Worksheet- 1.4
(Playfair Cipher)
Student Name: Samridh Garg UID: 19BCS1815
Branch: BE CSE Section/Group: 19BCS_IS_7B
Semester: 6 Date of Performance:18-03-22
Subject Name: IS LAB Subject Code: CSP-356
1. Aim/Overview of the practical:
To write a c program for Implementation of Playfair Cipher.
2. Algorithm:
Playfair cipher for encryption
The Algorithm consists of 2 steps:
1. Generate the key Square(5×5):
• The key square is a 5×5 grid of alphabets that acts as the key for encrypting the plaintext. 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.
2. 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.
For example:
PlainText: "instruments"
After Split: 'in' 'st' 'ru' 'me' 'nt' 'sz'
Pair cannot be made with same letter. Break the letter in single and add a bogus letter to the previous letter.
Plain Text: “hello”
After Split: ‘he’ ‘lx’ ‘lo’
Here ‘x’ is the bogus letter.
2. If the letter is standing alone in the process of pairing, then add an extra bogus letter with the alone letter
Plain Text: “helloe”
AfterSplit: ‘he’ ‘lx’ ‘lo’ ‘ez’
Here ‘z’ is the bogus letter.
Rules for Encryption:
• If both the letters are in the same column: Take the letter below each one (going back to the top if
at the bottom).
