Codebusters Test Codebusters Cryptography Theory and History 5

Question 1

In Codebusters competition, the Aristocrat cipher is a monoalphabetic substitution cipher presented with:

Accepted Answer

Word boundaries preserved and no punctuation

Answer

Aristocrat ciphers retain the original word spacing and punctuation, making them easier to solve than Patristocrats.

Question 2

A Patristocrat cipher differs from an Aristocrat in that a Patristocrat:

Accepted Answer

Removes all word divisions, presenting ciphertext as uniform 5-letter groups

Answer

Patristocrats remove word boundaries and present ciphertext in 5-letter groups, eliminating the word-length clues available in Aristocrats.

Question 3

Which digraph (two-letter combination) is the most frequent in standard English text and helps break substitution ciphers?

Accepted Answer

TH

Answer

The digraph 'TH' is the most common two-letter combination in English, appearing in words like 'the', 'this', 'that', and 'there'.

Question 4

The keyword 'ZEBRAS' in a Vigenère cipher means the first letter of the plaintext is shifted by how many positions?

Accepted Answer

25

Answer

'Z' is the 26th letter (index 25), so the first plaintext letter is shifted forward by 25 positions (equivalent to shifting back by 1).

Question 5

The Hill cipher uses which branch of mathematics as its foundation?

Accepted Answer

Linear algebra (matrix multiplication)

Answer

The Hill cipher encrypts blocks of letters by multiplying them as vectors by an invertible matrix modulo 26.

Codebusters Test Practice Test