Cryptocurrency Blockchain Technology Fundamentals 4 — Questions and Answers
Question 1: What is the Byzantine Generals Problem in relation to blockchain?
- A historical attack on early Bitcoin nodes
- The challenge of reaching consensus among distributed nodes that may be dishonest (Correct answer)
- A conflict between miners over block rewards
- The difficulty of synchronizing clocks across global nodes
Correct answer: The challenge of reaching consensus among distributed nodes that may be dishonest
The Byzantine Generals Problem describes how decentralized systems must reach reliable consensus even when some participants send conflicting or malicious messages.
Question 2: What is the UTXO model used in Bitcoin?
- A system where each user has a single running balance
- A model where transactions consume previous outputs and create new unspent outputs (Correct answer)
- A method to track validator stakes
- An off-chain payment channel structure
Correct answer: A model where transactions consume previous outputs and create new unspent outputs
The Unspent Transaction Output model treats coins as discrete outputs; a transaction spends existing UTXOs as inputs and creates new UTXOs, with no global account balance.
Question 3: What is 'double spending' and why is preventing it critical to cryptocurrencies?
- Paying transaction fees twice by accident
- Using the same digital coins in two transactions simultaneously, undermining monetary value (Correct answer)
- Mining the same block twice for extra reward
- Sending two payments to the same address
Correct answer: Using the same digital coins in two transactions simultaneously, undermining monetary value
Double spending is the digital equivalent of counterfeiting; blockchain consensus prevents it by ensuring only one version of a transaction history is accepted network-wide.
Question 4: What is 'block propagation' in a blockchain network?
- The process of creating a new block
- The speed at which a newly mined block spreads to all nodes in the network (Correct answer)
- The mechanism for increasing block size over time
- The algorithm that selects which transactions enter a block
Correct answer: The speed at which a newly mined block spreads to all nodes in the network
Fast block propagation reduces the chance of orphaned blocks and chain splits; slow propagation gives large mining pools a centralization advantage.
Question 5: What does 'gas' represent on the Ethereum blockchain?
- A separate token used to pay miners
- A unit measuring the computational effort required to execute an operation (Correct answer)
- The storage fee for data on the blockchain
- The inflation rate of newly minted ETH
Correct answer: A unit measuring the computational effort required to execute an operation
Gas quantifies computation on Ethereum; each operation (e.g., addition, storage write) has a fixed gas cost, and users pay gas_used × gas_price in ETH to compensate validators.
Question 6: What is a 'sidechain' in blockchain architecture?
- A backup copy of the main chain stored off-site
- A separate blockchain that runs in parallel and is pegged to a main chain (Correct answer)
- A second layer of validators on the same chain
- A chain created during a network fork that is later discarded
Correct answer: A separate blockchain that runs in parallel and is pegged to a main chain
Sidechains allow assets to be transferred from a main chain via a two-way peg, enabling experimentation or specialized functionality without burdening the main chain.
Question 7: What is the purpose of a blockchain 'mempool'?
- Long-term archival storage for old blocks
- A holding area for unconfirmed transactions waiting to be included in a block (Correct answer)
- A cache for recently accessed wallet balances
- The memory used to store smart contract state
Correct answer: A holding area for unconfirmed transactions waiting to be included in a block
The memory pool (mempool) is where broadcast transactions queue before miners/validators select them for block inclusion, typically prioritizing higher-fee transactions.
Cryptocurrency Blockchain Technology Fundamentals 4
What is the Byzantine Generals Problem in relation to blockchain?