On January 16, 2024, Daniel Wang, the founder of the Ethereum Layer 2 project Taiko, initiated a discussion on Twitter to interact with Zeng Jiajun, the founder of AA wallet Soul Wallet. Under this tweet, Ethereum founder Vitalik made some remarks, emphasizing that the key to Rollup is to provide unconditional security, and users can successfully withdraw assets even if they face confrontation from everyone. He also pointed out that such unconditional secure withdrawals would not be possible if Layer 2 relied on external systems outside of Ethereum.Vitalik's comments attracted a lot of attention, especially after he mentioned his views on Validium. Many people had previously generally believed that the Ethereum Foundation equated Layer 2 with Rollup, but Vitalik’s remarks seemed to raise some doubts about this. When discussing the DA concept in the Ethereum community, the focus is on whether newly generated data from Layer 2 can be obtained, rather than retrieving historical data long ago.Vitalik's point of view is not rigorous. First of all, he emphasizes that only assets bridged from Layer1 to Layer2 can be crossed back to the ETH chain, while pure Layer2 native assets cannot be crossed to Layer1 unless a bridging asset contract is deployed on Layer1.Secondly, "safe withdrawal without conditions" does not have to rely on the DA system. He mentioned that early Layer 2 solutions and Plasma, which implements DA data release under the Ethereum chain, can both allow users to submit asset certificates through historical data, even if the DA system fails. I think Plasma’s safe withdrawals do not rely on the DA system, and Vitalik’s remarks may have been influenced by the mindset of the previous scheme.The “safe withdrawal without conditions” mentioned by Vitalik and the “data availability challenge” he did not mention are to explain why third-party DA projects such as Celestia, Avail, and EigenDA are not necessary to achieve Layer 2 security.Vitalik’s remarks were actually discussing ZK Rollup’s escape hatch, a withdrawal mode that is triggered directly on Layer1. The design of the escape hatch enables users to prove their asset status in Layer 2 through Merkle Proof. Even if the Layer 2 node does not cooperate, they can still withdraw assets on Layer 1.The operation process of the escape cabin mode includes forced withdrawal, trigger conditions of the escape cabin and how to construct Merkle Proof. After EIP-4844, all Ethereum nodes automatically discarded some historical data, so that historical data of Layer 2 for more than 18 days is no longer backed up by the entire ETH node network, thus introducing a certain trust assumption.The relationship between Escape Pod and DA, especially the possible "ransomware attack" in the Validium scheme. Validium, where DA is off-chain, is vulnerable to "data withholding attacks", that is, the sequencer may withhold transaction data and not release it, resulting in users being unable to construct Merkle Proof for withdrawals. However, this is not a problem with DA itself, but rather the design of the Validium solution is not perfect enough. This problem can be solved by introducing corresponding challenge mechanisms or data availability challenges.The "data availability challenge" mechanism being implemented by projects such as Arbitrum and Redstone allows the sequencer to only publish DA Commitment and Stateroot on the chain, and then ensure that the transaction data published off-chain can be verified through the challenge mechanism. The design of this mechanism is simple and effective, and does not need to rely on third-party DA projects, such as Celestia. However, it is also noted that data availability challenges may present economic issues and require careful consideration.Interpreting Vitalik’s remarks highlights the relationship between censorship-resistant withdrawals and the DA system, and explores the impact of escape hatches and data availability challenges on Layer 2 security. He emphasized the importance of censorship-resistant withdrawals and pointed out that good DA and proof systems are sufficient conditions for achieving censorship-resistant withdrawals, but they are not necessary conditions.
