Question Bank on Cryptography & Network Security

Frequently Asked Questions (FAQ) on CNS

UNIT-I

Topics Covered:

• History and overview of Cryptography

• Classical Encryption Technique

• Symmetric Cipher Model

• Substitution Techniques

• Transposition Techniques

• Rotor Machines and

• Stegnography

Descriptive Questions (2 Marks):

1. Define Cryptography.
2. What are the two basic functions used in encryption algorithms?
3. What is steganography? How does it differ from cryptography?
4. What is masquerade?  Which principle of security is breached because of that?
5. What are replay attacks?  Give an example of a replay attack.
6. Write the differences between symmetric and asymmetric ciphers.
7. What is the main difference between a stream cipher and a block cipher?
8. Differentiate between substitution and transposition techniques in classical cryptography.

Descriptive Questions (5 Marks):

1. Explain the importance of cryptography in the evolution of secure communication with suitable historical examples.
2. Discuss any one of the passive attacks in detail.
3. Discuss any two substitution techniques and list their merits and demerits.
4. Explain the working principle of the Caesar cipher. Encrypt the text "NETWORK" using a key value of 3.
5. Briefly define the monoalphabetic cipher.  What is the difference between a mono alphabetic cipher and a poly alphabetic cipher?
6. Explain the Play Fair cipher algorithm? Encrypt the message ‘MY BALLOON’ using the key ‘MONACHRY’
7. Explain about Hill Cipher. Consider the plaintext "paymoremoney" and use the encryption key: K=.  Find the cipher text.
8. Convert “MEET ME” using Hill cipher with the key matrix .  Convert the cipher text back to plaintext.
9. Explain the following ciphers: (a) Playfair cipher and (b) Vernam cipher
10. Describe the working of a columnar transposition cipher by encrypting the message “CRYPTOGRAPHY IS FUN” using the keyword “NETWORK.” Show column arrangement, transposition steps, and final ciphertext.
11. Explain the basic principle of rotor machine.
12. Explain the work of a rotor machine with a simple example. Show how a single plaintext letter is transformed through multiple rotors into ciphertext.

UNIT-II

Topics Covered:

• Stream ciphers and Block ciphers

• Attacks on Block ciphers

• Block cipher principles

• The Data Encryption Standard (DES)

• Block cipher design principles

• Group, Ring, and Field

• Polynomial arithmetic

• The Euclidean algorithm

• Finite fields of the form GF(2n)

Descriptive Questions (2 Marks):

1. Define stream ciphers.
2. Define Block ciphers
3. Briefly explain the design principles of block cipher.
4. List the attacks that can happen on block ciphers.
5. Define group and ring.
6. What is the use of Euclidean Algorithm in cryptography?

Descriptive Questions (5 Marks):

1. How is GCD calculated with Euclid’s algorithm? Calculate the GCD of (270, 192).
2. Compare and contrast stream ciphers and block ciphers.
3. What are the design parameters of Feistel cipher network?
4. Explain the DES algorithm with neat sketch.
5. Explain the key expansion round key generation logic used in DES. How do round keys enhance security?
6. Write the difference between ECB and CBC with neat diagram
7. Describe common attacks on block ciphers like brute-force, differential, linear cryptanalysis. Explain how block cipher design principles help resist these attacks.
8. Explain step-by-step multiplication of two polynomials and over GF(2). Show all intermediate steps.

UNIT-III

Topics Covered:

• Advance Encryption Standard (AES)

• Stream ciphers

• RC4

• The Chinese Remainder theorem

• Public Key Cryptography

• RSA Algorithm

• Diffie-Hellman Key Exchange

• Elliptic Curve Cryptography (ECC)

Descriptive Questions (2 Marks):

1. What is the block size used in the Advanced Encryption Standard (AES)?
2. What is Substitute Byte transformation in AES?
3. Write the difference between public key and private key.
4. State one application of the Chinese Remainder Theorem (CRT) in cryptography.

