Editing Playfair cipher (section)

== Use in modern crosswords ==
Advanced thematic [[cryptic crosswords]] like [[The Listener (magazine)#Crossword|''The Listener'' Crossword]] (published in the Saturday edition of the British newspaper ''[[The Times]]'') occasionally incorporate Playfair ciphers.<ref>[http://www.listenercrossword.com/List_Puzzles.html Listener crossword database]</ref> Normally between four and six answers have to be entered into the grid in code, and the Playfair keyphrase is thematically significant to the final solution.

The cipher lends itself well to crossword puzzles, because the plaintext is found by solving one set of clues, while the ciphertext is found by solving others. Solvers can then construct the key table by pairing the digrams (it is sometimes possible to guess the keyword, but never necessary).

Use of the Playfair cipher is generally explained as part of the preamble to the crossword. This levels the playing field for those solvers who have not come across the cipher previously. But the way the cipher is used is always the same. The 25-letter alphabet used always contains Q and has I and J coinciding. The key table is always filled row by row.