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 is at index 13; adding 13 gives 26, which wraps to 0, the letter A.

Question 2

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

Accepted Answer

HELLO

Answer

Shifting each letter back 3 gives K→H, H→E, O→L, O→L, R→O, spelling HELLO.

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

Because Caesar shifts all letters by the same amount, E's high frequency is preserved in the ciphertext.

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

Z→A, O→L, O→L, so ZOO becomes ALL.

Question 5

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

Accepted Answer

-1

Answer

Shifting forward 25 is the same as shifting backward 1 in a 26-letter alphabet.

Codebusters Test Practice Test

Codebusters Test Practice Test

Codebusters Test Codebusters Cipher Decryption 2