Multiple Choice Questions on Caesar Cipher Encryption and Decryption

📚 Quick Study Guide

• 🔑 The Caesar Cipher is a simple substitution cipher where each letter in the plaintext is shifted a certain number of positions down the alphabet.
• 🧮 The encryption formula is: $E(x) = (x + n) \mod 26$, where $x$ is the letter's position in the alphabet (A=0, B=1, ..., Z=25), and $n$ is the shift value.
• 🔓 The decryption formula is: $D(x) = (x - n) \mod 26$, where $x$ is the letter's position in the alphabet, and $n$ is the shift value.
• 🔄 To encrypt, shift each letter forward by $n$ positions. To decrypt, shift each letter backward by $n$ positions.
• 🛡️ Caesar Cipher is easily breakable due to its limited key space (only 25 possible keys).
• 📝 Example: With a shift of 3, A becomes D, B becomes E, and so on.

🧠 Practice Quiz

1. What is the result of encrypting the letter 'A' with a Caesar Cipher using a shift of 3?
   1. X
   2. B
   3. D
   4. Z
2. What shift value is needed to decrypt 'D' back to 'A' in a Caesar Cipher?
   1. 1
   2. 2
   3. 3
   4. 0
3. Encrypt the word "HELLO" using a Caesar Cipher with a shift of 4.
   1. LIPPS
   2. OLLEH
   3. LIXXO
   4. LMPPS
4. Decrypt the word "KHOOR" which was encrypted using a Caesar Cipher with a shift of 3.
   1. HELLO
   2. WORLD
   3. JGNNO
   4. LIPPS
5. If 'G' is the encrypted letter and the shift value is 5, what was the original letter?
   1. B
   2. C
   3. D
   4. A
6. What is a major weakness of the Caesar Cipher?
   1. It is computationally expensive.
   2. It has a small key space.
   3. It requires a large amount of memory.
   4. It is vulnerable to quantum computers.
7. Which of the following is the correct decryption formula for the Caesar Cipher?
   1. $D(x) = (x + n) \mod 26$
   2. $D(x) = (x - n) \mod 26$
   3. $D(x) = (x * n) \mod 26$
   4. $D(x) = (x / n) \mod 26$