CBSA Blockchain Architecture & Design Principles 5 — Questions and Answers
Question 1: What is the primary advantage of using a directed acyclic graph (DAG) topology instead of a linear chain for blockchain data structure?
- Simpler consensus algorithm requirements
- Higher throughput by allowing parallel block confirmation without a single chain bottleneck (Correct answer)
- Elimination of all double-spend risk
- Full compatibility with existing EVM smart contracts
Correct answer: Higher throughput by allowing parallel block confirmation without a single chain bottleneck
DAG-based ledgers (e.g., IOTA's Tangle, Hedera Hashgraph) allow multiple blocks or transactions to be confirmed in parallel, dramatically increasing theoretical throughput.
Question 2: In a blockchain solution design, what does 'chain reorganization' (reorg) imply for application developers?
- Nodes must download the entire chain history after each block
- Previously confirmed transactions may be replaced if a longer competing chain emerges (Correct answer)
- Smart contract state is wiped and must be redeployed
- Validator keys must be rotated to prevent replay attacks
Correct answer: Previously confirmed transactions may be replaced if a longer competing chain emerges
A reorg replaces a portion of the canonical chain with a longer fork, potentially reversing transactions that appeared confirmed, requiring developers to wait for sufficient confirmations.
Question 3: Which approach best supports regulatory compliance requirements like data deletion (GDPR right to erasure) in a blockchain system?
- Store all personal data directly in transaction payloads on-chain
- Use cryptographic commitments on-chain with personal data stored off-chain in a deletable store (Correct answer)
- Hash all data on-chain to make it unreadable by default
- Implement a private chain with admin delete privileges
Correct answer: Use cryptographic commitments on-chain with personal data stored off-chain in a deletable store
Keeping personal data off-chain (deletable) while committing only a hash or pointer on-chain satisfies GDPR erasure rights without violating blockchain immutability.
Question 4: What is the architectural purpose of a 'channel' in Hyperledger Fabric?
- To encrypt inter-node gossip messages
- To create isolated sub-networks with their own ledger, enabling data privacy between participant subsets (Correct answer)
- To batch chaincode invocations for performance
- To route transactions to the fastest available orderer
Correct answer: To create isolated sub-networks with their own ledger, enabling data privacy between participant subsets
Channels in Fabric create private communication sub-networks; only channel members see transactions, allowing different consortia to share infrastructure while keeping data confidential.
Question 5: When designing tokenomics for a blockchain protocol, what does 'token velocity' indicate about economic health?
- The speed at which new tokens are minted per block
- How frequently tokens change hands; high velocity can reduce the incentive to hold and depress price (Correct answer)
- The rate at which tokens are burned to reduce supply
- The number of unique addresses holding the token
Correct answer: How frequently tokens change hands; high velocity can reduce the incentive to hold and depress price
High token velocity means tokens are quickly spent rather than held, weakening demand and potentially destabilizing the token's value in the ecosystem.
Question 6: Which architectural characteristic makes blockchain-based systems inherently resistant to retroactive data tampering?
- Symmetric encryption of all block data
- Chained cryptographic hashes where each block references its predecessor's hash (Correct answer)
- Distributed storage across geographically dispersed nodes
- Role-based access control on validator nodes
Correct answer: Chained cryptographic hashes where each block references its predecessor's hash
Each block header contains the hash of the previous block; altering any historical block changes its hash, invalidating all subsequent block hashes and requiring re-mining the entire chain.
Question 7: In the context of Layer 2 scaling, what is the key difference between an optimistic rollup and a ZK-rollup?
- Optimistic rollups require staking; ZK-rollups do not
- Optimistic rollups assume validity and rely on fraud proofs during a challenge window, while ZK-rollups post cryptographic validity proofs immediately (Correct answer)
- ZK-rollups support only token transfers; optimistic rollups support full smart contracts
- Optimistic rollups are faster to finalize than ZK-rollups
Correct answer: Optimistic rollups assume validity and rely on fraud proofs during a challenge window, while ZK-rollups post cryptographic validity proofs immediately
Optimistic rollups (e.g., Arbitrum, Optimism) have a dispute window (days) for fraud challenges, while ZK-rollups (e.g., zkSync, StarkNet) finalize as soon as the validity proof is verified on L1.
CBSA Blockchain Architecture & Design Principles 5
What is the primary advantage of using a directed acyclic graph (DAG) topology instead of a linear chain for blockchain data structure?