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Rotor-based cipher machine - wanted item

HX-63 was an electromechanical rotor-based cipher machine, introduced in 1964 by Crypto AG in Zug (Switzerland). It features nine electrically wired permutations wheels, or rotors, that have more contacts than the 26 letters of the alphabet. It was patented by Boris Hagelin, and uses an operating principle that is very similar to that of the – also patented – American AFSAM-7 (KL-7).

The image on the right shows the HX-63, which is housed in a molded plastic enclosure. At the front right is the keyboard. The 9 cipher wheels are visible through a narrow window at the top.

The machine was developed during the 1950s, and is mentioned in reports filed by NSA crypto­grapher William Friedman in 1955 and again in 1957 [2]. It is likely though, that it was not finished before 1963, and that it was first sold in 1964 [A]. The first and only customer was the French Army, who ordered 12 units [4]. It is very likely that no more than 15 init were ever made.
HX-63 seen from the front. Image kindly provided by Klaus Kopacz [5].

Apart from the TKG-35, a joint development of Boris Hagelin and Dr. Edgar Gretener, the HX-63 was first and only rotor-based cipher machine that was ever built by Crypto AG. Around 1964, Crypto AG made the transition to electronic shift-register-based designs, and moved away from (electro)mechanical cipher machines. In 1970, the HX-63 was succeeded by the electronic H-460.

At present, no further information about this machine is available.

Re-injection patent
During the 1950s, the US National Security Agency (NSA) had a secret deal with Boris Hagelin, the owner of Crypto AG, that controlled to which countries he could sell unreadable 1 equipment. It was known as the Gentleman's Agreement. During the 1950s, NSA's chief cryptologist William Friedman visited Hagelin a number of times to negotiate and alter the terms of the agreement. One of these visits was on 22 September 1957 at Hagelin's home in Zug (Switzerland) [2].

The first thing to be discussed between Hagelin and Friedman, was patent 2,802,047 that Hagelin had filed in the US in October 1953 and that had been granted a month earlier. Although it was granted in the US, the patent was declined in Japan, and Hagelin was clearly wondering why.

The patent describes a cipher machine in which more contacts are used on the cipher wheels than are actually needed and where the extra contacts of the output of the drum are looped back to the input. This method can be described as re-entry or re-injection and would be used in Hagelin's new HX-machine that was underway.

Friedman was shocked when he saw the patent, but didn't say that to Hagelin. The principle of re-injection was registered by the US in 1944 in a secret patent, so Hagelin's attempt should have raised a declaration of interference.
The American AFSAM-7 (later: KL-7) that uses the re-injection patent

The re-entry principle was conceived during WWII by Albert Small, whilst working for the Army Signal Intelligence Service (SIS), trying to solve the high-level Japanese diplomatic Purple cipher. It is covered by US Patent 2,984,700 and has since been used at the heart of the high-level American cipher machine AFSAM-7 (later: KL-7) shown above, that was also adopted by NATO.

Although officially Hagelin should not have been aware of the existence of the AFSAM-7, in later talks he mentioned that many of its operators were experiencing contact problems with the rotors. 2 This proves that Hagelin was aware of the existence of the machine and that he might have been aware of the re-injection principle that it features. He also explained how he conceived the idea after a trip to Bonn in 1952, were he was told something 3 by Dr. Huttenhain, followed by discussions with his chief developer Oskar Stürzinger, but insists that it was his own idea.

 More about the KL-7

  1. The term unreadable means that the algorithm could not be broken by NSA. Also known as unfriendly or secure. In contrast: algorithms that are breakable by NSA, are called friendly or readable or exploitable.
  2. This is actually correct; the KL-7 was known for its many contact problems if the maintenance instruction were not strictly followed. This proves that Hagelin had knowledge about the KL-7.
  3. It is currently unclear as to what Hüttenhain told Hagelin on this occasion, or what Hagelin discussed with Stürzinger afterwards, as the original document is redacted at this point. It is entirely possible though, that Hüttenhain was talking about the AFSAM-7. The same principle was later also used in the Russian Fialka.

  1. Schlüsselgerät Typ HX-63, Vorläufige Beschreibung
    A-1130-c. Oskar Stürzinger, March 1964.

  2. Boris Hagelin, US Patent 2,802,047
    Filed 16 October 1953
  1. Oskar Stürzinger, Chiffriertechnik Heute
    Vorlesung 'Krieg im Aether' 1976/1977, ETH Zürich (German). pp.15-16. 1

  2. Crypto Museum, The Gentleman's Agreement
    30 July 2015.

  3. US Patent 2,984,700, Method and Aparatus for Cryptography
    Albert W. Small. Filed 22 September 1944.

  4. Wikipedia, HX-63
    Retrieved January 2020.

  5. Klaus Kopacz, Images of HX-63 exterior and interior
    Received January 2020.
  1. Retrieved from HAMFU History, December 2018.

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Crypto Museum. Created: Wednesday 01 January 2020. Last changed: Sunday, 14 June 2020 - 12:12 CET.
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