Cryptocurrency Blockchain and Consensus Mechanisms Questions and Answers

Question 1

Which of the following problems is a blockchain's consensus mechanism, such as Proof-of-Work, designed to solve in a decentralized and trustless network?

Accepted Answer

The Byzantine Generals' Problem

Answer

The Double-Spending Problem

Answer

The Oracle Problem

Answer

The Scalability Trilemma

Question 2

An attacker gains control of 52% of the total hashing power on a Proof-of-Work (PoW) blockchain. Which of the following malicious actions can they now successfully execute?

Accepted Answer

Reverse their own transactions after they appear confirmed, allowing them to double-spend coins.

Answer

Create new coins out of thin air.

Answer

Steal cryptocurrency from another user's wallet without their private key.

Answer

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

Question 3

What is the primary characteristic that distinguishes Proof-of-Stake (PoS) from Proof-of-Work (PoW) as a consensus mechanism?

Accepted Answer

In PoS, validator selection is based on the amount of cryptocurrency a participant holds and is willing to 'stake' as collateral, whereas PoW relies on computational power.

Answer

PoS requires validators to solve complex mathematical puzzles, while PoW does not.

Answer

PoS blockchains are inherently more centralized than PoW blockchains.

Answer

Only PoW blockchains are vulnerable to 51% attacks.

Question 4

A blockchain network uses a Delegated Proof-of-Stake (DPoS) consensus mechanism. How are the nodes that validate transactions and produce new blocks determined?

Accepted Answer

Token holders vote to elect a limited number of 'delegates' or 'witnesses' who are then responsible for producing blocks.

Answer

All nodes with a sufficient stake are randomly selected to produce blocks.

Answer

The nodes with the most powerful hardware are chosen to be block producers.

Answer

A centralized company that created the blockchain appoints all the block producers.

Question 5

A consortium of international banks wants to create a private, permissioned blockchain for settling cross-border payments. The network requires high transaction throughput and fast finality, and all participants are known and have a degree of trust. Which consensus mechanism would be most suitable for this scenario?

Accepted Answer

Practical Byzantine Fault Tolerance (PBFT)

Answer

Proof-of-Work (PoW)

Answer

Proof-of-Stake (PoS)

Answer

Proof-of-Burn (PoB)

Question 6

Which of the following best describes the concept of 'probabilistic finality' as it applies to consensus mechanisms like Proof-of-Work?

Accepted Answer

The assurance that a transaction will not be reversed increases as more blocks are added after it, but never reaches absolute certainty.

Answer

A transaction is considered final as soon as it is included in a single block.

Answer

The network's validators vote on each block, and once a supermajority agrees, the block is absolutely final.

Answer

The system randomly selects a block to be final after a certain time period.