CBCP Consensus Mechanisms 3

Question 1

What is the primary security assumption behind Nakamoto consensus used in Bitcoin?

Accepted Answer

An attacker controlling less than 50% of hash rate cannot consistently outpace the honest chain

Answer

Nakamoto consensus assumes that as long as honest miners control the majority of hash rate, the longest chain produced by honest nodes will outpace any attacker's chain.

Question 2

In a Practical Byzantine Fault Tolerant (PBFT) system with 3f+1 nodes, what is the maximum number of faulty nodes (f) it can tolerate?

Accepted Answer

One-third of total nodes minus one

Answer

PBFT requires 3f+1 total nodes to tolerate f Byzantine faults, meaning it can tolerate up to ⌊(n-1)/3⌋ faulty nodes.

Question 3

What is 'finality' in the context of blockchain consensus, and which type is typically provided by BFT protocols?

Accepted Answer

Finality means transactions are irreversible; BFT provides absolute (deterministic) finality

Answer

BFT-based protocols provide deterministic (absolute) finality — once a block is committed, it cannot be reverted, unlike the probabilistic finality of PoW chains.

Question 4

Which consensus mechanism is most suitable for a consortium blockchain where all participants are known and semi-trusted?

Accepted Answer

Practical Byzantine Fault Tolerance (PBFT)

Answer

PBFT is well-suited for consortium blockchains with a known, limited set of semi-trusted validators due to its deterministic finality and low energy consumption.

Question 5

What is the 'long-range attack' vulnerability specifically associated with Proof of Stake systems?

Accepted Answer

An attacker with old private keys can rewrite history from a past point where they held significant stake

Answer

In a long-range attack, an adversary uses old keys (from when they had large stake) to rewrite blockchain history from a past checkpoint, which PoW naturally prevents through cumulative work.

CBCP - Certified Blockchain Professional Practice Test

CBCP - Certified Blockchain Professional Practice Test

CBCP Consensus Mechanisms 3