CX-52/30

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CX-52/30

30-character version of CX-52 - under construction

CX-52/30 ¹ was a mechanical pin-and-lug cipher machine, developed around 1952 by the Swede Boris Hagelin, manufactured by AB Cryptoteknik in Stockholm (Sweden) and sold by Crypto AG in Zug (Switzerland). It is the 30-character variant of the standard 26-character CX-52, and was intended for alternative languages. It should be considered the secure version of the C-52/30.

Like the standard CX-52, this machine has six removable and pin-configurable cipher wheels, each with a different coprime number of steps, plus a rotating cage, or drum, with sideways movable bars with configurable tabs, or lugs.

The main difference with the regular CX-52, is that it is made for a 30-character alphabet, such as Russian ² or Arabic. This affects the letter selector disc at the front left, but also the double print head inside. The machine shown here, is a Latin variant. In addition to the letters A-Z, it has four additional markup symbols: ∧, ∨, ≡ and |||.

The extra symbols could be used for a variety of (user-defined) purposes, such as spaces, line-breaks, shift-up, shift-down, etc. Converting the machine for, say, Cyrillic or Arabic alphabets, only requires swapping of the letter disc and the two print heads, and can be done in minutes.

The suffix '/30' was a secret identifier, used internally at Crypto AG. It is not displayed on the serial number tag, where it is simply designated CX-52. The secret suffixes are listed in the Gentleman's Agreement [1].
The Russian (Cyrillic) alphabet has more than 30 characters, but 30 are generally enough to write comprehensible text. For example: the Russian M-125 Fialka cipher machine also uses 30 letters.

1 / 7

2 / 7

3 / 7

4 / 7

5 / 7

6 / 7

7 / 7

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Features

The diagram below gives a quick overview of the features of the CX-52/30. The machine is nearly identical to the standard CX-52, but supports 30 different characters, rather than just 26. For this reason, the letter selection disc at the front left, has 30 positions. Although this machine was initially intended for alternative languages, such as Arabic and Russian, the machine shown here demonstrates that there were also machines with 30 character positions for the Latin alphabet.

The print heads – hidden under the letter selection disc at the front left – have the same 30 symbols around their circumference. At the right are the six removable – and interchangeable – cipher wheels, each of which has a different number of steps. The number of steps on the wheels are relative primes, or coprimes, ¹ in order to ensure a maximum length cipher period. ²

The wheels are identical to those of a regular CX-52. Some machines came with a total of 12 wheels, 6 of which were installed in the machine at any given time, subject to the current KEY instructions. Behind the cipher wheels is a cage that rotates when the advance lever at the right side is operated. The cage has 32 sideways movable bars, each of which can be configured with removable lugs (tabs). Some of these bars are responsible for the number of steps the printer, and hence the letter selection disc, makes when operating the advance lever.

Each machine came with a set of tools and supplies, that were stowed inside the cover, each held in place by one or more metal clips. The image above shows the items that were found inside the cover of the machine featured here. Note that the screwdriver has become brittle over the years.

The machine shown here, has the following features:

No F/V selector
Removable letter ring with fixed symbols (symbols can not be swapped)
30 characters, rather than 26
Latin alphabet with 4 additional symbols

The number of steps of a particular wheel does not share a common factor with any of the other wheels [3].
The number of characters (steps) before the key stream repeats itself.

1 / 8

2 / 8

3 / 8

4 / 8

Cogwheel under the letter selection disc

5 / 8

6 / 8

Tools and supplies stowed inside the cover

7 / 8

8 / 8

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Security

The CX-52 was considered a more secure version of the C-52. It features irregular stepping of the cipher wheels, and was internally known at Crypto AG as a Class 2 machine, ³ whereas the C-52 was a Class 1 machine and featured regular stepping. It was generally assumed that the latter was easily breakable by the US National Security Agency (NSA), using automated solutions.

It is known from surviving documents – in particular the Gentleman's Agreement and Operation RUBICON – that, at the time of its introduction, the CX-52 was virtually unbreakable for the NSA [1][2]. This is why NSA (and later the CIA as well) did everthing in their power to ensure that the machines that were made for certain countries or customers, were cryptographically weakened from 1955 onwards. Such deliberate weakening of a cipher system is also known as a backdoor.

It is likely that the machine featured here, does not suffer from such a backdoor, as it appears to come from a very early production run. According to the serial number tag, it was manfuctured in the old factory in Stockholm (Sweden), before production of the CX-52 was moved entirely to Zug (Switserland), and before the Gentleman's Agreement of 1955 had come into effect.

In 1955. See: the Gentleman's Agreement.


Restoration

When we received the CX-52/30 featured here, it was completely blocked. The mechanism could not be moved and the letter selector was binding. The previous owner had been unable to open the hinged lid over the printing mechanism. The machine showed minor traces of rust, especially at the center of the letter dial, indicating that the cause of te problems was below the hinged lid.

First, the cipher wheels were removed to ensure that they were not binding, and to reduce the load on the drum mechanism. Next, with a lot of patience, the blocked letter selection knob – at the left side of the machine – was gently moved back and forth by just a few millimeters, until it was in the right position to allow the hinged lid over the printing mechanism to be opened.

With the lid open, it was possible to remove the axle with the print heads, and to find out why the mechanism was blocked. In turned out that the root cause was the letter selection disc.

Removing the letter ring using the push-pin

After many years of storage, possibly in a humid environment, a thin layer of rust had built-up between the letter selection disc and the lid, effectively binding the disc to the lid. The rust may also have been caused by gases from the acid-containing ink. As a result, the letter selection knob – which drives the letter selection disc via a 90° cogwheel – could not be rotated either.

First the letter ring was removed from the lid, by loosening a recessed screw in the side of the lid, and pressing the push-pin on the inside of the lid to tilt the ring, as shown in the image above.

The disc could now be removed by releasing the screw at the centre, but this was slightly more difficult than anticipated, as it was rusted to the disc. But finally, after a treatment with a bit of penetrating oil, it gave in and the disc could be removed. The rear side of the disc appeared to have a thin layer of rust, which had affected the green paint on the top surface of the metal lid.

Paint partly removed from the surface under the dial

The rust was gently removed from the rear of the disc, by means of a brass-brush, which leaves virtually no traces. Next it was decided to remove the paint residue from the top surface of the lid — the part that is hidden under the letter selection disc — in order to make it smooth again.

Next, the axle with the print head – shown in the image on the right – was examined. Normally, the two heads can be separated by pulling-out the knob at the left. In this case however, all parts were firmly binding together, due to a combination of dust, dried oil (possibly WD-40) and ink, that had accumulated over the years.

After removing the items from the axle – each held in place by a bended steel spring – all items were carefully derusted and cleaned, before they were reassembled, as shown in the image on the right. The additional symbols are clearly visible.

The two print heads can now be separated again for altering the letter-offset. Releasing the knob, which is spring-loaded, registers the two print heads again. At the left, just behind the knob, is the 90° cogwheel that drives the rear of the letter selection disc. At the right is the cogwheel that is driven by the cage (drum) when operating the advance lever at the right of the machine. Both cogwheels and the axle were oiled with a modern synthetic engine oil. Do not use WD-40.