## NPTEL Ethical Hacking Assignment 6 Answers (Week 6)

**Q1. Which of the following statement is true for Masquerade attack?**

**Answer:** d. In this attack, the attacker pretends as a legitimate entity.

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**Q2. Which of the following statement(s) is/are true?**

**Answer:** b. In private key encryption, a single key is used by sender and receiver.

c. In public key encryption, separate keys are used by sender and receiver.

**Q3. Consider the following statement:(i) In symmetric key cryptography, the security depends on secrecy of the key.(ii) In symmetric key cryptography, the security depends on encryption/decryption algorithm.**

**Answer:** a. Only (i) is true

**Q4.** **25 parties want to exchange messages securely. The number of distinct key required by a symmetric key encryption algorithm and public key encryption technique like RSA will be _ and _ respectively.**

**Answer:** e. 300 and 50

**Q5. How will be the plaintext for the cipher text “LETTY CEIV” encrypted using a substitution cipher approach, where each letter is replaced by the k-th next letter. (Assumption: (i) the alphabets are wrapped around, i.e. Z is followed by A, (ii) each alphabets (A to Z) is assigned a number (1to 26), (iii) the value of secrete key k is 4).**

**Answer:** b. HAPPU YAER

**Q6. In data encryption standard (DES), longer plain text are processed in _ bit blocks.**

**Answer:** 64

**Q7. The effective key lengths used in AES encryption algorithms can be:**

**Answer:** b. 128 bit

c. 192 bit

d. 256 bit

**Q8. For decryption using public-key cryptography __ is used.**

**Answer:** b. Receiver’s private key]

**Q9. Which of the following statement(s) is/are true.**

a. The security of RSA algorithm is dependent on prime factorization problem.

b. RSA algorithm is vulnerable to man-in-the middle attack.

c. Diffie-Hellman approach can be used for encryption/decryption of message.

d. Symmetric encryption approaches are faster than asymmetric encryption.

e. None of these.

**Answer:** Option A & D.

**Q10. Which of the following techniques cannot be used for message authentication?**

**Answer:** d. SHA-O

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