**1) What is meant by authentication?**

a. Ensuring confidentiality of data.

b. Verifying the identity of the sender.

c. Digitally signing of a document.

d. None of these.

**Answer:** b

**Solution:** Authentication refers to the process of verifying the identity of the sender of a message. Hence, the correct option is (b).

**2) Consider a mono-alphabetic cipher with the following key value:(A B C D H G F E I J K L P O N M Q R S T X W V U Y Z)What will be the encrypted form of the message โV I O L E Tโ ?**

a. W I N L H T

b. W K N J H R

c. I O L E T V

d. None of these.

**Answer: **a

**Solution:** According to the specified key, the letter โVโ maps to โWโ, โIโ maps to โIโ, โOโ maps to โNโ, โLโ maps to โLโ, โEโ maps to โHโ, and โTโ maps to โTโ. Hence the encrypted form of โVIOLETโ will be โWINLHTโ. Hence, the correct option is (a).

**3) For key sizes 128 bits, 192 bits and 256 bits respectively, the number of AES rounds required is**

a. 10, 11 and 12

b. 8, 10 and 12

c. 10, 12 and 14

d. 9, 10 and 11

**Answer: **c

**Solution:** Follows from the definition of the AES algorithm.

**4) For authentication using public-key cryptography, encryption is carried out using**

a. Receiverโs public key

b. Receiverโs private key

c. Senderโs public key

d. Senderโs private key

**Answer: **d

**Solution: **If you want to carry out authentication between a sender A and a receiver B using public-key cryptography, A will encrypt some known message using Aโs private key, so that it can be correctly decrypted by the receiver B using Aโs public key and confirm the source. Hence, the correct option is (d).

**5) One weakness of Diffie-Hellman key exchange protocol is**

a. It can be easily broken using brute force attack.

b. It is susceptible to man-in-the-middle attack.

c. The key size is small.

d. None of these.

**Answer:** b

**Solution: **Diffie-Hellman key exchange protocol is vulnerable to the man-in-the-middle attack. Hence, the correct option is (b).