Codebusters Test Codebusters Frequency Analysis Techniques 2

Question 1

When using frequency analysis on a Caesar cipher ciphertext, what is the quickest way to find the shift value?

Accepted Answer

Find the most frequent ciphertext letter and assume it represents E

Answer

Count all vowels

Answer

Divide the ciphertext length by 26

Answer

Look for double letters

Question 2

In frequency analysis, which set of letters is known as ETAOIN SHRDLU and why is it useful?

Accepted Answer

The 12 most common English letters in order of frequency

Answer

A secret military code

Answer

The first two rows of a Dvorak keyboard

Answer

Letters that never appear in ciphertext

Question 3

Which letter is the most common final letter in English words, making it a useful anchor point in monoalphabetic cipher analysis?

Accepted Answer

E

Answer

S

Answer

T

Answer

D

Question 4

What is a 'criб' in the context of frequency analysis and cipher-breaking?

Accepted Answer

A known or guessed plaintext segment used to attack the cipher

Answer

A table of letter frequencies

Answer

A type of polyalphabetic cipher

Answer

The key length of a Vigenère cipher

Question 5

If a ciphertext shows very uneven letter frequency distribution (some letters very common, some absent), this suggests it was encrypted with which type of cipher?

Accepted Answer

Monoalphabetic substitution

Answer

Polyalphabetic substitution

Answer

Transposition

Answer

One-time pad

Question 6

In the Aristocrat cipher used in Science Olympiad Codebusters, a two-letter ciphertext word ending in a repeated letter (e.g., 'XZ' where X=Z is not the case, but a word like 'AA') most likely represents which English word?

Accepted Answer

No two-letter English word has doubled letters; it signals a proper noun or error

Answer

IT

Answer

OF

Answer

TO