Playfair Cipher Encryption

The known multiple-letter secret writing cipher is that the Playfair, that treats digrams
in the plaintext as single units and interprets these units into ciphertext .

The Playfair algorithmic rule relies on the utilization of a five × five matrix of letters created
using a keyword. Here is AN example, solved by Lord Peter Wimsey in
Dorothy Sayers’s Have His Carcase.

This cipher was truly fictitious by British human Sir Charles physicist in 1854, however it bears the name
of his friend Baron Playfair of St.Andrews, World Health Organization championed the cipher at the British ministry.

The book provides AN fascinating account of a probable-word attack.

M O N A R
C H Y B D
E F G I/J K
L P Q S T
U V W X Z

In this case, the keyword is autocracy. The matrix is built by filling in
the letters of the keyword (minus duplicates) from left to right and from high to bottom,
and then filling within the remainder of the matrix with the remaining letters in
alphabetic order. The letters I and J count jointly letter. Plaintext is encrypted 2
letters at a time, in keeping with the subsequent rules:

1. continuance plaintext letters that square measure within the same combine square measure separated with a filler
   letter, such as x, so balloon would be treated as ba lx lo on.

2. 2 plaintext letters that fall within the same row of the matrix square measure every replaced by
   the letter to the correct, with the primary part of the row circularly following the
   last. as an example, ar is encrypted as RM.

3. 2 plaintext letters that fall within the same column square measure every replaced by the letter
   beneath, with the highest part of the column circularly following the last. For
   example, alphabetic character is encrypted as CM.

4. Otherwise, every plaintext letter in an exceedingly combine is replaced by the letter that lies in its
   own row and therefore the column occupied by the opposite plaintext letter. Thus, hs
   becomes BP and Semitic deity becomes IM (or JM, because the encipherer wishes).

The Playfair cipher may be a nice advance over easy monoalphabetic ciphers.
For one factor, whereas there square measure solely twenty six letters, there square measure twenty six × twenty six = 676 digrams