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