Blockchain Developer Consensus Algorithms and Protocols 2 — Questions and Answers
Question 1: In Practical Byzantine Fault Tolerance (PBFT), how many total nodes are required to tolerate f faulty nodes?
- 2f + 1
- 3f + 1 (Correct answer)
- f + 1
- 4f
Correct answer: 3f + 1
PBFT requires 3f + 1 total nodes to safely tolerate f Byzantine faults.
Question 2: What problem does the 'nothing-at-stake' issue describe in Proof of Stake systems?
- Validators can cheaply vote on multiple competing chains (Correct answer)
- Miners waste electricity
- Nodes cannot reach finality
- Transactions have zero fees
Correct answer: Validators can cheaply vote on multiple competing chains
Nothing-at-stake means validators face no cost to validate multiple forks, undermining consensus.
Question 3: In Proof of Work, what does the 'difficulty' parameter primarily control?
- The block reward amount
- The number of transactions per block
- The expected time to find a valid block (Correct answer)
- The maximum chain length
Correct answer: The expected time to find a valid block
Difficulty adjusts how hard the hash puzzle is to keep block times roughly constant.
Question 4: Which consensus mechanism does Ethereum use after 'The Merge'?
- Proof of Work
- Proof of Stake (Correct answer)
- Proof of Authority
- Delegated Proof of Stake
Correct answer: Proof of Stake
Ethereum transitioned from Proof of Work to Proof of Stake during The Merge in 2022.
Question 5: What is a key characteristic of Delegated Proof of Stake (DPoS)?
- Every node mines blocks
- Token holders vote for a limited set of block producers (Correct answer)
- It requires solving hash puzzles
- It has no validators
Correct answer: Token holders vote for a limited set of block producers
In DPoS, stakeholders elect a small group of delegates who produce blocks on their behalf.
Question 6: What does 'finality' mean in a blockchain consensus context?
- The point at which a transaction cannot be reversed (Correct answer)
- The last block ever produced
- The total supply cap
- The end of a mining epoch
Correct answer: The point at which a transaction cannot be reversed
Finality is the guarantee that a committed transaction is permanent and irreversible.
Question 7: Which attack involves an entity controlling more than half of a network's mining or staking power?
- Sybil attack
- 51% attack (Correct answer)
- Eclipse attack
- Replay attack
Correct answer: 51% attack
A 51% attack lets an attacker control the majority of hashpower or stake to rewrite history.
Blockchain Developer Consensus Algorithms and Protocols 2
In Practical Byzantine Fault Tolerance (PBFT), how many total nodes are required to tolerate f faulty nodes?