Codebusters Test Codebusters Frequency Analysis Techniques 3

Question 1

The Chi-squared (χ²) test is used in codebreaking to compare what two distributions?

Accepted Answer

Observed ciphertext letter frequencies vs. expected English letter frequencies

Answer

Key length vs. ciphertext length

Answer

Number of vowels vs. consonants

Answer

Digraph counts vs. trigraph counts

Question 2

Which common English word pattern—a four-letter word where the second and fourth letters are the same—is a powerful crib in monoalphabetic analysis?

Accepted Answer

THAT

Answer

THIS

Answer

THEN

Answer

THEY

Question 3

What does a flat (near-uniform) frequency distribution in a ciphertext strongly indicate about the cipher type?

Accepted Answer

A polyalphabetic or transposition cipher was used

Answer

A simple Caesar shift was used

Answer

The plaintext is very short

Answer

The key is a single letter

Question 4

In Science Olympiad Codebusters, the 'hill' or 'spike' in a ciphertext frequency graph typically points to which substituted letter?

Accepted Answer

E, the most common English letter

Answer

Z, the least common English letter

Answer

Q, which always precedes U

Answer

X, used as a null character

Question 5

Double-letter patterns in English ciphertext are most often the substitutes for which plaintext doubled letters?

Accepted Answer

LL, SS, EE, TT, FF, OO

Answer

QQ, ZZ, XX, JJ, VV

Answer

AA, BB, CC, DD

Answer

PP, RR, GG, WW

Question 6

When solving an Aristocrat cipher, which approach is generally most efficient as a starting strategy?

Accepted Answer

Identify single-letter words first, then high-frequency letters, then common word patterns

Answer

Guess the key word and work backwards

Answer

Try all 26 Caesar shifts first

Answer

Count only consonant frequencies