Cryptocurrency Blockchain and Consensus Mechanisms 5 — Questions and Answers
Question 1: What is 'Proof of History' (PoH) used by Solana?
- A consensus mechanism where validators prove they held tokens historically
- A cryptographic clock that creates a verifiable sequence of events over time (Correct answer)
- A record of all past validators' voting history stored on-chain
- A reputation system that weights validators by their age on the network
Correct answer: A cryptographic clock that creates a verifiable sequence of events over time
Proof of History is a verifiable delay function that encodes the passage of time cryptographically, allowing Solana nodes to agree on event ordering without network communication.
Question 2: In blockchain terminology, what is a 'fork choice rule'?
- The governance process by which miners vote on protocol upgrades
- The algorithm nodes use to determine which chain to follow when multiple valid chains exist (Correct answer)
- The rule that decides when to increase or decrease block size
- The method of selecting transaction ordering within a proposed block
Correct answer: The algorithm nodes use to determine which chain to follow when multiple valid chains exist
A fork choice rule (like Bitcoin's longest chain or Ethereum's LMD-GHOST) is the algorithm that determines the canonical chain when the network sees competing block proposals.
Question 3: What is 'Proof of Burn' as a consensus mechanism?
- Miners must overheat their GPUs to prove computational effort
- Participants send coins to an unspendable address to earn the right to mine new coins (Correct answer)
- Validators must destroy a percentage of transaction fees each epoch
- Nodes burn CPU cycles by running intentionally inefficient hashing algorithms
Correct answer: Participants send coins to an unspendable address to earn the right to mine new coins
Proof of Burn requires participants to provably destroy cryptocurrency by sending it to a verifiably unspendable address, granting mining rights proportional to coins burned.
Question 4: What is the 'nothing-at-stake' problem in early proof-of-stake designs?
- Validators earn rewards even when they are offline, disincentivizing participation
- Validators could vote on multiple competing forks at no cost, undermining consensus (Correct answer)
- Nodes with no stake can still read the blockchain, creating privacy risks
- Block proposers could propose empty blocks to collect the base fee without effort
Correct answer: Validators could vote on multiple competing forks at no cost, undermining consensus
Unlike PoW where mining one fork means wasting hash rate on another, early PoS validators had no computational cost to vote on every fork simultaneously, undermining security.
Question 5: What is a 'checkpoint' in the context of blockchain consensus?
- A scheduled snapshot of the mempool used to calculate mining fees
- A block or state designated as finalized, before which reorganization is disallowed (Correct answer)
- A validator rotation point where committee assignments are reshuffled
- A mandatory sync point that light clients must reach before relaying transactions
Correct answer: A block or state designated as finalized, before which reorganization is disallowed
Checkpoints mark blocks as irreversible anchors in the chain history, preventing deep reorganizations beyond that point.
Question 6: What is the primary trade-off of increasing block size in a proof-of-work blockchain?
- Larger blocks require more validators, increasing decentralization pressure
- Larger blocks take longer to propagate, increasing orphan rates and centralization risk (Correct answer)
- Larger blocks require harder cryptographic puzzles to maintain security
- Larger blocks reduce the mining difficulty, making attacks cheaper
Correct answer: Larger blocks take longer to propagate, increasing orphan rates and centralization risk
Bigger blocks take longer to propagate across the network, giving large mining pools a propagation advantage and pushing smaller miners toward centralized pools.
Question 7: What role does the 'mempool' play in blockchain transaction processing?
- It stores finalized blocks before they are written to disk
- It is a holding area for unconfirmed transactions waiting to be included in a block (Correct answer)
- It is the off-chain layer where layer-2 transactions are settled before posting to L1
- It is the validator set registry that tracks active proof-of-stake participants
Correct answer: It is a holding area for unconfirmed transactions waiting to be included in a block
The mempool (memory pool) is each node's local queue of broadcast transactions that have not yet been confirmed in a block, from which miners or validators select transactions to include.
Cryptocurrency Blockchain and Consensus Mechanisms 5
What is 'Proof of History' (PoH) used by Solana?