Codebusters Test Codebusters Polyalphabetic Ciphers 3

Question 1

The Porta cipher uses a tableau where each key letter selects one of how many alphabets, each covering a pair of key letters?

Accepted Answer

13 alphabets, one per pair of adjacent letters (AA/BB … YY/ZZ)

Answer

The Porta cipher uses 13 mixed alphabets, each shared by a pair of consecutive key letters (A/B, C/D, … Y/Z), giving a compact polyalphabetic system.

Question 2

What key property makes the Vigenère cipher significantly harder to break than a simple Caesar cipher?

Accepted Answer

The same plaintext letter can be enciphered as different ciphertext letters depending on its position

Answer

Because each plaintext letter is shifted by the corresponding key letter, the same plaintext letter maps to different ciphertext letters at different positions, defeating simple frequency analysis.

Question 3

In the context of Codebusters, what does 'key period' refer to in a polyalphabetic cipher?

Accepted Answer

The length of the repeating keyword before it cycles back to the start

Answer

The key period is the length of the keyword; after that many plaintext letters are enciphered, the key repeats from the beginning, which is what Kasiski analysis exploits.

Question 4

Which manipulation of a polyalphabetic ciphertext would NOT help a cryptanalyst break a Vigenère cipher?

Accepted Answer

Rearranging the ciphertext letters alphabetically

Answer

Simply sorting ciphertext letters alphabetically destroys positional information needed for Kasiski analysis and IC calculations, providing no useful analytical leverage.

Question 5

The Quagmire ciphers (I–IV) used in advanced Codebusters are all polyalphabetic. What distinguishes Quagmire IV from the others?

Accepted Answer

Both the plaintext and key alphabets are mixed (scrambled), not in standard A–Z order

Answer

Quagmire IV uses a mixed plaintext alphabet and a mixed key alphabet, making both the row and column headers non-standard, which significantly increases difficulty compared to Quagmire I–III.

Codebusters Test Practice Test

Codebusters Test Practice Test

Codebusters Test Codebusters Polyalphabetic Ciphers 3