## EXPERT ANSWER

**Q.2: You agreed to use a Caesar cipher with a key of k = 5 with a friend. While sitting in a group, the friend hands you over a message that says “QNGWFWD”. Decrypt the message?**

Here, the encrypted text is “QNGWFWD” and value of the key is 5. So, we need to substitute each letter of the word with the key value.

Q – 5 => L

N – 5 => I

G – 5 => B

W – 5 => R

F – 5 => A

W – 5 => R

D – 5 => Y

So, the encrypted text is **LIBRARY.**

**Q.3: Suppose you actually forgot the key. How many decryption computations of the cipher text “QNGWFWD” do you need to perform to reach to the plaintext?**

In Ceaser cipher, the rules of decryption of a encrypted text is to take the first letter of the ciphertext and the first letter of the key, and subtract their value . No, as the number of alphabates is 26. So, we need to perform **26** decryption computations of the cipher text **“QNGWFWD” t**o reach to the plaintext.