Playfair Cipher & Variants

Playfair Cipher

A mixed alphabet is generated and used to fill a table. The table may be filled line by line or column by column:

If the alphabet doesn't permit square tables - like the 27 letter alphabet - you may chose to transpose the table, e.g. use 9 x 3 instead 3 x 9.

For example, the key word KEY applied to the 27 letter alphabet gives the following table:

K E Y A B C D F G
H I J L M N O P Q
R S T U V W X Z &
To encipher the text, is is split into groups of tow letter. If the number of the letters in the text is odd, a random letter must be appended (CipherClerk's Applet appends the first letter of the message): MESSAGE becomes ME SX SA GE
  1. If the two letters found in the in the same row of the table, they are replace by the letters found right of them.
  2. If the two letters are found in the column, they are replaced by the letters found below of them.
  3. If the two letters are neither in the same row nor in the same column each letter is replaced by the letter found in the same row in the column of the other letter: ME becomes IB (not BI!)
Double letters (like the SS from MESSAGE) must be separated by nulls. CipherClerk's Applet does this automatically, it needs at least two different letters, the first and second must be different.


Seriated Playfair Cipher

The Playfair cipher may improved by seriating its input text: The text is written in groups of N letters in two lines. For example, the text THIS IS A TOP SECRET MESSAGE becomes, when seriated in groups of 5 letters:

        T H I S I   S E C R E   A G
        S A T O P   T M E S S   E X

Now, vertical pairs of letters are enciphered as described above. When seriating, nulls are inserted to suppress pairs of equal letters. In addition to the parameters for the Playfair cipher, you must specify the number of letters per group:



 

Doppelkastenschlüssel

This cipher is a german field cipher used in WWII.

Originally, two 5 x 5 tables with a randomly mixed alphabet where used. CipherClerk's Applet derives the mixed alphabet from two key words.

F
I
R
S
T
S
E
C
O
N
K
E
Y
A
B
D
K
Y
A
B
C
D
G
H
L
F
G
H
I
L
M
N
O
P
Q
M
P
Q
R
T
U
V
W
X
Z
U
V
W
X
Z
At first, the text was seriated in groups of 21 letters (see above). A pair of letters is enciphered in the following way: Originally, this procedure was done twice with each pair. Later in the war, it was done only once.


To proceed, you may