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Hagelin CD-57   CD-55
Pin-and-lug pocket cipher machine

CD-55 and CD-57 were hand-held mechanical cipher machines, developed by Boris Hagelin and introduced by Crypto AG in Zug (Switzerland) around 1957. The CD-57 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 just 137 x 80 x 40 mm and weights about 1 kg. It consists of a robust two-part die-cast aluminium enclosure in which all moving parts are mounted in the bottom half. The upper half is a hinged lid that is opened by pressing a small button 1 at the top of the case.

The CD-55 and CD-57 are not interoperable, but each version is at least compatible with one other Hagelin desktop cipher machine. The case was available in grey or green-ish hammerite and in a military 'olive drab' green. The latter is shown with the instruction manual on the right.
  
Green CD-57 with instruction booklet and inspection card

Both models were introduced around 1957 and remained in service until the mid-1970s. In some countries even longer. Due to their small size and the fact that they are compatible with another (desktop) cipher machine, the machine became popular with a number of Armies in Europe and elsewhere. The Austrian and the Swiss Army used it for tactical field messages for many years.

As the CD-57 could be concealed easily, for example in the pocket of a coat, it became a popular encryption device during the Cold War with a number of intelligence agencies, in particular French intelligence. A special version of the machine with a gold-plated dial was produced as a luxury gift to loyal customers. It was given to the Shah of Persia 2 and was also supplied to the Vatican.

In the late 1950s and the early 1960s, the CD-57 was also built under licence by the German Manufacturer Rudolf Hell as the STG-61. 3 The CD-57 was succeeded in 1977 by the HC-520, one of the first fully electronic cipher machines, that marked the end of the mechanical era.
 
  1. On some versions the lid is opened with a rotary knob rather than a push-button.
  2. Persia is known today as Iran. The Shah was overthrown in 1979.  Wikipedia
  3. It is currently uncertain whether the STG-61 is fully compatible with the Hagelin CD-57.

Green CD-57 with instruction booklet and inspection card Green CD-57 with instruction booklet Hagelin CD-57 in military olive drab case Case variants Two cipher wheels CD-57 pocket cipher machine CD-57 ready for use Standard CD-57 with RT/CD option

 
Features
The CD-57 measures no more than 13 x 8 x 4 cm and weights just 710 grams. It has a metal operating lever that extends from the left side of the case, as shown in the images below. When in transit, the operating lever can be pushed all the way in, and held in place by a locking lever. Input and output of plaintext and ciphertext takes place via a circular window at the front top.

CD-57 In transit position

When operating the device, the outer letter ring should be set to a fixed position, as specified in the daily key settings. In the example above, the outer letter ring is set to 'A', which means that the 'A' is lined up with the index mark at the top edge of the case. When encoding a text, the metal operating lever should be pressed-in and released once for each letter. This rotates the inner letter ring to an arbitrary position. The outer ring then serves as the input (plaintext), whilst the inner ring represents the output (ciphertext). In the example below, A is translated to Q.

CD-57 ready for use

When a mistake is made, the keying mechanism can be turned back one or more positions, using a small crank that is normally stored inside the top lid of the case. The crank can be inserted into a small hole in the front panel, which is in fact the main axle of the cipher wheels. By turning the crank counter clockwise, the mechanism can be stepped back. Each ¼ circle represents one step.

CD-57 ready for use

The interior can be accessed by pressing a small button at the top (or turning a knob in case of the military variant). The diagram above shows the interior of a typical CD-57. All moving parts are mounted in the bottom half of the case. At the left is the stack of six cipher wheels, installed on the main axle. The wheels are held in place by the drum locking lever. A metal rod in front of the wheels marks the index at which the current position of the ciper wheels is read.
 
