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Concept
Cyclometer
Summary
The cyclometer was a cryptologic device designed, "probably in 1934 or 1935," by Marian Rejewski of the Polish Cipher Bureau's German section (BS-4) to facilitate decryption of German Enigma ciphertext. The original machines are believed to have been destroyed shortly before the German invasion of Poland that launched the Second World War, to prevent the Germans learning that their cipher had been broken.
Using drawings made by Rejewski, Hal Evans and Tim Flack at the Department of Engineering, University of Cambridge, in 2019 constructed a working version of the cyclometer.
Frode Weierud provides the procedure, secret settings, and results that were used in a 1930 German technical manual.
Daily key (shared secret):
Wheel Order : II I III
Ringstellung : 24 13 22 (XMV)
Reflector : A
Plugboard : A-M, F-I, N-V, P-S, T-U, W-Z
Grundstellung: FOL
Operator chosen message key : ABL
Enciphered starting with FOL: PKPJXI
Cleartext message to send and resulting cleartext:
Feindliche Infanteriekolonne beobachtet.
Anfang Südausgang Bärwalde.
Ende drei km ostwärts Neustadt.
FEIND LIQEI NFANT ERIEK
OLONN EBEOB AQTET XANFA
NGSUE DAUSG ANGBA ERWAL
DEXEN DEDRE IKMOS TWAER
TSNEU STADT
Resulting message:
1035 – 90 – 341 –
PKPJX IGCDS EAHUG WTQGR
KVLFG XUCAL XVYMI GMMNM
FDXTG NVHVR MMEVO UYFZS
LRHDR RXFJW CFHUH MUNZE
FRDIS IKBGP MYVXU Z
The first line of the message is not encrypted. The "1035" is the time, "90" is number of characters encrypted under the message key, and "341" is a system indicator that tells the recipient how the message was encrypted (i.e., using Enigma with a certain daily key). The first six letters in the body ("PKPJXI") are the doubled key ("ABLABL") encrypted using the daily key settings and starting the encryption at the ground setting/Grundstellung "FOL". The recipient would decipher the first six letters to recover the message key ("ABL"); he would then set the machine's rotors to "ABL" and decipher the remaining 90 characters. Notice that the Enigma does not have numerals, punctuation, or umlauts.
Official source
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