Nihilist Substitution

History

The Nihilist Substitution cipher dates back to around 1878 when it was used by Russian Nihilists in their war against the Tsarist regime. It is a variation of the checkerboard using a Polybius square to create a numerical cipher to which is added another numerical key to disguise the simple substitution effect of the checkerboard to make it more secure. The Polybius square was devised by the Greek historian and writer, Polybius (circa. 200 BC - 120 BC) and used a 25-letter alphabet written into a 5x5 grid with rows and columns numbered 1 to 5.

Description

In the Nihilist Substitution cipher the 5x5 square matrix is filled with a keyed alphabet using all the letters of the alphabet, with J being replaced by I. A keyed alphabet is created from a keyword, with repeated letters being omitted, followed by the unused letters of the alphabet in alphabetic order. For example using the key word YOUNGMAN and appending unused alphabet letters produces the keyed alphabet:

YOUNGMABCDEFHIKLPQRSTVWXZ

The keyed alphabet is written into the matrix in a selected route, e.g. horizontal, diagonal or clockwise giving the following grid:

1 2 3 4 5

1 Y O U N G

2 M A B C D

3 E F H I K

4 L P Q R S

5 T V W X Z

A second keyword is selected and converted to a numerical key using the keysquare where each letter is replaced by the row-column coordinates. The length of this key also determines the cipher period length. For example with the key word HENNY and using the above table H becomes 33, E becomes 31 and so on to produce the numerical key 33 31 14 14 11. The plaintext is then converted to numbers using the same method as the key and written below this key in period length. The cipher is generated by adding each plaintext number to the numerical key in the same column. If the total is greater than 100 then subtract 100.

Example

Keyword #1: YOUNGMAN

Keyword #2: HENNY

Plaintext: My wife dresses to kill. She cooks the same way.

H E N N Y

33 31 14 14 11

--------------

m y w i f

21 11 53 34 32

54 42 67 48 43

e d r e s

31 25 44 31 45

64 56 58 45 56

s e s t o

45 31 45 51 12

78 62 59 65 23

k i l l s

35 34 41 41 45

68 65 55 55 56

...

Plaintext: m y w i f e d r e s s e s t o k i l l

Ciphertext: 54 42 67 48 43 64 56 58 45 56 78 62 59 65 23 68 65 55 55

Plaintext: s h e c o o k s t h e s a m e w a y

Ciphertext: 56 66 62 38 26 23 68 76 65 47 42 78 53 35 45 64 55 42

Final ciphertext: 54 42 67 48 43 64 56 58 45 56 78 62 59 65 23 68 65 55 55 56 66 62 38 26 23 68 76 65 47 42 78 53 35 45 64 55 42

Solving

Solving method: Hill Climbing search.

After selecting the Nihilist Substitution cipher, select the cipher period from the Cipher Settings drop down menu. The default setting of 0 means that all periods starting from the minimum keyword range set in the Options window up to a maximum period of 15 will be tested.

If a plaintext tip is entered the score will be increased if the tip pattern is found in the resulting text.

If keys are known these can be entered into the Enter key, if known field on the main window, See 5.2 Keyword Entry. This field will accept either the period and key square keywords or a numbered key separating the numbers by commas. E.g. “NOVEL,PASTIME” or “41,42,51,22,35”.