CD-57 with operating lever in storage position CD-57 ready for use Case lock (push-button) Rotary case lock Setting the outer letter ring Crank inserted in the main axle Operating the crank

 
Models
The CD machines were available in four basic models and in a number of (case) variants. The following basic models are known:
 
  • CD-55
    This version has 6 pin-wheels and features a simple keying mechanism that works like the C-38, C-446 and M-209. It looks identical to the CD-57, but is much easier to break. It was supplied to non-NATO countries, as agreed in a secret arrangement with the NSA [4]. The CD-55 is compatible with the C-52 (the non-NATO variant of the CX-52).

  • CD-57
    This version has 6 pin-wheels, but features a much improved keying mechanism that is similar to that of the CX-52. It was supplied to NATO and NATO-friendly countries. This version could be converted into an unbreakable OTT cipher machine (see below).

  • CD-57/RT
    The CD-57 could be converted into an unbreakable one-time tape (OTT) cipher machine in just a few seconds, by removing the wheel stack and replacing it with a so-called RT/CD option. The abbreviation 'RT' means Random Tape.

  • STG-61
    This was a slightly improved and modified variant, built under licence by the German manufacturer HELL, for use by the German Bundesgrenzschuts (BGS).

Non-NATO version   CD-55
When Hagelin unfolded his plans for a new -much more secure- cipher machine around 1951, it caused great upset at the American AFSA. 1 The new CX-52 had an advanced keying mechanism that defeated all current methods for automatically breaking Hagelin pin-wheel cipher machines.
 
This resulted in series of secret talks between AFSA and Boris Hagelin, which eventually lead to a secret arrangement between the two parties, in which it was agreed that Hagelin would develop at least two versions of each new crypto device, a secure and a less-secure version, and that the secure version would only be sold to NATO and NATO-friendly countries, i.e. the allies of the US.

The less-secure version featured the old C-38 keying mechanism and would be presented to 'less-friendly' countries and countries that were considered to be enemies of the United States.
  
Civil version of the CD-57

In the case of the CX-52, this led to the development of the C-52, which looked identical, but had the old keying mechanism. It could easily be broken by the NSA with the existing methods. When Hagelin developed a pocket variant of the CX-52, the CD-57, the same strategy was followed. The CD-55 is the less-secure version of the CD-57 and is inter­operable with the C-52. In secret Hagelin/NSA terminology, the CD-55 was known as a Class 1 machine. 2 As per agreement with the NSA, Class 1 machines can not be converted into an OTT cipher machine.

 More about the secret agreement between Hagelin and the NSA
 
  1. The AFSA was the predecessor of the NSA.
  2. Class 1 machines feature the old 'simple' keying mechanism.  More...

NATO friendly version   CD-57
NATO and NATO-friendly countries were given access to the new technology and, hence, the full-blown CD-57 with its new -advanced- keying mechanism that features irregular stepping. The machine has six removable pin-wheels that can be placed on the axle in any of 270 orders.
 
Some machines were even supplied with a total of 12 cipher discs, of which 6 could be placed in the machine in any of 665280 possible orders. 1

Like the CD-55, the CD-57 is available in a few case variants. The colour of the enclosure is grey (or green-ish) hamerite or military olive drab.

The case is opened either with a push-button at the top, or by means of a rotary knob in that position. Military users often preferred the rotary knob as it prevented the case from opening accidentally when carrying it in a pocket.
  
CD-57 ready for use

The image above shows a typical CD-57 ready for use, with its operating lever fully extended. In secret Hagelin/NSA terminology, the CD-57 was known as a Class 2 machine, which means that it features the new -advanced- keying mechanism. The CD-57 is interoperable with the CX-52. Some CD-57 machines could be converted into a One-Time-Tape (OTT) machine, in which case a metal fitting is present at the bottom. It was used to hold a cassette with the (random) key tape.
 
  1. Calculated as 12!/6! = 479001600/720 = 665280.

CD-57 ready for use Case lock (push-button) Opening the case Hagelin CD-57 in military olive drab case CD-57 interior Rotary case lock Opening the case

 
Random tape version   RT/CD
In cryptography, there is one system that is truly unbreakable: the One-Time Pad (OTP), or its tape variant: the One-Time Tape (OTT). The latter works by adding a random value from a key tape to each letter of the plaintext by means of an XOR-operation (modulo-2 addition). At the receiving end, the same XOR-operation is applied to the ciphertext, to reveal the plaintext again.
 
