Translation: Blockchain in Vernacular
As rollups become core to Ethereum’s scalability, interoperability between L2s is critical to the success of its rollup-centric roadmap. Fragmentation between L2s creates inefficiencies and slows adoption.
A few months ago, we published a study exploring “The state of rollup interoperability in 2024.” Here are our findings.
1. Current Problem: L2 Fragmentation
L2 rollups, such as Arbitrum, zkSync, and Optimism, operate independently of each other, and cross-chain communication is costly and slow. Without seamless cross-rollup transactions, the Ethereum ecosystem will continue to be fragmented, affecting liquidity and composability.
2. Optimistic Rollups: Standard Bridging Problem
The Rollup bridge proves its state to Ethereum L1 to inherit its security. However, OP Rollups introduce delays caused by the "challenge window" (usually 7 days).
This delay becomes a bottleneck for cross-chain transactions — no one wants to wait a week for a DEX transaction to complete!
3. ZK Alternatives
ZK rollups provide faster finality by using zero-knowledge proofs, but their bridge finality still takes hours (@zksync Era: 21 hours, @Starknet: 9 hours). The delay mainly comes from the execution buffer and expensive proof verification on L1. Although ZK proofs are faster to verify than OP Rollups, they are still computationally expensive.
Source: @l2beat
4. Keystore Rollups: Simplifying Account Management
Last year, @VitalikButerin proposed keystore rollups, an approach that focuses on storing account keys rather than a complete virtual machine (VM). This simplifies wallet interactions between different rollups by using Merkle proofs of keys stored on L1 to verify transactions. Users can verify and manage accounts across L2 from their main wallet, improving the user experience.
However, aside from Vitalik’s original design, there are three leading keystore rollup models:
1) @Scroll_ZKP’s approach: Store keystore data in L1, and zkEVM rollups use L1SLOAD to pre-compile and synchronize account configurations, thereby achieving low-cost L1 reads.
2) @base’s design: Only state roots are stored in L1, and calldata is used to sort transactions. Merkle proofs are used to synchronize account data between L2s.
3) @0xStackr’s design: Very similar to Base, but uses a “micro-rollup” framework that uses a minimal virtual machine.
Despite these advances, gas fees for proof-of-stake verification remain a key challenge.
5. Aligned Layer: Efficient ZK Proof Verification
@alignedlayer provides a solution to the expensive proof verification problem of ZK rollups. As @EigenLayer's AVS, it enables Ethereum validators to verify ZK proofs at a very low cost by leveraging bonded validators.
Aligned reduces verification costs to just 3000 gas per proof — almost zero on Ethereum L1, making it a scalable solution for smaller rollups.
However, this also introduces trust assumptions - if the total locked value (TVL) of a rollup exceeds the pledged margin, attacks may become profitable.
6. Proof Aggregation Layer: Improving Proof Efficiency
Proof aggregation is another innovation that allows multiple ZK proofs to be combined into a single proof, reducing the burden of on-chain verification.
There are two main proof aggregation protocols:
• Universal Aggregation: Supports multiple proof types (Groth16, Halo2, Plonky2) and reduces gas fees for applications.
• Aggregate Rollup Bridging: Built into the ZK stack, such as @0xPolygon’s AggLayer and @zksync’s Hyperbridge, designed to minimize verification costs and enhance composability across rollups.
7. Efficient intent-based bridging and Keystore+ Rollups
Most cross-chain bridges, such as @StargateFinance (using @LayerZero_Core), are message-based. They lock tokens on the source chain, send a message to the target chain, and then unlock the same amount of tokens. However, this approach relies heavily on the messaging protocol at the trust level.
Intent-based bridging eliminates the need for messaging.
How does it work?
Funds are locked as a "cross-chain order" and anyone can fulfill the order by sending tokens on the target chain. After the fulfiller confirms the transaction on the target chain, they can claim the locked funds on the source chain.
Example: Protocols like @AcrossProtocol leverage optimistic oracles like @UMAprotocol to obtain the final state of Layer 2 before reaching finality.
Unified all chains ENS
Imagine having a single Ethereum Name Service (ENS) address that can be used across all rollups. Keystore rollups make this possible by deploying mini accounts on-chain, bytecode equivalents.
By using CREATE2 and Multichain Factory, users can keep the same address across all rollups, simplifying account management and the overall user experience.
Sorting mechanism in Keystore+ Rollups
Ordering is another critical aspect in rollup interoperability. In keystore rollups, centralized orderers can be replaced by a blockchain-based ordering mechanism, eliminating single points of failure and enhancing censorship resistance.
The ordering mechanism based on rollup allows transactions to be processed within a time window of approximately 12 seconds, ensuring fast cross-rollup transactions without sacrificing decentralization.
8. Why we don’t rely on shared sorting
Shared ordering is often discussed as a solution for OP rollup interoperability, but our research highlights its limitations. Shared ordering centralizes control by allowing a single orderer to manage multiple rollups, which could lead to oligopolistic control of the rollup ecosystem.
In contrast, ZK rollups with shared proof aggregation bridges maintain decentralization while achieving fast finality between multiple rollups — a more sustainable and secure solution for rollup interoperability.
This research article focuses primarily on ZK rollups and ZK technology, as OP rollups fundamentally lack fast objective finality. Objective finality is only achievable through ZK proofs, making ZK rollups ideal for long-term interoperability solutions.
Although optimistic rollups are limited in this regard, there is also significant development within their ecosystem. For example, Optimism is working on effectiveness-centered design and partnered with @RiscZero a few months ago to explore new integrations.
9、ZK Rollups 与 OP Rollups
Due to the use of zero-knowledge proofs, ZK Rollups are able to confirm transactions faster than OP Rollups. They do not require a challenge period (OP Rollups have a challenge period of up to 7 days), which makes them more advantageous in cross-Rollup interoperability.
• ZK Rollup Advantages: Independent aggregation proofs enable ZK Rollups to achieve composability between different Rollups without having to worry about centralization issues.
• Current state of Optimistic Rollups: Despite some technical limitations, optimistic Rollups like @Optimism, @arbitrum, and @base dominate due to their strong ecosystem, excellent development tooling, and user-friendly infrastructure.
Interoperability remains the most pressing challenge in the Ethereum Rollup roadmap. To dive into our full analysis and comprehensive findings, read the full paper here 🔗 https://research.2077.xyz/the-state-of-rollup-interoperability. This post was written by @alexhooketh.
