CY-802-C Lightweight 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
   aExplain the concept of a mode of operation in cryptography. Provide an example of a specific mode used with lightweight block ciphers.
   How to answer

   • Define mode of operation as method to extend block cipher to arbitrary-length data
   • Explain purpose: confidentiality, integrity, handling repetition/IV/nonce
   • Describe one lightweight-suitable mode e.g. CTR, CBC, OCB, GCM with steps
   • Suitability for lightweight block ciphers with example
2. 7 Marks
   bAnalyze the trade-offs involved in reducing the key size of a cryptographic algorithm. How does it impact security and efficiency?
   How to answer

   • Define key size role in brute-force security level
   • Explain efficiency gains: area, power, memory, speed
   • Analyze security loss: brute force, time-memory trade-offs, long-term security
   • Conclude balanced choice for constrained devices
3. 7 Marks
   aBriefly describe the unique features of one of the less common ciphers listed (PRINCE, MIDORI, RECTANGLE or GRANULE).
   How to answer

   • Select one cipher from PRINCE, MIDORI, RECTANGLE or GRANULE
   • Describe block/key size, structure and rounds
   • Highlight unique feature: low latency, low energy, bit-slice, etc.
   • Mention target IoT use case
4. 7 Marks
   bLightweight block ciphers often target specific resource constraints (e.g., area, power consumption). How can these design choices impact the resistance of the cipher against different cryptanalytic attacks?
   How to answer

   • Define area/power/energy constraints in lightweight design
   • Explain simplifications: small S-box, few rounds, simple key schedule
   • Link to vulnerabilities: differential, linear, side-channel attacks
   • Give mitigation vs cost trade-off
5. 7 Marks
   aCompare and contrast centralized and distributed key management approaches for lightweight cryptography. Discuss the security implications of each approach.
   How to answer

   • Define centralized vs distributed key management
   • Compare scalability, overhead, single point of failure
   • Discuss security implications: trust, compromise, revocation
   • Suitability for lightweight IoT networks
6. 7 Marks
   bLightweight MACs often utilize lightweight block ciphers or hash functions as building blocks. How do the security properties of the underlying primitive impact the security of the MAC?
   How to answer

   • Define lightweight MAC and its building blocks
   • Explain dependence on PRP/PRF, collision and forgery resistance
   • Show how weak primitive enables forgery or key recovery
   • Note lightweight trade-offs: short tags, reduced rounds
7. 7 Marks
   aExplain how asymmetric key management can be used in a group key management protocol for IoT devices.
   How to answer

   • Define group key management for IoT
   • Explain asymmetric use: public-key distribution, authentication, rekeying
   • Describe join/leave, forward/backward secrecy handling
   • Note lightweight adaptation need
8. 7 Marks
   bWhile asymmetric cryptography offers benefits, it can be computationally expensive for resource-constrained devices. Describe specific techniques used to make asymmetric key management more lightweight for IoT.
   How to answer

   • State cost problem of RSA/ECC on constrained nodes
   • List lightweight techniques: ECC with small keys, NTRU, implicit certs
   • Explain optimization: offline precomputation, hardware acceleration, session hybrid use
   • Mention standards: lightweight ECC, DTLS with raw public keys
9. 7 Marks
   aHow can lightweight key management are integrated into protocols like IPSec or TLS for securing communication in resource-constrained environments?
   How to answer

   • Outline IPSec/TLS handshake and key establishment
   • Explain lightweight integration: pre-shared keys, raw public keys, session resumption
   • Mention DTLS/TLS-PSK, IKEv2 lightweight profiles, 6LoWPAN
   • Discuss energy/latency benefits
10. 7 Marks
    bCyber Physical Systems (CPS) and IoT devices. How do the key management requirements differ between these domains, and how does this influence the choice of a lightweight key management approach?
    How to answer

    • Define CPS vs IoT characteristics and lifetimes
    • Contrast requirements: real-time, safety, heterogeneity, scale
    • Explain influence on key update, storage, authentication choice
    • Recommend lightweight approach per domain
11. 7 Marks
    aHow do the specific lightweight operations used in ciphers like SIMON and SPECK impact their performance compared to traditional block ciphers?
    How to answer

    • Describe SIMON Feistel with AND/rotation and SPECK ARX operations
    • Compare to AES-like S-box and MixColumns cost
    • Explain performance: small code, low power, hardware efficiency
    • Note security-rounds trade-off
12. 7 Marks
    bIdentify two block ciphers from the list (LED, SIMON and SPECK, or TWINE) that utilize lightweight versions of existing operations.
    How to answer

    • Pick two from LED, SIMON, SPECK, TWINE
    • Identify inherited operation: AES-like S-box, Feistel, ARX, generalized Feistel
    • Explain lightweight adaptation: smaller state, 4-bit S-box, simple diffusion
    • State benefit in area/power
13. 7 Marks
    aCompare and contrast the design principles of traditional hash functions (e.g., SHA-256) with lightweight hash functions. How do these differences impact performance and security?
    How to answer

    • Outline SHA-256 design: Davies-Meyer, 32-bit ops, large state
    • Contrast lightweight hash: sponge, small permutation e.g. PHOTON, SPONGENT
    • Compare performance: memory, throughput, energy
    • Compare security level and collision resistance
14. 7 Marks
    bIdentify two different application domains (e.g., wearable devices) that heavily rely on lightweight cryptography.
    How to answer

    • Define lightweight cryptography use constraint
    • Identify two domains: wearables, smart home, healthcare, automotive, etc.
    • Explain why constrained: battery, size, cost
    • Give example cipher/protocol per domain
15. 14 Marks
    Attempt any three.

    1. i)Briefly define the Internet of Things (IoT).
    2. ii)What is the concept of key management in cryptography?
    3. iii)What is the difference between cryptography and encryption?
    4. iv)What does "lightweight" mean in the context of cryptography?
    How to answer

    • Define IoT, key management, encryption vs cryptography, lightweight meaning
    • Give concise definition for any three chosen items
    • Add one example per item
    • Maintain distinction between terms