CY-603-B Applied Cryptography - Jun 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat are the goals of network security? Discuss.
   How to answer

   • Define network security and CIA triad
   • Confidentiality, Integrity, Availability goals
   • Additional goals: authentication, non-repudiation, access control
   • Discussion of threats and need for security services
2. 7 Marks
   bEnumerate the difference between passive attacks and active attacks? Give examples for each.
   How to answer

   • Define passive attacks: eavesdropping, traffic analysis
   • Define active attacks: masquerade, replay, modification, DoS
   • Comparison table on nature, detection, prevention
   • Examples for each category
3. 7 Marks
   aList and briefly define categories of Security Services and attacks.
   How to answer

   • List X.800 security services: authentication, access control, confidentiality, integrity, non-repudiation
   • Brief definition of each service
   • Categories of security attacks: passive and active
   • Mapping of services to attacks
4. 7 Marks
   bHow would you test a piece of cipher text to determine quickly if it was likely the result of simple substation? Explain.
   How to answer

   • Frequency analysis and Index of Coincidence concept
   • Preserved single-letter frequencies in monoalphabetic substitution
   • Test steps: count, compare to English distribution
   • Decision rule for simple substitution vs polyalphabetic/transposition
5. 7 Marks
   aExplain about Traffic Confidentiality.
   How to answer

   • Definition of traffic confidentiality
   • Threat of traffic analysis even with encryption
   • Techniques: padding, dummy traffic, unlinkability
   • Role in network security and X.800
6. 7 Marks
   bCompare Secret Key, Private Key and Public Key.
   How to answer

   • Define secret/symmetric key, private key, public key
   • Comparison on key distribution, number of keys, usage
   • Asymmetric vs symmetric roles
   • Examples: DES/AES vs RSA
7. 7 Marks
   aCritically analyze the security of RSA.
   How to answer

   • Brief RSA basis: factoring problem
   • Mathematical, brute-force and timing attacks
   • Key size, padding (OAEP) and implementation issues
   • Conclusion on current security level
8. 7 Marks
   bList the main features of SHA-2 cryptographic hash function. What kind of compression function is used in SHA-2?
   How to answer

   • SHA-2 family: SHA-224/256/384/512, digest sizes
   • Features: Merkle-Damgard, collision/preimage resistance
   • Davies-Meyer compression using block cipher
   • Message schedule and round function overview
9. 7 Marks
   aExplain Message Authentication Requirements and what are the attacks related to message communication? Discuss.
   How to answer

   • Message authentication: integrity, authenticity, non-repudiation
   • Requirements: disclosure, traffic analysis, masquerade, content/sequence modification
   • Attacks: forgery, key recovery, collision
   • Use of MAC, hash, digital signatures
10. 7 Marks
    bExplain about RSA Algorithm.
    How to answer

    • Key generation: primes p,q, n, phi, e,d
    • Encryption $C=M^e \bmod n$ and decryption $M=C^d \bmod n$
    • Example with small primes
    • Security based on factoring and performance notes
11. 7 Marks
    aWhat are block cipher design principles? Explain.
    How to answer

    • Confusion and diffusion principles by Shannon
    • Feistel structure, S-box, P-box, rounds
    • Avalanche effect and key schedule requirements
    • Design for security vs efficiency
12. 7 Marks
    bExplain the operation of DES algorithm.
    How to answer

    • 64-bit block, 56-bit key, 16-round Feistel
    • Initial/final permutation, expansion, S-boxes, P-box
    • Key schedule generation of 16 subkeys
    • Decryption same structure and security notes
13. 7 Marks
    aDescribe the functionalities of Internet Key Exchange Protocol.
    How to answer

    • IKE purpose in IPsec: SA negotiation and key exchange
    • Phases 1 and 2, Oakley, SKEME, ISAKMP
    • Authentication, Diffie-Hellman, key derivation
    • IKEv1 vs IKEv2 functionalities
14. 7 Marks
    bHow to provide security during Inter-branch Payment Transactions? Discuss.
    How to answer

    • Threats in inter-branch transactions: interception, fraud
    • Encryption, authentication, secure channels (VPN/TLS)
    • Access control, audit logs, transaction integrity/MAC
    • PKI and key management for banks
15. 14 Marks
    Write a short note on any three of the following:

    1. a)Merkle-Hellman
    2. b)Asymmetric encryption
    3. c)Computational efficiency vs hardness
    4. d)GCM mode
    How to answer

    • Select any three topics with definition and working
    • Key properties, formulas or steps for each
    • Applications and security strengths/weaknesses
    • Concise comparison or diagram where relevant