Practice Test Geeks(CBSE) Certified Blockchain Security Expert Practice Test
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Consensus Algorithm Security Flashcards

7 cards from real CBSE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is a 'grinding attack' in the context of Proof-of-Stake consensus?

    Answer: An adversary iterates over many block header values to bias the next validator selection

    In a grinding attack, a validator tries many candidate block values to manipulate the randomness source used for future leader selection.

  2. Delegated Proof-of-Stake (DPoS) introduces which unique centralization-related security risk compared to standard PoS?

    Answer: Collusion among a small set of elected delegates to censor transactions or double-spend

    DPoS concentrates block-production power in a small elected group, making delegate collusion or cartel formation a realistic attack vector.

  3. In Practical Byzantine Fault Tolerance (PBFT), the protocol phases are prepare, pre-prepare, and commit. Which phase ensures that all honest nodes agree on a single value before committing?

    Answer: Prepare phase

    The prepare phase collects 2f+1 matching prepare messages (where f is the fault threshold), ensuring quorum agreement on the proposed value before the commit phase finalizes it.

  4. What security property distinguishes 'safety' from 'liveness' in distributed consensus?

    Answer: Safety guarantees no two honest nodes commit conflicting values; liveness guarantees the system eventually makes progress

    Safety means the system never produces contradictory finalized outputs; liveness means honest nodes will eventually reach a decision even under adversarial conditions.

  5. Ethereum's Gasper consensus combines Casper FFG with LMD-GHOST. What does LMD-GHOST stand for?

    Answer: Latest Message Driven Greediest Heaviest Observed SubTree

    LMD-GHOST uses each validator's latest message to weight the fork-choice rule, selecting the subtree with the most accumulated validator support.

  6. An attacker who controls 34% of staked ETH in Ethereum's PoS can threaten which consensus property?

    Answer: They can prevent finality by withholding enough votes to block the 2/3 supermajority

    Ethereum's Casper FFG requires a 2/3 supermajority to finalize checkpoints; 34% stake allows an attacker to indefinitely block finality without achieving majority control.

  7. What is the primary security purpose of a 'view-change' protocol in PBFT-based consensus systems?

    Answer: To replace a faulty or unresponsive primary (leader) node while preserving safety

    The view-change protocol allows replicas to elect a new primary when the current leader is suspected of failure or malice, maintaining liveness without sacrificing safety.