Apparently, the ACCP 212 is a very simple device, even for the 1950s. It has neither a keyboard nor any kind of display. The One Time Pad encryption had to be done manually, which means that it was not suited for longer messages. The production of this device must have been quite cheap compared to machines like the Enigma.

It goes without saying that I would like to know a little more about the ACP 212 (especially, as I want to cover it in my presentation). How was it used? What kind of messages was it used for? How were the keys generated? Was it used in practice or did it remain a prototype?

If areader can answer one of these questions, I would be very intereested to know.

Further reading: My visit at the Cheltenham Listening Stones


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Kommentare (9)

  1. #1 David Wilson
    5. Oktober 2017

    Apparently it’s in the Imperial War Museum, but it’s not pictured on their web site.:

    I’d contact them if you want more information.

  2. #2 Thomas
    5. Oktober 2017

    Was it used in practice? Yes, for the NATO General Cipher since 1952:

  3. #3 Thomas
    6. Oktober 2017

    The answers you can find in this NATO document:

  4. #4 Thomas
    6. Oktober 2017

    The device was named after the ACP (Allied Communication Publication) 212 and was used for the NATO General Cipher and as a cryptographic System for merchant ships in time of war. The instructions are given in ACP 213 (starting on page 1 -1): (unfortunately I can´t copy and paste the PDF).

  5. #5 Thomas
    6. Oktober 2017

    Was it really a German device? The NATO document:
    “the Military Representatives Committee approved the adoptions for NATO use of the Merchant Ships Crypto Systems (MERSEX) as set forth in ACP 213, Merchant Ship Cipher Instructions, copy attached , MERSEX has been made available for this
    use by the United Kingdom and the United States.
    2. The United Kingdom and the United States are requested to supply the other Member Nations now with ACPs 212 and 213”

  6. #6 Gerd
    6. Oktober 2017

    @Thomas: Oje, wenn damals SOLCHE Schreibmaschinen zur Verfügung standen, ist klar, dass ein man da kein aufwändigeres Chiffriergerät als das ACP 212 einführen konnte…

  7. #7 Klaus Schmeh
    6. Oktober 2017

    @Thomas: Thank you very much! This information is very helpful. Apparently the ACP 212 was a NATO encryption device, which was also used by the Germans.

  8. #8 Breaker
    12. Oktober 2017

    A strange thing happened again Klaus, you posted another kryptos key.decoding tool that perhaps holds a variance to the puzzle’s second layer……

    The rearrangement of the vigenere tableau forms an extra segment of 2 lines and a side panel section.

    I believe that the slide rule methods are the intended theme but that the foundations of this type of crypto tool that you showed is based on the original ideas based on the rules of cryptography.

    Below is the segment that I feel is related to these tools that is found from operating a ‘t square’ shape of lettering across a vigenere tableau for an additional layer of encryption.


  9. #9 Christopher Howell
    11. September 2021

    When I was in the British Royal Navy, I used this frame in anger. The pictures given above are not quite correct but does give a good representation. Used by the NATO, UK and Merchant Services it was a fairly good but slow method of cryptography. Would have been limited to approximately 250 five letter groups.