Codebusters Test Codebusters Polyalphabetic Ciphers

Question 1

The Vigenère cipher is described as polyalphabetic because it uses how many different substitution alphabets?

Accepted Answer

One per letter of the keyword, cycling through them

Answer

Exactly 26, one for each letter

Answer

Only 2, alternating

Answer

A single alphabet shifted differently each time by random amounts

Question 2

The Kasiski test helps break a Vigenère cipher by looking for what?

Accepted Answer

Repeated ciphertext sequences and measuring distances between them to find key length

Answer

Single-letter ciphertext words

Answer

Double-letter patterns

Answer

The index of coincidence

Question 3

Once the key length of a Vigenère cipher is determined, each position's letters can be solved using which technique?

Accepted Answer

Frequency analysis on every nth letter (where n is the key length)

Answer

Brute-force all possible keys

Answer

Columnar transposition

Answer

XOR of adjacent letters

Question 4

In the Beaufort cipher, how does encipherment differ from the standard Vigenère cipher?

Accepted Answer

The key letter is subtracted from the plaintext (reciprocal/involutory), not added

Answer

It uses a 25-letter alphabet

Answer

It requires two keywords

Answer

It applies a columnar transposition after substitution

Question 5

Which Science Olympiad Codebusters cipher type involves a keyword-based columnar arrangement to encipher text rather than substituting individual letters?

Accepted Answer

Columnar transposition

Answer

Vigenère

Answer

Baconian

Answer

Aristocrat

Question 6

The running key cipher is similar to the Vigenère cipher but theoretically unbreakable if the key is what?

Accepted Answer

As long as the message and chosen from a non-repeating, random source

Answer

A single letter repeated

Answer

A common English word

Answer

Exactly 13 characters long