Codebusters Test Data-Driven Instruction 3

Question 1

In Codebusters, a student applies frequency analysis to a 40-letter ciphertext and gets unreliable results. Why is a short ciphertext problematic for frequency analysis?

Accepted Answer

Small samples deviate significantly from expected letter frequencies due to statistical noise

Answer

Short texts produce unreliable frequency counts because random variation dominates when the sample size is small.

Question 2

A teacher tracks that students often confuse the Kasiski test purpose. What does the Kasiski test help determine?

Accepted Answer

The likely key length of a Vigenère cipher by finding repeated ciphertext segments

Answer

The Kasiski test finds repeated sequences in a Vigenère ciphertext and analyzes the distances between them to estimate the key length.

Question 3

Using data from competition results, a coach identifies that students struggle with consonant frequency ordering. In English, which group lists high-frequency consonants correctly?

Accepted Answer

T, N, S, R

Answer

T, N, S, and R are among the most common consonants in English, making them strong candidates during frequency analysis.

Question 4

A student analyzes error data and learns that single-letter words in aristocrat ciphers are highly diagnostic. Which two letters can appear as single-letter words in English?

Accepted Answer

A and I

Answer

In English, only 'A' and 'I' are valid single-letter words, so any single-letter ciphertext word must map to one of these.

Question 5

A Codebusters instructor reviews data showing students use frequency analysis but forget to check digraph patterns. What is the second most common digraph in English after 'TH'?

Accepted Answer

HE

Answer

'HE' is the second most common English digraph, following 'TH', and is a reliable pattern to exploit in ciphertext analysis.

Codebusters Test Practice Test

Codebusters Test Practice Test

Codebusters Test Data-Driven Instruction 3