The or Playfair square, is a manual symmetric encryption technique and was the first literal digraph substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair who promoted the use of the cipher. The Playfair cipher uses a 5 by 5 table containing a keyword or phrase. Memorization of the keyword and 4 simple rules are all that’s required to create the 5 by 5 table and use the cipher. For this mission, we will do one better and use a 6 by 6 table. For the key table, we should use ASCII letters in lowercase ('abcdefghijklmnopqrstuvwxyz') and digits (').
Dec 6, 2018 - In this article you will learn about the PlayFair Cipher. Playfair cipher is a multi- alphabet letter encryption cipher, which deals with letters in. Playfair Cipher Implementation C Program. To generate first and follow for given Grammar > C ProgramSystem Programming and Compiler ConstructionHere's a C Program to generate First and Follow for a give Grammar Program.
They are have the following order: 'abcdefghijklmnopqrstuvwxyz' To generate the key table, the spaces in the table must be filled with the letters contained in the keyword (dropping any duplicate letters and digits), then the remaining spaces are filled with the rest of the letters and digits of the alphabet in order. The key is written in the top rows of the table, from left to right. The keyword together with the conventions for filling in the 6 by 6 table constitute the cipher key. To encrypt a message, we will need to prepare a block of text. Upper case letters get transposed into lower case of letters, we’d break the message into digraphs (groups of 2 letters) and skip white spaces and punctuation symbols. The result would turn a message like 'Hello World!'
Into 'he ll ow or ld', and would get mapped out in the key table. The two letters of the digraph are considered to be the opposite corners of a rectangle in the key table.
Note the relative position of the corners of this rectangle. To decrypt, use the inverse (opposite) of the last 3 rules and you will get the processed (cut version). For example, the keyword is 'checkio101'. Then the key table will be looked as c h e k i o 1 0 a b d f g j l m n p q r s t u v w x y z 2 3 4 5 6 7 8 9 Let's the message is 'Fizz Buzz is x89 XX.'
After using rule 1 (text preparation) we will get - 'fi zx zb uz zi sx 89 xz xz'. 'fi' = 'do'; - 'zx' = '2y'; - 'zb' = '7m'; - 'uz' = 't2'; - 'zi' = '2k'; - 'sx' = 'ry'; - '89' = '94'; - 'xz' = 'y2'; - 'xz' = 'y2'. And the encoded message is 'do2y7mt22kry94y2y2'.
You should write two functions - 'encode' and 'decode'. Each function receives a message (ciphered or opened) and keyword. The 'encode' function processes and encrypts a message.
The 'decode' function decrypts the encoded message (of course in the processed version). Two arguments. A message as a string (unicode) and a keyword as a string (unicode). The encoded or decoded message (related to function).
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). 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.