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Lorenz Mi544
One-time tape cipher machine · 1956 - this page is a stub

The Lorenz Mischer 544 (English: Lorenz Mixer 544), also known as Mi544 or LoMi, was a one-time tape (OTT) cipher machine (mixer), developed around 1956 by C. Lorenz Aktien­gesell­schaft in Stuttgart (Germany). It was used by the German Army (the Bundeswehr), and within NATO. The machine was compatible with other OTT cipher machines — such as the Dutch Philips Ecolex II and Ecolex IV, and the Norwegian ETCRRM — but only if key tape was shifted by one position [1].

The Mi-544 is housed in a large heavy enclosure with a green/blue hamerite finish, as shown in the image on the right. It consist of a die-cast aluminium base that houses the relays and the electronic circuits, plus a removable cover.

The device is intended as an add-on for existing teleprinter installations and should be connected between the teleprinter and the line. It takes the 5-level output from the teleprinter and mixes it with the characters from a key tape, using XOR arithmetic, also known as modulo-2 addition.

This principle, described in US patent 1,320,729, is known as the Vernam Cipher, named after the American inventor Gilbert Vernam who invented it in 1917, along with the One-Time Pad (OTP). When used correctly (i.e. the key tape contains truely random characters, is used only once and is destroyed after use) the cipher is unbreakable.
Lorenz Mi-544B. Image kindly provided by Heinz Blumber [2].

The Mi-544 was developed in the mid-1950s, and was first delivered to the Bundeswehr in 1956. It was first described by Lorenz employee G. Grimsen in SEG·Nachrichtenheft 4 of 1956 [4]. In 1958, it was succeeded by the slightly improved Mi 544B. The price for a bare Mi-544B machine in 1963 was DM 11,260 (EUR 5,630), or DM 15,885 (EUR 7,942) when the SYZ-634 synchroniser was also required [3]. 1 In the 1970s, the Mi544 was replaced by the Siemens M-190.

  1. These prices do not include the teleprinter to which it had to be connected.

At present, this page only acts as a placeholder for (future) information about the Mi544 (LoMi).
Lorenz Mi-544B. Image kindly provided by Heinz Blumber [2].
Interior of the Lorenz Mi-544B. Image kindly provided by Heinz Blumber [2].
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Lorenz Mi-544B. Image kindly provided by Heinz Blumber [2].
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Interior of the Lorenz Mi-544B. Image kindly provided by Heinz Blumber [2].

  • Lorenz Mischer 544
  • Mi544
  • LoMi 544
  • LoMi
  • Mi544
    Primary version of 1956
  • Mi554B
    Improved version of 1958, with meter at the front
  1. Mischgerat Mi 544, Technical description (in German language) 1
    Nr. 041-560 LD. Lorenz AG, Stuttgart (Germany). Issue 3, July 1958.

  2. Mischgerat Mi 544, Operating instructions (in German language) 1
    Nr. 041-1020 LD. Lorenz AG, Stuttgart (Germany). Issue 1, July 1959.

  3. Mischgerat Mi 544, Einstell- und Ölvorschrift (in German language)
    Nr. 041-913 LD. Lorenz AG, Stuttgart (Germany), August 1958.
    Provisional release.
  1. Document kindly provided by Heinz Blumberg [2].

  1. Ecolex II User Manual, Supplement
    Description of interoperability with Lorenz Mixer (in Dutch language).
    Koninklijke Landmacht. 8A-II-IUB 504427. 15 April 1965.

  2. Heinz Blumberg, Lorenz Mi 544 documentation
    Received 24 January 2019.

  3. ITT Standard Austria, Verschlüsselungsgeräte 1
    Letter to Bundesministerium für Auswärtige Angelegenheiten.
    Vienna, 8 April 1963. 3 pages.

  4. G. Grimsen, Das Mischgerat Mi 544 1
    C. Lorenz AG. Seg·Nachrichten, 1956, Heft 4, pp. 181-188.
  1. Document kindly provided by Heinz Blumberg [2].

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Crypto Museum. Created: Monday 02 February 2015. Last changed: Monday, 24 May 2021 - 07:20 CET.
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