Codebusters Test Codebusters Cipher Decryption 2

Question 1

In a Caesar cipher with shift 13 (ROT13), what does the letter 'N' encrypt to?

Accepted Answer

A

Answer

N

Answer

Z

Answer

M

Question 2

If the ciphertext 'KHOOR' was encrypted with a Caesar shift of 3, what is the plaintext?

Accepted Answer

HELLO

Answer

WORLD

Answer

CIPHER

Answer

CODED

Question 3

The most frequent letter in English text is 'E'. In a Caesar-encrypted ciphertext, what does the most frequent ciphertext letter most likely represent?

Accepted Answer

The encryption of E

Answer

Always the letter Z

Answer

The shift value itself

Answer

A space character

Question 4

An Atbash cipher maps A→Z, B→Y, C→X, etc. What does the word 'ZOO' encode to under Atbash?

Accepted Answer

ALL

Answer

ZOO

Answer

DOG

Answer

CAT

Question 5

A Caesar cipher uses a shift of 25. What is the equivalent negative (backward) shift?

Accepted Answer

-1

Answer

-2

Answer

-3

Answer

-25

Question 6

Why is ROT13 considered self-reciprocal — meaning applying it twice returns the original plaintext?

Accepted Answer

The shift of 13 is exactly half of 26

Answer

The letters loop back to the start randomly

Answer

It uses a symmetric private key

Answer

It has no repeated letters in its key

Question 7

In a Codebusters event, a Caesar ciphertext letter 'M' decrypts to plaintext 'D'. What shift was used?

Accepted Answer

9

Answer

3

Answer

12

Answer

17