CBP Bitcoin Mining and Consensus 2 — Questions and Answers
Question 1: What is the primary purpose of the nonce field in a Bitcoin block header?
- To identify the miner who found the block
- To store transaction fee totals
- To provide a value miners iterate over to find a valid hash (Correct answer)
- To encode the block's timestamp
Correct answer: To provide a value miners iterate over to find a valid hash
Miners increment the nonce repeatedly until the block header hash meets the difficulty target.
Question 2: What happens to the Bitcoin block subsidy approximately every 210,000 blocks?
- It doubles
- It is cut in half (Correct answer)
- It resets to the genesis amount
- It is eliminated entirely
Correct answer: It is cut in half
The halving event cuts the block subsidy in half roughly every four years, reducing new coin issuance.
Question 3: Which consensus rule determines which chain Bitcoin nodes consider valid when two chains of equal length exist?
- The chain with the most transactions
- The chain with the lowest difficulty
- The chain with the most accumulated proof-of-work (Correct answer)
- The chain created by the oldest node
Correct answer: The chain with the most accumulated proof-of-work
Bitcoin nodes follow the chain with the greatest cumulative proof-of-work, often called the 'heaviest' chain.
Question 4: What is an 'orphan block' in Bitcoin mining?
- A block with no transactions
- A valid block that is not part of the main chain because another block won the race (Correct answer)
- A block whose miner is unknown
- A block containing invalid transactions
Correct answer: A valid block that is not part of the main chain because another block won the race
Orphan blocks are valid blocks that were not selected as part of the longest chain when two miners solved a block simultaneously.
Question 5: What is the significance of the 'extraNonce' field used by miners?
- It stores the miner's wallet address
- It extends the nonce search space within the coinbase transaction (Correct answer)
- It records the pool's fee percentage
- It encodes the software version used
Correct answer: It extends the nonce search space within the coinbase transaction
Since the 32-bit nonce space exhausts quickly, miners use the extraNonce in the coinbase to expand their search space.
Question 6: Which of the following best describes 'selfish mining'?
- Mining without joining a pool
- Withholding discovered blocks to gain a competitive advantage over honest miners (Correct answer)
- Charging extra fees for transaction inclusion
- Using more energy than average per hash
Correct answer: Withholding discovered blocks to gain a competitive advantage over honest miners
Selfish mining is a strategy where a pool withholds valid blocks to waste honest miners' effort and earn a disproportionate share of rewards.
Question 7: What is the target block interval Bitcoin's difficulty adjustment aims to maintain?
- 1 minute
- 5 minutes
- 10 minutes (Correct answer)
- 30 minutes
Correct answer: 10 minutes
Bitcoin's protocol is designed to produce a new block approximately every 10 minutes on average.
CBP Bitcoin Mining and Consensus 2
What is the primary purpose of the nonce field in a Bitcoin block header?