Original Title: "Interpreting SCP: Breaking the Trustless Infrastructure Paradigm of Rollup"

Original Author: Wuyue, Geek Web3

Introduction: This article will prospectively introduce a somewhat unique Web3 infrastructure design paradigm - Storage-based Consensus Paradigm (SCP). Although this product design pattern has significant differences in theory from mainstream modular blockchain solutions such as Ethereum Rollup, it is highly feasible in terms of implementation simplicity and integration with Web2 platforms. This is because SCP does not intend to limit itself to a narrow implementation path like Rollup from the beginning, and aims to integrate Web2 platforms with Web3 facilities in a broader and more open framework, making it a highly imaginative and innovative approach.

Content: Let's imagine a public chain expansion plan with the following characteristics:

·With speeds comparable to traditional Web2 applications or exchanges, far surpassing any public chain, L2, rollup, sidechain, etc.

·No Gas fees, usage cost is almost zero.

·High security of funds, far exceeding centralized facilities such as exchanges, inferior to Rollup but greater than or equal to sidechains.

·Same user experience as Web2, no need for any knowledge of blockchain's public and private keys, wallets, infrastructure, etc.

This plan is indeed very exciting: on the one hand, it has basically reached the limit in terms of expansion; on the other hand, it has laid a very solid foundation for the mass adoption of Web3, basically eliminating the gap in user experience between Web2 and Web3.

However, we seem to be unable to come up with many solutions that can be so comprehensive, because mainstream discussions and practices are indeed too few.

We use the familiar topic of expansion as an introduction, but in fact, SCP is not limited to expansion use. Its design inspiration comes from the scaling solutions and community discussions of public chains such as Bitcoin and Ethereum. Its vision and practical application are to build a new generation of trustless infrastructure, even a non-blockchain computing platform.

SCP Basic Components and Working Principles

Generally speaking, SCP is also referred to as a "modular blockchain" by the Ethereum and Celestia communities, with modules divided into data availability layer, execution layer, consensus layer, settlement layer, and so on.

·Data Availability Layer: It is supported by a widely recognized and well-tested public chain, or storage facilities such as Ethereum, Arweave, Celestia, etc.

·Execution Layer: A server used to receive user transactions and execute them, while also submitting the signed transaction data in batches to the DA layer, similar to the Rollup sequencer. However, the execution layer does not necessarily have to have a blockchain-style linked list structure. It can be a Web2 database + computing system, but the entire computing system must be open source and transparent.

·Consensus Layer: Composed of a group of nodes, it pulls data submitted by the execution layer to the DA layer and uses the same algorithm as the execution layer to perform calculations on this data to confirm the correctness of the execution layer's output results. It can also serve as a disaster prevention redundancy for the execution layer. Users can also read the data returned by each node in the consensus layer to ensure that there is no fraudulent behavior in the execution layer.

·Settlement Layer: Composed of a group of nodes and other contracts or addresses on the chain, used to process user deposits into SCP or withdrawals from SCP. It is similar to the operation mode of cross-chain bridges. Settlement layer nodes control the withdrawal function of the deposit address through multi-signature contracts or TSS-based addresses. When depositing, users deposit assets into the designated address of the chain they are on. When withdrawing, they send a request, and settlement layer nodes release the assets through multi-signature or TSS after reading the data. The security level of the settlement layer depends on the cross-chain mechanism used.

SCP Practice Framework

We can understand the SCP paradigm through the following framework. A product that meets the SCP framework can have main functions such as recharge, transfer, withdrawal, swap, etc., and can be further expanded on this basis. The following diagram shows the principle of such a product:

The DA layer of this project uses the permanent storage facility Arweave, represented by the large circle in the image.

·Coordinator, also known as the execution layer. Users submit transactions to the coordinator, which performs calculations and displays the results, and then submits the user's original input data in batches to the DA layer.

·Detector, a verifier that pulls transaction raw data submitted by coordinators from Arweave, uses the same algorithm as the coordinator to verify the data and results. The client of the detector is also open source and can be run by anyone.

·守望者 Watchmen, a group of validators who oversee the multi-signature withdrawal system. They verify and approve withdrawal requests based on transaction data. Additionally, Watchmen are responsible for signing proposals.

We can see the entire system, and the consensus they have reached is all off-chain, which is the core of the storage consensus paradigm - it abandons the node consensus system of the blockchain and allows the execution layer to get rid of the heavy consensus communication and confirmation process, only need to do the work of a server, thus achieving almost unrestricted TPS and economy. This is very similar to Rollup, but SCP takes a different path from Rollup, trying to turn it from a scaling-specific use case to a new transitional mode from Web2 to Web3.

The coordinator mentioned above is a server, but this does not mean that the coordinator can do whatever it wants. Similar to the sorter of Rollup, after submitting the raw data submitted by users in batches on Arweave, anyone can run a verifier program to verify it and compare it with the state returned by the coordinator. To some extent, this is similar to the idea of ​​inscription-based applications.

