Blockchain Technology Architecture and Platforms 5 — Questions and Answers
Question 1: What is 'slashing' in Proof of Stake consensus mechanisms?
- Reducing block rewards during high network congestion
- Penalizing validators by destroying a portion of their staked tokens for provably malicious behavior (Correct answer)
- Cutting transaction fees to zero for priority users
- Reducing a validator's voting weight over time
Correct answer: Penalizing validators by destroying a portion of their staked tokens for provably malicious behavior
Slashing is a penalty mechanism that burns a portion (or all) of a validator's staked tokens if they double-sign blocks or attempt to attack the network.
Question 2: What is a 'private blockchain' and what is its primary use case?
- A blockchain using private keys for all transactions
- A fully controlled blockchain where access is restricted to a single organization for internal business processes (Correct answer)
- A blockchain that hides all transaction data from validators
- A blockchain that operates without a consensus mechanism
Correct answer: A fully controlled blockchain where access is restricted to a single organization for internal business processes
A private blockchain is centrally controlled by one organization, used primarily for internal data management, auditability, or process automation where public access is unnecessary.
Question 3: What is the 'Block Header' in blockchain architecture and what data does it typically contain?
- The first transaction in a block, always a coinbase transaction
- Metadata including the previous block hash, Merkle root, timestamp, nonce, and difficulty target (Correct answer)
- The list of all public keys authorized to sign blocks
- The block's transaction count and total fees collected
Correct answer: Metadata including the previous block hash, Merkle root, timestamp, nonce, and difficulty target
A block header contains metadata that links the block to the chain, including the hash of the previous block, the Merkle root of all transactions, timestamp, and consensus-specific fields.
Question 4: What distinguishes an 'optimistic rollup' from a 'ZK-rollup' as layer-2 scaling solutions?
- Optimistic rollups are on-chain; ZK-rollups are off-chain
- Optimistic rollups assume transactions are valid and use fraud proofs if challenged, while ZK-rollups use cryptographic validity proofs upfront (Correct answer)
- ZK-rollups are only compatible with Ethereum; optimistic rollups work on any chain
- Optimistic rollups are faster to finalize than ZK-rollups
Correct answer: Optimistic rollups assume transactions are valid and use fraud proofs if challenged, while ZK-rollups use cryptographic validity proofs upfront
Optimistic rollups post transactions assuming validity, allowing a challenge window for fraud proofs, while ZK-rollups attach a cryptographic validity proof with each batch, enabling faster finality.
Question 5: In a Directed Acyclic Graph (DAG) based blockchain architecture like IOTA, how are transactions confirmed?
- By miners competing to solve hash puzzles in linear blocks
- By each new transaction validating two previous transactions, creating a web-like structure instead of a chain (Correct answer)
- By a single committee of elected validators per epoch
- By smart contracts running consensus algorithms automatically
Correct answer: By each new transaction validating two previous transactions, creating a web-like structure instead of a chain
In DAG architectures like IOTA's Tangle, users must validate two prior transactions when submitting their own, creating a mesh of confirmations rather than a linear chain of blocks.
Question 6: What is the significance of the 'nonce' field in a Bitcoin block header?
- It uniquely identifies the block's creator (miner)
- It is the variable miners increment repeatedly to find a hash below the target difficulty (Correct answer)
- It encodes the number of transactions in the block
- It specifies the block's position in the blockchain
Correct answer: It is the variable miners increment repeatedly to find a hash below the target difficulty
The nonce is a 32-bit number that miners systematically change to alter the block header hash, seeking one that meets the current difficulty target — the core of Proof of Work mining.
Question 7: What is 'cross-chain atomic swap' technology?
- A method to merge two separate blockchains into one
- A trustless exchange of cryptocurrencies between different blockchains without a centralized intermediary (Correct answer)
- A consensus mechanism shared across multiple chains
- A smart contract upgrade mechanism that works across EVM chains
Correct answer: A trustless exchange of cryptocurrencies between different blockchains without a centralized intermediary
Atomic swaps use Hashed Timelock Contracts (HTLCs) to ensure that a cross-chain trade either fully completes on both chains or is entirely refunded, eliminating counterparty risk.
Blockchain Technology Architecture and Platforms 5
What is 'slashing' in Proof of Stake consensus mechanisms?