Consensus Algorithms and Protocols Flashcards
21 cards from real Blockchain Technology practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 20 Consensus Algorithms and Protocols flashcards as text
In Practical Byzantine Fault Tolerance (PBFT), how many total nodes are required to tolerate f faulty nodes?
Answer: 3f + 1
PBFT requires 3f + 1 total nodes to safely tolerate f Byzantine faults.
What problem does the 'nothing-at-stake' issue describe in Proof of Stake systems?
Answer: Validators can cheaply vote on multiple competing chains
Nothing-at-stake means validators face no cost to validate multiple forks, undermining consensus.
In Proof of Work, what does the 'difficulty' parameter primarily control?
Answer: The expected time to find a valid block
Difficulty adjusts how hard the hash puzzle is to keep block times roughly constant.
Which consensus mechanism does Ethereum use after 'The Merge'?
Answer: Proof of Stake
Ethereum transitioned from Proof of Work to Proof of Stake during The Merge in 2022.
What is a key characteristic of Delegated Proof of Stake (DPoS)?
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.
What does 'finality' mean in a blockchain consensus context?
Answer: The point at which a transaction cannot be reversed
Finality is the guarantee that a committed transaction is permanent and irreversible.
Which attack involves an entity controlling more than half of a network's mining or staking power?
Answer: 51% attack
A 51% attack lets an attacker control the majority of hashpower or stake to rewrite history.
In the Raft consensus algorithm, what role is responsible for handling all client requests?
Answer: Leader
In Raft, the elected leader handles client requests and replicates the log to followers.
What is the primary purpose of a 'slashing' mechanism in Proof of Stake?
Answer: To penalize validators for misbehavior
Slashing destroys part of a validator's stake to punish malicious or faulty behavior.
Which consensus property guarantees that all honest nodes eventually agree on the same value?
Answer: Agreement (safety)
Agreement, a safety property, ensures all honest nodes decide on the same value.
In Proof of Stake, what generally determines a validator's chance of being selected to propose a block?
Answer: Amount of stake committed
Selection probability typically scales with the amount of tokens a validator stakes.
What does the FLP impossibility result state about distributed consensus?
Answer: No deterministic protocol guarantees consensus in an async system with one faulty process
FLP proves no deterministic asynchronous protocol can guarantee consensus if even one process may fail.
Which consensus mechanism is commonly used by permissioned blockchains like Hyperledger Fabric?
Answer: Raft / BFT-style ordering
Hyperledger Fabric uses ordering services based on Raft or BFT rather than mining.
What is the main goal of a Sybil attack on a consensus network?
Answer: To create many fake identities to gain disproportionate influence
A Sybil attack floods the network with fake nodes to gain outsized control.
In Ethereum's PoS, what is the role of an 'attestation'?
Answer: A validator's vote on the validity of a block
An attestation is a validator's signed vote confirming a block and the current chain head.
What is 'chain reorganization' (reorg) in a blockchain?
Answer: Replacing blocks with a different competing branch
A reorg occurs when nodes switch to a longer or heavier competing chain, discarding some blocks.
Which rule does Bitcoin use to choose the canonical chain among forks?
Answer: Longest/heaviest cumulative work chain
Bitcoin follows the chain with the greatest cumulative proof-of-work.
What is the purpose of the GHOST / fork-choice rule (e.g., LMD-GHOST) in Ethereum?
Answer: To select the head of the chain using accumulated votes
LMD-GHOST chooses the canonical head based on the latest attestations (votes) by validators.
In Proof of Stake, what is a 'validator deposit' or bond?
Answer: Capital locked as collateral to participate in consensus
Validators lock up a bonded deposit as collateral that can be slashed for misbehavior.
What does 'liveness' guarantee in a consensus protocol?
Answer: The system continues to make progress and process new transactions
Liveness ensures the protocol keeps producing decisions and does not stall.
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