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

The Vigenère cipher uses a keyword to apply multiple Caesar shifts, making it polyalphabetic.

Question 2

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

Accepted Answer

Simple substitution cipher

Answer

A simple substitution cipher maps each plaintext letter to a unique ciphertext letter using a fixed scrambled alphabet.

Question 3

The Playfair cipher encrypts text using which unit?

Accepted Answer

Digraphs (pairs of letters)

Answer

The Playfair cipher encrypts pairs of letters (digraphs) using a 5×5 key square.

Question 4

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

Accepted Answer

26!

Answer

There are 26! possible permutations of 26 letters, giving a key space of about 4×10²⁶.

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

Julius Caesar used a shift cipher (now called the Caesar cipher) to protect military messages.

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