In recent times, there has been a heated debate within the Ethereum Rollup community regarding the true definition of promising Rollups like Arbitrum, Optimism, ZKSync, and others. The current Rollup serves as an off-chain transaction executor, equipped with a "native bridge" connecting Rollup and Ethereum. We refer to this native bridge as the Enshrined Bridge. This bridge allows users to lock assets originating from Ethereum and mint equivalent wrapped assets on the Rollup. Conversely, when the bridge is confident that the wrapped assets on the Rollup have been destroyed, it can unlock the assets originating from Ethereum. The Enshrined Bridge operates on a basis of minimal trust, relying on fraud proofs or validity proofs to ensure the validity of the Rollup state.

Enshrined:

First, let's take a look at what "Enshrined" means. In English, the word "enshrined" is typically used to describe something that is considered sacred or important, and is respected or protected. In the context of blockchain and cryptocurrency, "enshrined" may be used to describe a characteristic, rule, or protocol that is solidified or embedded into a system or network to ensure its persistence and immutability. For example, the consensus rules of a blockchain network may be "enshrined" (embedded) into the code or protocol of the network to ensure that all participants adhere to these rules.

The AltLayer team has been contemplating this topic for over 1.5 years, although it is more focused on a closed loop through Rollup-as-a-Service (RaaS) offerings.

From a perspective of network design, this network design supports our RaaS offering.

Beacon Layer: The intermediate layer for Enshrined Rollup built on Ethereum

For a regular RaaS (Rollup as a Service) offering, users would utilize an SDK or a dashboard to initiate a Rollup that employs Ethereum as the data availability layer.

Therefore, the modular stack appears as follows:

Rollup (execution) -> Ethereum (data availability) -> Ethereum (settlement)

The RaaS network of AltLayer, however, features a slightly different architecture:

Rollup (execution) -> Beacon Layer (Enshrined intermediate layer) -> Ethereum (data availability) -> Ethereum (settlement)

The Beacon Layer serves as an intermediate layer between the execution and data availability layers. All Rollups instantiated through AltLayer are Enshrined within the Beacon Layer. The term "Enshrined" implies that the state of any Rollup launched via AltLayer can be directly verified by the Beacon Layer, facilitated by an Enshrined bridge for each Rollup on the Beacon Layer. Additionally, as an intermediate layer between the execution and data availability stack, the Beacon Layer provides the following key services:

Detailed Explanation

1. Beacon Layer: The Beacon Layer is a network where interested nodes act as rollup sorters and register themselves. When end users request a rollup through AltLayer's RaaS platform, they specify the minimum and maximum number of sorters required for the rollup, as well as the minimum amount of economic collateral and the token list from which collateral can be obtained for each sorter. The collateral is then staked on the Beacon Layer and later used to slash any misbehaving sorters. Once the required number of sorters has been staked with the minimum collateral, these sorters can start sorting transactions for the rollup. The selected sorters then run a local consensus protocol, providing resistance to censorship and better liveness guarantees, while offering stronger pre-confirmation than what a single sorter would provide.

2. Verification Layer: As mentioned in the introduction, rollup's validation nodes can independently decide on the specification of rollup states. However, this would mean that every client who doesn't want to wait for the typical 7-day withdrawal period of an enshrined bridge needs to run their own full-node rollup validator. This may not be ideal for many, especially for light clients of optimistic rollups. Therefore, the Beacon Layer serves as the enshrined verification layer for all rollups. Since the Beacon Layer knows all the rollups and their respective state transition functions, it has the ability to fully validate newly submitted rollup states. To achieve this, the Beacon Layer consists of a set of validators that regularly validate all newly proposed states in all rollups. Unlike the pre-confirmation provided by rollup sorters, the confirmation provided by the Beacon Layer is stronger, as it allows for immediate withdrawals of assets.

3. Collateral/Slashing Layer: As both shared sorting and verification assume the presence of a node network, it is necessary to ensure that the network is not forged. Therefore, the Beacon Layer includes a collateral mechanism that requires each network participant to deposit a sufficient amount of economic collateral, which can be slashed when malicious behavior is detected and proven.

4. Interoperability Layer: If an RaaS provider has multiple instantiated rollups, achieving interoperability between rollups often involves establishing an enshrined bridge on the DA layer, one for each rollup. Another option is to create a bridge between every two rollups using the same DA layer.

In AltLayer's design, the third approach is adopted, utilizing the Beacon chain as the bridging hub that coordinates all rollups. In this design, each rollup enshrines a bridge on the Beacon Layer, which serves as a shared intermediary "settlement layer" on top of the underlying DA layer. By enshrining bridges to this shared intermediary layer, rollups gain a direct and trust-minimized bridge. Additionally, this also results in indirect trust-minimized bridges to other rollups that are also enshrined on the Beacon Layer. Essentially, as a common settlement layer, the Beacon Layer acts as a bridging hub, facilitating asset transfers between rollups and enabling general messaging. It can also assist in detecting any invalid state transitions between rollups and even provide dispute resolution for validating fraud proofs.

5. Upgradability Layer: As mentioned in the introduction, most of today's Rollups have an enshrined bridge to Ethereum. This bridge tracks the state of the Rollup, verifies fraud proofs (or validity proofs for ZK Rollups), and allows for asset withdrawals from the Rollup to Ethereum. However, these enshrined bridges are mostly controlled by multisignature wallets, giving them the capability to maliciously upgrade and arbitrarily steal users' funds.

The Beacon Layer serves as a social layer for upgrading all Rollups. By collectively operating the Rollup sequencers and the Rollup validators of the Beacon Layer, Rollups can be socially forked regardless of whether the enshrined bridge contract on Ethereum is upgraded or not. Remember, the enshrined bridge is just another observer of the Rollup state, like other Rollup validators. Sequencers and Rollup validators on the Beacon Layer who disagree on the fork may decide not to support the new fork.

6. Social Consensus Layer: The Beacon Layer can also function as a governance layer, where Beacon Layer nodes can run on-chain governance mechanisms to approve upgrades to Rollup logic. Therefore, they can represent the community in upgrading any bridge contracts of the Beacon Layer or the Data Availability (DA) Layer.

Conclusion

In summary, the Beacon Layer is a crucial component of the AltLayer network architecture. It serves as a shared intermediate layer between the rollup-as-a-service platforms launched through AltLayer and the underlying data availability layer (such as Ethereum). The design goal of the Beacon Layer is to provide shared services for ordering, verification, staking/slashing, interoperability, scalability, and social consensus, enabling a more efficient, secure, and scalable rollup network.

The introduction of the Beacon Layer allows participants in the rollup network to interact on a unified platform without the need for individual operations within their respective rollup networks. This design not only enhances the operational efficiency of the rollup network but also ensures its security and reliability.

Furthermore, the Beacon Layer provides a new mechanism for upgrading the rollup network, enabling upgrades to be carried out under community consensus without relying on a single multisignature wallet. This design promotes openness, transparency, and fairness in the rollup network upgrade process, thereby increasing trust and user acceptance.

Finally, the introduction of the Beacon Layer opens up new possibilities for the development of the rollup network, signaling the beginning of a new chapter in the Web3 community. As the Beacon Layer continues to evolve and improve, we look forward to witnessing more innovations and breakthroughs in the rollup network.