The Playfair cipher or Playfair square or Wheatstone-Playfair cipher is a manual symmetric encryption technique and was the first literal diagram substitution cipher. The scheme was invented in 1854 by Charles Wheatstone but bore the name of Lord Playfair for promoting its use.

You can read about encoding and decoding rules at the Wikipedia link referred to above. Below you can find the calculator for encryption and decryption to play with. It uses the most common rules for Playfair cipher:

1. ‘J’ is replaced with ‘I’ to fit 5×5 square
2. ‘X’ is used as a substitution in case you need to fill the second letter in the diagram or split two identical letters
3. Playfair square is filled row-by-row, starting with the keyword.