Quantum Computing and Blockchain BDC Practice Questions (Page 1)

Questions 1–5

1. 1application · medium

   A blockchain developer is evaluating post-quantum signature schemes for a new blockchain. The network has limited bandwidth and storage, and transactions must be verified quickly. Which scheme is most appropriate?

   • ASPHINCS+, because it has the smallest signatures of all post-quantum schemes.
   • BCRYSTALS-Dilithium, because it has small signatures and fast verification.
   • CRSA with 4096-bit keys, because it is widely supported.
   • DXMSS, because it is stateless and easy to implement.
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2. 2expert · hard

   A blockchain developer is implementing a post-quantum signature scheme for a new cryptocurrency. They need to ensure that the scheme is stateless, has small signatures, and is fast to verify. Which scheme should they choose?

   • AXMSS
   • BSPHINCS+
   • CCRYSTALS-Dilithium
   • DRSA with 4096-bit keys
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4. 3expert · hard

   A financial institution is implementing QKD to secure communication between two blockchain data centers. They have a QKD link that generates keys at a rate of 1 Mbps. The blockchain network requires a continuous stream of random keys for encrypting transactions. What is the most critical limitation they need to address?

   • AQKD cannot be used over long distances, so they need to use trusted relays.
   • BQKD is not secure against quantum computers, so they should use post-quantum KEMs instead.
   • CQKD requires a classical channel for authentication, which is a security bottleneck.
   • DQKD key generation rate may be insufficient for high-throughput blockchain traffic, so they should use QKD to periodically refresh a classical symmetric key.
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5. 4expert · hard · select all that apply

   A blockchain network is planning to integrate QKD for secure communication between nodes. The network spans multiple cities, and the team is concerned about the practical limitations of QKD. Which of the following are valid considerations? (Select all that apply.)

   • AQKD can be used over the public internet without any special hardware.
   • BTrusted relays can extend the range of QKD, but they introduce a security assumption.
   • CQKD provides information-theoretic security for key exchange, making it immune to quantum attacks.
   • DQKD can be used to replace all classical cryptographic algorithms in the blockchain.
   • EQKD requires a dedicated fiber-optic link between each pair of communicating nodes.
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6. 5expert · hard

   A security auditor is assessing a blockchain network that uses RSA for node authentication and ECDSA for transaction signing. They are evaluating the impact of a future quantum computer. Which statement is most accurate?

   • AECDSA is more vulnerable than RSA because it uses smaller keys.
   • BNeither RSA nor ECDSA is vulnerable because quantum computers are not powerful enough yet.
   • COnly RSA is vulnerable to Shor's algorithm; ECDSA is safe because it uses elliptic curves.
   • DBoth RSA and ECDSA are vulnerable to Shor's algorithm, but the immediate risk is to node authentication because RSA keys are often long-lived.
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