Codebusters Test Learning Standards 4

Question 1

What does the term 'keyword alphabet' mean in the context of monoalphabetic substitution?

Accepted Answer

A cipher alphabet built by writing a keyword first, then the remaining unused letters

Answer

Any alphabet used only with words

Answer

The original plaintext alphabet reversed

Answer

A randomly generated alphabet stored with the message

Question 2

Which of the following best describes a polyalphabetic cipher?

Accepted Answer

A cipher that uses multiple substitution alphabets, switching between them

Answer

A cipher that rearranges letters without substitution

Answer

A cipher using only vowels for substitution

Answer

A cipher where each word has its own fixed alphabet

Question 3

If a ciphertext has an IC close to 0.065, what does this suggest about the cipher?

Accepted Answer

It is likely a monoalphabetic substitution cipher

Answer

It is likely a one-time pad

Answer

It is likely a columnar transposition

Answer

It is likely a rail fence cipher

Question 4

In a Caesar cipher, if the letter 'X' is enciphered to 'A', what is the shift value?

Accepted Answer

3

Answer

24

Answer

2

Answer

4

Question 5

What distinguishes a 'K1' alphabet from a 'K2' alphabet in a Codebusters Aristocrat?

Accepted Answer

K1 uses a keyword to build the cipher alphabet; K2 uses a keyword to build the plain alphabet

Answer

K1 has 26 letters; K2 has 24

Answer

K1 is monoalphabetic; K2 is polyalphabetic

Answer

K1 uses a random key; K2 uses a repeated keyword

Question 6

What is 'chi-squared analysis' used for in codebreaking?

Accepted Answer

To measure how closely a ciphertext's letter frequencies match expected English frequencies

Answer

To compute the number of possible keys

Answer

To convert binary to hexadecimal encoding

Answer

To rank candidate digraphs by length

Question 7

What is the key space (number of possible keys) for a simple Caesar cipher over a 26-letter alphabet?

Accepted Answer

26

Answer

25

Answer

676

Answer

403,291,461,126,605,635,584,000,000