Question

What is the rule for encryption in playfair cipher if the letters in a pair are identical?

(a) then that pair is neglected

(b) a null is added in between the letters

(c) one of the identical letter is replaced by some other letter

(d) then both of the letters are replaced by the letter appearing just next in the row

The question was posed to me in an online interview.

I'm obligated to ask this question of Cryptography topic in chapter Cryptography of Data Structures & Algorithms II

Answer 1

Correct option is (b) a null is added in between the letters

Easy explanation - In playfair cipher if the letters in a pair are identical then a null is added in between the letters. Any letter can be used as a null as long as that letter is not the one being repeated.