The Playfair cipher is a digraph substitution cipher. It employs a table where one letter of the alphabet is omitted, and the letters are arranged in a 5x5 grid. Playfair cipher #: encrypt # -d: decrypt import re, sys, random # use alphabet with no j alph = 'abcdefghiklmnopqrstuvwxyz' assert len(alph)==25 filler = 'qxz' def.
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Playfair encryption uses a grid, which can be generated by a key word. Example: Crypt DCODE with the grid: 1 2 3 4 5 1 A B C D E 2 F G H I J 3 K L M N O 4 P Q R S T 5 U W X Y Z into pairs of letters and apply the following rules according to the in the grid: - if the 2 letters are identical (or if there is only one remaining) put another letter (for example a X or a Q) after the first letter and cipher the new thus formed Example: AABCD becomes AXABCD - if the 2 letters are on the same line, replace them by the ones on their right (loop to the left if the edge of the grid is reached), Example: C and D are ciphered DE. if the 2 letters are on the same column, replace them by the ones directly under (loop to the top if the bottom of the grid is reached), Example: A and F are ciphered FK. else, by the ones forming a rectangle with the original pair. The ciphered begins with the letter on the same line as the first letter to cipher. Example: AG is crypted BF, FB is crypted GA.
Playfair decryption requires a grid, which can be generated by a key word. Example: Decrypt DCODE with the grid: 1 2 3 4 5 1 A B C D E 2 F G H I J 3 K L M N O 4 P Q R S T 5 U W X Y Z into pairs of letters and apply the following rules according to the in the grid: - if the 2 letters are on the same line, replace them by the ones on their left (loop to the right if the edge of the grid is reached), Example: DE is decrypted CD. if the 2 letters are on the same column, replace them by the ones directly above (loop to the bottom if the top of the grid is reached), Example: FK is decrypted AF. else, by the ones forming a rectangle with the original pair.
Beginning with the letter on the same line as the first letter to crypt. Example: BF is decrypted AG, GA is decrypted FB. 1854 by Charles Wheatstone Ask a new question Source code dCode retains ownership of the source code of the script PlayFair Cipher online.
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When it was first put to the British Foreign Office as a cipher, it was rejected due to its perceived complexity. However, it was later adopted as a military cipher due to it being reasonably fast to use, and it requires no special equipment, whilst also providing a stronger cipher than a.
It was used in the Second Boer War, and both World War I and World War II to different degrees. It is no longer used by military forces since the advent of powerful computers, but in its day it provided a relatively secure cipher which was easy to implement quite quickly.
We must now split the plaintext up into digraphs (that is pairs of letters). On each digraph we peform the following encryption steps:. If the digraph consists of the same letter twice (or there is only one letter left by itself at the end of the plaintext) then insert the letter 'X' between the same letters (or at the end), and then continue with the rest of the steps. If the two letters appear on the same row in the square, then replace each letter by the letter immediately to the right of it in the square (cycling round to the left hand side if necessary). If the two letters appear in the same column in the square, then replace each letter by the letter immediately below it in the square (cycling round to the top of the square if necessary).
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Otherwise, form the rectangle for which the two plaintext letters are two opposit corners. Then replace each plaintext letter with the letter that forms the other corner of the rectangle that lies on the same row as that plaintext letter (being careful to maintain the order). Because it is done on pairs of letters, this Frequency Analysis is significantly harder to crack. Firstly, for a monoalphabetic cipher we have 26 possible letters to check. For a general Digraph Cipher we have 26 x 26 = 676 possible pairings we need to check in our frequency analysis. In the instance of the Playfair Cipher, we cannot encrypt to a double letter, so we remove the 26 possibilities of double letters, giving us 650 possible digraphs we need to check.
By hand this task in monumental, but with the help of a computer, it can be done in a matter of seconds.