Question

Which of the following is hardest to break using frequency analysis?

(a) Vigenere cipher

(b) Autokey cipher

(c) Playfair cipher

(d) Rotor cipher

The question was posed to me in unit test.

My query is from Cryptography in chapter Cryptography of Data Structures & Algorithms II

Answer 1

Right option is (c) Playfair cipher

For explanation: Out of the given options playfair cipher is the hardest cipher to break using frequency analysis. It is because it does not substitute letters of the word individually but it encrypts them in pairs of two.