Proof of Work (PoW) and Its Variations BDC Practice Questions (Page 6)

Questions 26–30

1. 26expert · hard

   A security researcher is analyzing a PoW blockchain that has a very short block time (e.g., 1 second) and a difficulty adjustment that only occurs every 1,000 blocks. An attacker with 30% of the hash rate wants to double-spend. What is the most significant vulnerability in this design?

   • AThe attacker can use the short block time to flood the network with invalid blocks.
   • BThe short block time and infrequent difficulty adjustment allow the attacker to mine a large number of blocks quickly, increasing the chance of a successful reorganization.
   • CThe attacker can manipulate the difficulty adjustment to lower the target.
   • DThe attacker can simply create more nodes to gain a majority vote.
   Reveal Solution Discussion Select an answer first
2. 27expert · hard

   A miner is trying to find a valid block. They have exhausted all 4 billion nonce values without finding a hash below the target. What is the most efficient next step?

   • AReuse the same nonce values but change the order in which they are tried.
   • BChange the block's timestamp to a new value and restart the nonce search.
   • CIncrease the difficulty target in the block header to make it easier to find a valid hash.
   • DWait for the network to lower the difficulty, since the current difficulty is too high.
   Reveal Solution Discussion Select an answer first
4. 28foundation · easy

   What is the main security property that prevents double-spending in a Proof of Work blockchain?

   • AThe encryption of the blockchain, which makes it impossible to modify past blocks.
   • BThe requirement that all transactions be approved by a central authority.
   • CThe use of digital signatures on every transaction, which prevents the same coin from being spent twice.
   • DThe immutability of the hash chain, which makes it computationally infeasible to alter a confirmed block without redoing the work for that block and all subsequent blocks.
   Reveal Solution Discussion Select an answer first
5. 29foundation · easy

   What is the primary purpose of the Proof of Work mechanism in a blockchain network?

   • ATo encrypt the transaction data stored in each block
   • BTo provide a backup copy of the blockchain on every node
   • CTo verify the digital signatures of all transactions in a block
   • DTo make it computationally expensive to propose a new block, thereby deterring malicious actors
   Reveal Solution Discussion Select an answer first
6. 30foundation · easy

   What is the primary environmental concern associated with Proof of Work blockchains like Bitcoin?

   • AThe generation of electronic waste from obsolete mining equipment.
   • BThe use of rare earth metals in mining hardware.
   • CThe emission of greenhouse gases from the blockchain's data centers.
   • DThe large amount of electricity consumed by mining hardware.
   Reveal Solution Discussion Select an answer first