25 different combinations exist, but only 18 are used. 81 (20 occurences) is the most frequent one, followed by 75, 82 and 85 (17 occurences each).

Does every pair stand for a letter of the alphabet? So, far nobody could prove this hypothesis.


More information

Alexander D’Agapeyeff himself is said to have forgotten how he had encrypted this message. It is well possible that a mistake happened during the encryption procedure or the printing process. In later editions of the book the challenge was not included.

More information about the D’Agapeyeff challenge is available on Wikipedia. Nick Pelling has covered this challenge severals times on his Ciphermysteries blog. A pretty good analysis of this cryptogram is available in a charged Cryptologa article from 1977.

The D’Agapeyeff challenge is also covered in my book Codeknacker gegen Codemacher. However, I didn’t take it on my top 50 unsoved cryptograms list – in my view there are 50 more interesting crypto mysteries.

Today, Codes and Ciphers is available as an eBook for a few Dollars. There are also several print editions. However, according to Tobias Schrödel, original prints of the first edition (the one with the unsolved challenge) are pretty rare.

Further reading: Who can make sense of this strange document?

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Kommentare (8)

  1. #1 George Lasry
    18. Juni 2017

    I recently I did some in-depth research about the most common hypothesis, which is transposition combined with substitution (two digits -> one letter), checking all possible transposition schemes (row tr., column tr., row major/column major read/write etc…). I can confirm with a high degree of confidence that d’Agapayeff cipher is not of that type.

  2. #2 Klaus Schmeh
    18. Juni 2017

    Bart Wenmeckers via Facebook:

    Ah this is very interesting Klaus. I have not seen this one before in detail. Thank you for posting. I already see some details which make me want to investigate. 🙂

  3. #3 anderer Michael
    18. Juni 2017

    Maybe it was a early hoax, only a joke. Don’t forget please, he was an English man, and he was born in Russia.

  4. #4 Narga
    20. Juni 2017

    @GeorgeLasry: Did you see this blog-article from Nick Pelling here? https://ciphermysteries.com/2017/03/05/new-clue-dagapeyeff-challenge-cipher

    Perhaps d’Agapeyeff really just applied the encryption technique wrong and that’s what makes it so difficult to decrypt?

  5. #5 George Lasry
    20. Juni 2017

    Interesting (Double Transposition clue)…. worth a trial

    A mistake in encryption seems very likely. Another option which has been mentioned (by Jim Gillogly) is a botched Mirabeau encryption.

  6. #6 Thomas Ernst
    4. Juli 2017

    Two simple observations, which probably are not new: the plain text of d’Agapeyeff’s earlier Polybios example – see wiki – did not end on a final fiver, but on only three letters (EDC). With a total of 395 individual numbers in the “Challenge”, I assume that one or three of the final “0” indeed are “nulls”, but do not know what underlying encipherment rule makes them so. – Secondly, I think that this, too, is a mono-alphabetic Polybios, but that the pairs simply are arranged differently. It would be worthwhile to write out different pairs, 1-3, for example, or every fourth letter (also considering backward writing), whathaveyou, till one comes up with a suitable frequency count. Furthermore, there exists the possibility that the plain text is in another language than English, such as Russian or Latin.

  7. #7 Abhishek Ramchandran
    9. Juli 2017

    Perhaps he used a Beale cipher where each number corresponded to a page number, line number, word number, letter position in his book! I have a copy of Codes and Ciphers with me, I could try investigating.

  8. #8 Christof Rieber
    7. November 2020

    This hopefully is the correct transcription of bigrams into – still encrypted – cipher text:


    Remarkably often double letters/bigrams do occur.