Quantum Computing and Blockchain BDC Practice Questions (Page 7)

Questions 31–35

1. 31expert · hard

   A large enterprise blockchain network is planning a post-quantum migration. The network has thousands of nodes, and a hard fork is extremely difficult to coordinate. The team is considering a soft fork that introduces a new signature scheme while maintaining backward compatibility. Which approach is most viable?

   • AImmediately invalidate all old-format transactions and require all users to switch to the new signature scheme.
   • BUse a sidechain for post-quantum transactions and leave the main chain unchanged.
   • CIntroduce a new transaction type that uses a hybrid signature (classical + post-quantum) and have miners/validators accept both old and new transaction types during a transition period.
   • DKeep the old signature scheme but add a quantum-resistant hash to the transaction ID.
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2. 32foundation · easy

   What is the primary goal of post-quantum cryptography (PQC)?

   • ATo develop cryptographic algorithms that are secure against both classical and quantum computers.
   • BTo replace all classical cryptography with quantum key distribution.
   • CTo make quantum computers obsolete by improving classical algorithms.
   • DTo use quantum computers to encrypt data more securely than classical methods.
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4. 33application · medium

   A blockchain developer is designing a new cryptocurrency that must be resistant to quantum attacks. The design includes a mechanism to hide public keys until they are used in a transaction. Which additional measure is most important to ensure quantum resistance?

   • AUse a proof-of-work consensus to slow down quantum attacks.
   • BUse a longer hash output, such as SHA-512, for addresses.
   • CRequire users to rotate their keys after every transaction.
   • DUse a post-quantum signature scheme for all transactions.
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5. 34foundation · easy

   What is a potential future impact of quantum computing on blockchain technology?

   • AQuantum computers will eliminate the need for consensus mechanisms.
   • BQuantum computers will make blockchain networks obsolete because they can process all transactions instantly.
   • CQuantum computers will automatically make all blockchains more secure.
   • DQuantum computers could break current public-key cryptography, forcing blockchain networks to adopt quantum-resistant algorithms.
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6. 35expert · hard

   A blockchain network is considering using QKD to secure communication between nodes. However, the nodes are spread across a metropolitan area, and the maximum distance for QKD over fiber is limited. What is the most practical solution to extend QKD coverage?

   • AUse satellite-based QKD to cover the entire metropolitan area.
   • BUse trusted relay nodes that perform QKD with each neighbor and then forward encrypted data.
   • CUse a classical post-quantum KEM instead of QKD for the metropolitan network.
   • DIncrease the power of the laser to extend the QKD distance.
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