Question

What will be the ciphered text corresponding to “SANFOUNDRY” if bifid cipher is used for encryption with key as “KEY” with period as 5?

(a) SBPISZTKZH

(b) PLNSOWGKQM

(c) SELFQEXBHM

(d) YFSGWNFBW

This question was posed to me in an interview for internship.

The doubt is from Cryptography in portion Cryptography of Data Structures & Algorithms II

Answer 1

The correct choice is (b) PLNSOWGKQM

Easy explanation - For encrypting the plain text using bifid cipher we first form the polybius square with the help of given key. After this, the plain text is divided into blocks of length 5 and corresponding coordinates are noted. So the corresponding cipher text would be “PLNSOWGKQM”.