Blockchain Consensus Mechanisms Questions and Answers

Question 1

A major criticism of the Proof of Work (PoW) consensus mechanism is its high energy consumption. Which of the following consensus mechanisms was primarily designed as a more energy-efficient alternative by replacing computational work with an economic stake?

Accepted Answer

Proof of Stake (PoS)

Answer

Proof of Stake (PoS) was developed to address the high energy consumption of PoW. Instead of requiring miners to perform energy-intensive computations, PoS selects validators to create new blocks based on the number of coins they hold and are willing to 'stake' as collateral. This method is significantly more energy-efficient.

Question 2

A consortium of international banks plans to create a private blockchain for interbank settlements. They require high transaction throughput, low latency, and the ability to function even if some participating nodes become malicious or faulty. The participants are all known and permissioned entities. Which consensus mechanism would be most suitable for this scenario?

Accepted Answer

Practical Byzantine Fault Tolerance (pBFT)

Answer

Practical Byzantine Fault Tolerance (pBFT) is well-suited for private or consortium blockchains where participants are known. It provides high throughput, low-latency finality, and is designed to tolerate a certain number of malicious (Byzantine) nodes (up to one-third). Since the banking consortium consists of permissioned entities, pBFT's efficiency and fault tolerance make it an ideal choice.

Question 3

Which of the following describes a key difference between Proof of Stake (PoS) and Delegated Proof of Stake (DPoS)?

Accepted Answer

In DPoS, token holders vote for a limited number of delegates to validate blocks, whereas in PoS, any user meeting the stake requirement can potentially be a validator.

Answer

The primary distinction between PoS and DPoS is the selection process for block validators. In a typical PoS system, any participant who stakes the required amount of cryptocurrency has a chance to be selected to create a new block. In DPoS, token holders use their stake to vote for a smaller, fixed number of 'delegates' or 'witnesses' who are then responsible for block production and validation. This system is often considered more efficient and scalable but can lead to a higher degree of centralization.

Question 4

In the context of Proof of Work (PoW) blockchains, what does the term 'probabilistic finality' mean?

Accepted Answer

The certainty of a transaction being irreversible increases as more blocks are added after it, but never reaches 100%.

Answer

Probabilistic finality, a characteristic of Nakamoto consensus (used in PoW), means that the likelihood of a transaction being reversed decreases as more blocks are built on top of the block containing it. While the probability of a reversal becomes extremely low after several confirmations (e.g., 6 blocks in Bitcoin), it never becomes an absolute certainty. This is in contrast to mechanisms like pBFT which offer absolute or deterministic finality.

Question 5

A malicious actor gains control of 52% of the total hashing power on a Proof of Work (PoW) network. Which of the following actions can this actor successfully perform?

Accepted Answer

Prevent specific new transactions from being confirmed and potentially reverse their own recent transactions.

Answer

A 51% attack on a PoW network gives the attacker control over the block creation process. This allows them to censor transactions by refusing to include them in their blocks and to perform a 'double-spend' by creating a secret longer chain where they reverse their own transactions and then broadcasting it to the network. However, they cannot steal funds from addresses they don't own the private keys to, change the core protocol rules, or create coins outside of the established block reward system.

Blockchain Practice Test

Blockchain Practice Test

Blockchain Consensus Mechanisms Questions and Answers