Technical Deconstruction of B² Network: Why BTC L2 needs to be “modular”

Source: View on the chain

In the Ethereum L2 field, modularization has become the only way to challenge the monolithic chain. Celestia started a DA War, Espresso used the shared Sequencer ultimate move, and Altlayer threw Rollup AS A Service.

A To C operation market that was originally driven by users and ecology has turned into a To B market with unlimited imagination through Stack’s strategic planning. We can’t help but ask, what will happen if “modularization” is implemented in BTC layer 2?

Why is the BTC network more suitable for modularization? Which components of BTC Layer2 are suitable for modularization? What new business landscape will modularity bring to BTC layer2? This article will discuss @BSquaredNetwork as an example:

The main reason why modularization works is due to the composable nature of the blockchain public chain architecture. A mature public chain includes:

1) The settlement layer (Settlement layer) is responsible for the transfer and determination of the transaction status of assets;

2) The DA layer (Data Availability) is responsible for the status change data availability of transaction data for transaction verification: < /p>

3) The Execution layer is responsible for processing the execution logic of transactions, including the invocation and execution of smart contracts; 4) The Consensus Layer is responsible for all nodes reaching consistency on a certain version of transaction history. ;

5) The Interoperability Layer is responsible for message communication and status management of different blockchain networks.

The above-mentioned blockchain components have a clear division of labor, and each performs its own duties, which constitutes the trustworthy and decentralized characteristics of the blockchain.

The Ethereum network is a smart contract network that can store and verify historical states. The functions of the components at each layer above can be completed. However, some components face expansion problems that need to be outsourced due to performance or capacity limitations, and The BTC network is a stateless non-smart contract network. The UTXO model is a minimalist asset transfer and settlement technology architecture. In addition to the settlement function, other execution layers, DA layers, consensus layers, and cross-chain interoperable layers etc. are all suitable for "modular" packaging composition.

Ethereum supports a wide range of applications through its built-in complex function layer, while Bitcoin only supports its Payment function through a minimalist UTXO architecture, and more complex functions can only rely on external modular expansion. Undoubtedly, BTC needs "modularity" more than Ethereum.

So, if BTC layer2 (non-UTXO structure) wants to implement complex transaction execution logic, how to modularize the core DA layer, execution layer, and settlement layer components? What adjustments must be made to adapt to the characteristics of the BTC main network? Next, I will give you a detailed technical analysis around @BSquaredNetwork’s solution:

1) DA layer: The BTC main network can only rely on the limited space in the Taproot Script script for storage, and the main network has full nodes Complex status verification cannot be done on the stored data.

To this end, B² Network has modularly built an independent DA layer, including: Decentralized Storage + B² Nodes:

The storage part needs to store all local historical transaction record data for the entire Node verification data provides an authoritative and non-tamperable trusted data source, which is equivalent to the Calldata and Blob of the Ethereum system; the node part is responsible for processing Rollup data, which is equivalent to the Procer system of Ethereum L2, and will perform Prove verification on these data to confirm The correctness of its transaction data and state transitions.

Through the cooperation of these two parts, B² Network has implemented a DA network that can efficiently store data and achieve calculation + verification, using this to make up for the lack of DA capabilities of the BTC main network. Interestingly, after fully verifying the feasibility of the architecture, B² Network upgraded it to B² Hub, which is equivalent to providing the DA layer as a modular service solution to other BTC layer 2 that require a DA layer.

Why other layer2 platforms choose B² Hub instead of directly using IPFS storage solution or Celestia’s DA outsourcing service? This is mainly due to B²’s special design for the characteristics of the Bitcoin main network, such as: To save the limited space of the main network, the DA layer will compress the data verification results of the Prover system into circuits and generate Commitment commitments.

2) Execution layer: The "execution" done by the BTC main network is only the conditional transfer of assets. The layer2 platform often needs to build a local execution layer that can execute complex contract logic to supplement it.

In response to this, B² Network uses ZK-Rollup as the execution layer to handle off-chain data and communication interaction consistency through zero-knowledge proof. During this process, Sequencer collects and batches transactions, then generates various proofs through the ZKEVM system, and finally aggregates and summarizes the data to the DA layer.

B² Network uses ZK as its core technology to handle the consistency of local data and transaction status. It can also be regarded as a modular shared Sequencer execution layer solution. After all, ZK is unique in connecting communications between multiple subjects and granting privacy credit.

3) Settlement layer: If it is a UTXO structure, the BTC main network can be based on light nodes + Schnorr signature + MAST and other frameworks, and realize asset security status changes through state channels + one-time sealing, etc. If it is a non-UTXO structure , you can only rely on the multi-signature subject of the local consensus to settle assets with the main network. This actually assumes that multi-signature alone cannot effectively ensure 100% security of assets. What if a multi-signature subject does evil?

Therefore, the settlement layer design of B² Network includes two parts: BTC mainnet conditional unlocking + B² Hub local challenge:

The B² Hub part is to ensure the second-layer local consensus and reduce the possibility of evildoing. , a challenge mechanism is designed based on BitVM technology to allow local nodes to challenge Commitment commitments on the main network based on historical data fragments:

1. The DA layer of B² Network will compress the final data change status into Commitment is committed and uploaded to the Bitcoin mainnet in the form of an inscription. Inscription's innovative input data mechanism is introduced here, which is equivalent to announcing historical status data to the BTC main network to serve as a fair referee for challenges. B² Nodes will have a public decentralized indexer system to parse and record the mainnet data status, allowing other nodes to differentially challenge the data submitted to the mainnet based on their local data records.

2. Since the inscription data after Inscribe cannot be tampered with, and the local indexer data in layer 2 is very transparent, once the challenge data fragment submitted by the challenger is inconsistent with the existing historical Commitment commitment result, although the whole node cannot The commitment content is directly verified, but this inconsistency can trigger the confirmation of the mainnet settlement status and impose a Slash penalty on the forged commitment provider (the BTC locked in its UTXO will be transferred to the challenger).

In my opinion, B² Network’s Commitment + Challenge mechanism based on BitVM is equivalent to an effective “settlement layer” security consensus supplementary solution and can become an effective modular challenge solution. To complete the security consensus that layer2 chain lacks in asset settlement. After all, relying solely on the main network to build light nodes and multi-signatures may lead to problems of node evildoing. If an effective evildoer accountability mechanism is formed, wouldn’t the problem be solved?

Above.

The debate over the standards of BTC layer 2 has begun again in the past two days. Whether it is the Eastern forces blooming in BTC layer 2, or the Western mainstream trying to shape standards at the consensus layer, in the end it is just the development process of the BTC layer 2 market. fragment.

In my opinion, the biggest charm of BTC layer2 at the moment is its infinite inclusiveness, which gives the market enough room for imagination, and it is far from the time to set a standard.

On the contrary, the decentralization problem of BTC index, the lack of capability of BTC DA layer, the challenging security mechanism of BTC settlement layer, the slow development problem of BTC mainstream UTXO structure expansion plan, etc., are all problems that need to be solved urgently. .

The key is that once these problems are effectively solved and modularized, they will most likely become a common need for the entire ecosystem. In other words, isn’t solving problems and modularizing business output the same thing as setting “standards”?

Note: This article’s interpretation is centered on the non-UTXO structure BTC layer2 market. The problems and development ideas of the UTXO structure are not the same. I will explain them in detail when I have the opportunity in the future.