CBP Bitcoin Mining and Consensus Mechanisms 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 fees collected
- To allow miners to iterate through values seeking a valid hash (Correct answer)
- To record the timestamp of the block
Correct answer: To allow miners to iterate through values seeking a valid hash
The nonce is a 32-bit integer that miners increment repeatedly to find a block hash that meets the current difficulty target.
Question 2: What happens to the Bitcoin block subsidy approximately every 210,000 blocks?
- It doubles
- It halves (Correct answer)
- It resets to 50 BTC
- It is eliminated entirely
Correct answer: It halves
The block subsidy halves every 210,000 blocks (roughly every 4 years), reducing new bitcoin issuance over time.
Question 3: Which consensus rule ensures Bitcoin nodes reject blocks with timestamps too far in the future?
- The two-hour rule (Correct answer)
- The difficulty adjustment rule
- The longest chain rule
- The coinbase maturity rule
Correct answer: The two-hour rule
Bitcoin nodes reject blocks whose timestamp is more than two hours ahead of the node's local time.
Question 4: In Bitcoin mining, what is 'pool luck'?
- The ratio of actual shares submitted to expected shares for a given payout
- The total hashrate a mining pool controls
- The variance in block times experienced by a pool (Correct answer)
- The fee percentage retained by the pool operator
Correct answer: The variance in block times experienced by a pool
Pool luck describes the variance in block-finding intervals relative to the statistical expectation, which averages out over time.
Question 5: What distinguishes an ASIC miner from a GPU miner in the context of Bitcoin?
- ASICs can mine any cryptocurrency while GPUs are Bitcoin-specific
- ASICs are designed solely for SHA-256 hashing and are far more efficient than GPUs (Correct answer)
- GPUs are more energy-efficient than ASICs for Bitcoin mining
- ASICs use proof-of-stake while GPUs use proof-of-work
Correct answer: ASICs are designed solely for SHA-256 hashing and are far more efficient than GPUs
ASICs (Application-Specific Integrated Circuits) are purpose-built for SHA-256 and achieve orders-of-magnitude better efficiency than GPUs.
Question 6: What is the 'extranonce' in Bitcoin mining?
- An extra nonce field in the coinbase transaction used to expand the search space (Correct answer)
- A secondary proof-of-work required for merged mining
- A nonce stored in the block's output scripts
- An optional header field introduced in SegWit
Correct answer: An extra nonce field in the coinbase transaction used to expand the search space
Because the 32-bit nonce field is exhausted quickly by modern ASICs, miners also modify bytes in the coinbase transaction (extranonce) to extend the search space.
Question 7: Which of the following best describes a 'selfish mining' attack?
- A miner refuses to relay transactions to neighboring peers
- A miner withholds found blocks to gain a disproportionate share of rewards (Correct answer)
- A miner submits invalid blocks to disrupt the network
- A miner colludes with exchanges to manipulate the bitcoin price
Correct answer: A miner withholds found blocks to gain a disproportionate share of rewards
In selfish mining, a pool secretly mines on its private chain and strategically releases blocks to waste competing miners' work, gaining more than its fair share of rewards.
CBP Bitcoin Mining and Consensus Mechanisms 2
What is the primary purpose of the nonce field in a Bitcoin block header?