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Hagelin CX-52
Advanced pin-and-lug cipher machine

CX-52 was a mechanical pin-and-lug cipher machine, developed around 1952 by Boris Hagelin and manufactured by Crypto AG in Zug (Switzerland). It was intended as a replacement for earlier machines, like the C-446 and M-209. CX-52 is a more secure version of the C-52, and has an irregular movement of the cipher wheels, which made it virtually unbreakable by NSA at the time.

Compared to earlier designs, it offers several improvements. It has six interchangeable cipher wheels that can be removed easily by pulling out the main spindle from the right side. Each of the wheels has a different number of steps on its circumference, which ideally should be coprimes.

The wheels were normally black, as shown in the image on the right. In some cases, users had six additional wheels, which were usually white. Of the total set of 12 wheels, six were placed in the machine, subject to the current KEY, whilst the remaining six were stowed in a metal container.
  
CX-52 with open lid

The machine was available in a civil (grey) and military (green) variant, which were functionally identical. When used properly, the CX-52 was highly secure and very difficult to break by the US National Security Agency (NSA). It was possible however, to set it up in such a way that it had a short cycle (period), in which case it was easy to break. This was fixed in the CX-52M, which was modified by NSA cryptomathematician Peter Jenks, to always produce a long cycle, albeit one that was predictable by NSA. It looked safe from the outside, but was in fact weaker than before [5].

For customers who did not move from the CX-52 to the CX-52M, special manuals were available to learn them how to make 'proper' (secure) use of the machine. By supplying different manuals to different customers, this too became a way of manipulating the strength in favour of the NSA.

For use in base stations, the CX-52 could be expanded with a B-52 or B-62 keyboard unit, in which case the function of the advance lever was taken over by a motor. This greatly improved the throughput of the machine. The combination of CX-52 and a B-52/B-62 was known as BCX-52.
  
CX-52/RT with key tape

The machine was also available in a Random-Tape (RT) version (shown above), in which case the cipher wheels had been replaced by a 5-level tape reader. As these machines are based on the One-Time Tape (OTT) principle, they are theoretically unbreakable. For this reason they were only advertised and sold to friendly nations 1 like NATO countries, Switzerland and Sweden. This was part of a secret deal between Hagelin and NSA, today known as The Gentleman's Agreement [1].

Despite a slow start – mainly caused by the implementation of the The Gentleman's Agreement – the machine became very popular. By the mid-1950s, it was already in use in 50 countries [3]. In 1970, the CX-52 was succeeded by the electronic H-460. Nevertheless, many of them were kept as backups during the Cold War, well into the 1980s — in Belgium even well into the 1990s.

  1. As NSA refused to tell Hagelin which countries were on their target list, Hagelin assumed he could also sell these machines to South American countries, like Argentina and Brasil. When in 1960, the CIA Licencing Agreement came into effect, he learned that this was not the case [5].

CX-52 ready for use CX-52 with open lid CX-52 with open lid CX-52 front view Printer Wheels removed from the machine Removing the cipher wheels B-621 with CX-52/RT
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CX-52 ready for use
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CX-52 with open lid
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CX-52 with open lid
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CX-52 front view
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Printer
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Wheels removed from the machine
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Removing the cipher wheels
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B-621 with CX-52/RT

Features
The diagram below provides a quick overview of the many controls and settings on the CX-52. Note that many versions and variants exist, and that not all controls are available on all versions. The machine is shown here with it cover open, revealing the six removable cipher wheels (at the front) and the revolving cage with sideways movable (sliding) bars behind them. At the front left is a strip printer with a settable letter wheel at the top. It is used as the input/output device.

Click to see more

Setting they cryptographic KEY, involves setting the pins on each of the wheels, and inserting the selected wheels in the machine in the desired order, as instructed by the (daily) KEY sheet. Next, the MODE selector at the left side is set to C – for ciphering – or D for deciphering. A message is enciphered letter-by-letter, by setting the letter selection disc at the front left to the input letter, and operating the advance lever at the right. Input and output letter are then printed on the paper strip at the left rear. A built-in rotating knife, automatically cuts the paper strip in two halves.

With open printer cover Print head Mechanism Various CX-52 models
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With open printer cover
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Print head
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Mechanism
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Various CX-52 models

Models
  • CX-52
    Standard (initial) version of the machine. Very secure when used properly, and extremely difficult to break by NSA at the time. It defeated the existing methods for solving Hagelin ciphers. NSA tried to persuade Hagelin not to sell these machines to denied countries, but refused to share the denied-list with him, as they didn't want to reveal their targets [5].

    It was possible to setup this machine in such as way that it produced a short cycle, as a result of which it became easier to break. Unwitting users could easily select a weak setting. For this reason, the CX-52 was never adopted for use by the US Army and NATO.

