The D'Agapeyeff cipher is an as-yet unbroken
cipher
In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...
that appears in the first edition of ''Codes and Ciphers'', an elementary book on cryptography published by the Russian-born English
cryptographer and
cartographer
Cartography (; from grc, χάρτης , "papyrus, sheet of paper, map"; and , "write") is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an im ...
Alexander D'Agapeyeff in 1939.
Offered as a "challenge cipher" at the end of the book, the ciphertext is:
It was not included in later editions, and D'Agapeyeff is said to have admitted later to having forgotten how he had encrypted it.
Use of nulls in ciphertext
It is possible that not all the ciphertext characters are used in decryption and that some characters are
nulls. Evidence for this is given by the author on p. 111 of the text under the sub-section heading ''Military Codes and Ciphers'':
"The cipher is of course easily made out, but if every third, fourth, or fifth letter, as may be previously arranged, is a dummy inserted after a message has been put into cipher, it is then extremely difficult to decipher unless you are in the secret."
While the
index of coincidence
In cryptography, coincidence counting is the technique (invented by William F. Friedman) of putting two texts side-by-side and counting the number of times that identical letters appear in the same position in both texts. This count, either as a r ...
for the D'Agapeyeff cipher is 1.812 when taken in pairs horizontally (e.g., '75' '62' '82'), the
letter frequency
Letter frequency is the number of times letters of the alphabet appear on average in written language. Letter frequency analysis dates back to the Arab mathematician Al-Kindi (c. 801–873 AD), who formally developed the method to break ...
distribution is too flat for a 196 character message written in English.
Additionally, D'Agapeyeff left two ciphers for the reader to solve. Each are approximately 100 characters in length and have an index of coincidence much higher than what is expected for English plaintext.
Use of Polybius square methods in ''Codes and Ciphers''
The structure of the D'Agapeyeff Cipher has similarities to the
Polybius square, which the author used as examples in his book. He explicitly solves an example of a Polybius square based cipher from a friend in his cryptanalysis section of the book. This worked example consisted of 178 characters:
When deciphered with a Polybius square, the plaintext contains a mistake (based on mis-encoding "E" as "BE" rather than "CE"), but reads:
"THE NEW PLAN OF ATTACK INCLUDES OPERATIONS BY THREE BOMBER SQUADRONS OVER FACTORY ARYA REA
REA or Rea may refer to:
Places
* Rea, Lombardy, in Italy
* Rea, Missouri, United States
* River Rea, a river in Birmingham, England
* River Rea, Shropshire, a river in Shropshire, England
* Rea, Hungarian name of Reea village in Totești Commun ...
SOUTHWEST OF THE RIVER"
{, class="wikitable"
, -
!
! A !! B !! C !! D !! E
, -
! A
, S , , D , , U , , M , , I/J
, -
! B
, F , , W , , A , , O , , Y
, -
! C
, V , , N , , * , , T , , E
, -
! D
, L , , H , , R , , C , , Q
, -
! E
, B , , P , , K , , * , , *
References
* Shulman, David (nom: Ab Struse). "The D'Agapeyeff Cryptogram: A Challenge"
The Cryptogram April/May 1952: 39-40, 46.
* Shulman, David (nom: Ab Struse). "D'Agapeyeff Cipher: Postscript"
The Cryptogram March/April 1959: 80-81.
* Barker, Wayne G (1978). "The Unsolved D'Agapeyeff Cipher", Cryptologia, 2(2): 144-147
maintained by cryptographer
Elonka Dunin
Elonka Dunin (; born December 29, 1958) is an American video game developer and cryptologist. Dunin worked at Simutronics Corp. in St. Louis, Missouri from 1990–2014, and in 2015 was Senior Producer at Black Gate Games in Nashville, Tennes ...
* D'Agapeyeff, Alexander. ''Codes and Ciphers'', 1939, Oxford University Press, p. 158
External links
Description of properties and potential decryption strategies for D'Agapeyeff cipherby Robert Matthews
by
Nick Pelling
Nick Pelling is a British-born computer programmer and investigative writer best known as the creator of the 1984 game '' Frak!''."Desert Island Disks: Nick Pelling". ''Retro Gamer'' 26, pp. 82-85.
Games
Developed
As Aardvark Software ...
Discussion of possible causes of failure to solve D'Agapeyeff cipher at the
American Cryptogram Association website
D'Agapeyeff Cipher Yahoo GroupD'Agapeyeff Cipher Yahoo Group
D'Agapeyeff Cipher Analysisby Tiago Rodrigues
Undeciphered historical codes and ciphers