Four-square Cipher

Advanced polygraphic cipher using four 5x5 matrices for secure encryption.

Four-Square Cipher

A digraph substitution cipher using four 5×5 Polybius squares

Mode

Keyword 1 (Top-Right Square)

Keyword 2 (Bottom-Left Square)

Plain Text

Characters: 0Digraphs: 0

Encrypted Output

Example Texts

Click any example to load it

ATTACK AT DAWN

Keywords: MONARCHY / KEYWORD

Military message

MEET ME TONIGHT

Keywords: SECRET / MESSAGE

Secret meeting

THE QUICK BROWN FOX

Keywords: CIPHER / SQUARE

Common phrase

Free Online Tool

How to Use Four-square Cipher

Enter plaintext and keep or replace the two keywords; defaults are EXAMPLE and KEYWORD.
Choose Encrypt; letters are uppercased, J becomes I, and an odd final letter is padded with X.
The component encrypts each digraph through four 5×5 squares and groups output in fives.
Use Decrypt with the same keywords to reverse the rectangle lookup.

Four-square maps the first and second letters of each pair through opposite corners formed by two plaintext and two keyed Polybius squares.

Default keywords EXAMPLE / KEYWORD:

HELLO

Output:

FYGFI X

Default keywords EXAMPLE / KEYWORD:

ATTACKATDAWN

Output:

MMOWP AMMEW WG

All processing happens in your browser. No data is sent to servers.

No registration, no limits, completely free to use.