Codebusters Test Learning Standards 2

Question 1

In a Patristocrat cipher, how is the plaintext formatted before encipherment?

Accepted Answer

Letters are grouped into 5-character blocks with spaces removed

Answer

Patristocrat ciphers remove all spaces and punctuation, then group letters into 5-character blocks for encipherment.

Question 2

What is the Index of Coincidence (IC) used for in Codebusters?

Accepted Answer

To estimate the key length of a polyalphabetic cipher

Answer

The Index of Coincidence measures the probability that two randomly chosen letters are the same, helping estimate key length in Vigenère ciphers.

Question 3

In a Vigenère cipher with keyword 'CAT', what shift is applied to the second plaintext letter?

Accepted Answer

0 (A=0)

Answer

The keyword 'CAT' applies shifts C=2, A=0, T=19 cyclically; the second letter uses A which gives a shift of 0.

Question 4

Which letter is statistically the most frequent in standard English text?

Accepted Answer

E

Answer

The letter E is the most frequent in English, appearing approximately 12.7% of the time.

Question 5

A Baconian cipher encodes each plaintext letter using how many binary-like symbols?

Accepted Answer

5

Answer

Francis Bacon's cipher uses groups of 5 symbols (A or B) to represent each of the 24–26 letters.

Codebusters Test Practice Test