  • CX-52M
    This version was marketed by Crypto AG as the improved – more secure – version of the CX-52, which always produced a long cycle (period). The modification was developed by Peter Jenks at NSA. In reality, the cycle was predictable, and allowed NSA to break it [5].

  • CX-52/RT
    This is the most secure version of the CX-52, in which the cipher wheels are replaced by a 5-level reader for punched paper tape. It is also known at the RT/CX or OTT or Mixer. It was only advertised and sold to friendly nations, auch as the NATO countries, Switzerland and Sweden. When used properly, this machine is theoretically unbreakable, as it is based on the One-Time Pad (OTP) cipher.

    In 1960, Hagelin had sold a large batch of CX-52/RT machines to Brasil, but this met with fierce opposition from NSA/CIA, as Brasil was on the proscribed list (the list of countries to which secure machine had to be denied) — which Hagelin didn't have. Hagelin acted immediately and persuaded the Brasilians to swap the RT-machines for the (exploitable) CX-52-M-27. He also stopped advertising this model below the Mexican border [5].
Secret designators
According to the The Gentleman's Agreement – which controlled which machines could be sold to whom – Hagelin had secretly designated a range of version and variant numbers, which were not printed on the machine's label. He identified the CX-52 as a Class-2 machine. It was more advanced than the C-52, which was a Class-1 machine. The following designators are known:

  • CX-52a
    This model is supplied with Standard A slide bars, which produce irregular or varying angular displacements of the key wheels, each wheel advancing 0, 1, 2, 3, 4 or 5 steps on each operation. This is the default and most secure version of the machine.

  • CX-52b
    This model is supplied with Standard B slide bars, which produce regular or fixed anglular displacements of the key wheels, all advancing the same number of steps, but the number of steps may be any one from 1 to 32. It is weaker than the a-variant.

  • CX-52c
    This model is compatible with the old types of C-machines, the M-209, the C-446 and a certain version of the C-52. It is the weakest of the models.

  • CX-52ak
    This is basicially a CX-52a that is enhanced with the so-called Complementary feature (here written as 'Komplimentary'), also known as the Hüttenhain 1 feature.

  • CX-52bk
    This is a CX-52b that is enhanced with the Hüttenhain 1 feature. This variant is built by HELL (licenced by Hagelin) for the German and Austrian market, for which HELL had an exclusive contract. It is the only version that is approved by Dr. Erich Hüttenhain 1 for use by the German Bundeswehr (Army), where it is known as the HELL H-54.

  • CX-52ck
    CX-52c with Hüttenhain 1 feature.

  • CX-52/10
    This is a 10-digit numerical-only variant of the CX-52. These machines can be of the a, b or c type and may have the complementary feature as well. For example: CX-52ak/10.

  • CX-52/30
    This is a 30 character version of the CX-52, suitable for the Arabic (and possibly Russian) alphabets. It is similar to the C-52/30 Arab.

  • CX-52/RT
    This is the Random Tape or One-Time Tape (OTT) variant of the machine.
  1. During WWII, Dr. Erich Hüttenhain was the chief cryptologist of the Third Reich. After the war, he was employed by the new German Intelligence Agency, the Organisation Gehlen (OG), in 1956 renamed to Bundesnachrichtendienst (BND). Until 1970, he was the head of the German cipher authority ZfCh.

HELL H-54 (CX-52bk) aside a CX-52ak (right)

Parts
Standard (civil) version of CX-52 Military version of CX-52 CX-52/RT with key tape
OTT
Cut-away version for instruction purposes HELL H-52 (improved CX-52 clone) Special version gifted to former users B-52, B-62 or B-261 keyboard Additional cipher wheels
Operational Instructions and service manuals
Civil version   CX-52
The basic version of the machine was sold in a grey painted enclosure. It is also known as the civil version, although the military version was identical (apart from the colour).

Note that there are many versions and variants of this machine, with different locks, print heads, reconfigurable letter selection discs and with or without certain features. The version shown here does not have the F/V selector at its left side.
  
CX-52 with open lid

Military version   CX-52
The image on the right shows a military version of the CX-52. It is identical to the standard (civil) version, but it painted in a military green colour.

The case is locked by means of a cross-lock-and-key, whereas the civil version has a regular cylinder lock. The version shown here has an F/V selector at the left side (towards the rear) which is missing from the civil version shown above.
  
CX-52 military version - with open lid

One-Time Tape version   CX-52/RT
By far the most secure model of the CX-52 was the Random Tape (RT) version, commonly known as CX-52/RT or RT/CX. It a One-Time Tape (OTT) machine, or mixer, that is based on the principle of the One-Time Pad (OTP). When correctly used, OTT machines are unbreakable.

