CBSA Consensus Mechanisms 2 — Questions and Answers
Question 1: Which consensus mechanism is used by Hyperledger Fabric to order transactions before they are committed to the ledger?
- Raft or Kafka-based ordering service (Correct answer)
- Proof of Work
- Delegated Proof of Stake
- Byzantine Fault Tolerance voting
Correct answer: Raft or Kafka-based ordering service
Hyperledger Fabric uses a pluggable ordering service (Raft or previously Kafka) to sequence transactions into blocks before peers validate and commit them.
Question 2: In a Practical Byzantine Fault Tolerant (PBFT) network with 10 nodes, what is the maximum number of faulty nodes the system can tolerate?
- 1
- 2
- 3 (Correct answer)
- 4
Correct answer: 3
PBFT tolerates at most f faulty nodes in a network of 3f+1 nodes, so 10 nodes can tolerate floor((10-1)/3) = 3 faulty nodes.
Question 3: What is the primary purpose of the 'finality' property in blockchain consensus mechanisms?
- To maximize transaction throughput
- To ensure a committed block cannot be reversed or reorganized (Correct answer)
- To reduce block propagation latency
- To encrypt transaction data permanently
Correct answer: To ensure a committed block cannot be reversed or reorganized
Finality guarantees that once a block is added to the chain, it is irrevocable and no reorganization can remove or alter it.
Question 4: Ethereum's move from Proof of Work to Proof of Stake (The Merge) primarily aimed to achieve which benefit?
- Increase block size limit
- Reduce energy consumption by ~99.95% (Correct answer)
- Enable smart contract execution
- Eliminate transaction fees
Correct answer: Reduce energy consumption by ~99.95%
The Merge transitioned Ethereum to PoS, drastically cutting energy use since validators stake ETH instead of performing energy-intensive mining.
Question 5: In Delegated Proof of Stake (DPoS), token holders participate in consensus by:
- Running full mining nodes themselves
- Voting for a fixed set of elected delegates who produce blocks (Correct answer)
- Locking tokens in a smart contract to earn rewards directly
- Solving cryptographic puzzles proportional to their stake
Correct answer: Voting for a fixed set of elected delegates who produce blocks
DPoS uses a democratic voting model where token holders elect delegates (witnesses/block producers) who are responsible for block production and validation.
Question 6: Which characteristic best distinguishes Proof of Authority (PoA) from Proof of Stake (PoS)?
- PoA validators are selected based on their token holdings
- PoA relies on verified real-world identities rather than economic stake (Correct answer)
- PoA achieves consensus through computational puzzles
- PoA requires more validators than PoS to reach finality
Correct answer: PoA relies on verified real-world identities rather than economic stake
In PoA, consensus authority is granted to pre-approved, KYC-verified participants whose reputation is at stake rather than cryptocurrency holdings.
Question 7: The 'nothing-at-stake' problem is a known vulnerability in which type of consensus mechanism?
- Proof of Work
- Proof of Authority
- Naive Proof of Stake implementations (Correct answer)
- Federated Byzantine Agreement
Correct answer: Naive Proof of Stake implementations
In naive PoS, validators have no cost to vote on multiple competing forks simultaneously, since staking tokens on one fork doesn't preclude voting on another without slashing mechanisms.
CBSA Consensus Mechanisms 2
Which consensus mechanism is used by Hyperledger Fabric to order transactions before they are committed to the ledger?