FREE Blockchain Security Training Consensus Mechanism Attacks Questions and Answers

Question 1

A mining pool in a Proof-of-Work blockchain finds a new block but intentionally withholds it from the rest of the network.
The pool then continues to mine on its own private chain, hoping to find another block before the public chain grows.
What is the primary goal of this attack strategy?

Accepted Answer

To increase the attacker's revenue relative to their hash power by orphaning blocks from honest miners.

Answer

To cause a network-wide denial of service by halting block production.

Answer

To execute a double-spend attack by creating a longer chain in secret.

Answer

To introduce a hard fork by releasing a chain with different protocol rules.

Question 2

Which of the following consensus mechanism attacks is a primary concern for Proof-of-Stake (PoS) systems but is generally considered economically infeasible in Proof-of-Work (PoW) systems due to the immense computational cost required to rewrite history?

Accepted Answer

Long-Range Attack

Answer

51% Attack

Answer

Sybil Attack

Answer

Race Attack

Question 3

An attacker creates thousands of pseudonymous nodes on a blockchain network to gain a disproportionately large influence in the consensus process. This strategy, where identity is cheap to generate, is known as what type of attack?

Accepted Answer

Sybil Attack

Answer

Eclipse Attack

Answer

Finney Attack

Answer

Liveness Denial Attack

Question 4

In a Proof-of-Stake blockchain, a validator discovers they can slightly alter their input data (e.g., by including different transactions) to influence the deterministic process of who gets to propose the next block, thereby increasing their own chances. What is this specific type of attack called?

Accepted Answer

Stake Grinding Attack

Answer

Nothing-at-Stake Attack

Answer

Majority Attack

Answer

Censorship Attack

Question 5

A malicious entity gains control of more than 50% of a Proof-of-Work network's hashrate. Which of the following actions can they successfully execute?

Accepted Answer

Prevent new transactions from gaining confirmations and reverse their own recent transactions.

Answer

Steal cryptocurrency directly from an arbitrary user's wallet.

Answer

Create new coins out of thin air, violating the protocol's issuance rules.

Answer

Change the fundamental consensus rules of the blockchain, such as the block reward amount.

Question 6

A validator in a Proof-of-Stake system observes two competing forks of the blockchain. Since there is no significant financial cost to validating a block, the validator signs and broadcasts a block on both forks to maximize their potential rewards, regardless of which fork ultimately wins. This behavior is a key aspect of which specific vulnerability?

Accepted Answer

Nothing-at-Stake Problem

Answer

Long-Range Attack

Answer

Censorship Attack

Answer

Liveness Denial

A mining pool in a Proof-of-Work blockchain finds a new block but intentionally withholds it from the rest of the network.The pool then continues to mine on its own private chain, hoping to find another block before the public chain grows.What is the primary goal of this attack strategy?

A mining pool in a Proof-of-Work blockchain finds a new block but intentionally withholds it from the rest of the network.
The pool then continues to mine on its own private chain, hoping to find another block before the public chain grows.
What is the primary goal of this attack strategy?