Blockchain Security Training Consensus Mechanism Vulnerabilities 2

Question 1

In a 51% attack on a Proof-of-Work blockchain, what can the attacker primarily accomplish?

Accepted Answer

Double-spend coins by reorganizing the chain

Answer

Steal private keys from any wallet

Answer

Mint unlimited new tokens at will

Answer

Read encrypted transaction contents

Question 2

Which type of network is MOST economically vulnerable to a 51% attack?

Accepted Answer

A small-cap PoW altcoin with low total hash rate

Answer

Bitcoin mainnet

Answer

Ethereum after the Merge

Answer

A permissioned enterprise chain

Question 3

What is 'selfish mining'?

Accepted Answer

Withholding found blocks to gain a disproportionate share of rewards

Answer

Mining only your own transactions

Answer

Refusing to share mining pool profits

Answer

Mining without paying electricity costs

Question 4

A 'finality reversion' attack is most concerning because it undermines which property?

Accepted Answer

The guarantee that confirmed transactions are irreversible

Answer

Transaction privacy

Answer

Smart contract gas pricing

Answer

Wallet address generation

Question 5

Why does increasing the number of block confirmations reduce double-spend risk?

Accepted Answer

Each added block makes reorganizing the chain exponentially harder

Answer

It encrypts the transaction more strongly

Answer

It lowers transaction fees

Answer

It hides the sender's identity

Question 6

In Proof-of-Stake, a 'long-range attack' typically exploits what?

Accepted Answer

Old validator keys whose stake has since been withdrawn

Answer

High electricity consumption

Answer

Faster block propagation

Answer

Quantum computing weaknesses

Question 7

Which mitigation makes a 51% attack on PoW more expensive to execute?

Accepted Answer

A larger, more decentralized pool of honest hash power

Answer

Reducing block size

Answer

Disabling transaction fees

Answer

Shorter confirmation times