This version was only advertised and sold to friendly nations, such as all NATO countries, Switzerland, Sweden and very few others.
  
CX-52/RT with key tape

Cut-away version
The image on the right shows a modified CX-52, of which part of the body has been removed, so that the inner mechanics have become visible.

This item was found on eBay in 2009, and was probably made for instruction purposes, or just for fun. The machine has been repainted in blue hamerite, and the edges of the cut-out sections have been highlighted in red.
  
Cut-away version of CX-52

HELL H-54
In the mid-1950s, the German company HELL was contracted by the German Army — Bundes­wehr — to build this CX-52 clone. At the time, Germany was not allowed to develop its own encryption devices, but building them under licence from a foreign developer was allowed.

The machine was designated H-54, has has several improvements over the original CX-52, including one that was developed by Dr. Erich Hüttenhain, the head of the German cipher authority ZfCh (and former head of OKW-Chi).

 More information

  
HELL H-54 with open lid

Silver version   CX-52/RT
Over the years, many mechanical Hagelin cipher machines like the CX-52, found their way to the Netherlands, where they were used by the Army, the Air Force, the Navy and the Foreign Office.

In later years, when mechanical cipher machines had been replaced by electronic ones, it became common practice to give former crypto-users or decision makers, a silver-painted Hagelin cipher machine as a retirement present. The one shown here was given as a farewell present to the (then) head of the Dutch cipher authority.

  
Silver CX-52/RT with open lid

Keyboard   B-52, B-62, B-621
The basic CX-52 is a fully mechanical device, that requires a text to be encrypted letter-by-letter. As this is a very time-consuming task, it was possible to use a special motor-drive with keyboard, that had a bay for the CX-52.

The expansion, or B-unit, was mainly used in base stations and command centres. The design faced many mechanical and electrical problems, as a result of which there are many production variants, designated B-52, B-62, B-621, etc. The combination CX-52/B-52 was known as BCX-52.

  
B-621 keyboard with motor-drive

Additional wheels
Each CX-52 was supplied with six (usually black) cipher wheels, that had 25, 26, 29, 31, 34 and 37 steps respectively. It could be extended with six further (usually white) cipher wheels, with 38, 41, 42, 43, 46 and 47 steps respectively.

The additional wheels were stored in a slimline metal container, such as the one shown in the image on the right.
  
Close-up of an additional cipher wheel

User and service manuals
Each CX-52 came with a blue printed manual in three languages. Note however, that there were different manuals for each variant, customer and/or country, and that some manuals may have been rigged, to prevent the machine from being used properly (i.e. make it breakable).

In addition, there was a wide range of service manuals, parts lists, application notes, leaflets, brochures, etc., some of which are available from the Documentation section below.

 CX-52 documentation

  
C-52 and CX-52 manuals

CX-52 military version CX-52 military version CX-52 military version - with open lid CX-52/RT with key tape CX-52/RT with key tape Silver CX-52/RT Silver CX-52/RT with open lid Silver CX-52/RT with open lid
Tape reader removed from the machine B-621 keyboard with motor-drive B-621 keyboard with motor-drive B-621 with CX-52/RT CX-52 (closed) and box with additional cipher wheels Six additional wheels for CX-52 Additional cipher wheels in metal container Close-up of an additional cipher wheel
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CX-52 military version
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CX-52 military version
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CX-52 military version - with open lid
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CX-52/RT with key tape
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CX-52/RT with key tape
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Silver CX-52/RT
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Silver CX-52/RT with open lid
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Silver CX-52/RT with open lid
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Tape reader removed from the machine
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B-621 keyboard with motor-drive
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B-621 keyboard with motor-drive
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B-621 with CX-52/RT
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CX-52 (closed) and box with additional cipher wheels
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Six additional wheels for CX-52
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Additional cipher wheels in metal container
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Close-up of an additional cipher wheel

Description
When the C-52 was introduced, it caused ripples throughout the cryptanalytic community [2]. Basically, the C-52 has 6 pin-wheels, chosen from a set of 12 different wheels. Each wheel has a different number of steps (and hence pins) to complete a full revolution, all of which are relative prime numbers in order to achieve the maximum possible cryptographic period. The wheels carried a number that corresponded to the number of steps:

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

The 6 wheels are removable, making it easier to swap them and to configure the pin-settings. The higher number of steps on each wheel increased the cipher period drastically, reducing the probability of key sequence overlap. The wheels were numbered from 01 to the number of steps, e.g. 47, but there were also wheels with interleaved letters and numbers (A-02-B-04-C-06 etc.).