In this architecture, a centralized server and database do not pose a fundamental challenge. This is another point of the SCP paradigm, which decouples the concepts of "centralization" and "single entity" - in a trustless system, there can be centralized components, even as a core component, without affecting the overall trustlessness.

We can shout out such a slogan - "The next generation of trustless infrastructure should not rely on consensus protocols, but should be an open-source system with P2P node networks."

The original intention of inventing and using blockchain technology is to achieve decentralization, consistent ledger, tamper-proof, and traceability, which are the basic principles that have been talked about for a long time. This is clearly stated in the Bitcoin white paper. However, after the emergence of Ethereum, whether it is the scaling solution of the old public chains, or Rollup or modular blockchains, everyone has formed a mindset: what we do must be a blockchain (composed of the consensus protocol of nodes), or a solution like Rollup (which looks like a chain, but has the data structure of a blockchain, but nodes do not directly exchange consensus messages).

However, now it seems that even outside of blockchain, a series of requirements such as trustlessness, consistent ledger, non-falsifiability, and traceability can be achieved based on the SCP framework, provided that there are clearer implementation details.

Currently, there is no clear solution to the anti-censorship problem, which is an issue within the SCP paradigm.

Consensus Layer

This layer is composed of loose nodes, which do not actively form a network, so it is not a strictly consensus layer, but only used to confirm the current execution layer status to the outside world (such as users).

For example, if you have doubts about the running status of these nodes, you can download their detector client, which will run the same program code as the coordinator.

However, similar to Rollup, due to the batch submission of data, the status returned to the user by the execution layer is always more updated than that on the DA layer. This involves a pre-confirmation issue:

The execution layer provides users with pre-confirmation and soft final results, because it has not yet been submitted to the DA layer;

而共识层给用户提供的是硬最终性。Users may not be particularly concerned about this, but for applications such as cross-chain bridges, hard finality must be followed. For example, the deposit and withdrawal system of an exchange will not trust the data broadcasted by the Rollup sequencer off-chain, and must wait for this data to be uploaded to Ethereum before it is recognized.

除了能用来确认结果以外，共识层还有一点很重要的作用，就是作为执行层的防灾冗余。如果执行层永久罢工、严重作恶，这个时候理论上任意的共识层都可以接手执行层的工作，接收用户的请求。如果发生如此严重的情况，社区应该会选择出稳定可靠的节点来作为执行层的服务器。

Aside from being used to confirm results, the consensus layer also plays an important role as a disaster prevention redundancy for the execution layer. In the event that the execution layer permanently stops working or behaves maliciously, theoretically any consensus layer can take over the execution layer's work and receive user requests. If such a serious situation occurs, the community should choose stable and reliable nodes to serve as the execution layer's servers.

Settlement Layer

Due to SCP not being Rollup, it is not possible to achieve the trustless withdrawal layer that Rollup provides, which requires no human intervention and is entirely based on cryptography and smart contract code. The security level of SCP's cross-chain bridge is the same as that of sidechain or third-party witness cross-chain bridges, and it relies on authorized multisig managers to release assets, which we refer to as the witness mode.

Witnessing the decentralization of the bridge created by the witness is a topic of research for many cross-chain bridge projects. Due to space limitations, we will not go into detail here. A well-designed SCP platform must also have reputable decentralized bridge multi-signature partners in practice.

Some people may ask why SCP doesn't use a chain with smart contracts as the DA layer? This can create a settlement layer that is contract-based and completely trustless.

In the long run, as long as some technical difficulties are overcome, if the DA layer is placed on a contract-based DA layer such as Ethereum and corresponding contracts for verification are constructed, SCP can also achieve settlement security similar to Rollup without the need for multi-signature.

However, in practice, this may not be the optimal choice:

1. Ethereum is not specifically designed for data storage, and its price is too high compared to pure data storage public chains. However, for the SCP paradigm, low or fixed storage costs are crucial. Only in this way can it support Web2-level throughput.

2. The proof system is very difficult to develop because SCP can not only simulate EVM, but also implement any logic. Looking at teams like Optimism, whose fraud proofs are still not online, and the difficulty of developing zkEVM, it can be imagined that proving various systems on Ethereum is an extremely difficult task.

Therefore, Rollup is only more feasible in specific situations, if you plan to implement a more broad and open solution, free from the EVM system and incorporating more Web2 features, then the Ethereum Rollup approach is not suitable.

SCP is not a scaling solution for a specific public blockchain, but a larger Web3 computing platform architecture, so it obviously does not need to follow the Ethereum Layer2 approach.

One picture compares SCP with other paradigms

Original article link

Welcome to join the official BlockBeats community:

Telegram Subscription Group: https://t.me/theblockbeats

Telegram Discussion Group: https://t.me/BlockBeats_App

Official Twitter Account: https://twitter.com/BlockBeatsAsia