Descriptive Questions (5 Marks):

1. Explain in detail about AES algorithm.
2. Which four tasks are performed in each round of AES Cipher? Explain.
3. Explain the structure and working of the Advanced Encryption Standard (AES). Include key sizes, block size, and the role of Sub-Bytes, Shift-Rows, Mix-Columns, and Add-Round-Key operations.
4. Explain RSA algorithm in detail with an example.
5. Given p=19, q=23, and e=3 Use RSA algorithm to find n, (n) and d.
6. Explain about Chinese Remainder theorem.
7. How do you use Chinese Remainder Theorem to reconstruct integers from their residues modulo functions.
8. Explain the Chinese Remainder Theorem (CRT) with a numerical example. Solve for x in the system: x ≡ 1 (mod 3), x ≡ 2 (mod 4), x ≡ 3 (mod 5).
9. Briefly explain Diffie Hellman key exchange with an example.
10. How man in middle attack can be performed in Diffie Hellman algorithm.

UNIT-IV

Topics Covered:

• Cryptographic hash functions

• Applications of cryptographic hash functions

• Two simple hash functions

• Requirements and security

• Secure Hash Algorithm (SHA)

• SHA-3

Descriptive Questions (2 Marks):

1. Define hash function.
2. Name any two applications of Cryptographic Hash functions.
3. What are the requirements of Hash functions?
4. State any two basic requirements of a secure hash function.
5. What is the output size of SHA-3 compared to SHA-2?

Descriptive Questions (5 Marks):

1. What are the requirements of hash functions? Explain.
2. Explain in detail Hash Functions.
3. Explain the basic working of a simple hash function like modular addition hash. Give suitable example.
4. Explain the applications of cryptographic hash functions.
5. Explain the Secure Hash Algorithm (SHA) with neat sketch.
6. Describe SHA-1 algorithm in detail.
7. Compare SHA-2 and SHA-3 in terms of structure, security, and performance. Why was SHA-3 introduced despite SHA-2 being secure?
8. Explain the SHA-512 algorithm in detail using its block diagram. Discuss the steps involved in message padding, message scheduling, and compression.
9. Describe MD5 algorithm in detail.
10. Derive a birthday attack on a simplified hash function H(x) = (sum of letters mod 10) using two different messages.

UNIT-V

Topics Covered:

• Introduction to Block Chain

• Bitcoin basics

• Smart contracts

• Block chain development platforms and APIs

• Block chain ecosystem

• Ethereum

• Distributed consensus

• Block chain applications

Descriptive Questions (2 Marks):

1. What are the challenges of creating a sustainable ecosystem?
2. What is blockchain? Define it.
3. Define Smart Contract.
4. What is a smart contract in blockchain?
5. What is the importance of Consensus in Block Chain technology?

Descriptive Questions (5 Marks):

1. How does decentralisation in block chain provide advantages over traditional centralised systems. Explain.
2. What are the various Blockchain development Platforms available for creating and managing block chains? 
3. Deep describe and compare the blockchain development platforms "Ethereum, Hyperledger and Corda".
4. Describe the Bitcoin protocol in detail.
5. Discuss the key features of Bitcoin. Explain how transactions are validated and how miners earn rewards.
6. Explain about Ethereum in detail with an example.
7. Explain the importance of smart contract in Block Chain technology.
8. Explain what smart contracts are and how they operate on a block chain network.
9. Consider supply chain management and explain the role of Blockchain technology in managing the supply chain process.
10. Analyze the advantages and limitations of blockchain applications in finance, and healthcare sectors.
11. Explain the concept of distributed consensus in blockchain. Compare proof-of-work (PoW) and proof-of-stake (PoS) mechanisms with examples.
12. Compare and contrast Proof-of-Work (PoW), Proof-of-Stake (PoS), and Delegated Proof-of-Stake (DPoS).