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K-37   Crystal
Russian copy of Hagelin B-211 - wanted item

K-37, codenamed CRYSTAL (Russian: КРИСТАЛЛ), was an electromechanical cipher machine, introduced at the beginning of World War II (WWII), in 1940, by the former Soviet Union (USSR). It was a functional copy of the Hagelin B-211, but had an externally configurable matrix plugboard. The K-37 was used by the Russians throughout WWII, and also for a several years after the war. The machine was known by the AFSA/NSA in the United States under the codename SAUTERNE.

The K-37 is basically a copy of the B-211, as developed in 1932 by Boris Hagelin in Sweden. Based on the B-21 it prints directly onto a paper strip and has a built-in encryption mechanism that uses Hagelin's (now) famous pin-wheels.

The machine physically resembles the German Enigma, but uses a different operating principle. Rather than electrical alphabet substitution, it uses a double (in/out) matrix for the encryption, probably to circumvent patent infringement. The image on the right shows the opened K-37 from the top and is taken from Hagelin's memoirs [2].

The original Hagelin B-211 machine featured a 5 x 5 matrix in order to accomodate 25 letters of the Latin alphabet. 1 The Russians modified it into a 5 x 6 matrix, so that 30 (of the 33) characters of the Cyrillic alphabet could be used. In addition, the internal input/output matrix plugboard was brought out, so that it could be configured without opening the machine [2 p.22]. This is illustrated by the three wire bundles that leave the machine in the rear left corner.

K-37 was manufactured at Plant No. 209 in Leningrad (Russia) from mid-1940 onwards. By the summer of 1941, approx. 150 unit had been made, most of which were used for Russian traffic in the Far East. The K-37 was used throughout the war and also for a couple of years during the Cold War. AFSA managed to break the machine from 1946, until it was disbandonned in 1947.

  1. The letter 'W' is missing and could be replaced by typing the 'V' twice.

The image below shows a top view of the K-37 after the top cover has been removed. At the front is the keyboard with its 30 letters plus a spacebar. At the left are two groups of cipher wheels: two electric codewheels — a 5-point and a 6-point one — at either side of a commutator (rear), and four large keywheels — the pin-wheels — that control the stepping of the codewheels (front).

At the center is the printing mechanism of which the bars are activated directly by the arms of the keyboard. It is driven by the electromotor via gear with a keyboard-activated clutch. The paper strip is guided from a supply reel in the bottom compartment of the machine, through a narrow metal gutter behind the keyboard, from right to left. The print thead (type wheel) is at the centre.

To the right of the printer, just in front of the motor, are twelve electrical relays. Eleven of these relays are used to prevent the current from flowing in reverse direction through the 5 × 6 contact matrix when a key is pressed. An extra relay is connected to the spacebar and is used to insert spaces in the printed text. Hagelin later replaced the relays of his B-211 by selenium diodes.

The interrogations of Dr. Otto Buggisch
For many years, the black & white photograph from Boris Hagelin's memoirs was the only surviving evidence of the Russian K-37. In his memoirs, Hagelin describes how he was forced by the Russians to sell them two of his B-211 machines, which they then copied [2 p. 22]:

I also might mention that I was obliged before the War to sell
"two cipher machines" to the Russian Trade Commission in Stock-
holm (according to the purchase order). I sold them two B-211
machines which we had in stock in Stockholm.

The machines were copied in Russia and used during World War II.
They were provided with a 5 x 6 grid. The Cyrillic alphabet had
more than 30 letters but a few of them occured very seldom,
and could be omitted.
In 2012, Christos Triantafyllopoulos in Greece discovered additional information in recently released TICOM documents [3]. During the post-war interrogation of Dr. Otto Buggisch of OKW/Chi, the latter revealed that in 1941 the Germans had captured and analysed a K-37, which they could solve with a 10-letter crib. He found it to be less secure than the Hagelin B-211 as the internal plugboard matrix was missing [6]. He repeated this in a later interrogation [7]:

10. K37 differed from B211 in lacking the "Surchiffreur", or
"Ueberschluesseler", a sort of Enigma wheel by which the path of
the current was turned to another channel at one point, crossing over and exchanging positions with another path instead of continuing
parallel. Buggisch called this an X effect, and said it greatly
complicated analysis, as it was hard to tell when it was being em-
ployed in place of the parallels.
A very complicated way of saying that the programmable matrix of the B-211 is missing from the K-37. It seems likely however, that Buggisch was deliberately misleading the TICOM interrogators at this point, or that he did not remember the operation of the K-37 correctly. In any case, Boris Hagelin wrote in his memoirs that the machine had an external matrix [2 p. 22]:

... Also the modificators were plugged in
outside of the machine, probably under locked cover so that
the operator would not know which inner settings were in use
at any given time (Fig. 14).
The latter is confirmed by a German wartime report of 1942 about the K-37, which was translated by AFSA – the predecessor of NSA – in September 1950 1 [8 p. 5]:

... The leads to the 11 selector bar contacts, to the 11 magnets and to the 22 inlets and outlets of the wheel switches are all gathered together in a cable which terminates in a multiple plug. The matching plugbox (which was missing in the machine examined) is obviously connected to a switch system which allows any desired association of the contacts, magnets and switch wheel inlets within the R and the S groups. (Supplemental change of wiring!).
Apparently, the K-37 did have a plugboard, and it was even more advanced than the internal one of the B-211. It was connected externally, but the Germans had never seen it, as it was missing from the captured device. It is also missing in the photograph in Hagelin's memoirs, but the cable leading to the external plugboard is visible in the rear left corner.

  1. According to the translated German document [8], the AFSA had already translated another German document about the K-37 — DF 74 — which so far has not been released to the public however.

