The concept of Layer2 is well known because of the Ether ecosystem, but the concept of Layer2 is not original to the Ether ecosystem, but comes from Bitcoin.


Bitcoin version 0.1 retained a copy of the original version of the code in its code, left behind by Satoshi Nakamoto. This code supports users updating transactions before they are packaged and confirmed by miners. If one user's balance increases, another user's balance decreases, and once a user completes a transaction, they can transmit only one transaction result to the main chain network and then close their payment gateway. Based on the "payment channel," the Lightning Network was created, which was the first Layer2 for Bitcoin, and one of the first viable Layer2s in the crypto world.


Both Bitcoin Layer2 and Ether Layer2 were born out of the need to move Layer1 assets to Layer2 when Layer1 hosts were unable to realize more complex and high-performance application scenarios. Ether needs Layer2 to expand its performance, while Bitcoin needs Layer2 even more, for example, BTC can realize fast and efficient payment scenarios in the Lightning Network, and ETH can cross over to Arbitrum to realize faster, lower-gas and more complex smart contract scenarios.


Therefore, whether it is Bitcoin Layer2 or Ether Layer2, the essence is the same, both are to allow the main network assets of Layer1 to cross to Layer2 to realize more complex and higher performance application scenarios. Therefore, the essence of Layer2 is a decentralized cross-chain solution + a high-performance and trust-less Layer 2 network.

What are the design similarities and differences between Bitcoin Layer2 and Ether Layer2?

Layer1 assets must be realized to cross over to Layer2 without trust

In terms of solving this problem, Ethernet's approach is that Layer2 officials first deploy a smart contract that hosts assets on the main Ether network, and when a user crosses ETH from the main Ether network to Layer2, the user's ETH is locked to that smart contract and generates a new ETH 1:1 on the Layer2 network. when the user sends a command to cross back to the main network, the Layer2 ETH is When the user sends a command to cross back to the main network, the ETH on Layer2 is destroyed and the smart contract on Layer1 is triggered to unlock the ETH to the user. This is the cross-chain implementation of Ethernet Layer1 and Layer2. It is realized through the smart contract of Ether and the communication between Layer1 and Layer2 network, which can realize the de-trusting.


So how should Bitcoin's Layer2 implement a de-trusted BTC cross-chain?


Before the Bitcoin Taproot upgrade in 2021, it was not possible to achieve a fully decentralized BTC cross-chain, but the Taproot upgrade brought in Schnorr signatures and MAST contracts to make a fully decentralized Bitcoin cross-chain a reality. As you can see from the above, by using the combination of Mast contracts + Schnorr signatures brought by Taproot, Bitcoin can also achieve fully de-trusted cross-chaining just like ethereum Layer2, which is the most important first step to achieve a fully decentralized BTC Layer2.

The Layer2 network's ledger must be secure and trustless

The ledger of Ethernet Layer2 is managed by the sequencer, and when processing transactions, it is packaged and uploaded to the main Ethernet network after the Layer2 ledger is rouled according to a certain ratio, usually 10:1, and then verified by the Ethernet nodes, but the sequencer of Ethernet Layer2 (that is, the operating node of the Layer2 network, which is usually only the official 1 node) is completely centralized and is run and mastered by Layer2 officials.


How can such a centralized design gain users' trust? Mainly by packaging Layer2's ledger roullp into the main Ethernet network for miner nodes to verify, if users don't trust the ledger, they can verify the ledger by initiating off-chain whistleblowing, therefore, Op-Roullp is also known as optimistic proof, that is, its trust assumption is optimistic that the official doesn't do any evil, and if it does, it can be proved by whistleblowing. These combinations are designed to basically guarantee that the Layer2 ledger is trustworthy.


So how does Bitcoin Layer2 achieve a trusted ledger?


Let's still take BEVM as an example. As we mentioned earlier, BEVM is a combination of Mast contracts + Schnorr signatures to achieve Bitcoin decentralized cross-chain, and in order to achieve real-time communication between Layer2 and Layer1, the network of BEVM is a fully operational Bitcoin light node, so BEVM is a trusted network composed of 1000 Bitcoin light nodes.


In order to guarantee the absolute security of the Layer2 ledger and ensure that the network nodes do not do evil, BEVM draws on the economics game mechanism of the Bitcoin network, and BEVM combines the nodes hosting Bitcoin and the nodes running the Layer2 network into one, i.e., the nodes that are running the Layer2 network by pledging the assets are also nodes hosting the BTC assets, and at the same time, BEVM designs a set of automated dynamic pledging mechanisms that are completely based on the At the same time, BEVM has designed an automated dynamic pledging mechanism based entirely on economics, i.e., it guarantees that the total value of BTC/main network tokens pledged by BEVM's Layer2 nodes will always be greater than the value of their custodial assets, so as to guarantee that Layer2 network nodes have no incentive to do evil by means of the mechanism of the game of economics, thus guaranteeing that Layer2's ledger is absolutely secure and trustworthy.