Codebusters Test Curriculum Framework 4

Question 1

In Codebusters, the Affine cipher encrypts a letter with value x using the formula E(x) = (ax + b) mod 26. What constraint must 'a' satisfy?

Accepted Answer

'a' must be coprime to 26 (gcd(a,26) = 1)

Answer

'a' must be a prime number

Answer

'a' must be an even number

Answer

'a' must be less than 13

Question 2

During a Codebusters competition, a 'xenocrypt' is a cipher where:

Accepted Answer

The plaintext is in a foreign language, typically Spanish

Answer

The ciphertext contains no repeated letters

Answer

The message has been encrypted twice using different ciphers

Answer

All vowels have been removed before encryption

Question 3

Which Codebusters cipher type uses a tableau of 26 shifted Caesar alphabets and a keyword to determine which row to use for each letter?

Accepted Answer

Vigenère cipher

Answer

Beaufort cipher

Answer

Running key cipher

Answer

Autokey cipher

Question 4

In a route cipher transposition, what distinguishes it from a standard columnar transposition?

Accepted Answer

Route ciphers read the grid along a specified geometric path (spiral, diagonal, etc.)

Answer

Route ciphers use a keyword while columnar ciphers do not

Answer

Route ciphers apply a Caesar shift after transposing letters

Answer

Route ciphers only work with square grids of text

Question 5

What does the term 'digraph frequency analysis' help Codebusters solvers detect?

Accepted Answer

Common two-letter combinations like TH, HE, and IN that persist in substitution ciphers

Answer

The total number of letters in the ciphertext

Answer

Whether a transposition or substitution cipher was used

Answer

The number of unique symbols in a symbolic cipher

Question 6

In Codebusters, a 'hill cipher' is notable because it encrypts using:

Accepted Answer

Matrix multiplication modulo 26 applied to blocks of letters

Answer

A set of hill-shaped frequency curves

Answer

Alternating substitution and transposition operations

Answer

A keyword derived from the geographic elevation of a location

Question 7

When a Codebusters cipher problem states that the ciphertext is a 'null cipher,' what technique is used to hide the message?

Accepted Answer

The real message is embedded within a larger innocuous text using a pattern

Answer

Every letter is shifted by zero positions (null shift)

Answer

All vowels have been removed and replaced with null characters

Answer

The message is encrypted with a key of all zeros