Proof of Work (PoW) and Its Variations BDC Practice Questions (Page 1)

Questions 1–5

1. 1expert · hard

   A blockchain startup is considering switching from PoW to PoS to reduce energy costs. The CTO is concerned about the 'nothing at stake' problem. What is the best way to mitigate this issue in a PoS system?

   • AImplement slashing conditions that penalize validators who validate conflicting blocks.
   • BRequire validators to lock up tokens for a longer period.
   • CUse a hybrid PoW/PoS mechanism to retain the security of PoW.
   • DIncrease the block reward to incentivize honest behavior.
   Reveal Solution Discussion Select an answer first
2. 2expert · hard

   A company is choosing between PoW and PoA for a private blockchain. They need to ensure that transactions are irreversible and that the network is resistant to takeover by a malicious actor. Which consensus mechanism is more appropriate?

   • APoA, because it provides deterministic finality and is more energy-efficient.
   • BPoW, because it provides stronger security against a malicious actor who might gain control of the validator set.
   • CBoth PoW and PoA provide the same level of security against malicious actors.
   • DPoA, because it is permissionless and allows anyone to become a validator.
   Reveal Solution Discussion Select an answer first
4. 3expert · hard

   A developer is optimizing a PoW miner for a new algorithm. The miner currently tries nonces sequentially. The developer wants to increase the chance of finding a valid block. What is the most effective strategy?

   • AReduce the difficulty target to make the puzzle easier.
   • BUse a different hash function that is faster on the CPU.
   • CIncrease the block timestamp to a future value to change the hash.
   • DUse multiple threads to try different nonce ranges in parallel.
   Reveal Solution Discussion Select an answer first
5. 4application · medium

   A security auditor is assessing a PoW blockchain's resistance to double-spending. The auditor notes that an attacker has acquired 40% of the network's total hash rate. What is the most significant limitation the attacker faces in attempting a double-spend?

   • AThe attacker cannot reliably outpace the honest chain because they lack majority hash power.
   • BThe attacker would need to wait for the difficulty adjustment to lower the target.
   • CThe attacker would be immediately detected by the network's monitoring tools.
   • DThe attacker would need to also control 40% of the network's nodes.
   Reveal Solution Discussion Select an answer first
6. 5expert · hard

   A security consultant is evaluating the security of a small PoW cryptocurrency. The network's total hash rate is relatively low, and an attacker has acquired a significant amount of hash power. Which attack is the most immediate threat?

   • AA 51% attack, where the attacker can mine blocks faster than the honest network and reverse transactions.
   • BA Sybil attack, where the attacker creates many fake nodes to outvote honest nodes.
   • CA replay attack, where the attacker resends old transactions to double-spend.
   • DA timejacking attack, where the attacker manipulates timestamps to create a longer chain.
   Reveal Solution Discussion Select an answer first