The Black Chamber

The Playfair Cipher was popularised by Lyon Playfair, but it was invented by Charles Wheatstone, one of the pioneers of the telegraph. The cipher replaces each pair of letters in the plaintext with another pair of letters, so it is a type of digraph cipher.As an example, let's encrypt the message 'Meet me at the Hammersmith Bridge tonight'.

Firstly, the sender and receiver must agree on a keyword. In this example, the keyword is Wheatstone's name, CHARLES. The letters of the alphabet are written in a square, as shown, beginning with the keyword and with I-J combined into one element. Now, click on 'Form Digraphs' to break the message into pairs of letters. The two letters in a digraph must be different, so an X has been added to split the double M in 'hammersmith'.

Encryption depends on the type of digraph. The digraphs fall into one of three categories - both letters are in the same row, or both letters are in the same column, or the letters share neither a row nor a column.


Update Keyword

To encipher a message, type it into the plaintext box, click the button labelled 'From Digraphs' and then click 'Encipher Plaintext'.

Slow Encrypt:
Fast Encrypt:



Form Digraphs
Encipher Plaintext
Decipher Ciphertext
Print Ciphertext