Codebusters Test Data-Driven Instruction 5

Question 1

A Codebusters instructor uses assessment data to teach students about letter contact frequency. Which letter in English has the highest frequency of appearing adjacent to the letter E?

Accepted Answer

R

Answer

The letter R is one of the most frequent contacts of E in English, appearing in common words like 'there', 'here', 'every', and 'over'.

Question 2

A team reviews competition data and finds poor performance on cipher type identification. Which statistical property most reliably distinguishes a Caesar cipher from a Vigenère cipher?

Accepted Answer

Index of Coincidence—Caesar scores ~0.065 while Vigenère scores closer to 0.038–0.050

Answer

The Index of Coincidence is the standard tool for distinguishing monoalphabetic ciphers (high IC ~0.065) from polyalphabetic ciphers (lower IC ~0.038–0.050).

Question 3

A student applies data-driven instruction and builds a contact table. What is a 'contact table' used for in cryptanalysis?

Accepted Answer

Recording which letters appear before and after each ciphertext letter to identify common plaintext patterns

Answer

A contact table records the left and right neighbors of each ciphertext letter, helping identify common plaintext letter pairings like 'TH', 'ER', and 'AN'.

Question 4

After reviewing error logs, a Codebusters coach notes students struggle with xenocrypt ciphers. What makes a xenocrypt different from a standard aristocrat?

Accepted Answer

Xenocrypts are monoalphabetic substitution ciphers of text written in a foreign language

Answer

A xenocrypt is an aristocrat-style monoalphabetic cipher applied to text in a foreign language, requiring knowledge of that language's letter frequencies.

Question 5

A coach tracks data showing students fail to apply columnar transposition analysis correctly. In a simple columnar transposition cipher, what determines the column order during decryption?

Accepted Answer

The alphabetical order of the letters in the keyword

Answer

In a columnar transposition cipher, the keyword letters are ranked alphabetically to assign column numbers, which determines the reading order during decryption.

Codebusters Test Practice Test

Codebusters Test Practice Test

Codebusters Test Data-Driven Instruction 5