Codebusters Test Curriculum Framework 5

Question 1

In the Codebusters event, which of the following best describes a 'running key cipher'?

Accepted Answer

A polyalphabetic cipher that uses a long meaningful text (like a book passage) as the key

Answer

A cipher that automatically increases the key shift by 1 each letter

Answer

A cipher where the key is derived from the plaintext itself

Answer

A Vigenère cipher whose keyword has exactly 26 unique letters

Question 2

A Codebusters problem uses a Beaufort cipher. How does the Beaufort cipher differ from the standard Vigenère cipher?

Accepted Answer

The Beaufort cipher subtracts the plaintext from the key (C = K − P mod 26) rather than adding

Answer

The Beaufort cipher uses a 25-letter alphabet excluding one vowel

Answer

The Beaufort cipher applies two rounds of Vigenère encryption

Answer

The Beaufort cipher requires a Polybius square as its key tableau

Question 3

In Codebusters, when performing frequency analysis on a short ciphertext, why might observed frequencies differ significantly from expected English frequencies?

Accepted Answer

Short texts have too few samples for statistical frequencies to match theoretical values reliably

Answer

Codebusters ciphertexts always use uniform letter distributions by design

Answer

Frequency analysis only works on ciphertexts of exactly 100 letters

Answer

Short ciphertexts are always polyalphabetic, making frequency analysis inapplicable

Question 4

In the Codebusters curriculum, what is the purpose of an 'autokey cipher'?

Accepted Answer

It extends the key by appending the plaintext itself after the initial keyword

Answer

It automatically determines the best key for a given ciphertext

Answer

It generates a new random key after each letter is encrypted

Answer

It uses the ciphertext of each letter as the key for the next letter

Question 5

Which Codebusters cipher is also known as the 'Caesar box' or 'Cardano grille' and involves a cut-out mask placed over ciphertext?

Accepted Answer

Transposition grille cipher

Answer

Playfair cipher

Answer

Straddling checkerboard cipher

Answer

Bifid cipher

Question 6

In Codebusters, the Bifid cipher combines which two classical techniques to encrypt messages?

Accepted Answer

Polybius square coordinates and transposition of those coordinates

Answer

Columnar transposition and Caesar substitution

Answer

Vigenère encryption and rail fence transposition

Answer

Playfair digraph encoding and columnar rearrangement

Question 7

Under the Codebusters Science Olympiad rules, which statement about the 'timed question' is most accurate?

Accepted Answer

The timed question earns a time-based bonus in addition to its base point value when completed correctly

Answer

Teams may not use reference materials on the timed question

Answer

The timed question is worth more base points than other questions regardless of speed

Answer

Only one team member is allowed to work on the timed question