Playfair Cipher.
This cipher uses a grid to encipher pairs of letters from the plaintext. A cipher like this has a very flat frequency graph with no J present. It has an even number of letters and none of the letter pairs are of the same letter.
Follow these steps to encode with Playfair.
First make the grid using your keyword. Carry the alphabet on from the end of the keyword, missing out repeated letters.
Now break your message up into pairs. You must pad any pairs of repeated letters with an X. Pad the end of the message with an X as well if need be.
Playfair Encipherment Rules | |
Letters in the SAME ROW | |
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Letters in the same row encipher using the letter immediately to the RIGHT. The grid wraps around itself. Thus SV→TQ RH→DR HR→RD |
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Letters in the SAME COLUMN | |
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Letters in the same column encipher using the letter immediately BELOW. The grid wraps around itself. Thus MA→TY AM→YT |
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Letters in DIFFERENT ROWS AND COLUMNS | |
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Find the rectangle formed by the rows and columns containing the letter pair. The plain text letter pair forms one diagonal of this rectangle. The ciphertext letters are given by the other diagonal. Each plaintext letter is encoded by the letter on its row belonging to the ciphertex diagonal of the rectangle DU→GS UD→SG |
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The message is encoded as follows:
playfair.xls This XL worksheet will decipher the Cipher Challenge 2004 5b Playfair cipher, provided that you know the right keyword.
double playfair.xls This XL worksheet will decipher the Cipher Challenge 2004 7b double Playfair cipher, provided that you know the right keywords and how to arrange them in the grid.
Double Playfair Cipher Nova TV Nazi Secrets Program webpage on the Double Playfair Cipher. This is exactly the system used for Cipher Challenge 2004 7B.
last updated 10th September 2011