Yesterday the Arbitrum network stopped operating for about 90 minutes from 10:29-11:57, why did Ethereum L2 go down?
Arbitrum官方给出的回答是：
Because of the surge in the number of users brought about by the inscription protocol, the sequence of Arbitrum stopped working, and eventually caused the network to go down. Why can a surge in user volume cause Arbitrum to go down? There are no downtime for hundreds of thousands of inscriptions on the Bitcoin chain? Because Arbitrum's sequencer is centralized, and only one official node is running the network, so when this node (sequencer) fails, the network will definitely go down.
In fact, you can simply understand that the operation of Arbitrum's POS network ledger relies on the official own nodes (sequencers), but why do users still dare to use it, because Arbitrum's ledger will be Roullp (rolled up and compressed) packaged to the Ethereum network, so that the Ethereum network nodes can verify the ledger, so as to ensure the security of the ledger, Ethereum L2 is basically this idea. Both OP-Roullp and ZK-Roullp package the ledger to the Ethereum mainnet and let the mainnet nodes verify the layer 2 ledger. The core goal of this is to make the Layer 2 ledger credible.
To use an unsightly analogy: the son has no money, and the son's credit is not worth much, so the son takes a check from Lao Tzu as money to spend and uses Lao Tzu's credit to guarantee his son. The credit of the layer-2 ledger of Ethereum is attached to the first layer of Ethereum, which is the mainstream design of Ethereum L2. Of course, this design is currently the optimal solution, but there are several problems:
1. There will be a single point of risk in the second layer, because the sequencer is centralized, for example, it is prone to downtime.
2. The assets of the second layer are not resistant to review and can be forcibly frozen. This is a problem that almost all Ethereum layers 2 face!
Does Ethereum layer 2 network have such problems? So can Bitcoin layer 2 solve these problems, and what are the similarities and differences between the design of Bitcoin layer 2 and Ethereum layer 2?
Before we get to this question, we need to understand a few questions:
1. What is Layer 2 and what is the essence of Layer 2?
2. What are the design principles of Layer 2 and what are the similarities and differences between Bitcoin Layer 2 and Ethereum Layer 2 in terms of design?
3. The right path to Bitcoin Layer 2
1. What is Layer 2 and what is the essence of Layer 2?
The concept of Layer 2 is well-known because of the Ethereum ecosystem, but the concept of Layer 2 is not original to the Ethereum ecosystem, but comes from Bitcoin. The Bitcoin 0.1 version of the code retains a copy of the original version of the code, which was left by Satoshi Nakamoto. This code allows the user to update a transaction before it is packaged and confirmed by the miner.
If one user's balance increases, the other user's balance decreases accordingly, and once the user completes the transaction, they can transmit only one transaction result to the mainchain network and then close their payment channel.
Based on the "payment channel", the Lightning Network was born, which is the earliest Layer 2 of Bitcoin and the earliest and feasible Layer 2 in the crypto world Ethereum Layer 2 is the first to look forward, and it is not possible to take the design scheme of Ethereum Layer 2 as the only criterion (after all, Ethereum Layer 2 has basically determined the feasibility of the design direction of roullp after two years of development), but to see the essence through the phenomenon, we need to understand what is the essence of Layer 2, so as to design a feasible Layer 2. Whether it is Bitcoin Layer 2 or Ethereum Layer 2, the background of its birth is that when the Layer 1 mainnet cannot achieve more complex and high-performance application scenarios, it is necessary to jump Layer 1 assets to Layer 2 to realize. Ethereum needs Layer 2 to expand its performance, and Bitcoin needs Layer 2 even more.
For example, BTC can enable fast and efficient payments in the Lightning Network, while ETH can cross over to Arbitrum for faster, lower gas, and more complex smart contract scenarios.
Therefore, whether it is Bitcoin Layer 2 or Ethereum Layer 2, its essence is the same, which is to make Layer 1's mainnet assets cross to Layer 2 to achieve more complex and high-performance application scenarios. Therefore, the essence of Layer 2 is a decentralized cross-chain solution + a high-performance and trustless layer 2 network. Then, whether it is Bitcoin Layer 2 or Ethereum Layer 2, there are some basic principles that must be followed when designing:
1. It is necessary to realize that Layer 1 assets can cross to Layer 2 trustlessly, which is the most important first step.
2. The ledger of the Layer 2 network must be secure and trustless
Only when the above two conditions are met at the same time can it be a practical and fully decentralized Layer 2.
