CY-802-C Lightweight Cryptography - May 2024 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

   • Definition of mode of operation for block ciphers
   • Purpose: handling multi-block messages, confidentiality/integrity
   • Example mode e.g. CTR/CBC/ECB suitable for lightweight ciphers
   • Brief working and why suitable for constrained devices
2. 7 Marks
   bDescribe design strategies for lightweight block ciphers. How do these differ from the design of traditional block ciphers like AES?
   How to answer

   • Goals of lightweight design: low area, power, memory
   • Strategies: small block/key, simple S-box, lightweight key schedule
   • Comparison with AES in rounds, S-box size, diffusion
   • Trade-off security vs efficiency
3. 7 Marks
   aBriefly describe the design philosophies behind two of the listed lightweight block ciphers (DESL/DESXL or PRESENT/CLEFIA).
   How to answer

   • Select two ciphers from DESL/DESXL or PRESENT/CLEFIA
   • Design philosophy: minimize hardware, reuse DES, SPN/Feistel
   • Key/block sizes and round structure
   • Target use-case in RFID/IoT
4. 7 Marks
   bThe security of a cryptographic algorithm relies heavily on its public scrutiny. Discuss the importance of open design and cryptanalysis in ensuring the long-term viability of lightweight block ciphers.
   How to answer

   • Kerckhoffs principle and need for public scrutiny
   • Role of cryptanalysis in finding weaknesses
   • Trust and long-term viability for standards
   • Examples of attacks improving lightweight designs
5. 7 Marks
   aExplain the concept of key management in cryptography. Describe a specific challenge associated with key management for resource-constrained devices.
   How to answer

   • Definition of key management: generation, distribution, storage, revocation
   • Lifecycle overview
   • Challenge for constrained devices: memory, power, no secure storage
   • Impact on IoT deployments
6. 7 Marks
   bDescribe the purpose of a cryptographic hash function. Provide an example of a real-world application that utilizes lightweight hashing.
   How to answer

   • Properties of cryptographic hash: preimage, collision resistance
   • Purpose: integrity, authentication
   • Lightweight hashing example e.g. PHOTON, SPONGENT, QUARK
   • Real-world IoT/RFID application
7. 7 Marks
   aCompare and contrast centralized and distributed key management approaches for lightweight cryptography. Discuss the security implications of each approach.
   How to answer

   • Definition of centralized vs distributed key management
   • Comparison on scalability, single point of failure, overhead
   • Security implications: compromise, trust, revocation
   • Suitability for lightweight/IoT networks
8. 7 Marks
   bHow can lightweight key management are integrated into protocols like IPSec or TLS for securing communication in resource-constrained environments?
   How to answer

   • Lightweight key management requirements for IPSec/TLS
   • Adaptations: DTLS, compressed headers, pre-shared keys
   • Integration steps for constrained environments
   • Trade-offs in handshake overhead and energy
9. 7 Marks
   aNew lightweight group key management protocols are constantly being proposed. What are the key considerations when evaluating the suitability of a new protocol for a specific IoT application?
   How to answer

   • Criteria: security level, cost, energy, scalability
   • IoT-specific: heterogeneity, dynamic membership, latency
   • Evaluation of forward/backward secrecy
   • Suitability analysis method
10. 7 Marks
    bDescribe how symmetric key management can be integrated into a lightweight group key management protocol for IoT devices.
    How to answer

    • Role of symmetric keys in group management
    • Distribution via group controller / LKH
    • Integration steps for IoT devices
    • Benefits: low computation and storage
11. 7 Marks
    aBriefly describe the function of a substitution box (S-Box) in a block cipher.
    How to answer

    • Definition of S-Box as non-linear substitution
    • Function: confusion, resist linear/differential cryptanalysis
    • Small 4-bit S-boxes in lightweight ciphers
12. 7 Marks
    bProvide two reasons why traditional cryptographic algorithms might not be suitable for resource-constrained devices.
    How to answer

    • High computation/memory requirements of traditional algorithms
    • High power/energy consumption unsuitable for battery devices
    • Large code size and latency issues
13. 7 Marks
    aWhy might traditional cryptographic algorithms be unsuitable for resource-constrained devices?
    How to answer

    • Resource demands: CPU, RAM, power, area
    • Mismatch with RFID/sensor capabilities
    • Need for lightweight alternatives
14. 7 Marks
    bStream ciphers can be vulnerable to specific attacks like the "birthday attack". How can the design of a stream cipher be optimized to resist such attacks while maintaining efficiency?
    How to answer

    • Birthday attack on keystream/IV reuse
    • Increase IV/state size, re-keying
    • Design trade-off to maintain throughput and low area
15. 14 Marks
    Attempt any three:

    1. i)What is the key difference between symmetric and asymmetric cryptography?
    2. ii)How might security threats for tiny devices differ from those for traditional computers?
    3. iii)What does an "operation" mean in the context of a computer?
    4. iv)In simple terms, why might standard encryption methods not be suitable for small devices (e.g., phones, sensors)?
    How to answer

    • Symmetric vs asymmetric key use
    • Threat differences: physical access, scale, power
    • Meaning of operation and encryption suitability for small devices