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Playfair Cipher

Build a 5 by 5 key square, encrypt and decrypt digraphs, and insert X between repeated letters.

Playfair cipher

Key square: not built yet.
Only letters are used and J is merged with I, which is why Q is dropped from the square. Non letter characters are removed before the cipher runs.

How to use the Playfair Cipher

  1. Type a keyword to build the five by five key square.
  2. Enter your letters and choose encrypt or decrypt.
  3. Copy the digraph result, or use it as input to check the round trip.

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Frequently Asked Questions

Common questions about the free online playfair cipher.

It encrypts pairs of letters instead of single letters. Each pair is shifted in a five by five key square, which hides single letter frequencies.
The unique letters of the keyword come first, then the rest of the alphabet in order. The letter J is merged with I, so only twenty five letters fit.
When a pair holds the same letter twice, an X is inserted between them. On decrypt the filler is removed again when that option is selected.
The square holds twenty five cells but the alphabet has twenty six letters, so I and J share one cell. Any J you type is treated as an I.
Letters in the same row shift right, letters in the same column shift down, and a rectangle swaps columns. Decrypting shifts the other way.
An X is appended to fill the last pair, because the cipher works on two letters at a time. Decrypting with removal enabled drops that trailing X.
No. Only letters take part in the cipher, so spaces, digits and punctuation are removed before encryption. Decryption returns letters in upper case.
No. Playfair was strong by hand in the nineteen hundreds, but a computer can break it easily today. It is best used for puzzles and teaching.
No. The key square and the digraph rules are applied entirely inside your browser, so nothing is ever sent anywhere.
Yes. The tool is completely free and unlimited, with no account, no sign-up and no data collection.

Last updated: October 10, 2026