In addition, the cage of the C-52 has 32 bars whereas the M-209/C-38 only has 27 bars. The extra five bars (1-5) control the irregular stepping of the rightmost five wheels. The downside of this design is that the rightmost wheel either moves continuously or is hardly ever moved at all during encipherment.

This problem was more or less solved in two further variants, the CX-52 and in the CX-52M, which had an improved stepping mechanism. The CX-52 was in fact so strong that agencies had to develop new methods of attack.
  
CX-52 cipher wheel with 31 pins removed from the machine

An extra feature of the machine was the possibility to scramble the final output alphabet by swapping the individual letters on the selector (the large rotating knob on the left) into any possible order. This improved cipher security and posed an extra challenge for cryptanalists.

Removing the axle Removing the pin-wheels from a CX-52 Each wheel has a different number of steps and has numbers on its circumference. Left side of wheel 31 Right side of wheel 31 CX-52 cipher wheel with 31 pins removed from the machine Perspective view of wheel 31 The 6 pin-wheels of a military CX-52, with alternating letters and numbers.
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Removing the axle
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Removing the pin-wheels from a CX-52
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Each wheel has a different number of steps and has numbers on its circumference.
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Left side of wheel 31
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Right side of wheel 31
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CX-52 cipher wheel with 31 pins removed from the machine
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Perspective view of wheel 31
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The 6 pin-wheels of a military CX-52, with alternating letters and numbers.

BC-52 Simulator for Windows
Crypto researcher Dirk Rijmenants in Belgium 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 CX-52
    User Manual in English, French and German. 36 pages.
    Crypto AG. 1 January 1962.

  2. The Hagelin Cryptographer, Type CX-52 (photographs)
    Photographs belonging to the above manual [A]. 4 pages.
    Crypto AG. 16 January 1951.

  3. Instructions for the tape controlled cryptographer CX/RT
    User Manual for the CX-52 with random tape (RT) (English). 7 pages.
    Crypto AG. June 1968.

  4. Spare parts catalogue CX-52 (No 21101 etc)
    Spare parts list with instructions in English, French and German. 35 pages.
    Crypto AG. 1 January 1962.

  5. RT/CX One Time Tape auxiliary device
    CX-52/RT sales brochure (English). 3 pages.
    Crypto AG. December 1958.

  6. Appareillage pour Chiffrement à Bandes Perforées
    Instructions for CX-52/RT (RT/CX), B-621 and PEB-61 (French).
    Doc. 2268. Crypto AG, Oskar Sturzinger. February 1969. 5 pages.

  7. Die Klaviatur B-621 (B-62)
    B-621 (B-62) keyboard attachment for CX-52 (German). 14 pages (with schematics).
    Doc. 1188a. Crypto AG, Oskar Sturzinger. June 1968.

  8. CX-52 Condensed Instructions
    Doc. 3035b. Crypto AG, BH. November 1957.

  9. CX-52 Description
    Doc. 3027. Crypto AG, Oskar Stürzinger, August 1956.

  10. CX-52 Service Instructions and Maintenance
    Doc. 3099. Crypto AG, BH, January 1959.

  11. CX-52 Spare parts catalogue
    Doc. L-013. Crypto AG, May 1956.

  12. CX-52 Specification
    Doc. I-3006c. Crypto AG, Oskar Stürzinger, November 1957.

  13. B-52 Service Instructions
    Doc. E-3121a. Crypto AG, Oskar Stürzinger, 12 November 1956 — July 1961.

  14. B-52 Ersatzteilkatalog (spare parts catalogue)
    Doc. L-027. Crypto AG, 10 October 1957.

  15. B-52 Keyboard attachment unit
    Doc. 3052a. Crypto AG, Sn, January 1958.

  16. C-52 Trouble Shooting
    Doc. 3225a. Crypto AG, date unknown.

  17. Usage of Hagelin cryptographer CX-52
    Doc. <unknown>. 25 November 1964.
References
  1. Crypto Museum, The Gentleman's Agreement
    30 July 2015.

  2. Deavours and Kruth, Machine Cryptography and Modern Cryptanalysis
    ISBN 0-89006-161-0. 1985, p. 197.

  3. Boris Hagelin, Die Geschichte der Hagelin-Cryptos
    Original manuscript by Boris Hagelin in German language. Zug, Fall 1979. 1

  4. Wikipedia, Coprime integers
    Retrieved February 2020.

  5. Crypto Museum, Operation RUBICON
    February 2020.
  1. This story was later translated by Boris Hagelin into English. It can be downloaded here.

Further information
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Crypto Museum. Created: Tuesday 04 August 2009. Last changed: Monday, 02 March 2020 - 11:39 CET.
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