
16 Cryptography with Open-Source Software
(in this case two letters) is used as input to the encryption procedure. Like
all ciphers pre-dating the use of computers, it has since been broken.
Historical note: The Playfair c ipher was developed by Charles Wheatstone
in 1854, and popularized and promo ted by his friend Lord Playfair. Althoug h
Playfair was scrupulous in crediting Whea tstone with the cipher, it is his name
now which is associated with it. It was used by the British in both the Boer
War and the First World War. It was also used during the Second World War
in 1943, by the future US President Jo hn F. Kennedy.
The key for this cipher is