CBSA Blockchain Architecture & Design Principles 3 — Questions and Answers
Question 1: In Byzantine Fault Tolerant systems, what is the maximum fraction of faulty nodes a network can tolerate while maintaining safety?
- Less than 1/4
- Less than 1/3 (Correct answer)
- Less than 1/2
- Less than 2/3
Correct answer: Less than 1/3
Classical BFT consensus (e.g., PBFT) requires fewer than one-third of nodes to be Byzantine faulty to guarantee both safety and liveness.
Question 2: Which pattern separates the execution of business logic from the storage of state to enable contract upgradability?
- Factory pattern
- Proxy-delegate pattern (Correct answer)
- Singleton pattern
- Observer pattern
Correct answer: Proxy-delegate pattern
The proxy-delegate (or transparent proxy) pattern stores state in a proxy contract and delegates logic calls to an implementation contract that can be swapped.
Question 3: What is the key architectural difference between a permissioned and a permissionless blockchain?
- Permissioned chains always use PoW consensus
- Permissioned chains restrict who can join and transact, while permissionless chains are open to anyone (Correct answer)
- Permissionless chains are always faster than permissioned ones
- Permissioned chains cannot support smart contracts
Correct answer: Permissioned chains restrict who can join and transact, while permissionless chains are open to anyone
Permissioned blockchains require identity verification and authorization to participate, enabling stronger privacy controls and higher throughput for enterprise use.
Question 4: Which Ethereum scaling solution batches many transactions off-chain and posts compressed data plus a validity proof to L1?
- Plasma
- State channels
- ZK-rollups (Correct answer)
- Sidechains
Correct answer: ZK-rollups
ZK-rollups execute transactions off-chain and submit a succinct cryptographic validity proof to L1, enabling high throughput with L1 security guarantees.
Question 5: In blockchain architecture, what is the 'nothing-at-stake' problem associated with?
- Proof of Work mining pools
- Proof of Stake consensus (Correct answer)
- Hash time-locked contracts
- Merkle proof verification
Correct answer: Proof of Stake consensus
In naive PoS, validators have no cost in voting on multiple competing forks, so they may support all forks simultaneously; slashing mechanisms address this.
Question 6: What architectural mechanism do hash time-locked contracts (HTLCs) primarily enable?
- On-chain random number generation
- Cross-chain atomic swaps and payment channel networks (Correct answer)
- Decentralized identity verification
- Sharded state management
Correct answer: Cross-chain atomic swaps and payment channel networks
HTLCs use cryptographic hash locks and time-based expiries to enforce atomicity across chains or payment channels without a trusted intermediary.
Question 7: When a blockchain architect evaluates 'finality,' what property are they assessing?
- The speed at which transactions are broadcast to peers
- The guarantee that a committed transaction cannot be reversed or altered (Correct answer)
- The maximum number of transactions per second
- The encryption strength of transaction signatures
Correct answer: The guarantee that a committed transaction cannot be reversed or altered
Finality describes the point after which a transaction is irreversibly settled; probabilistic finality (PoW) grows over time, while deterministic finality (BFT) is immediate.
CBSA Blockchain Architecture & Design Principles 3
In Byzantine Fault Tolerant systems, what is the maximum fraction of faulty nodes a network can tolerate while maintaining safety?