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On-line mixing cipher machine

ETCRRM was one of the first online/offline One-Time Tape (OTT) cipher machines (mixers), developed around 1953 by Standard Telefon og Kabelfabrik A/S (STK) in Oslo (Norway). It uses the Vernam Cipher and mixes clear text with random characters from a key tape, using electronic valve-based circuits. The ETCRRM was used from 1963 onwards by the US and the USSR on the Washington-Moscow hotline, until it was succeeded in 1980 by solid-state the Siemens M-190.
The idea for the machine came from Bjørn Rørholdt, Colonel, engineer, veteran and liason of the Norwegian Army. In close collaboration with Kåre Meisingset at STK, the idea was further developed, resulting in 1952 in a patent for a new cipher machine with One-Time Tape [1]. 1

Other NATO countries were immediately interested in this new cipher machine and the ETCRRM soon became a standard crypto device within NATO. If the machine was used properly, i.e. with a truely random key tape that would only be used once, it was truely unbreakable.

Three different versions of the ETCRRM were manufactured over the years, each with minor differences and improvements. They were identified by the addition of a Roman number (I, II and III) to the model name. The image on the right shows a typical ETCRRM-II version.

A standard Creed paper tape reader is mounted to the front panel of the machine, but there are also versions where the reader is detached. The key tape is fed into the reader from a reel that is mounted to the right side of the machine.

ETCRRM is the abbreviation of Electronic Teleprinter Cryptographic Regenerative Repeater Mixer. The machine was developed in 1953 and 1954 by STK as an alternative to the ageing British 5-UCO and the American SIGTOT, which had been in short supply since NATO was established in 1949 [6]. The machine was approved by NATO for traffic at all levels of classification in April 1954 [7] and arguably became one of the most popular cipher machines of the 1950s.

The machine was used by many NATO countries and even by non-NATO countries such as Austria. By August 1955, the ETCRRM was being produced at a rate of 200 machines per month with a unit cost of US$ 1200 [9]. After the Cuban Missile Crisis of 1962, the machine even became a critical components at both ends of the Washington-Moscow Hotline.

In 1959, a synchronised version of the machine, the ETCRRM-III, was introduced [10]. It allowed the machine to be used over unreliable narrowband Short Wave (SW) radio channels, without loosing synchronisation with the key tape. The machine was finally superceeded by other machines with similar capabilities, such as the Philips Ecolex IV and the Siemens M-190.
  1. Although this patent is frequenty mentioned in literature, for example in [1], we have not been able to find it. If anyone has access to this patent, please contact us.

ETCREM machine next to a Lorenz Mizer (LOMI) Control panel of the ETCRRM ID plate of an ETCRRM-II

The ETCRRM was developed by STK as a smaller, transportable and more affordable alternative to the Britsh 5-UCO, which was left-over from WWII. Along with SIGTOT, an American OTT machine, these two were the only ones that were initially approved for NATO traffic of all classifications. In a meeting of 13 January 1954, the lack of availability of these two machines was reported to the chairman of the Ad-hoc Cryptographic Coordination Agency (ACCA) of NATO, who replied that a new machine, named ETCRRM, would soon become available to the NATO members [6].

The ETCRRM was developed during 1953 and 1954 and was finally approved for COSMIC and NATO messages of all classifications on 19 April 1954 [7]. Alternative OTT machines were also developed, such as the Dutch PTT/Philips Ecolex I and the French T-53, but neither of them ever gained the popularity of the ETCRRM. A month later, in the first meeting of NATO's C-E Board on 21 May 1954, the bad supply situation of cipher equipment was once more confirmed, but this time it was announced that the first ETCRRM machines had just been ordered by SHAPE [8].

By August 1955, the situation had improved drastically and the ETCRRM was being produced at a rate of 200 units per month [9]. The price of a single ETCRRM unit at that time was US$ 1200, compared to US$ 3000 - 6000 for the Ecolex and US$ 12,000 for the 5-UCO [9]. It should come as no surprise that the ETCRRM became the more popular machine throughout the 1950s. Apart from NATO and NATO-countries, it was also used by the Army of the neutral country of Austria.
The ETCRRM also played an important role in the Cold War. After the Cuban Missile Crisis of 1962, it was decided to establish a permanent direct teleprinter link between the Kremlin in Moscow (Russia) and the White House in Washington (US).

