Crack playfair cipher

Both 5x5 and 6x6 Playfair solvers have been implemented. The square size is determined automatically depending on whether the cipher contains any numbers.

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Viewed 4k times. Any help would be appreciated. The Playfair cipher was the first practical digraph substitution cipher. The scheme was invented in by Charles Wheatstone but was named after Lord Playfair who promoted the use of the cipher. In playfair cipher unlike traditional cipher we encrypt a pair of alphabets digraphs instead of a single alphabet. This was because Playfair is reasonably fast to use and requires no special equipment.

Each of the 25 alphabets must be unique and one letter of the alphabet usually J is omitted from the table as the table can hold only 25 alphabets. If the plaintext contains J, then it is replaced by I. The initial alphabets in the key square are the unique alphabets of the key in the order in which they appear followed by the remaining letters of the alphabet in order.

Algorithm to encrypt the plain text: The plaintext is split into pairs of two letters digraphs. If there is an odd number of letters, a Z is added to the last letter. Troubles come when we encounter pair of identical letters, e. Here the rule is: don't take the whole pair, instead take single letter and add Q to it. Decoding is obviously almost the same and gives programqming. Since Q is almost never found without following U and never in the end of word , it is easy to get rid of extra Q s.

More precaution is needed: if pair to encrypt consists of different letters, and the second letter is Q , let's do the same as with pair of same letters - encode only the first with addition of Q shifting original Q to the beginning of the next pair. If text ends with incomplete pair - also add Q to it. On decoding we just threw away any second letter in the pair if it is Q.