CBCP Consensus Mechanisms and Mining 3 — Questions and Answers
Question 1: What is the '51% attack' vulnerability in Proof of Work blockchains?
- An attacker exploits a smart contract bug to steal 51% of funds
- An entity controlling the majority of hash power can double-spend and reverse recent transactions (Correct answer)
- A miner who solves 51% of blocks earns all block rewards
- A network fork that splits 51% of nodes from the main chain
Correct answer: An entity controlling the majority of hash power can double-spend and reverse recent transactions
If a single entity controls more than 50% of the network's hash rate, they can rewrite recent blockchain history and execute double-spend attacks.
Question 2: In the context of mining pools, what is a 'share'?
- An equity stake in the mining pool company
- A proof-of-work solution that meets a lower difficulty target, submitted to demonstrate mining effort (Correct answer)
- A fractional block reward paid per transaction validated
- A cryptographic token representing partial block ownership
Correct answer: A proof-of-work solution that meets a lower difficulty target, submitted to demonstrate mining effort
Shares are partial proof-of-work solutions with a lower difficulty than the actual network target, used by pools to measure each miner's contributed work for reward distribution.
Question 3: Which property of Byzantine Fault Tolerance (BFT) consensus describes the guarantee that all honest nodes agree on the same value?
- Liveness
- Safety (Correct answer)
- Finality
- Availability
Correct answer: Safety
Safety in BFT consensus ensures that no two honest nodes decide on different values, preventing forks or conflicting chain states.
Question 4: What is the primary trade-off when a blockchain prioritizes 'liveness' over 'safety' in consensus?
- The chain processes transactions faster but with higher fees
- The chain always makes progress but may temporarily allow conflicting states (Correct answer)
- The chain achieves finality instantly but halts under partition
- The chain reduces energy consumption but increases storage requirements
Correct answer: The chain always makes progress but may temporarily allow conflicting states
Prioritizing liveness means the network keeps producing blocks even under adverse conditions, but may create forks or temporary inconsistencies that require later resolution.
Question 5: In Proof of Stake, what is 'nothing at stake' problem and how is it typically addressed?
- Validators can vote for multiple chain forks at no cost; addressed by slashing penalties for equivocation (Correct answer)
- Validators stake nothing and are chosen randomly; addressed by minimum stake requirements
- Small stakeholders have no incentive to validate; addressed by delegation mechanisms
- Empty blocks can be staked; addressed by requiring transaction inclusion
Correct answer: Validators can vote for multiple chain forks at no cost; addressed by slashing penalties for equivocation
Without cost for voting on multiple forks, validators could support all competing chains; slashing economically punishes this behavior by destroying stake for signing conflicting blocks.
Question 6: What is 'merge mining' (Auxiliary Proof of Work)?
- Combining multiple mining pools into a single entity
- Simultaneously mining two blockchains that use the same hashing algorithm without additional computational work (Correct answer)
- Merging orphaned blocks back into the main chain
- A technique where ASICs handle multiple proof-of-work algorithms at once
Correct answer: Simultaneously mining two blockchains that use the same hashing algorithm without additional computational work
Merge mining allows miners to use the same proof-of-work computation to mine on a parent chain and auxiliary chains simultaneously, as used by Namecoin and Bitcoin.
Question 7: In Hyperledger Fabric, which component is responsible for consensus on transaction ordering?
- Peer nodes
- Chaincode containers
- The Ordering Service (Orderer) (Correct answer)
- Certificate Authority (CA)
Correct answer: The Ordering Service (Orderer)
The Ordering Service in Hyperledger Fabric receives endorsed transactions and establishes a definitive order, creating blocks distributed to peers for commitment.
CBCP Consensus Mechanisms and Mining 3
What is the '51% attack' vulnerability in Proof of Work blockchains?