Blockchain 101 Certification Blockchain 101 Certification Consensus Mechanisms & Protocols 2 — Questions and Answers
Question 1: What is the primary purpose of a nonce in Proof of Work mining?
- To encrypt the block data
- To identify the miner's wallet
- To find a hash that meets the difficulty target (Correct answer)
- To timestamp the block
Correct answer: To find a hash that meets the difficulty target
Miners increment the nonce value repeatedly until the resulting block hash falls below the current difficulty target.
Question 2: What does 'finality' mean in blockchain consensus?
- The last block in a chain
- The irreversibility of a confirmed transaction (Correct answer)
- The closing of a smart contract
- The maximum block size
Correct answer: The irreversibility of a confirmed transaction
Finality means that once a transaction is confirmed, it cannot be reversed or altered, providing certainty to participants.
Question 3: Which consensus algorithm uses a 'leader election' process to designate one node to propose each block?
- Proof of Work
- Proof of Burn
- Raft Consensus (Correct answer)
- Proof of Elapsed Time
Correct answer: Raft Consensus
Raft Consensus elects a single leader node to manage log replication and propose new entries to the cluster.
Question 4: What is the '51% attack' in blockchain security?
- When 51% of users abandon the network
- When an attacker controls the majority of mining/staking power (Correct answer)
- When 51 blocks are orphaned
- When a node rejects 51% of transactions
Correct answer: When an attacker controls the majority of mining/staking power
A 51% attack occurs when a single entity controls more than half of the network's consensus power, enabling transaction manipulation.
Question 5: What is 'chain reorganization' (reorg) in a blockchain network?
- Restructuring node connections
- Replacing a portion of the chain with a longer competing chain (Correct answer)
- Reordering pending transactions
- Updating the genesis block
Correct answer: Replacing a portion of the chain with a longer competing chain
A chain reorganization happens when the network switches to a longer competing chain, making previously confirmed blocks orphaned.
Question 6: In the context of blockchain, what is a 'selfish mining' attack?
- Mining without sharing block rewards
- Withholding discovered blocks to gain a competitive mining advantage (Correct answer)
- Mining only high-fee transactions
- Refusing to validate peer transactions
Correct answer: Withholding discovered blocks to gain a competitive mining advantage
Selfish mining involves a miner privately withholding newly found blocks to waste honest miners' effort and gain disproportionate rewards.
Blockchain 101 Certification Blockchain 101 Certification Consensus Mechanisms & Protocols 2
What is the primary purpose of a nonce in Proof of Work mining?