CBCP Consensus Mechanisms and Mining 4 — Questions and Answers
Question 1: What is the key difference between 'probabilistic finality' and 'deterministic finality' in blockchain consensus?
- Probabilistic finality is faster; deterministic finality requires more validators
- Probabilistic finality means reversals become increasingly unlikely over time; deterministic finality means a committed block cannot be reversed (Correct answer)
- Probabilistic finality applies only to smart contracts; deterministic applies to payments
- Probabilistic finality requires PoW; deterministic requires PoS
Correct answer: Probabilistic finality means reversals become increasingly unlikely over time; deterministic finality means a committed block cannot be reversed
PoW chains like Bitcoin have probabilistic finality where deep confirmations make reversal impractical, while BFT-based PoS systems provide absolute finality once a block is committed.
Question 2: What is the role of 'validators' in a Proof of Stake network compared to 'miners' in Proof of Work?
- Validators perform the same hash computation but with less energy
- Validators lock up cryptocurrency as collateral to propose and attest to blocks instead of expending computational energy (Correct answer)
- Validators only verify transactions while miners create blocks
- Validators are selected by the network developer team rather than algorithmically
Correct answer: Validators lock up cryptocurrency as collateral to propose and attest to blocks instead of expending computational energy
PoS validators stake ETH or other tokens as economic collateral and take turns proposing/attesting to blocks, replacing the energy-intensive hash competition of PoW miners.
Question 3: In the PBFT (Practical Byzantine Fault Tolerance) algorithm, what is the minimum number of nodes required to tolerate f Byzantine faulty nodes?
- 2f + 1
- 3f + 1 (Correct answer)
- 4f + 1
- f + 1
Correct answer: 3f + 1
PBFT requires at least 3f + 1 total nodes to tolerate f Byzantine failures, ensuring a two-thirds majority of honest nodes for safe consensus.
Question 4: What is 'long-range attack' in Proof of Stake systems, and what is the common defense?
- An attack where old private keys are used to rewrite history from a distant checkpoint; defended by weak subjectivity checkpoints (Correct answer)
- An attack where validators stake for unusually long lock-up periods to gain outsized rewards; defended by cap on stake duration
- An attack where network latency is exploited across geographic distances; defended by geographic validator distribution
- An attack targeting validators who have staked for more than one year; defended by mandatory rotation
Correct answer: An attack where old private keys are used to rewrite history from a distant checkpoint; defended by weak subjectivity checkpoints
Long-range attacks use old validator keys (possibly sold or compromised) to fork the chain from a past point; weak subjectivity requires nodes to trust a recent checkpoint when syncing.
Question 5: Which consensus mechanism does Solana use to achieve its high throughput?
- Proof of Work with parallel ASIC mining
- Proof of History combined with Tower BFT (Correct answer)
- Directed Acyclic Graph (DAG) consensus
- Federated Byzantine Agreement
Correct answer: Proof of History combined with Tower BFT
Solana uses Proof of History (a verifiable delay function creating a cryptographic clock) combined with Tower BFT to achieve consensus without requiring nodes to communicate timestamps.
Question 6: What is 'uncle blocks' (ommer blocks) in Ethereum's original PoW consensus?
- Blocks containing only coinbase transactions
- Valid blocks discovered simultaneously with the winning block that are included for partial rewards (Correct answer)
- Blocks rejected due to invalid transactions
- Blocks produced by mining pool coordinators rather than individual miners
Correct answer: Valid blocks discovered simultaneously with the winning block that are included for partial rewards
Uncle blocks are valid PoW solutions found at the same time as a winning block; Ethereum included them in the chain and rewarded their miners to reduce centralization pressure from stale blocks.
Question 7: In the context of blockchain mining, what does 'hashrate' measure?
- The number of transactions a miner can validate per second
- The number of hash computations a miner performs per second (Correct answer)
- The total value of blocks mined over a period
- The speed at which blocks are transmitted across the network
Correct answer: The number of hash computations a miner performs per second
Hashrate is the computational speed of a mining operation, measured in hashes per second (H/s), indicating how many proof-of-work attempts can be made each second.
CBCP Consensus Mechanisms and Mining 4
What is the key difference between 'probabilistic finality' and 'deterministic finality' in blockchain consensus?