Question

Which of the following correctly defines poly graphic substitution cipher?

(a) a substitution based cipher which uses multiple substitutions at different positions

(b) a substitution based cipher which uses fixed substitution over entire plain text

(c) a substitution based cipher in which substitution is performed over a block of letters

(d) a transposition based cipher which uses fixed substitution over entire plain text

This question was posed to me in an international level competition.

My doubt stems from Cryptography in portion Cryptography of Data Structures & Algorithms II

Answer 1

Correct choice is (c) a substitution based cipher in which substitution is performed over a block of letters

The best I can explain: Poly graphic cipher is a type of substitution cipher in which substitution is performed over a block of letters. Playfair cipher is an example of poly graphic cipher.