Cadenus
History
The Cadenus cipher is a double transposition cipher and was described in Traité de Cryptographie by Emile-Arthur Soudart and André Lange, 1925. Soudart was the Chief of the French Army's Cipher Section and Lange his assistant. The system used 20 numbered disks arranged on a common axle with space to write the message on the edge of each disk though this can easily be converted to a pencil and paper method. A limitation of the cipher is that the plaintext length must be a multiple of 25.
Description
To encipher text first select a keyword whose length is the same as the message length divided by 25 and write the plaintext horizontally in a block below the key. The keyword is used to determine the order in which columns are read and the starting position of the column.
Using the example below with the keyword CALM the column order is 2134 which reflects the alphabetic order of the letters in the keyword. The starting position in which each column is read is determined by adding a 25-letter Key column to the side of the block with V/W combined. The keyword letter at the top of each column is found in this key and the column is read starting at the letter adjacent to this position.
Using the message below the first column to be read is Column 2 below the A of CALM. A is the first position in the vertical Key so the first cipher column begins URONY.... The second column to be read is Column 1 below the C of CALM. C is in position 24 of the Key so the column is read off starting at TIHUY.... This is repeated for the final columns until the cipher block is produced as shown below. The final cipher is produced by reading the text horizontally in the Cipher block.
Example
Key: CALM
Plaintext: Humor: If you can stay calm, while all around you is chaos then you probably haven't completely understood the situation. xx
Plain Cipher
CALM ACLM
2134 1234
---- Key ----
HUMO A UULB
RIFY Z IOVY
OUCA Y UHCE
NSTA X SRLO
YCAL V COLE
MWHI U WNDY
LEAL T EYTE
LARO S AMTO
UNDY R NLIH
OUIS Q ULTT
CHAO P HUXI
STHE O TOMX
NYOU N YCFO
PROB M RSCY
ABLY L BNTA
HAVE K APAA
NTCO J TAHL
MPLE I PHAI
TELY H ENRL
UNDE G NMDO
RSTO F STIY
ODTH E DUAS
ESIT D SRHO
UATI C AOOE
ONXX B NEOU
Ciphertext: UULBI OVYUH CESRL OCOLE WNDYE YTEAM TONLI HULTT HUXIT OMXYC FORSC YBNTA APAAT AHLPH AIENR LNMDO STIYD UASSR HOAOO ENEOU
Solving
Solving methods: Hill Climbing and Dictionary keyword search.
The cipher length must be a multiple of 25 and the maximum key length is set to 26.