A cipher disk introduced on Reddit looks like a mass-produced item from the 20th century. Does a reader have any information about this crypto tool?

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The crypto-related topic I’m going to cover today is once again taken from the Codes & Ciphers group on Reddit (/r/codes). Earlier this week, a Reddit user calling himself YanniRotten posted a picture of a cipher disk. Here it is:

Source: Reddit

To my regret, YanniRotten‘s  Reddit post doesn’t provide much background information. He wrote: “Unfortunately, I have zero context for this thing. I just found it randomly, it didn’t belong to a relative or suchlike. Wheels are made of plastic, center appears to be brass.”

Cipher disks are nothing uncommon. Starting in the 15th century, tools of this kind have been in wide-spread use. The following one belongs to Autrian collector Günter Hütter:

Source: Schmeh/Hütter

Here are two cipher disks I saw at the Bundesamt für Sicherheit in der Informationstechnik (BSI) and at the Heinz Nixdorf MuseumsForum:

Source: Schmeh, BSI, HNF

The cipher disk I found on Reddit is special in many respects. Most of all, it looks like a mass-produced item from the second half of the 20th century. This is unusual, as cipher disks haven’t played much of a role any more in recent decades, except when they were used as toys (but this specimen is certainly not a toy).

In addition, it is unusual that many of the characters on the disk are mapped to letter pairs. This concept makes the ciphertext longer than the plaintext without increasing security. I have no idea why this disk is constructed this way.

The alphabet used on the disk contains digits as well as a number of special signs (“@”, “#”, …), but no language-specific characters such as Ä, È, or Ÿ. This suggests that the disk was used for English texts.

Has a reader ever seen a cipher disk of this kind? If so, where was it used and for which purpose? Any help is welcome.

Further reading: Revisited: Enigma’s enigmatic sister

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Kommentare (10)

  1. #1 Richard SantaColoma
    3. Mai 2020

    One observation: The cipher characters and character groups seem to be carefully chosen so that they can be strung together with no spaces, with no confusion.

    For instance, any single letter, such as “A”, is only after V, C, F when used in double sets. So then V, C, and F are not every used alone, which would have been a problem if they happened to be before an “A”, with no space… because the translator would not have known if “VA” was meant, or on the contrary, V, then A, were being intended. Another example is “C”, in this case never alone. It will always be followed by A, B, or C, as it is only used in a two-letter cipher set. This would not work if “C” appeared alone, as the set CC could be confused with C, then C. It then also follows that, for instance, “CCA” would be safe, as the reader would know that it must be broken down as “CC”, then “A”, and not C, then “CA”, as there is no single C.

    And so on. The intention then (unless I missed something here) was to allow the stringing of cipher characters with no spaces, hopefully making decoding a bit more difficult than if the cipher characters had to be separated.


  2. #2 Thomas
    3. Mai 2020

    Could it be used to convert a word easy to memorize (outer ring) in a password (inner ring)? Though also the position has to be memorized.

  3. #3 Kerberos
    3. Mai 2020

    since when were “backlashes” used on which kind of
    I do not know them from typewriters or telex machines.

  4. #4 Gerd
    3. Mai 2020

    For the purpose of converting an “easy” word into a password, the structure described by Richard is not necessary. With this disc you can also convert from the inner ring to the outer ring.

  5. #5 Rich SantaColoma
    3. Mai 2020

    Good point, Kerberos… it seems the backslash was introduced in 1961. And I can’t find any reference to it on a typewriter, only computer keyboards and the like. So this wheel probably dates to recent times, and for computer users.

    “Bob Bemer introduced the \ character into ASCII on September 18, 1961, as the result of character frequency studies. In particular, the \ was introduced so that the ALGOL boolean operators ∧(and) and ∨(or) could be composed in ASCII as /\ and \/ respectively. Both these operators were included in early versions of the C programming language supplied with Unix V6, Unix V7 and more currently BSD 2.11.”


  6. #6 Magnus Ekhall
    3. Mai 2020

    I’m not convinced that this is a cipher device. It seems to be at least inspired by ASCII: sequences of characters on the outer wheel appear in the order of the ASCII “alphabet”.

    For example: “” and “#$%&”.

    However on the whole, the outer wheel is not ordered purely by it’s ASCII value.

  7. #7 David Oranchak
    4. Mai 2020

    This cipher disc reminds me of when I was a kid, when computer games sometimes came with types of code wheels as part of their copy protection schemes to prove that you owned a legitimate copy of the game. Here’s an example from Bards Tale III:


    The software would prompt you for a combination that you input into the wheel and you had to type in the correct output otherwise the game wouldn’t let you play.

    Perhaps there is some game this cipher disc belongs to for a similar purpose.

  8. #8 Hubert Allgäuer
    4. Mai 2020

    Hello David,
    Apparently we are the same age. That was also my thought when I saw this disc. 🙂
    Such code disks were sold with original C64 games to fill out a password that was recalculated each time the game was started from the game code.
    Then e.g. “A VO” as code and “Paper” as text was displayed after loading and start the game. Then the user had to enter the result of this code-encrypted word by the disk in response to the confirmation.
    It was very tedious.
    If you loaded the game diskette from an illegal copy source, you still could not start the game without this code diskette.

  9. #9 Thomas
    4. Mai 2020

    Ok, password generator was no good idea. Based on Richard’s observations, this seems to be a very secure cipher: Since some plaintext characters get enciphered with single characters, others with bigrams, the ciphertext is longer than the plaintext and the cryptanalyst doesn’t know how to partition the ciphertext to obtain its elements. But the recipient of the message does, since the sophisticated composition of the letter combinations on the inner ring decribed by Richard ensures unambiguity of partition. I’ve never seen such a cipher that partly assigns bigrams to plaintext characters and thus disguises the ciphertext elements, a good idea!

  10. #10 Bill Briere
    Wyoming, USA
    4. Mai 2020

    @Richard GO:UP