Briefing
Centralized sequencers pose a systemic risk to Layer 2 (L2) rollup security and censorship resistance, creating a single point of control over transaction ordering and data availability. This paper introduces the “Decentralized Arranger,” a unified service combining transaction sequencing and the Data Availability Committee (DAC) functions into a single, provably correct primitive. The mechanism is built upon an extension of Set Byzantine Consensus (SBC), a protocol where nodes agree on a subset of proposed transaction sets, ensuring a decentralized ordering and a synchronized data commitment. This new primitive establishes a foundational, trustless architecture for L2s, guaranteeing full decentralization from the initial transaction submission to the final Layer 1 (L1) data posting.
Context
The established architecture of optimistic and zero-knowledge rollups relies on a singular, centralized sequencer to collect, order, and batch transactions before committing a hash to Layer 1. This design choice, while highly efficient in the short term, fundamentally compromises the system’s trust model, creating a single point of failure susceptible to censorship, malicious reordering (Maximal Extractable Value, or MEV, extraction), and liveness failure. The prevailing theoretical limitation was designing a mechanism that achieves the necessary high throughput of sequencing while maintaining the Byzantine fault tolerance and permissionless nature of the underlying L1.
Analysis
The core innovation is the application of Set Byzantine Consensus (SBC) to the L2 ordering problem. Traditional Byzantine Fault Tolerance (BFT) protocols require nodes to reach agreement on a single, canonical value, such as a block. The Arranger, by utilizing SBC, reaches consensus on a set of proposed transaction batches and their corresponding data availability proofs. This process decouples the final ordering from any single entity.
The Arranger nodes collectively propose transaction sets, and the SBC protocol then determines the canonical union of these proposals and the final, agreed-upon hash commitment for L1. This mechanism ensures that no single node can censor transactions or unilaterally manipulate the transaction order while simultaneously guaranteeing the data required for state reconstruction is available.
Parameters
- Formal Arranger Definition ∞ The paper establishes a rigorous, first-principles definition for the combined sequencer and DAC role, enabling provable security analysis.
- Set Byzantine Consensus ∞ The foundational consensus primitive used to achieve decentralized agreement on the transaction set and data commitment.
- Proof of Correctness ∞ The mechanism includes formal mathematical proofs guaranteeing the security and liveness properties of the decentralized arranger implementation.
Outlook
This research provides the essential theoretical blueprint for the next generation of truly decentralized Layer 2 solutions. This model will likely be adopted as the standard for rollup infrastructure in the next 3-5 years, enabling a competitive market of permissionless sequencers that are verifiably fair and censorship-resistant. It opens new research avenues in optimizing the communication complexity of Set Byzantine Consensus for extremely high-throughput environments and exploring incentive mechanisms to ensure optimal participation within the decentralized arranger set.
Verdict
The Decentralized Arranger mechanism is a foundational breakthrough, formally resolving the critical centralization-of-sequencer problem and securing the long-term architectural integrity of Layer 2 scaling solutions.
