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#Playfair cipher manual

The pair TH forms a rectangle, replace it with ZBĤ. The pair DE is in a column, replace it with ODģ. The pair HI forms a rectangle, replace it with BMĢ. Using "playfair example" as the key, (assuming I and J are interchangeable) the table becomes:įile:Playfair Cipher building grid omitted letters.png A Q U E LĮncrypting the message "Atacaremos al amanecer":ġ. To decrypt, use the INVERSE (opposite) of the first 3 rules, and the 4th as-is (dropping any extra "X"s (or "Q"s) that don't make sense in the final message when finished). The order is important – the first letter of the encrypted pair is the one that lies on the same row as the first letter of the plaintext pair.

If the letters are not on the same row or column, replace them with the letters on the same row respectively but at the other pair of corners of the rectangle defined by the original pair.

If the letters appear on the same column of your table, replace them with the letters immediately below respectively (wrapping around to the top side of the column if a letter in the original pair was on the bottom side of the column).

If the letters appear on the same row of your table, replace them with the letters to their immediate right respectively (wrapping around to the left side of the row if a letter in the original pair was on the right side of the row).

Some variants of Playfair use "Q" instead of "X", but any uncommon monograph will do.

If both letters are the same (or only one letter is left), add an "X" after the first letter.

Then apply the following 4 rules, in order, to each pair of letters in the plaintext: Note the relative position of the corners of this rectangle. The two letters of the digraph are considered as the opposite corners of a rectangle in the key table. To encrypt a message, one would break the message into digraphs (groups of 2 letters) such that, for example, "HelloWorld" becomes "HE LL OW OR LD", and map them out on the key table. By the time the enemy cryptanalysts could break the message, the

A typical scenario for Playfair use would be to protect important but non-critical secrets during actual combat. This was because Playfair is reasonably fast to use and requires no special equipment. It was used for tactical purposes by British forces in the Second Boer War and in World War I and for the same purpose by the Australians and Germans during World War II.

Lord Playfair, who heavily promoted its use. The frequency analysis of digraphs is possible, but considerably more difficult – and it generally requires a much larger ciphertext in order to be useful. Frequency analysis can still be undertaken, but on the 600 possible digraphs rather than the 26 possible monographs. The Playfair is thus significantly harder to break since the frequency analysis used for simple substitution ciphers does not work with it. The technique encrypts pairs of letters ( digraphs), instead of single letters as in the simple substitution cipher and rather more complex Vigenère cipher systems then in use. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair who promoted the use of the cipher.

#Playfair cipher manual

The Playfair cipher or Playfair square is a manual symmetric encryption technique and was the first literal digraph substitution cipher. The Playfair system was invented by Charles Wheatstone, who first described it in 1854.

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