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.
Read the first 7 Consensus Algorithm Security flashcards as text
In a Proof-of-Work blockchain, what condition must an attacker satisfy to execute a 51% attack successfully?
Answer: Control more than half of the network's total hash rate
A 51% attack requires the attacker to control the majority of the network's computational hash rate, enabling them to rewrite recent blocks and double-spend.
Which consensus mechanism is most vulnerable to a 'long-range attack' where an adversary rewrites blockchain history from genesis?
Answer: Proof of Stake
Pure Proof-of-Stake systems are susceptible to long-range attacks because old private keys can be used to rewrite history without requiring ongoing computational resources.
What is a 'nothing-at-stake' problem in Proof-of-Stake consensus?
Answer: Validators can vote on multiple competing forks at no additional cost
Nothing-at-stake means validators can simultaneously vote on all fork candidates without penalty, undermining finality and enabling double-spend attacks.
Slashing conditions in Ethereum's Casper PoS protocol are designed primarily to penalize which behavior?
Answer: Equivocation — signing two conflicting blocks at the same height
Slashing penalizes equivocation (double-voting or double-proposing) by destroying a portion of the offending validator's staked ETH.
In Byzantine Fault Tolerant (BFT) consensus, what is the maximum fraction of faulty nodes the system can tolerate while still reaching agreement?
Answer: Less than one-third of all nodes
Classical BFT requires that fewer than one-third of nodes are Byzantine (malicious or faulty) to guarantee safety and liveness.
What attack involves an adversary selectively withholding a found block to gain a statistical mining advantage in PoW?
Answer: Selfish mining attack
In selfish mining, a miner secretly extends their private chain and releases blocks strategically to waste honest miners' work, gaining a disproportionate share of rewards.
Which mitigation technique directly addresses the nothing-at-stake problem in Proof-of-Stake systems?
Answer: Implementing slashing penalties for validators who sign conflicting forks
Slashing creates an economic cost for signing multiple forks, making it irrational for validators to support competing chains simultaneously.