Codebusters Test Codebusters Cryptography Theory and History 3

Question 1

The ENIGMA machine used by Nazi Germany in WWII is best described as which type of cipher device?

Accepted Answer

Electro-mechanical polyalphabetic rotor cipher machine

Answer

Simple substitution machine

Answer

One-time pad generator

Answer

Transposition rail fence device

Question 2

What is the Index of Coincidence (IC) primarily used for in cryptanalysis?

Accepted Answer

Estimating the number of alphabets used in a polyalphabetic cipher

Answer

Counting the total number of letters in a ciphertext

Answer

Measuring the encryption speed of a cipher

Answer

Determining the plaintext language

Question 3

Which frequency analysis fact is most useful when attacking English monoalphabetic substitution ciphers?

Accepted Answer

The letter 'E' is the most frequent letter in English text

Answer

The letter 'Z' is always encrypted as 'Q'

Answer

Vowels are never adjacent in English

Answer

Consonants appear more often than vowels

Question 4

A transposition cipher differs from a substitution cipher in that transposition ciphers:

Accepted Answer

Rearrange the positions of letters without changing them

Answer

Replace each letter with a number

Answer

Use two alphabets simultaneously

Answer

Always require a numeric key

Question 5

What property makes a one-time pad theoretically unbreakable?

Accepted Answer

The key is truly random, used only once, and is as long as the message

Answer

It uses very long key words

Answer

It encrypts letters in blocks of 64 bits

Answer

It applies three rounds of substitution

Question 6

The Rail Fence cipher is an example of which cipher category?

Accepted Answer

Transposition

Answer

Polyalphabetic substitution

Answer

Monoalphabetic substitution

Answer

Stream cipher

Question 7

Which mathematical concept underlies modular arithmetic used in cipher shift calculations?

Accepted Answer

The remainder after division by the alphabet size

Answer

Prime factorization

Answer

Logarithmic scaling

Answer

Matrix inversion