Codebusters Test Codebusters Cryptography Theory and History 2

Question 1

The Vigenère cipher is classified as which type of cipher?

Accepted Answer

Polyalphabetic substitution

Answer

Monoalphabetic substitution

Answer

Transposition

Answer

Block cipher

Question 2

Which cipher replaces each letter with another letter using a fixed, scrambled alphabet?

Accepted Answer

Simple substitution cipher

Answer

Rail Fence cipher

Answer

Playfair cipher

Answer

Running key cipher

Question 3

The Playfair cipher encrypts text using which unit?

Accepted Answer

Digraphs (pairs of letters)

Answer

Single letters

Answer

Trigraphs (triplets of letters)

Answer

Entire words

Question 4

What is the key space size of a simple substitution cipher using the 26-letter English alphabet?

Accepted Answer

26!

Answer

26

Answer

26²

Answer

2²⁶

Question 5

Which historical figure is credited with inventing the cipher that bears his name and was used widely in the Roman military?

Accepted Answer

Julius Caesar

Answer

Augustus Caesar

Answer

Nero

Answer

Cicero

Question 6

In the context of ciphers, what does 'key length' affect in the Vigenère cipher?

Accepted Answer

The period of the repeating shift pattern

Answer

The number of letters encrypted per second

Answer

The length of the ciphertext

Answer

The size of the alphabet used

Question 7

Which attack method uses the index of coincidence to determine the key length of a Vigenère cipher?

Accepted Answer

Kasiski examination

Answer

Brute force attack

Answer

Dictionary attack

Answer

Meet-in-the-middle attack