Playfair Cipher

Encrypt letter pairs with a 5×5 keyword square and digraph rules.

Learn how the Playfair cipher works

Keyword square

Keyword Filler letter

The keyword builds the 5×5 square. Repeated plaintext letters inside a digraph are split with the filler letter.

Normalised key: PLAYFAIREXAMPLE Unique key letters: 10 Effective filler: X I/J share one cell: Yes

Same row: PL → LA Same column: PE → IB Rectangle: PX → MI

Options

Preserve case

Keep punctuation & numbers

Remove whitespace

Group letters

Playfair works on digraphs (letter pairs). Same row shifts horizontally, same column shifts vertically, otherwise the rectangle rule is used.

Output status

Mode: Encrypt Prepared letters: 0 Digraphs: 0 Inserted fillers: 0 Input chars: 0 Output chars: 0 Blocks: 0

Classic example: plaintext HIDETHEGOLDINTHETREESTUMP with key PLAYFAIR EXAMPLE encrypts to BMODZBXDNABEKUDMUIXMMOUVIF. Decrypting that gives HIDETHEGOLDINTHETREXESTUMP because filler letters are not removed automatically.

Input text

Output text

Using This Tool: Guide & Notes Show guide

Playfair encrypts pairs of letters using a 5x5 keyword square and row, column, and rectangle rules.

How to use it

Enter a keyword to build the square.
Choose the filler letter used for repeated-letter pairs or odd final letters.
Paste plaintext or ciphertext into the input box.
Check the prepared digraphs before relying on the output.

Options and settings

Keyword controls the key square after duplicate letters are removed.
Filler letter separates repeated letters in a pair and completes odd-length messages.
I/J handling is required because the 5x5 square has only 25 cells.
Grouping controls output readability, not the Playfair rules.

Notes

Playfair works on letter pairs, so prepared plaintext may differ slightly from the raw input.
The same keyword and filler assumptions are needed for clean decryption.

Playfair Cipher: When Letters Started Moving in Pairs

How a 5×5 keyword square turned simple substitution into one of classical cryptography's most elegant hand ciphers.

Read the article

Signal acquired

A note from the team

We build these tools because we love cryptography, encoding, and making difficult ideas easier to explore. If they've helped you, even a small coffee means the world to the project. Thank you!

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