CBCP Blockchain Scalability and Interoperability 5 — Questions and Answers
Question 1: In a Lightning channel, what happens if a party broadcasts an outdated channel state to cheat?
- The transaction is silently ignored by miners
- The cheater receives the old balance after one confirmation
- The channel automatically splits funds 50/50
- The counterparty can use a revocation key to claim all channel funds as a penalty (Correct answer)
Correct answer: The counterparty can use a revocation key to claim all channel funds as a penalty
Lightning's penalty mechanism lets the wronged party use the revocation secret to sweep the entire channel balance within the timelock.
Question 2: How do users commonly avoid the long withdrawal delay of an optimistic rollup?
- By using liquidity providers or fast bridges that front funds on L1 for a fee (Correct answer)
- By converting to a sidechain token
- By reverting the rollup's last batch
- By submitting a fraud proof themselves
Correct answer: By using liquidity providers or fast bridges that front funds on L1 for a fee
Liquidity providers pay users immediately on L1 and then wait out the challenge period themselves, charging a fee for the service.
Question 3: How does a Validium differ from a ZK-rollup?
- Validium posts all data to Bitcoin
- Validium has no proofs at all
- Validium uses fraud proofs instead of validity proofs
- Validium stores transaction data off-chain while still using validity proofs (Correct answer)
Correct answer: Validium stores transaction data off-chain while still using validity proofs
Validium keeps validity proofs on-chain but stores data off-chain, increasing throughput at the cost of data availability guarantees.
Question 4: What is a commonly cited risk of rollups that rely on a single centralized sequencer?
- Inability to post data to Layer 1
- Loss of validity proof security
- Transaction censorship, reordering (MEV), or liveness failure if the sequencer goes down (Correct answer)
- Automatic forking of Ethereum
Correct answer: Transaction censorship, reordering (MEV), or liveness failure if the sequencer goes down
A single sequencer controls ordering and inclusion, creating censorship, MEV and downtime risks, though forced-inclusion mechanisms can mitigate some of these.
Question 5: Which category in Vitalik Buterin's classic interoperability taxonomy relies on a trusted party or group to attest to events on another chain?
- Notary schemes (Correct answer)
- Sharding
- Hash-locking
- Relays
Correct answer: Notary schemes
Notary schemes use a trusted entity or multisig group to confirm cross-chain events, unlike trust-minimized relays or hash-locking.
Question 6: BTC Relay on Ethereum is an example of which interoperability approach?
- Federated sidechain
- Atomic swap using HTLCs only
- Relay/light client that verifies Bitcoin block headers in a smart contract (Correct answer)
- Centralized custodial bridge
Correct answer: Relay/light client that verifies Bitcoin block headers in a smart contract
BTC Relay stored and verified Bitcoin block headers on Ethereum so contracts could validate Bitcoin transactions via SPV proofs.
Question 7: What is a key technical challenge introduced by sharding a blockchain?
- Secure and efficient cross-shard communication and transaction atomicity (Correct answer)
- Preventing nodes from storing any data
- Eliminating the need for consensus
- Removing all transaction fees
Correct answer: Secure and efficient cross-shard communication and transaction atomicity
Transactions touching multiple shards require coordination to keep state consistent and atomic, which adds complexity and latency.
