CBSE Consensus Algorithm Security 2

Question 1

In a Proof-of-Work blockchain, what condition must an attacker satisfy to execute a 51% attack successfully?

Accepted Answer

Control more than half of the network's total hash rate

Answer

Own more than half of all circulating tokens

Answer

Compromise more than half of all validator nodes

Answer

Possess private keys for more than half of all wallets

Question 2

Which consensus mechanism is most vulnerable to a 'long-range attack' where an adversary rewrites blockchain history from genesis?

Accepted Answer

Proof of Stake

Answer

Proof of Work

Answer

Delegated Proof of Stake

Answer

Proof of Authority

Question 3

What is a 'nothing-at-stake' problem in Proof-of-Stake consensus?

Accepted Answer

Validators can vote on multiple competing forks at no additional cost

Answer

Validators lose all staked funds if they go offline

Answer

Nodes have no incentive to participate in block validation

Answer

Attackers can stake zero tokens to gain consensus power

Question 4

Slashing conditions in Ethereum's Casper PoS protocol are designed primarily to penalize which behavior?

Accepted Answer

Equivocation — signing two conflicting blocks at the same height

Answer

Failing to produce a block when selected as proposer

Answer

Staking below the minimum required validator balance

Answer

Connecting to too many peer nodes simultaneously

Question 5

In Byzantine Fault Tolerant (BFT) consensus, what is the maximum fraction of faulty nodes the system can tolerate while still reaching agreement?

Accepted Answer

Less than one-third of all nodes

Answer

Less than one-half of all nodes

Answer

Less than two-thirds of all nodes

Answer

Any fraction, as long as faulty nodes are identified

Question 6

What attack involves an adversary selectively withholding a found block to gain a statistical mining advantage in PoW?

Accepted Answer

Selfish mining attack

Answer

Eclipse attack

Answer

Sybil attack

Answer

Grinding attack

Question 7

Which mitigation technique directly addresses the nothing-at-stake problem in Proof-of-Stake systems?

Accepted Answer

Implementing slashing penalties for validators who sign conflicting forks

Answer

Increasing block size to reduce fork frequency

Answer

Requiring validators to wait 30 days before unstaking

Answer

Using hash-based puzzles to validate stake commitments