2. What are the similarities and differences between the design of Bitcoin Layer 2 and Ethereum Layer 2?
Now that we have figured out what the essence of Layer 2 is, and also figured out the basic principles of Layer 2 design, let's take a look at the similarities and differences between Bitcoin Layer 2 and Ethereum Layer 2 in terms of actual design?
1. Layer 1 assets must be trusted to cross to Layer 2.
In terms of solving this problem, Ethereum's approach is as follows: Layer 2 officially deploys a smart contract that hosts assets on the Ethereum mainnet, and when a user crosses ETH from the Ethereum mainnet to Layer 2, the user's ETH is locked in the smart contract and generates new ETH on the Layer 2 network 1:1. When a user sends a command to cross back to the mainnet, the ETH of Layer 2 is burned, and the smart contract on Layer 1 is triggered to unlock the ETH to the user. This is the cross-chain implementation of Ethereum Layer 1 and Layer 2. It is achieved through Ethereum's smart contracts and Layer 1 and Layer 2 network communication, which can achieve trustlessness.
So, how does Bitcoin's Layer2 achieve trustless BTC cross-chain?
Before the Bitcoin Taproot upgrade in 2021, it was not possible to achieve a fully decentralized BTC cross-chain, however, thanks to the Taproot upgrade, which brought Schnorr signatures and MAST contracts, fully decentralized Bitcoin cross-chain became a reality.
Schnorr signature is a signature algorithm that is more suitable for Bitcoin than elliptic curve signature (not what I said, when Satoshi Nakamoto created Bitcoin, he actually wanted to use Schnorr signature, but at that time Schnorr signature was not open source, after Schnorr signature was open source in 2009, after 12 years of investigation and verification, finally in 2021, Bitcoin Core officially introduced Schnorr signature into Bitcoin through Taproot upgrade, Ethereum has always wanted to support Schnorr signature, but because the upgrade signature algorithm involves complex issues such as Ethereum's account system, so Ethereum has not been upgraded to Schnorr signatures. ）
The biggest feature of Schnorr signature is polysignature, which can realize 1000 bitcoin addresses to sign and manage the same asset, which can not only realize the privacy of the signature, but also merge the data submitted by 1000 signatures into one, completely solving the data accumulation problem caused by multiple signatures, therefore, Schnorr signature can break through the original limit of 15 multi-signature of Bitcoin at most, and realize completely decentralized signature management.
The Mast contract, which stands for Merkle Abstract Syntax Tree, uses a Merkle tree to encrypt complex locking scripts, and its leaves are a series of non-overlapping scripts, and when spending, only the relevant scripts and the path from that script to the root of the Merck tree are disclosed. To put it simply, a Mast contract is a function equivalent to a VM (a smart contract-like function) that can perform a given operation through instructions, such as Mast contract+The combination of Schnorr signatures can be used to trigger the Mast contract to allow 1,000 nodes participating in decentralized asset management to sign, so as to intelligently execute the entry and exit and spending of bitcoin in accordance with the rules set by the contract, without any human intervention, completely relying on the contract execution, so as to realize the decentralized management of bitcoin.
The organic combination of Schnorr signature + Mast contract can achieve a fully decentralized BTC Layer 2. In order to facilitate understanding, let's take the BTC Layer2 project BEVM as an example (BEVM is implemented using Schnorr signature + Mast contract) to see how the fully decentralized BTCLayer2 is implemented. When the user crosses the BTC of the Bitcoin mainnet to the BEVM, the user's BTC enters the contract address hosted by 1000 nodes, and then, at the same time, a new BTC is generated in the BEVM that is, the BTC Layer2 network according to 1:1, when the user sends an instruction to cross the BTC from BEVM back to the mainnet, the BEVM network node will trigger the Mast contract, and the nodes of 1000 custodian assets will automatically sign according to the established rules and return the BTC to the user's address.
The whole process is completely decentralized and trustless. As can be seen from the above, by using the combination of Mast contract + Schnorr signature brought by Taproot, Bitcoin can also achieve a fully trustless cross-chain like Ethereum Layer 2, which is the most important first step to achieve a fully decentralized BTC Layer 2.
2. The ledger of the Layer 2 network must be secure and trustless.
The ledger of Ethereum Layer 2 is managed by a sequencer, and when processing transactions, the ledger of Layer 2 is packaged and uploaded to the Ethereum mainnet according to a certain ratio, generally a ratio of 10:1, and then verified by Ethereum nodes, however, the sequencer of Ethereum Layer 2 (that is, the running node of the Layer 2 network, generally only has one official node) is completely centralized, and it is run and mastered by the Layer 2 official.
