Lyon Playfair, 1st Baron Playfair of St. Andrews

…the British Foreign Office by Lyon Playfair, the first Baron Playfair of St. Andrews. Below is an example of a Playfair cipher, solved by Lord Peter Wimsey in Dorothy L. Sayers’s Have His Carcase (1932). Here, the mnemonic aid used to carry out the encryption is a 5 × 5-square…