CBSA Consensus Mechanisms 4 — Questions and Answers
Question 1: In Ethereum's Proof of Stake, what is the consequence of a validator performing a 'slashable offense' such as double voting?
- The validator is temporarily suspended for one epoch
- A portion of the validator's staked ETH is burned and they are ejected (Correct answer)
- The validator's rewards are withheld for 30 days
- The validator must re-stake with a larger minimum deposit
Correct answer: A portion of the validator's staked ETH is burned and they are ejected
Slashing penalizes validators for equivocation or surround voting by destroying part of their stake and forcibly removing them from the validator set to deter attacks.
Question 2: Which of the following best describes a '51% attack' in a Proof of Work blockchain?
- An attacker bribes 51% of validators to approve fraudulent transactions
- An attacker controls the majority of hash rate and can rewrite recent transaction history (Correct answer)
- An attacker floods the network with 51 large transactions per second
- An attacker compromises 51% of nodes' private keys
Correct answer: An attacker controls the majority of hash rate and can rewrite recent transaction history
A 51% attack occurs when a single entity controls more than half the network's computational power, enabling them to mine a longer private chain and double-spend by reorganizing blocks.
Question 3: What is the significance of the 'difficulty adjustment' algorithm in Bitcoin's Proof of Work consensus?
- It scales the block reward based on the number of active miners
- It recalibrates mining difficulty every 2016 blocks to target a ~10-minute block time (Correct answer)
- It adjusts transaction fees proportionally to network congestion
- It limits the total number of miners allowed on the network
Correct answer: It recalibrates mining difficulty every 2016 blocks to target a ~10-minute block time
Bitcoin recalculates mining difficulty every 2016 blocks (~2 weeks) so that blocks are produced approximately every 10 minutes regardless of total network hash rate changes.
Question 4: In the context of consensus mechanisms, what does 'fork choice rule' determine?
- Which programming language is used to write smart contracts
- How nodes select the canonical chain when multiple valid chain branches exist (Correct answer)
- The minimum stake required to become a validator
- How transaction fees are split between miners and validators
Correct answer: How nodes select the canonical chain when multiple valid chain branches exist
The fork choice rule defines which chain branch a node considers canonical—Bitcoin uses the heaviest chain (most work), while Ethereum PoS uses LMD-GHOST.
Question 5: Algorand's Pure Proof of Stake consensus uses cryptographic sortition to select committee members. What is the key advantage of this approach?
- It guarantees every token holder gets an equal number of committee slots
- Selection is private and non-interactive, preventing targeted attacks on future committee members (Correct answer)
- It eliminates the need for validators to maintain online nodes
- It requires committee members to stake tokens for exactly 24 hours
Correct answer: Selection is private and non-interactive, preventing targeted attacks on future committee members
Algorand's VRF-based sortition allows each user to privately and locally determine if they are selected, so potential committee members are unknown to attackers until they reveal their selection.
Question 6: In Hyperledger Besu's QBFT (Quorum Byzantine Fault Tolerance) consensus, what minimum number of validators is required to tolerate one faulty node?
- 3
- 4 (Correct answer)
- 5
- 7
Correct answer: 4
QBFT follows the BFT formula n ≥ 3f+1; to tolerate f=1 faulty node, you need at least 4 validators.
Question 7: What is 'long-range attack' and which consensus mechanism is most vulnerable to it?
- A DDoS attack on long-running nodes; most common in PoW networks
- An attacker uses old private keys to rewrite history from a past checkpoint; primarily affects PoS networks (Correct answer)
- A miner withholds blocks for extended periods; affects all blockchain types equally
- An attacker delays block propagation across geographic distances; affects PoA networks
Correct answer: An attacker uses old private keys to rewrite history from a past checkpoint; primarily affects PoS networks
In a long-range attack, an attacker who previously held stake uses old keys to create an alternative chain from a point far in the past, exploiting PoS's lack of the PoW computational cost barrier.
CBSA Consensus Mechanisms 4
In Ethereum's Proof of Stake, what is the consequence of a validator performing a 'slashable offense' such as double voting?