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

Controlling a majority of hash power lets an attacker rewrite recent blocks and double-spend, but not forge signatures or mint arbitrary coins.

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

Low total hash rate means renting enough hashing power to overpower the network is cheap, making small PoW coins prime targets.

Question 3

What is 'selfish mining'?

Accepted Answer

Withholding found blocks to gain a disproportionate share of rewards

Answer

Selfish miners withhold newly found blocks and release them strategically to waste honest miners' work and capture more than their fair reward share.

Question 4

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

Accepted Answer

The guarantee that confirmed transactions are irreversible

Answer

Finality means confirmed transactions cannot be undone; reverting it breaks settlement assurance that users and exchanges rely on.

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

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.

Blockchain Practice Test

Blockchain Practice Test

Blockchain Security Training Consensus Mechanism Vulnerabilities 2