K-37 in the NCM collection
Update: 1 July 2021

During the COVID-19 pandemic of 2020 and 2021, the National Cryptologic Museum (NCM) at the NSA headquarters in Fort Meade (USA) was closed to the public, whilst the building was being renovated. As there were no public activities, the curators and registrars had the ability to go through the entire collection to see whether any objects needed maintenance or special attention.

And it was on one of these occasions that the museum registrar stumbled on the machine shown in the image on the right. A complete and fully intact Russian K-37 cipher machine, with a wooden box connected to the end of a fixed cable that leaves the machine in the rear left corner. Three 15-way connectors are used for this, whilst an extra 15-way socket is present at the front.

It seems likely that the wooden box was used to configure the pluggable matrix externally, as described by Hagelin in [2] and in the translated German assessment of the machine of 1942 [8].

When examining the above photograph closer, it becomes obvious that the machine shown here – which is now in the collection of the NCM – is the same machine as the one shown in the photo­graph in Hagelin's memoirs. It has the same damages and all screws are in the same position.

The exact function of the wooden box, which apparently has a small hinged lid, is currently unknown, but will undoubtedly be the subject of further investigations. To be continued...

Russian K-37 (Crystal) in the collection of the NCM [9]
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Russian K-37 (Crystal) in the collection of the NCM [9]

Hagelin B-211
In 1932, Boris Hagelin had difficulty to stay afloat. After the death of Emanuel Nobel – the main investor in his company A.B. Cryptograph – the heirs of the Nobel estate did not want to make further funds available to him. In an ultimate attempt to make money, Hagelin travelled across Europe trying to sell his latest developement: the B-21 — a close relative of the German Enigma.

He managed to sell a few B-21 machines, but the big breakthrough came when the French Army asked him to develop a machine that was portable and could print directly onto paper.

Hagelin took the design of the B-21, added a printer and named it B-211. The French like it so much that they immediately ordered 500 units, that were subsequently built (under licence) at the L.M. Ericsson factory in Colombes (France).

Just before the start of WWII, Hagelin managed to transfer the profits from the sale to Sweden, where he used it to set up a new workshop [2].

On New Year's eve of 1940, the new workshop in Stockholm (Sweden) was opened and the company was renamed AB Ingeniörsfirman Cryptoteknik. Just before the war reached Sweden, Hagelin was visited by two members of the Russian Trade Commission in Stockholm, who forced him to sell them two of his B-211 machines. The Russians took the machines to the Soviet Union, where they were copied, modified and re-released as the Russian K-37 — codenamed CRYSTAL.

The K-37 went into production during the course of 1940 and was built at Plant No. 209 in Leningrad (Russia). By the summer of 1941 approx. 150 units had already been produced, which were subsequently used mainly for the encryption of Russian radio traffic in the Far East [4].

In the summer of 1941, the Germans captured a Russian K-37 and brought it back to Germany for investigation by Inspectorate 7/VI. It was concluded that the machine was less secure than the Hagelin B-211 and that it could be broken with a 10-letter crib. The latter was purely theoretical as the Germans were never able to test their theory due to lack of suitable K-37 intercepts.

Hagelin had meanwhile escaped from Sweden, in April 1940, and had made his way to the United States, where he befriended William Friedman — the chief cryptographer of the AFSA. Through his contacts in the US, Hagelin managed to sell the design of his C-36/C-38 machine to the US Army, where it became known as M-209. It made him the first crypto-millionaire in the world.

Towards the end of the war, in the fall of 1944, Hagelin left the US and returned to Sweden, where he reopened his factory in Stockholm. When the war was finally over, the French showed themselves to be loyal customers and ordered another 100 of Hagelin's B-211 machines.

At the end of WWII, the K-37 that had been captured by the Germans was handed over to the Allies, along with two German investigation reports, and probably ended up in the posession of the AFSA (later NSA). The German reports were later translated to English [8]. The Americans used the machine and the information from the Germans to build a K-37 analog that was used to break intercepted Russian K-37 traffic in the Far East — known by the US codename SAUTERNE.

The first break was made in February 1946 after the AFSA had been able to reconstruct the internal settings of the machine, and provided them with a steady flow of decrypts from April onwards. The intelligence was short-lived, as in 1947 the Russians stopped using the K-37 [3].

  1. Boris Hagelin, 100 Jahre Boris Hagelin 1892-1992
    Memoires of Boris Hagelin (German).
    Crypto A.G., Crypto Hauszeitung Nr. 11, September 1992.

  2. Boris Hagelin, The Story of Hagelin-Cryptos
    Crypto A.G., Zug, Spring 1981. Based on [6].
     Original manuscript in German

  3. Christos Triantafyllopoulos, The Soviet K-37 'Crystal' cipher machine
    Christos military and intelligence corner. 14 June 2012. Retrieved November 2012.

  4. VV Babievsky, LS Butyrsky, DA Larin; Soviet cryptographic service 1920-1940
    Website (Russian). Retrieved June 2012.

  5. Paul Reuvers and Marc Simons, Hagelin B-21 and B-211
    Crypto Museum, 5 August 2009.

  6. TICOM I-58, Interrogation of Dr. Otto Buggisch of OKW.CHI
    8 August 1945. Declassified. p. 5.

  7. TICOM I-91, The final interrogation of Wachtmeister Otto Buggisch...
    11 September 1945. p. 4.

  8. TICOM DF-217, The Russian Cipher Device K-37
    Translation of a German report of 1942.
    AFSA, September 1950. Declassified by NSA 13 September 2011.

  9. NCM, Image of Russian K-37 in NCM collection
    Fort Meade, USA. Personal correspondence, July 2021.
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Crypto Museum. Created: Thursday 06 November 2121. Last changed: Monday, 15 January 2024 - 17:12 CET.
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