Consensus Mechanism Vulnerabilities Flashcards
7 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 7 Consensus Mechanism Vulnerabilities flashcards as text
In a 51% attack on a Proof-of-Work blockchain, what can the attacker primarily accomplish?
Answer: Double-spend coins by reorganizing the chain
Controlling a majority of hash power lets an attacker rewrite recent blocks and double-spend, but not forge signatures or mint arbitrary coins.
Which type of network is MOST economically vulnerable to a 51% attack?
Answer: A small-cap PoW altcoin with low total hash rate
Low total hash rate means renting enough hashing power to overpower the network is cheap, making small PoW coins prime targets.
What is 'selfish mining'?
Answer: Withholding found blocks to gain a disproportionate share of rewards
Selfish miners withhold newly found blocks and release them strategically to waste honest miners' work and capture more than their fair reward share.
A 'finality reversion' attack is most concerning because it undermines which property?
Answer: The guarantee that confirmed transactions are irreversible
Finality means confirmed transactions cannot be undone; reverting it breaks settlement assurance that users and exchanges rely on.
Why does increasing the number of block confirmations reduce double-spend risk?
Answer: Each added block makes reorganizing the chain exponentially harder
More confirmations bury a transaction under additional proof-of-work, so an attacker must out-mine an ever-growing portion of the chain to reverse it.
In Proof-of-Stake, a 'long-range attack' typically exploits what?
Answer: Old validator keys whose stake has since been withdrawn
Long-range attacks use previously-bonded keys (whose stake is no longer at risk) to rewrite history from an old point, defended against with checkpoints/weak subjectivity.
Which mitigation makes a 51% attack on PoW more expensive to execute?
Answer: A larger, more decentralized pool of honest hash power
The more honest hash power securing the chain, the more expensive it becomes for an attacker to acquire a competing majority.