Four Square Cipher
Description
A four square tables are prepared. The squares are filled with the letters
of the alphabet, two of them with mixed alphabets.
For example, the key word KEY applied to a 25 letter alphabet
gives the following table:
| 1st plain text |
|
1st cipher text |
| A |
B |
C |
D |
E |
|
K |
E |
Y |
A |
B |
| F |
G |
H |
I |
K |
|
C |
D |
F |
G |
H |
| L |
M |
N |
O |
P |
|
I |
L |
M |
N |
O |
| Q |
R |
S |
T |
U |
|
P |
Q |
R |
S |
T |
| V |
W |
X |
Y |
Z |
|
U |
V |
W |
X |
Y |
| 2nd cipher text |
|
2nd plain text |
| W |
O |
R |
D |
A |
|
A |
B |
C |
D |
E |
| B |
C |
E |
F |
G |
|
F |
G |
H |
I |
K |
| H |
I |
K |
L |
M |
|
L |
M |
N |
O |
P |
| N |
P |
Q |
S |
T |
|
Q |
R |
S |
T |
U |
| U |
V |
X |
Y |
Z |
|
V |
W |
X |
Y |
Z |
To encipher the text, is is split into groups of two letters. 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
SS AG EM. The two letters are located in the plain text squares
and replaced by the letters found in the same row of the cipher text
squares above or below the other letter: ME is thus replaced
by OO, AG by EB.
CipherClerk's Applet's implementation requires two keyword, but doesn't check
that they are different. You may choose from alphabets with 25 and 36 letters:
To proceed, you may