Layer 2 (L2) solutions like Linea help Ethereum scale to meet the demands of a maturing blockchain industry without sacrificing on security. Linea and its zkEVM (zero-knowledge Ethereum Virtual Machine)-based solution are on a mission to optimize transaction execution and roll up compressed data to the Ethereum mainnet. A key milestone on this journey is the decentralization of the sequencer, which is responsible for ordering, building, and executing transactions within the network.

Below we'll explore how decentralizing the Linea sequencer enhances security, reliability, and trustworthiness.

The role of the sequencer in Linea

Before we dive into the details of Linea’s decentralization plans, let’s first focus on understanding the role of the sequencer. In L2 rollups, transactions are bundled together off-chain and submitted to the Ethereum blockchain as a single transaction. This whole process helps to reduce network congestion and gas fees on the main chain while still leveraging its security. A module called Coordinator is responsible for relaying information of the L2 batch to the L1. The sequencer then builds the blocks and appends them to the tip of the Linea chain.

Linea's sequencer is also responsible for ordering, building, and executing blocks in a manner that enables the generation of zero-knowledge (zk) proofs. A zk-proof is a cryptographic method that allows an individual to prove that a statement is true without conveying any additional information. This is commonly associated with privacy, but is great for scaling blockchain networks through rollups, because it reduces the amount of information you have to provide to lower layers.

Essentially, the sequencer is the core of Linea's execution client, tasked with several essential functions:

• Transaction ordering: The sequencer decides the sequence in which transactions will be executed, optimizing for efficiency and security.

• Block building: Once the transaction order is established, the sequencer builds blocks containing these transactions.

• Block execution: The sequencer executes the blocks, processing the transactions and updating the state of the rollup.

• Trace data generation: During block execution, the sequencer generates data related to the execution traces, which is later used by the zero-knowledge prover to generate proofs of the rollup's state transitions.

Currently, Linea uses linea-besu, which leverages the Besu client software used by Ethereum, to enhance compatibility, reliability, and maintainability.

Risks and limitations of centralized sequencers

Decentralizing the sequencer is a key part of the Linea roadmap because relying on a centralized sequencer presents several risks and limitations:

1. Single point of failure: A centralized sequencer can potentially disrupt the entire network and pause transaction processing if it faces any downtime or technical issues.

2. Censorship risks: Users or certain applications can face unfair/biased treatment when relying on a centralized sequencer.

3. Lack of transparency: Users have to trust that a centralized sequencer is acting fairly and not manipulating transaction ordering for personal gain without having any clarity or transparency.

Linea's vision for a decentralized sequencer

Linea recognizes the limitations of centralized sequencers and has outlined a roadmap for decentralizing to align with the core principles of blockchain technology:

1. Enhanced user control: Linea plans to implement mechanisms that allow users to initiate withdrawals independently, minimizing reliance on the L2 sequencer.

2. Decentralizing operators: The roles of provers (generating zero-knowledge proofs) and sequencers will be distributed across multiple participants, ensuring that no single entity has control over the network.

3. Decentralized governance: Linea aims to establish a system where the community can actively participate in deciding the network's future, fostering collective ownership and sustainable growth.

Benefits of a decentralized sequencer

By decentralizing Linea will unlock several key advantages:

1. Enhanced security and reliability: With multiple sequencers, the network becomes more resilient to outages, attacks, and single points of failure.

2. Mitigation of MEV exploitation: By distributing the sequencing role, Linea limits the ability of any one participant to extract excessive value through front-running or other MEV tactics.

3. Improved trust and transparency: Users can have greater confidence in the network's fairness, as they don't have to rely on a single entity to process transactions honestly.

4. Cross-rollup interoperability: Decentralized sequencers can potentially enable better communication and composability between different L2 solutions, fostering a more interconnected ecosystem.

Linea's phased approach to decentralization

Linea has outlined a detailed, multi-phase roadmap to decentralize its network, with a strong focus on the decentralization of the sequencer. Let's take a closer look at each phase and how they contribute to the overall goal of enhancing security and trust.

Phase 0 (Complete):

• Launched Linea Mainnet Alpha with default portability through EVM-equivalence.

• Established the initial Linea Security Council to monitor the network and protect users.

• Made client software publicly available for anyone to verify the Linea state.

Phase 1 (Current):

• Open-sourcing Linea's software stack to foster transparency and align with web3 values.

• Achieving full EVM coverage in the zkEVM arithmetization to enable trustless execution across all use cases.

Phase 2:

• Diversify the Security Council to expand participation and representation, while retaining a 6-of-8 multisig threshold (or stricter) for immediate upgrades, to ensure balanced governance and prevent concentration of power.

• Facilitating censorship-resistant withdrawals to ensure users maintain continuous access and control over their assets.

Phase 3:

• Decentralizing operators (provers and sequencers) to enhance the network’s trust and integrity.

• Decentralizing governance: Democratizing Linea's governance fosters an equitable, transparent system where all stakeholders participate, promoting collective ownership, trust, and sustainable growth.

Phase 4:

• Develop a multi-prover rollup to enhance reliability and reduce trust-related risks.

• Restricting governance powers to balance necessary oversight with decentralization principles.

Challenges and Considerations

While the benefits of a decentralized sequencer are clear, Linea acknowledges there are hurdles to overcome:

1. Performance trade-offs: Decentralized systems may initially face higher latency and potentially increased costs compared to centralized solutions. Linea is committed to addressing these issues through ongoing research and development.

2. Consensus mechanisms: Designing an effective system for sequencers to reach agreement on transaction ordering is a complex task that requires careful consideration of factors like security, efficiency, and incentive alignment.

3. Incentive alignment: Ensuring that sequencers are properly motivated to act in the network's best interest is crucial for long-term stability and growth. Linea is exploring various incentive mechanisms to achieve this goal.

4. Coordination complexity: As the network becomes more decentralized, coordinating multiple sequencers and provers may introduce additional complexity in terms of communication, synchronization, and reaching consensus on transaction ordering and block production.

Conclusion

Decentralizing the sequencer is a critical step in Linea's journey towards becoming a fully decentralized and trustless zkEVM L2 solution. By distributing the sequencing role across multiple participants, Linea can enhance network security and reduce censorship risks.

While challenges remain, Linea's commitment to decentralization demonstrates a deep understanding of the importance of aligning with blockchain's core principles. As Linea progresses through its roadmap, users can look forward to a more resilient, trustless, and community-driven zkEVM L2 solution that unlocks the full potential of Ethereum's security and scalability.