Lattice-Based and Post-Quantum Cryptography ECES Practice Questions (Page 3)

Questions 11–15

1. 11foundation · easy

   Why are lattice problems like SVP and CVP considered hard for quantum computers?

   • AQuantum computers are too slow to process high-dimensional lattices
   • BNo known quantum algorithm can solve them efficiently
   • CLattice problems are NP-hard and therefore impossible for any computer
   • DQuantum computers cannot run algorithms on lattices
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2. 12foundation · easy

   What is a hybrid scheme in the context of post-quantum migration?

   • AA scheme that uses quantum key distribution
   • BA scheme that uses only post-quantum algorithms
   • CA scheme that combines a classical algorithm with a post-quantum algorithm
   • DA scheme that uses only classical algorithms
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4. 13application · medium

   A developer is implementing a lattice-based KEM (Key Encapsulation Mechanism) using the CRYSTALS-Kyber algorithm. During the encapsulation process, the algorithm generates a random message m, hashes it to derive a key, and then uses the public key to encapsulate the key. Which step is crucial to prevent decryption failures and ensure correctness?

   • AAdding a large error vector e during encapsulation to increase security.
   • BEnsuring that the secret vector s has a large norm to make it harder to guess.
   • CUsing a hash function to derive the key from the message, which is essential for security but not for correctness.
   • DUsing a large enough modulus q to ensure that the error term does not cause decryption to fail.
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5. 14application · medium

   A security architect is evaluating code-based cryptography for a secure email system. They are considering the Niederreiter cryptosystem, which is a variant of McEliece. Which statement correctly describes a key difference between Niederreiter and McEliece?

   • ANiederreiter has smaller public keys than McEliece, making it more practical for real-world use.
   • BNiederreiter is faster than McEliece because it uses simpler error-correcting codes.
   • CNiederreiter uses a parity-check matrix instead of a generator matrix, and it is typically used for encryption and signatures.
   • DNiederreiter is based on the difficulty of decoding general linear codes, while McEliece is based on the difficulty of factoring.
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6. 15application · medium

   A large financial institution is planning to migrate its TLS infrastructure to post-quantum cryptography. They want to ensure that if a post-quantum algorithm is later found to be flawed, the security of their communications is not compromised. Which migration strategy best achieves this goal?

   • AUse only classical algorithms with larger key sizes, such as RSA-4096 and ECDH-521, to provide quantum resistance.
   • BSwitch entirely to Kyber for key exchange and Dilithium for signatures, removing all classical algorithms to simplify the stack.
   • CImplement a custom post-quantum algorithm that is not yet standardized to stay ahead of the curve.
   • DUse a hybrid key exchange that combines a classical algorithm (e.g., ECDH) with a post-quantum algorithm (e.g., Kyber) and derive the session key from both.
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