To encrypt a message e.g. Relieve Baden Powell at Mafeking
- Pick a keyword without repeated letters – e.g. HEATONS
- Fill in a 5 x 5 square, starting with the key, then continuing with the alphabet from A. Combine I and J and again avoid repetitions.
- Write out the message in digraphs (2 letter groups), again avoiding repetitions by inserting Q, X, or Z. The choices make the code harder for opponents to crack. With both choices, for the sake of your allies, be consistent. Let’s use Z and I here:
re – li – ev – eb – ad – en – po – we – lz – la – tm – af – ek – in – gz
- To encrypt the message, use the three rules of Playfair Ciphers.
- Rectangles: Same rows, opposite corners
e.g. re becomes PT
- Columns: The letter below, for each of the pair in turn. On the bottom row, imagine an identical table underneath.
e.g. lz becomes UO and we becomes ES
- Rows: One right, for each of the pair in turn. At the end of the row, imagine a duplicate table to the right.
e.g. li becomes FK
Encryption: PT FK HW AS OB HS UE ES UO IO HR HI TG FB LW
To decode, go up instead of down and left instead of right – and for ends of rows and columns, imagine duplicate tables above and to the left of your Playfair grid.
Can you crack this Playfair Cipher (again using the keyword HEATONS)?
XF KC TU XK DE MU DW
Can you solve the Playfair Puzzle ?