When correctly applied, the OTP/OTT technology provides an absolutely secure communication, that can not be broken with existing methods.

Hagelin developed all Class 2 machines in such a way that they could be converted into an OTT machine within seconds, simply by removing the cipher wheels and fitting a drop-in OTT unit.

The image on the right shows Hagelin's RT/CD option, that fits in the space that is normally taken by the wheels. Although it looks simple, it is actually an extremely clever tape sensing unit.
  
The (optional) RT unit

Note that the ability to convert the machine to an OTT device was only available on Class 2 machines, and that such machines were only sold to NATO and NATO-friendly countries. Other customers did not have access to the OTT technology. This was part of a secret agreement between Hagelin and the NSA that existed from 1951 onwards [4].

The complete machine (CD-57 with RT/CD option) was known as the CD-57/RT or CDR-57. More information about the RT variant will be added as and when it becomes available.
 
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
Maintenance The (optional) RT unit The (optional) RT unit

 
Licenced manufacturing   HELL STG-61
After World War II had ended, the occupying Allied Forces in Germany decided that Germany should not be allowed to develop high-grade technology, such as advanced cipher machines. Nevertheless, cipher machines were needed for the new German Army (Bundeswehr) and the new intelligence service that had just been established in 1956: the Bundesnachrichtendienst (BND).
 
The problem was solved by licencing the design of the CD-57 from Hagelin in Switzerland, and allowing Rudolf Hell's company in Kiel (Germany) to build it. The design was approved by Dr. Erich Hüttenhain 1 who suggested a few modifications.

After agreeing the modifications with Hagelin, HELL was allowed to manufacture the improved CD-57 from 1961 onwards. It became known as the HELL STG-61 and was primarily used by the Bundesgrenzschutz (BGS) 2 as a replacement for their bulky Enigma machines. The STG-61 was interoperable with the H-54 cipher machine. 3
  
HELL STG-61 (Hagelin CD-57 clone)

From a mechanical viewpoint, HELL was an extremely good company, and it was not uncommon for them to make some mechanical improvements to a design to make it work more reliably. In the case of the STG-61 several modifications were made, the most obvious of which is the addition of a reset-wheel to the letter counter. Apparently, this version can not be converted to an OTT cipher machine as the mounting for the key tape is missing from the case. Surprisingly, the case is opened by means of a push-button, rather than with the more secure rotary knob.

 More about the STG-61
 
  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 service Organisation Gehlen (OG). In 1956, the OG was renamed to Bundesnachrichtendienst (BND).
  2. In 2005, The Bundesgrenzschutz (BGS) was renamed Bundespolizei (Federal Police).
  3. The H-54 was a functional copy of Hagelin's CX-52, built under licence by Rudolf Hell from 1954 onwards. The H-54 also featured Hüttenhain's modifications. At the NSA the machine was known as the CX-52bk.

Case variants
Apart from the different models listed above, there were a number of case variants that could be applied to any of the models. The following variants are currently known:
 
  • Civil version
    This is the most common variant of the CD-57. It is housed in a grey or green-ish hamerite case. It is often called the 'civil version' but was also supplied to military users.

  • Military version
    A special military version was available in a dark green olive drab case. Although this version is fully compatible with the civil one, it was sold exclusively to military customers.

  • Limited edition
    As a luxury gift to special customers, a limited number of bright machines were produced with a gold-plated letter dial. This version, also known as LUX, was also supplied to the Vatican. It is believed that all LUX machines were based on the CD-55 model.

Some examples of case variants. At the far right is the HELL STG-61.


 
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 commonly known as the civil version, although it was also issued to some military customers. The case is opened by pressing the small push-button at the top.

