Classic and Sovereign Rollups and Rollup Design
The previous article in this series determined that rollups that scale Ethereum are EVM-equivalent, complete derivatives of the function of Ethereum data, and have a sequencing model. Moreover, they could have a trust-minimized validating bridge that links them to Ethereum.
Most of these characters help categorize rollups, with the validating bridge being the key identifier. According to this criterion, there are two types of rollups:
- Classic Rollups: Have an enshrined validating bridge join it to the L1 that secures its network.
- Sovereign Rollups: Lacks an enshrined validating bridge to join it to the L1 blockchain, which it depends on for security.
Classic Rollups
Classic rollups have an enshrined, validating bridge connecting them to Ethereum. This bridge facilitates a two-way, trust-minimized connection between the L2 and L1.
Classic rollups scale Ethereum by offering the native Ethereum experience in the rollup chains. They achieve this objective by undertaking EVM-equivalent execution off-chain, providing users with a similar user experience native to the Ethereum blockchain, only cheaper and faster. In addition, they introduce stronger interoperability capabilities.
Sovereign Rollups
Sovereign rollups do not enshrine a validating bridge between them and the underlying L1 that provides their DA and sequencing. Unlike classic rollups, sovereign rollups provide one-way trust-minimized bridging from the L1.
Sovereign rollups differ from Classic rollups in their approach to bridging with L1. Whereas Classic rollups are straight and intentional around their bridging structures and purpose, Sovereign rollups, on the other hand, strive to dictate the conditions of its underlying L1 out of the sphere of the said L1 blockchain. This means that whereas classic rollups may want to increase the circle of influence of the underlying L1, they have a hard time bringing to life their sphere of influence outside the umbrella of the underlying L1 or any other blockchain they establish bridging relationships with, for that matter.
Designs of Ethereum Rollups
The primary distinction between classic and sovereign rollups is straightforward. However, the design choices surrounding a rollup’s features can further refine its classification. Given the many ways to explore the rollup design space, this article presents one possible approach, considering the following aspects:
- Sequencing: Rollups can choose from a range of sequencing models. The key distinction is whether it independently manages its sequencing or relies on the underlying L1 DA layer for assistance. Based on this choice, a rollup can be classified as either based or non-based.
- Verification Method and Support for Trust-Minimized Rollups: Rollups can offer light-client-like functionality, enabling trust-minimized bridging to other blockchains. When incorporated into a rollup’s design, this feature enhances users’ secure bridging options. Additionally, the approach used to provide trust-minimized verification can distinguish different types of rollups.
Based on the descriptions captured in the numbered points above, a rollup that utilizes ZK proofs for trust-minimized verification is classified as a ZK rollup. In contrast, one that relies on fault proofs is considered an Optimistic rollup.
There is a whole table of discussion about the justification for using this classification methodology, or any for that matter, that the industry recognizes. However, such debates are out of the scope of this article.
However, we will highlight the obvious benefits of this design framework:
A more organized classification methodology of Ethereum rollup
Developing a more detailed classification system helps the Ethereum ecosystem better structure its understanding of the rollup landscape. Organizations like L2Beat are at the forefront of this effort but cannot and should not shoulder the responsibility alone. In the spirit of open collaboration, the Ethereum community should work to consolidate, expand, and critically evaluate ongoing efforts across the rollup space, including developing assessment frameworks for neutral system evaluation. This classification system aims to support that mission and complement the evolving global consensus on rollup assessment.
Designing context-aware security models for specific rollups.
This classification system enables fairer security assessments of rollups by using context-aware models. It avoids misleading comparisons based on varying reference points.
It offers a structured way to map the Ethereum rollup landscape, building on existing research to align expectations for Ethereum’s rollup-centric vision. This classification method could also incorporate insights like Vitalik Buterin’s rollup stages, a proposal for a three-stage decentralization scale for L2s that L2Beat has refined.
Conclusion to Segment II
So far, the framework prioritizes neutrality, capturing essential details without imposing subjective views. The goal is to encourage adoption while allowing for future extensions. With this foundation in place, let’s explore key security concerns to provide Ethereum with the context needed to refine or expand this—or any inspired—framework.
The last segment in this series delves into the security problems associated with Ethereum rollups and the various fixes that exist or are in the pipeline. Stay tuned.
For a deep dive on Ethereum rollups, go to the original version of this article, which was first published here.
