Blockchain and Consensus Mechanisms Flashcards

What is a 51% attack in a proof-of-work blockchain?

Answer: When a single entity controls more than half the network's mining hash rate

A 51% attack occurs when one miner or pool controls the majority of hash rate, allowing them to rewrite recent transaction history.

What is the purpose of a Merkle tree in a blockchain block?

Answer: To efficiently summarize and verify all transactions in a block

A Merkle tree hashes transaction pairs recursively into a single Merkle root, enabling efficient and tamper-evident verification of any transaction.

In Ethereum's proof-of-stake, what happens to a validator that behaves dishonestly?

Answer: Their staked ETH is partially or fully slashed

Slashing penalizes dishonest validators by destroying a portion of their staked ETH, making attacks financially costly.

Which consensus property ensures that all honest nodes eventually agree on the same chain?

Answer: Agreement

Agreement (also called consistency) guarantees that all honest nodes converge on the same blockchain state.

What distinguishes a hard fork from a soft fork?

Answer: Hard forks are backward-incompatible, splitting the chain if not universally adopted

A hard fork introduces rules that old nodes reject, potentially creating two separate chains if adoption is not unanimous.

What is the primary role of the nonce in Bitcoin's proof-of-work?

Answer: It is incremented by miners to find a hash below the target difficulty

Miners repeatedly change the nonce and rehash the block header until the resulting hash meets the current difficulty target.

What problem does the Byzantine Generals Problem model in distributed blockchain networks?

Answer: How nodes can reach consensus when some participants may be malicious or faulty

The Byzantine Generals Problem describes the challenge of achieving reliable consensus when some participants may send conflicting or dishonest messages.