Blockchain Technology Flashcards

An investigator notes that a Bitcoin block header contains a Merkle root. What does this value allow?

Answer: It summarizes every transaction in the block so any altered transaction changes the root

The Merkle root is a hash of all transaction hashes, so changing any single transaction changes the root and breaks the header hash.

How often does the Bitcoin network recalculate its mining difficulty?

Answer: Every 2,016 blocks

Bitcoin adjusts difficulty every 2,016 blocks (about two weeks) to keep the average block time near 10 minutes.

Which blockchain tracks balances using an account-based model rather than Bitcoin's UTXO model?

Answer: Ethereum

Ethereum maintains a global state of account balances, while Bitcoin and its forks track unspent transaction outputs.

In a Bitcoin block, what is the coinbase transaction?

Answer: The first transaction, which creates new coins and collects fees for the miner

The coinbase transaction has no inputs from prior outputs and pays the block subsidy plus fees to the miner.

In proof-of-work mining, what is the role of the nonce?

Answer: It is the value miners vary to find a block hash below the target

Miners repeatedly change the nonce and rehash the header until the result meets the difficulty target.

An attacker gains more than 50% of a proof-of-work network's hash rate. What can they realistically do?

Answer: Reverse their own recent transactions to double-spend

Majority hash power lets an attacker rewrite recent blocks and double-spend their own coins, but not forge signatures for others' funds.

What is Bitcoin's target average block interval?

Answer: About 10 minutes

Bitcoin's difficulty adjustment aims for one block roughly every 10 minutes.