Bitcoin Mining and Consensus Mechanisms Flashcards

What is the primary purpose of the nonce field in a Bitcoin block header?

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.

What happens to the Bitcoin block subsidy approximately every 210,000 blocks?

Answer: It halves

The block subsidy halves every 210,000 blocks (roughly every 4 years), reducing new bitcoin issuance over time.

Which consensus rule ensures Bitcoin nodes reject blocks with timestamps too far in the future?

Answer: The two-hour rule

Bitcoin nodes reject blocks whose timestamp is more than two hours ahead of the node's local time.

In Bitcoin mining, what is 'pool luck'?

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.

What distinguishes an ASIC miner from a GPU miner in the context of Bitcoin?

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.

What is the 'extranonce' in Bitcoin mining?

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.

Which of the following best describes a 'selfish mining' attack?

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.