Codebusters Test Learning Standards 2 — Questions and Answers
Question 1: In a Patristocrat cipher, how is the plaintext formatted before encipherment?
- Letters are grouped into 5-character blocks with spaces removed (Correct answer)
- Words are separated by slashes
- Each word is reversed individually
- Spaces are replaced with underscores
Correct answer: Letters are grouped into 5-character blocks with spaces removed
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?
- To estimate the key length of a polyalphabetic cipher (Correct answer)
- To count the number of unique letters in ciphertext
- To determine the Caesar shift value
- To identify null characters in a transposition cipher
Correct answer: To estimate the key length of a polyalphabetic cipher
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?
- 0 (A=0) (Correct answer)
- 2 (C=2)
- 19 (T=19)
- 1 (B=1)
Correct answer: 0 (A=0)
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?
- E (Correct answer)
- T
- A
- O
Correct answer: E
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?
- 5 (Correct answer)
- 4
- 6
- 8
Correct answer: 5
Francis Bacon's cipher uses groups of 5 symbols (A or B) to represent each of the 24–26 letters.
Question 6: In an Aristocrat cipher, what key advantage does the solver have over a Patristocrat?
- Word boundaries and spaces are preserved (Correct answer)
- The key is provided at the start
- Numbers replace vowels
- Only consonants are enciphered
Correct answer: Word boundaries and spaces are preserved
Aristocrat ciphers retain the spaces between words, giving solvers useful structural information for cryptanalysis.
Question 7: What does a Caesar cipher with a shift of 13 produce, and what is this special case called?
- ROT13, a self-inverse cipher (Correct answer)
- Atbash, a mirror cipher
- Null cipher, unreadable output
- Rail fence, a transposition
Correct answer: ROT13, a self-inverse cipher
A Caesar shift of 13 is called ROT13; applying it twice returns the original text since the alphabet has 26 letters.
Codebusters Test Learning Standards 2
In a Patristocrat cipher, how is the plaintext formatted before encipherment?