rotated drum (cage) with last bars visible
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Hagelin C-52 ciper machine
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C-52 front view
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Hagelin C-52
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C-52 with open lid
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Cipher wheels
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Cipher wheels and cage
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Right side with serial number tag
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Rotated drum (cage) with last bars visible

Features
The diagram below provides a quick overview of the controls and settings of the C-52. Note that a number of versions and variants exist, some of which may look different. The machine is shown here with its top lid open, so that the six pin-wheels (front) and the revolving bar drum with its 32 slide bars are visible. At the front left is a double printer that acts as the input/output device.

Click to see more

Setting the cryptographic KEY, involves setting of the pins on each of the pin-wheels, installing the wheels in a given order and setting the start position. When the lid is closed, it is protruded by the pin-wheels. A white line indicates the start position of the pin-wheels. A the left side is a knob that should be set to C when ciphering, or D when deciphering. A message is enciphered letter-by-letter, by rotating the large knob at the left until the dial at the front points to the desired input letter. It is then encrypted by pushing down the handle and releasing it again.

When operating the handle, the drum (cage) makes one full revolution, during which the cams and lugs on its slide bars interact with the pin-wheels. This causes an angular displacement of the print head and makes each of the pin-wheels step by one position. Although this guarantees the maximum possible cipher period – each wheel has a different (coprime) number of divisions – the stepping motion is regular and therefore easier to predict that with irregular stepping wheels.

Differences with CX-52
  • Regular stepping of the pin-wheels
  • No fixed/variable (F/V) feature
  • Different way of sensing the guide arms
  • Slightly different pin-wheels
  • Slightly larger diameter of the support discs inside the drum
  • Different guide arm locking mechanism
  • Not available in RT-version (one-time tape)
M-209 compatibility
Although the C-52 was more advanced than the earlier C-3 and C-4 machines, such as the C-38 (M-209) and the C-446, it was still possible to make it backwards compatible. This was a useful feature for existing customers. In such cases, the following wheels had to be used in this order:

C-38 → 26 25 23 21 19 17
C-52 → 26 25 46 42 38 34

Note that the rightmost four wheels of the C-52 have twice the number of steps of the C-38 wheels. With carefully chosen pin-settings it was possible to make the two models interoperable. In this mode, the first five bars of the cage (1-5) were not used, so that the remaining 27 bars could act like the 27 bars of the C-38 (M-209).

Arab version   C-52/30
The basic version of the C-52 was made for the 26 letters of the Latin alphabet (A-Z). It means that the indicator (dial) has 26 letters as well, as does the double print head. For support of different languages, such as Arabic or Russian, a special 30-character variant was also available.

The image on the right shows the Arab version of the C-52, which was used in countries like Saudi Arabia and Iran. The machine shown here comes from the personal collection of Hans Bühler — the Crypto AG sales representative who was arrested in Iran in 1992.

 More information

  
Arab C-52 with open lid

Interior
Although the interior of the C-52 is very similar to the CX-52, and many of the parts are shared between the two machines, there are some significant differences. First of all, the pin-wheels are slightly different and so is the way their guide arm are sensed. A guide arm senses whether a pin at a certain position on the circumference of the pin-wheel is inactive (set to left) or active (right).

In the CX-52 the guide arms are locked in place by means of a moving U-shaped locking bar at the start of a ciphering operation. The tip of the guide arm is then caught under the locking bar if the pin was active (i.e. set to the left) or stopped in front of it when the pin was inactive (right).

In the C-52 the guide arms are not really locked in place, but their movement is restricted within a certain window, by a six cut-outs, or slots, in the aluminium bar at the top of the machine. It is shown in the image on the right and is located between the pin-wheels and the drum (cage).
  
Guide arm locking bar

Due to the different construction of the pin-wheels, they are not interchangeable with the wheels of the CX-52. Another difference with the CX-52 is the construction of the drum. Although the bars are identical, the drum of the C-52 does not accept all of the slide bars that were available.

Unlike the CX-52, the drum of the C-52 does not accept bars that can cause wheel stepping in the first 30 positions (1-30). This was done by increasing the diameter of the six support discs inside the drum for most of the circumference.

The image on the right shows a close-up of part of the drum, in which two of the support discs are visible. The outer edges of these discs reach the hight of the cams on the bars. As the discs are cleverly positioned in front of the locking pawl of each of the pin wheels, they block the driving cog-wheels and inhibit wheel stepping.
  
Only the last two slide bars may cause wheel stepping (see the recessed support discs)

This means that only bars with six never-stepping cams — the so-called 0-cams — can be used in these positions. Only the last two positions of the drum (31 and 32) can hold slide bars that control wheel stepping, as the support disc is recessed at these positions. This is clearly visible in the image above. Move the mouse over it to highlight the raised and recessed parts of the discs.

Bars and support discs inside the drum of the CX-52

These drawings illustrate the difference between the C-52 and the CX-52. The drawing above shows the pin-wheels and the drum of the CX-52, in which slide bar 77 1 engages with the cog-wheel (red) and the blocking pawl (blue) of the pin-wheels. Move the mouse over the image to see what happens when the bar shifts to the left. The black vertical lines are the support discs.

Bars and support discs inside the drum of the C-52

In the C-52 (above), the diameter of the support discs is slightly larger, as a result of which they engage directly with the blocking pawl (blue), thereby effectively replacing the cams on the slide bars. As a result, the wheels are unable to advance (step). Only all-0-cam bars can be used here. Stepping is only possible with the last two slide bars, as that part of the support discs is recessed.


This means that, depending on the bars, the wheels can theoretically step 0, 1 or 2 positions per cycle. In practice however, only one bar controlled the stepping. It has six always-stepping cams (the so-called C-cams), so that each pin wheel makes exactly one step on each ciphering cycle. For a more detailed explanation of the slide bars, the angular displacement of the print head and the wheel stepping mechanism, please refer to the technical description of the CX-52 or read [1].

 More on the CX-52 page
 Overview of all known slide bars
 Check out the slide bar configuration of the C-52 machines in our collection

  1. Note that bar 77 is a fictive bar, on which all combinations of cams are present. This bar does not exist in real life. It is also used as an example in Bart Wessels paper [1].

Only the last two slide bars may cause wheel stepping (see the recessed support discs)
Guide arm locking bar
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Only the last two slide bars may cause wheel stepping (see the recessed support discs)
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Guide arm locking bar

BC-52 Simulator for Windows
Belgian crypto-researcher Dirk Rijmenants, has created a very realistic simulation of the BC-52 that runs on the Windows™ operating system. The BC-52 is actually a C-52 that is seated on a B-52 keyboard, hence the name BC-52. The software allows you to select between C-52 and CX-52 simulation, and customize the machine in various ways. Full instructions are included with the program.

The image on the right shows a screenshot of the BC-52 simulator running on Windows. It can also be used on Linux (WINE) and Mac (Parallels).

 Download (off-site)

  
Click here to download Dirk Rijmentants' BC-52 Simulator for Windows (off-site)

Documentation
  1. The Hagelin Cryptographer, Type C-52
    User Manual in English, French and German. 36 pages.
    D-036. Crypto AG, date unknown but probably early to mid-1960s.

  2. C-52 Trouble Shooting
    Doc. 3225a. Crypto AG, date unknown.
References
  1. Bart Wessel, The Hagelin Cryptographers C-52 and CX-52
    Crypto Museum, 24 February 2021.  Info
Further information
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Crypto Museum. Created: Sunday 16 February 2020. Last changed: Friday, 26 February 2021 - 22:52 CET.
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