Blockchain Developer Blockchain Scalability and Layer 2 Solutions 2 — Questions and Answers
Question 1: What is the 'data availability' problem in the context of Layer 2 rollups?
- The difficulty of syncing Layer 2 nodes with the latest Layer 1 state
- Ensuring that transaction data is published and accessible so anyone can reconstruct the rollup state and verify or challenge it (Correct answer)
- The challenge of storing large NFT metadata on-chain
- The latency introduced when querying historical blocks on Ethereum
Correct answer: Ensuring that transaction data is published and accessible so anyone can reconstruct the rollup state and verify or challenge it
If transaction data is withheld, users cannot independently verify the rollup state or generate fraud/validity proofs, making data availability a critical security property.
Question 2: In ZK-Rollup terminology, what does the 'sequencer' do?
- Generates the zero-knowledge proof for each transaction batch
- Orders, batches, and submits transactions to Layer 1 on behalf of users (Correct answer)
- Verifies the validity proof on Layer 1
- Acts as the bridge between Layer 1 and Layer 2 for token transfers
Correct answer: Orders, batches, and submits transactions to Layer 1 on behalf of users
The sequencer collects user transactions, determines their order, bundles them into batches, and posts batches (along with proofs) to Layer 1.
Question 3: What is Plasma in the context of Ethereum scalability?
- A programming language for writing Ethereum smart contracts
- A framework for creating child chains anchored to Ethereum, where only block roots are submitted to the main chain (Correct answer)
- An Ethereum consensus upgrade that replaced Proof of Work
- A Layer 2 solution based exclusively on zero-knowledge proofs
Correct answer: A framework for creating child chains anchored to Ethereum, where only block roots are submitted to the main chain
Plasma allows the creation of child chains that periodically commit Merkle roots of their state to Ethereum, enabling high-throughput processing with Ethereum as the final arbiter.
Question 4: What is the primary function of a cross-chain bridge in a multi-chain ecosystem?
- To validate zero-knowledge proofs across different blockchain networks
- To enable the transfer of assets and data between two separate blockchain networks (Correct answer)
- To synchronize block times between Layer 1 and Layer 2 chains
- To merge two blockchain networks into a single unified chain
Correct answer: To enable the transfer of assets and data between two separate blockchain networks
A cross-chain bridge locks or burns assets on one chain and mints or releases equivalent assets on another chain, enabling interoperability between separate blockchains.
Question 5: What is the standard challenge period duration used by most Optimistic Rollups like Arbitrum and Optimism?
- 24 hours
- 3 days
- 7 days (Correct answer)
- 30 days
Correct answer: 7 days
Most Optimistic Rollups use a 7-day challenge window to give honest validators sufficient time to detect and prove fraudulent transactions before they are finalized.
Question 6: Which scaling approach is used by Validium, differentiating it from standard ZK-Rollups?
- Validium uses optimistic proofs instead of zero-knowledge proofs
- Validium stores transaction data off-chain with a data availability committee rather than posting it to Layer 1 (Correct answer)
- Validium processes transactions on a sidechain without any cryptographic proofs
- Validium compresses all calldata using Merkle Patricia Tries before posting to Layer 1
Correct answer: Validium stores transaction data off-chain with a data availability committee rather than posting it to Layer 1
Validium uses validity proofs like ZK-Rollups but keeps transaction data off-chain, relying on a data availability committee, which reduces costs but introduces a data availability trust assumption.
Question 7: What major vulnerability class has most frequently exploited cross-chain bridges, resulting in hundreds of millions in losses?
- Front-running attacks on transaction ordering
- Reentrancy bugs in smart contracts
- Flaws in signature verification and validator key management (Correct answer)
- Integer overflow in token balance calculations
Correct answer: Flaws in signature verification and validator key management
High-profile bridge hacks like Ronin and Wormhole exploited weaknesses in multi-signature schemes, private key management, or signature verification logic used to authorize cross-chain messages.
Blockchain Developer Blockchain Scalability and Layer 2 Solutions 2
What is the 'data availability' problem in the context of Layer 2 rollups?