How to gain user trust with such a centralized design? It is mainly by packaging the Layer 2 ledger roullp to the Ethereum mainnet for miner nodes to verify, if users do not trust the ledger, they can verify the ledger by initiating an off-chain report, therefore, Op-Roullp is also known as optimistic proof, that is, its trust assumption is optimistic that the official does not do evil, and if it does evil, it can be proved by reporting. These combinations can basically ensure that the Layer 2 ledger is trusted.
However, this also leads to the single-point risk of the sequencer in Ethereum Layer 2, and also leads to the fact that assets such as ETH on Layer 2 are not censorship-resistant, and can be forcibly frozen by external forces, because the ETH Layer 2 sequencer is officially its own node and can be centrally controlled. This will also lead to the upper limit of the asset size of ETH Layer 2, because many large funds will not dare to enter because of the problem of non-censorship resistance, just imagine, if you have 100,000 ETH, do you dare to cross these assets to a non-censorship Ethereum Layer 2? Yesterday's Arbitrum network outage also exposed the problem of sequencer single point risk. At the same time, there are also two user-friendly problems arising here: a. Since Op-Roullp has a 7-day reporting mechanism, when users cross ETH from Layer 2 back to the Ethereum mainnet, they need to complete at least a 7-day reporting period.
b. Since the sequencer of ETH Layer 2 is completely controlled by the official node of the project, the cross-chain and transaction fees of ETH Layer 2 are completely exclusive to the official project (it is reported that the monthly revenue of ETH Layer 2 sequencers such as Base and ZKsync exceeds $5 million, and exceeds $10 million at peak times), and Layer 2 users cannot share these network growth dividends.
So, how does Bitcoin Layer 2 achieve ledger trustworthiness?
We still take BEVM as an example, as we mentioned earlier, BEVM is a combination of Mast contract + Schnorr signature to achieve Bitcoin decentralized cross-chain, and in order to achieve real-time communication between Layer 2 and Layer 1, the BEVM network is a fully operational Bitcoin light node, so BEVM is a trusted network composed of 1000 Bitcoin light nodes.
In order to ensure the absolute security of the Layer 2 ledger and ensure that the network nodes do not do evil, BEVM draws on the economic game mechanism of the Bitcoin network, BEVM combines the nodes that host Bitcoin and the nodes that run on the Layer 2 network, that is, the nodes that run the Layer 2 network by pledging assets are also the nodes that host BTC assets, and at the same time, BEVM has designed a set of automated dynamic staking mechanisms based on economics, that is, to ensure that the BTC/ pledged by the Layer 2 nodes of BEVM. The total value of the mainnet token is always greater than the value of the assets under its custody, and the mechanism of economic game is used to ensure that the network nodes of Layer 2 have no incentive to do evil, so as to ensure that the ledger of Layer 2 is absolutely safe and trustworthy.
In addition to this, the design of BEVM brings two benefits, which are also not available in Ethereum Layer 2:
a. The network nodes of BEVM are completely decentralized and not controlled by a certain project party, therefore, BTC is censorship-resistant on BEVM, a Layer 2, and cannot be frozen by any force, and can cross into and out of the Bitcoin mainnet at any time. Thus, the problem of trust in large funds can be solved.
b. Since the BEVM network is run by decentralized nodes, the cross-chain and network fees generated are shared with nodes and users, and are not exclusive to the project team.
3. The right path for Bitcoin Layer 2
Due to the inherent difference between Bitcoin and Ethereum, therefore, when designing Bitcoin Layer 2, we should not copy the Ethereum Layer 2 model, but should see through the essence of Layer 2 and combine the characteristics of Bitcoin to get out of the correct path of Bitcoin Layer 2.
The right design direction for Bitcoin Layer 2:
1. Bitcoin Layer1 is naturally not Turing complete, and Bitcoin's minimalist UTXO design and block space cannot verify complex data and programs, so it is not feasible to try to verify through the client or make improvements in Bitcoin's limited UTXO and block space. The only correct direction is to jump BTC out of Layer 2 in a decentralized way, so as to achieve more complex and high-performance scenario expansion.
2. We must solve the problem of Bitcoin decentralization and cross-chain to Layer 2, which is the foundation of everything. It is difficult to gain the trust of users through traditional Bitcoin cross-chain methods such as hash timelock, peeping, encapsulation, and multi-signature. The technical combination of Mast contract + Schnorr signature brought by Bitcoin's Taproot upgrade in 2021 can solve the problem of Bitcoin's decentralized cross-chain, and it is also a direction worth exploring for Bitcoin Layer 2.
