Nicodemus
History
The Nicodemus cipher is a combination of transposition and substitution and was first mentioned in Cryptanalysis: A Study of Ciphers and Their Solution, first published as Elementary Cryptanalysis, 1939 by Helen Fouché Gaines (1888-1940). It was developed by American Cryptogram Association (ACA) member Harold Berkley and described by ACA member DELAC in the August-September 1949 edition of the ACA's magazine The Cryptogram.
Description
To create the cipher a keyword is selected, which determines the width of a block, and then plaintext is written into the block horizontally below the keyword. Next the columns are reordered in numerical order determined by the alphabetic order of the letters of the keyword. Each column then undergoes a substitution with any of the Periodic substitution ciphers; a Vigenère, Beaufort, Variant Beaufort or Porta table. Finally the cipher is read off the block 5 letters at a time in column order.
Example
Key: MONEY (24315)
Plaintext: Money can't buy happiness. But it sure makes misery easier to live with.
MONEY EMNOY EMNOY
24315 12345 12345
money emnoy IYACW
cantb tcnab XOAOZ
uyhap auhyp EGUMN
pines epnis IBAWQ
sbuti tsubi XEHPG
tsure rtuse VFHGC
makes emkas IYXOQ
miser emsir IYFWP
yeasi syaei WKNSG
ertol oetrl SQGFJ
ivewi wievi AURJG
th t h F V
Plaintext: Money cantb uyhap pines sbuti tsure makes miser yeasi ertol ivewi th
Ciphertext: IXEIX YOGBE AAUAH COMWP WZNQG VIIWS FYYKQ HXFNG GOWSF CQPGJ AUFRJ VG
Solving
Solving method: Hill climbing and Dictionary keyword search.
If selecting the dictionary search method, the type should be selected from the Setup drop down menu on the toolbar - Vigenère, Beaufort, Variant or Porta.
With the brute force method after clicking the Solve cipher icon a small window will open to select the cipher period. A value of zero is provided to select a range of key lengths.
Tip: If the type is unknown try all three types with the dictionary search and the one with the highest score is likely to be the correct type. If the period is unknown select a period of zero to test all periods. The key length with the highest score is likely to be the correct period. If a solution hasn’t already been found then solve again with the brute force method using this period. This will provide a more in-depth search for the correct key.
Vigenère Table
Beaufort Table
Variant Beaufort Table
Porta Table