Lattice-Based and Post-Quantum Cryptography ECES Practice Questions (Page 8)

Questions 36–40

1. 36expert · hard

   A multinational corporation is migrating its VPN infrastructure to post-quantum cryptography. The VPN is used for remote access by employees in countries with strict data-residency laws. The company currently uses IKEv2 with ECDSA certificates and ECDH key exchange. They want to ensure that the migration does not violate data-residency requirements and that the VPN remains interoperable with legacy clients. Which approach best satisfies these constraints?

   • AUse only classical algorithms with larger key sizes to avoid the complexity of post-quantum migration.
   • BMigrate to a cloud-based VPN service that handles post-quantum cryptography, but ensure the service provider stores data in the required country.
   • CDeploy a hybrid key exchange using ECDH and Kyber, and use Dilithium for certificate signatures, while keeping ECDSA as a fallback for legacy clients.
   • DReplace all cryptographic algorithms with post-quantum ones immediately, and require all clients to upgrade to the latest version.
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2. 37expert · hard · select all that apply

   A cryptography engineer is designing a new post-quantum cryptographic library. The engineer wants to ensure that the library's security is based on problems that are believed to be hard for both classical and quantum computers. Which of the following problems should the engineer consider as the foundation for the library? (Select all that apply.)

   • ADiscrete logarithm problem
   • BLearning With Errors (LWE) problem
   • CClosest Vector Problem (CVP) in lattices
   • DShortest Vector Problem (SVP) in lattices
   • EInteger factorization
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4. 38application · medium

   A government contractor must replace its current public-key encryption and digital signature algorithms with NIST-standardized post-quantum algorithms. The contractor needs a KEM for encrypting data and a signature scheme with the smallest possible signature size for constrained network bandwidth. Which pair of NIST-selected algorithms should the contractor choose?

   • AKyber for KEM and Falcon for signatures
   • BDilithium for KEM and SPHINCS+ for signatures
   • CMcEliece for KEM and Kyber for signatures
   • DFalcon for KEM and Dilithium for signatures
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5. 39foundation · easy

   What is a notable characteristic of the SPHINCS+ signature scheme?

   • AIt is based on elliptic curve isogenies
   • BIt requires a trusted third party to generate keys
   • CIt has very small signatures compared to other post-quantum schemes
   • DIt is stateless, meaning it does not require tracking previous signatures
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6. 40application · medium

   A financial institution is migrating to post-quantum cryptography but wants to maintain interoperability with legacy systems that only support RSA and ECC. The institution also wants to protect current communications against future quantum attacks. Which strategy best meets both requirements?

   • AImmediately replace all classical algorithms with Kyber and Dilithium
   • BDeploy hybrid schemes that combine classical and post-quantum algorithms
   • CUse only hash-based signatures for all communications
   • DContinue using RSA and ECC until quantum computers are commercially available
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