CY-503 Network Security - Dec 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
   aExplain in detail cipher block modes of operation with merits and demerits.
   How to answer

   • Define block cipher modes: ECB, CBC, CFB, OFB, CTR
   • Explain working of each with encryption/decryption flow
   • Merits and demerits: error propagation, parallelism, IV requirement
   • Applications and comparison summary
2. 7 Marks
   bSummarize the public key cryptographic principles. Explain RSA algorithm for given example, where $p=3$, and $q=11$.
   How to answer

   • Summarize public-key principles: key pair, trapdoor function, confidentiality/authentication
   • Describe RSA key generation, encryption, decryption steps
   • Compute n, phi(n), e, d for p=3, q=11 with example
   • Show encryption/decryption example numerically
3. 7 Marks
   aExplain how public-key cryptography can be used for digital signatures. Why are digital signatures considered a crucial aspect of secure communication?
   How to answer

   • Explain signing with private key and verification with public key
   • Steps: hash, sign, transmit, verify
   • Properties: authentication, integrity, non-repudiation
   • Importance for secure communication
4. 7 Marks
   bExplain with a neat diagram how PGP provides authentication and confidentiality for email security?
   How to answer

   • Define PGP and its services
   • Explain authentication flow: hash, sign, compress
   • Explain confidentiality flow: session key, public-key encryption
   • Provide neat diagram combining both services
5. 7 Marks
   aDescribe the steps to find the message digest using SHA-512 algorithm. What is the order of finding the messages which have the same message digest?
   How to answer

   • Outline SHA-512 preprocessing, padding, 80-word schedule
   • Describe compression function with 8 working variables and 80 rounds
   • Output 512-bit digest steps
   • Discuss collision resistance and birthday attack order $2^{256}$
6. 7 Marks
   bDiscuss RC4 encryption algorithm. Considering a 5-bit RC4 key, generate the first 3 bytes of any pseudo-random key stream.
   How to answer

   • Explain RC4 KSA and PRGA structure
   • Show initialization with 5-bit key example
   • Generate first 3 bytes of keystream step-by-step
   • Note security issues of RC4
7. 7 Marks
   aWrite about Host based Intrusion detection systems.
   How to answer

   • Define HIDS and its placement on host
   • Components: agents, log analysis, file integrity checking
   • Detection methods: signature and anomaly based
   • Advantages and limitations
8. 7 Marks
   bMalicious software (malware) can infiltrate a network in various ways. Describe different types of malicious software and explain how IDS and firewalls can help safeguard against them.
   How to answer

   • List malware types: virus, worm, trojan, ransomware, spyware, rootkit
   • Explain infiltration vectors
   • Role of IDS in detection and alerting
   • Role of firewalls in prevention and filtering
9. 7 Marks
   aExplain in detail about Secure Electronic Transaction with suitable example.
   How to answer

   • Define SET and its participants: cardholder, merchant, acquirer
   • Explain dual signature and transaction phases
   • Give suitable purchase example
   • Security services achieved
10. 7 Marks
    bDefine SSL. What are the different services provided by SSL Record Protocol?
    How to answer

    • Define SSL and its position in TCP/IP
    • Describe SSL Record Protocol operation
    • List services: confidentiality, message integrity, authentication
    • Explain fragmentation, compression, MAC, encryption steps
11. 7 Marks
    aDescribe the main security concerns associated with online financial transactions and how the Secure Electronic Transaction (SET) protocol addresses them.
    How to answer

    • List concerns: confidentiality, authentication, integrity, non-repudiation, fraud
    • Explain SET features: certificates, dual signature, encryption
    • Map each concern to SET mechanism
    • Conclude effectiveness
12. 7 Marks
    bDiscuss the security challenges associated with Wireless LANS.
    How to answer

    • List WLAN threats: eavesdropping, rogue AP, MITM, DoS
    • Explain weak authentication and encryption issues
    • Discuss WEP/WPA vulnerabilities
    • Countermeasures overview
13. 7 Marks
    aExplain with an example how encryption and decryption is performed in AES?
    How to answer

    • Outline AES structure: State, rounds, key sizes
    • Explain SubBytes, ShiftRows, MixColumns, AddRoundKey
    • Show encryption example steps
    • Explain inverse operations for decryption
14. 7 Marks
    bExplain WAP security mechanisms, specifically focusing on WTLS. How does it help to secure wireless communications?
    How to answer

    • Define WAP architecture and need for WTLS
    • Explain WTLS services: privacy, integrity, authentication
    • Describe handshake, record layer
    • How it secures wireless communication
15. 14 Marks
    Write short notes on any two of the following :

    1. a)Cipher block modes of operation
    2. b)Trusted Operating system
    3. c)Circuit-level gateway firewalls and application-level gateway firewalls
    4. d)Security considerations and threats
    How to answer

    • Select any two topics from (a)-(d)
    • Give definition, key features and working
    • Add advantages/limitations or example
    • Conclude with applications in network security