3. In order to ensure the security and trustworthiness of the Layer 2 ledger, it is absolutely impossible to copy the model of Ethereum Layer 2 and try to compress and package the BTC Layer 2 ledger into the Bitcoin chain for verification through roullp, because the Bitcoin blockchain does not support the verification of OP or ZKP, and miners will not participate in the verification of the Layer 2 ledger, and storing these ledgers on the Bitcoin chain is just a proof, which has no meaning. To ensure the security of the Layer 2 ledger, you can learn Xi the economic game mechanism of Bitcoin, and design the dynamic staking mechanism of nodes through the level of economics and game theory, so as to realize that the nodes of the Layer 2 network have no incentive to do evil, so as to ensure the security of the Layer 2 ledger.
Of course, we also hope that Bitcoin will be upgraded to BIP level again in the future, so that the Bitcoin network can verify OP or ZKP, Bitcoin mining machines can perform ZKP calculations, ZK-roullp can enter the Bitcoin network, and at that time, Bitcoin Layer 2 can achieve a more ultimate solution. However, this may not be possible in the next 5-10 years or even longer.
Based on the above analysis, we can see that the most feasible BTC Layer2 solution is based on the Mast contract + brought by the Taproot upgradeSchnorr signature, combined with the Bitcoin light node dynamic staking network to achieve real-time communication and network security of Layer 2 and Layer 1, so as to achieve a truly decentralized Bitcoin Layer 2, and this is the solution that BEVM has achieved (for details, please refer to the BEVM white paper: https://github.com/btclayer2/BEVM-white-paper)
So, does Bitcoin Layer 2 have a chance to surpass the volume of Ethereum Layer 2?
The answer is almost yes:
I think there are at least a couple of reasons for this:
1. At present, there is a fully decentralized BTC Layer2 solution that can be used.
Before the full decentralization scheme, the largest bitcoin wrapped asset was WBTC issued through the centralized institution Bitgo, which is currently about $6.5 billion. After the emergence of fully decentralized solutions (such as BEVM), it is predicted that the market can grow by more than 5-10 times, and the volume can reach $32.5 billion-65 billion, which is far greater than the current total TVL of ETH Layer 2 of $20 billion (this data includes cross-chain ETH and other assets on ETH Layer 2, and the actual cross-chain ETH is far from reaching $20 billion)
2. Bitcoin is naturally Turing-incomplete, so Bitcoin needs Layer 2 more than Ethereum to develop its ecosystem, so there will be a large number of BTC to Layer 2 to build various decentralized BTC applications in the future. This is determined by market demand.
3. Bitcoin Layer 2 can be more censorship-resistant than Ethereum Layer 2, and it is easier to gain the trust and favor of users, especially large funds.
4. The market value of Bitcoin is three times the market value of Ethereum, and the total TVL of ETH Layer 2 is about 20 billion US dollars, accounting for about 10% of the market value of Ethereum; according to the same ratio, if 10% of BTC enters Bitcoin Layer 2 in the future, the entire TVL will reach 85 billion US dollars, which is three times the volume of Ethereum Layer 2.
Summary:
Layer2 solutions originated from the Bitcoin ecosystem and developed from the Ethereum ecosystem. The current solution of Ethereum Layer 2 is not perfect, nor is it the ultimate solution of L2, let alone the only reference standard for all L2s.
Bitcoin Layer 1 is inherently Turing-incomplete, and Bitcoin's minimalist UTXO and limited block space are unable to handle complex data and calculations. Therefore, Bitcoin must be a Layer 2 for the development of the ecosystem, and it is a fully decentralized Bitcoin Layer 2.
Before the Bitcoin Taproot upgrade in 2021, Bitcoin could not achieve a fully decentralized Layer2 solution, however, the Mast contract + Schnorr signature brought by the Taproot upgrade realized a fully decentralized BTC cross-chain, therefore, but the fully decentralized Bitcoin L2 became a reality, and the BTC Layer2 project - BEVM gave its own answer.
Bitcoin Layer 2 cannot completely copy the Ethereum Layer 2 scheme, and needs to be designed in combination with the characteristics of Bitcoin itself.
Finally, the Layer 2 volume of Bitcoin will surpass the volume of Ethereum Layer 2, which is an inevitable trend!