The hotline became operational in 1963 and four ETCRRM machines were used on a daily basis for many years. Each country communicated in its own language, using Teletype machines for the English language and (modified) Siemens T-37 teleprinters for cyrillic. The hotline was first used in 1967 during the six-day Egypt-Israel war.

Over the years, the Hotline was modified and upgraded with more modern equipment several times [2]. The ETCRRM machines were eventually replaced by Siemens M-190 mixers in 1980 [5].

 More about the hotline
Vernam Cipher
In telegraphy, each letter (or: character) is represented by a pattern of 5 bits, often stored on a paper tape as a series of punched holes. Most systems follow the Baudot standard for this. Each character from the keyboard, or from a reader that contains the plain-text tape, is mixed with one character from a key-tape. The key-tape contains random characters, and the two characters are mixed bit-wise by means of an XOR operation (modulo-2 addition). At the receiving end, a copy of the original key-tape is mixed with the cipher-text in order to reveal the plain-text.

As transistors were not yet available in the early 1950s, the electronic XOR-circuits inside the ETCRRM largely consist of 12AT7 electronic valves (tubes), some relays and selenium diodes. Some good photographs of the interior of the machine can be found on Jerry Proc's website [3].

Although it is claimed in [1] that the principle behind the ETCRRM is a Norwegian invention, this is unlikely. So far, we haven't been able to find the 1952 patent of the machine, and numerous other patents for similar devices, using the same principle, have been filed long before. During WWII, for example, Siemens developed the T-43, which was also a mixer machine. All these inventions are based completely or in part on patent US1,310,719 of 1918 by Gilbert Vernam.

 More about the Vernam Cipher
Similar machines

  1. STK, SEO-11150 Technical Manual
    Date unknown, but probably 1954. 1

  2. NATO, ETCRRM Training Manual Edition Number 3
    NATO, AFCENT, Cryptographic School. NATO Unclassified.
    1961. Circuit diagrams 1954-1958.

  1. We don't have this manual yet. You can help us expand this page by supplying additional information. If you have this manual, please contact us.

  1. Norwegian National Security Authority (NSM), Årsmelding 2008
    NSM Annual Report 2008 (Norwegian). Noen kryptosuksesser. p. 15.

  2. Wikipedia, Moscow-Washington hotline
    Retrieved, June 2012.

  3. Jerry Proc, Electronic Teleprinter Cryptographic Regenerative Repeater Mixer
    Website. Retrieved June 2012.

  4. NATO, ETCRRM Training Manual Edition Number 3
    NATO, AFCENT, Cryptographic School. NATO Unclassified.
    1961. Circuit diagrams 1954-1958.

  5. Crypto Museum, Washington-Moscow Hotline
    Retrieved December 2013.

  6. NATO/ACCA, On-Line Cipher Equipments
    SGM-279-54. 29 March 1954. NATO SECRET.
    Declassified by NATO in 2006 (IMSM-0001-2006).

  7. NATO, Approval of Electronic Mixer ETCRRM
    SGM-311-54. 19 April 1954. NATO SECRET.
    Declassified by NATO on 17 November 1999 (IMSM-431-99).

  8. NATO, C-E Board 1st Meeting Minutes, dated 21 May 1945 (revised)
    SGM-460-54. 25 June 1954. NATO SECRET. pp. 19-21.
    Declassified by NATO on 24 November 1999 (IMSM-0431-99).

  9. NATO, Automatic Crypto-Equipment Requirements for the Allied Command Atlantic
    SGM-560-55. 15 August 1955. NATO SECRET.
    Declassified by NATO on 24 November 1999 (IMSM-0431-99).

  10. NATO, Synchronous ETCRRM
    SGM-464-59. 12 August 1959. NATO SECRET. pp. 19-21.
    Declassified by NATO on 5 January 2000 (IMSM-0431-99).

Further information

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Crypto Museum. Created: Monday 11 June 2012. Last changed: Monday, 22 August 2016 - 20:27 CET.
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