Talk:Cryptography/Playfair cipher

The rules given for single-square encyprtion are incorrect. When encrypting a digraph of two letters not in the same row or column, the first letter of the cyphertext is the "opposite corner" that is in the same row as the first letter of the plaintext. Thus, AT is encrypted as ZE, not EZ as stated in the article. The Wikipedia article on Playfair (http://en.wikipedia.org/wiki/Playfair_cipher) gets it correct.

One could certainly argue that the system described here is (marginally) more secure than the one that Sir Charles Wheatstone devised, but all the same it is not Playfair.