Quantum Computing and Blockchain BDC Practice Questions (Page 4)

Questions 16–20

1. 16application · medium

   A consortium blockchain is planning a migration to post-quantum cryptography. The network currently uses ECDSA for transaction signing and relies on a large existing user base. Which migration approach is most likely to succeed without forcing every user to change their wallet simultaneously?

   • AUse a longer ECDSA key and assume quantum computers will not be powerful enough for years.
   • BKeep ECDSA but add a quantum-resistant key encapsulation mechanism to the network layer.
   • CDeploy a hybrid signature scheme that combines ECDSA with a lattice-based signature, allowing gradual adoption.
   • DReplace ECDSA with a hash-based signature scheme in a single hard fork.
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2. 17expert · hard

   A blockchain researcher is analyzing the long-term security of a blockchain that uses SHA-256 for mining and ECDSA for signatures. They are concerned about both Grover's algorithm and Shor's algorithm. Which statement correctly describes the relative urgency of these threats?

   • ANeither algorithm is a threat because quantum computers will never be powerful enough.
   • BGrover's algorithm poses a more immediate threat because it can break SHA-256 completely.
   • CShor's algorithm poses a more immediate threat to ECDSA signatures, while Grover's algorithm only reduces the effective security of SHA-256 from 256 bits to 128 bits, which is still considered secure for now.
   • DBoth algorithms pose an equal threat, so the blockchain must be redesigned immediately.
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4. 18expert · hard

   A blockchain research consortium is evaluating the long-term impact of quantum computing on blockchain. They have identified that Shor's algorithm could break RSA and ECC, and Grover's algorithm could weaken symmetric encryption. They are considering a roadmap that includes both post-quantum cryptography and quantum-resistant consensus mechanisms. Which approach is most balanced?

   • AImmediately migrate to post-quantum signatures and increase hash output sizes to mitigate Grover's algorithm.
   • BAdopt a hybrid approach that uses both classical and post-quantum algorithms during a transition period.
   • CWait until quantum computers are available before making any changes.
   • DReplace all classical cryptography with quantum key distribution.
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5. 19foundation · easy

   What is a hybrid quantum-classical system in the context of blockchain?

   • AA blockchain that uses both proof-of-work and proof-of-stake consensus.
   • BA blockchain that uses quantum computers as miners and classical computers as validators.
   • CA system that runs on both Windows and Linux operating systems.
   • DA system that uses both classical and quantum computing resources to perform tasks that are difficult for either alone.
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6. 20application · medium

   A blockchain startup is designing a new digital-asset platform and wants to future-proof it against quantum attacks. The team is particularly worried about Shor's algorithm being used to recover private keys from public keys. Which design decision would most directly mitigate this specific risk?

   • AImplement a proof-of-work consensus algorithm with a higher difficulty target.
   • BIncrease the elliptic curve key size from 256 bits to 512 bits.
   • CUse a longer hash output, such as SHA-512, for all transaction hashes.
   • DSwitch to a hash-based signature scheme where the public key is only revealed at the moment of spending.
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