#Cipher solver code#

In the encryption case, alphabets in the last row or last column had to be replaced by those in the first, and this code was taken care of by a modulus 5 operation.

The main difference between the encryption and decryption implementation are the corner cases when alphabets are in the first row or first column. Once the digrams are joined, a sentence can be made by looking at the letters and neglecting filler letters like x, etc. Based on the relative positions of characters in a pair, following the above detailed rules, decryption is performed, and the decrypted pair is returned.

Then the remaining alphabets are populated.Д®ach character in the ciphertext is then searched for in the digraph and its position is found. Using this, each cell in the matrix is populated with the key string alphabets first, and only once by reducing the count in the hashmap. For this, first a 26 character hashmap is used to store the count of each alphabet in the key string. The string is converted to lower case and the 5x5 key square is generated. Now we write a function to decrypt a ciphertext using the Playfair cipher. #include #include #include #define SIZE 100 C ImplementationДЇirst we import the required libraries and define a large enough size for allocation of the ciphertext to be decrypted. Otherwise, each ciphertext letter in a pair is replaced by the letter that lies in its own row and the column occupied by the other ciphertext letter.ДЇollowing these rules, the plaintext becomes вЂ Meet me at the bridgeвЂ™ (x is neglected at the end since its a filler letter). Two ciphertext letters that fall in the same column of the matrix are replaced by the letters above, with the bottom element of the column circularly following the top.ДЈ.

Two ciphertext letters in the same row of the matrix are each replaced by the letter to the left, with the last element of the row circularly following the first.Дў.

Gd do gd rq pr sd hm em bv Rules for Decryption For the ciphertext вЂ gddogdrqprsdhmembvвЂ™, the digrams would be. Given a ciphertext sentence, it is split into digrams. Image by author -Playfair matrix for the keyword вЂ CharlesвЂ™