The image on the right shows a typical grey hammerite civil version of the CD-57. Some cases have a more green(ish) hammerite finish, although it is not certain whether this is actually a different colour, or simply the effect of long-term exposure to sunlight on the varnish layer. The letter discs have white letters on a black background and a course black setting ring.
  
Civil version of the CD-57

Most civil CD-57 machines could be converted into an OTT cipher machine by installing the RT/CD option and fitting a key tape cassette to the mounting at the bottom. If the OTT option was not required, the mounting was commonly omitted, just like in the example above. On the CD-55 machine, the mounting was never present, as it could not be converted to an OTT device.
 
Military version
Especially for military customers, Hagelin developed a variant that was adapted to the military requirements. This version was fully compatible and interoperable with the civil version. The case was typically finished in a dark green 'olive drab' wrinkle paint. It made the machine far less shiny.
 
To prevent accidental opening of the device in a tactical environment, for example when carrying it in the pocket of, say, the trousers, most military machines have a different type of lock, whereby the push button on top of the device is replaced by a knurled knob. In order to open the device, the knob should be rotated clockwise.

Surprisingly, the rotary knob is not present on the HELL STG-61, the CD-57 clone that was manufactured under licence by Rudolf Hell in Kiel (Germany) in 1961, despite the fact that the STG-61 was also a military-grade machine.
  
Military version of the CD-57

To raise the contrast between the plaintext and ciphertext letter rings, the latter is inverted (i.e. black letters on a white background). All military machines could be converted to OTT machines and were fitted with the key tape mounting. Again, this feature is missing from the STG-61.
 
Limited edition   CD-55/LUX
Especially as a gift to loyal customers, such as the Shah of Persia, a limited run of 'special' CD-55 machines was made. They were housed in a bright painted enclosure and had a number of gold-plated parts, such as the big letter dial at the front and the curved operating lever at the left.
 
The Limited Edition of the CD-55 was known as CD-55/LUX. Although this case variant is fully operational, it was probably not intended for daily use, but merely as a showpiece on a desk.

This version was also supplied to the Vatican, but it is currently unknown whether it was actually used for encrypting messages.

The image on the right shows the extremely rare CD-55/LUX on a dark blue background. Many thanks to Gerhard Sulger Buel for supplying them and for permission to reproduce them [3].
  
Luxury version of the CD-55 produced especially for the vatican and as a gift to special customers. Photographs kindly supplied by Gerhard Sulger-Buel [3].

 
CD-55/LUX. Copyright Gerhard Sulger-Buel [3]. CD-55/LUX. Copyright Gerhard Sulger-Buel [3]. CD-55/LUX. Copyright Gerhard Sulger-Buel [3]. CD-55/LUX. Copyright Gerhard Sulger-Buel [3]. CD-55/LUX. Copyright Gerhard Sulger-Buel [3]. CD-55/LUX. Copyright Gerhard Sulger-Buel [3]. CD-55/LUX. Copyright Gerhard Sulger-Buel [3]. CD-55/LUX. Copyright Gerhard Sulger-Buel [3].

 
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 removed wheelset could then be used to repeat the procedure 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.
 
Current position of the cipher wheels (index)

 
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
Packaging
The CD-57 was usually delivered in a simple grey carton box that was slightly larger than the device itself. The instruction booklet and the quality-check card (if present) were store underneath the device. In case the device was delivered with accessories, such as additonal cipher wheels or an RT/CD drop-in OTT unit, it usually came in a box that was about twice its size.
 
Carton box with CD-57 CD-57 inside carton storage box Contents of the packaging Box containing the RT/CD-57 Contents of the box. At the bottom right the RT option.

 
Maintenance
...   
Maintenance

 
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.

  3. Gerhard Sulger Buel, Photographs of CD-55/LUX
    Received October 2016. Reproduced here by kind permission.

  4. Crypto Museum, Secret NSA/Hagelin agreement
    30 July 2015.

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Crypto Museum. Created: Wednesday 05 August 2009. Last changed: Wednesday, 02 November 2016 - 06:44 CET.
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