Briefing
Centralized Layer 2 sequencers compromise the core decentralization principle, introducing systemic risks of censorship and liveness failure. The Decentralized Arranger is a novel primitive that cryptographically unifies the sequencer and the Data Availability Committee (DAC) into a single, cohesive service. This service is realized through an extension of Set Byzantine Consensus (SBC) , where consensus is reached on a subset of proposed transaction sets, ensuring both transaction ordering and data availability simultaneously. This mechanism is foundational for L2 maturity, allowing rollups to inherit the full censorship resistance and decentralization guarantees of their underlying Layer 1.
Context
The prevailing architecture for Layer 2 rollups, designed to solve the Layer 1 scalability constraint, relies on a centralized sequencer to order transactions and post batches to the L1. This established model, while efficient for throughput, creates a critical single point of failure and a centralization bottleneck, fundamentally compromising the trust-minimization ethos of the blockchain system. This structure introduces systemic risks like unilateral Maximal Extractable Value (MEV) extraction and potential censorship, which the academic community has long sought to resolve without sacrificing performance.
Analysis
The core mechanism is the Decentralized Arranger , which reframes the sequencing problem as a consensus problem over sets of transactions. The Arranger operates by extending the Set Byzantine Consensus (SBC) protocol. In SBC, multiple participants propose sets of values (transactions and associated data), and the protocol guarantees that all honest participants agree on a final set that is a subset of the union of all proposed sets.
This consensus on the set ensures that the final, canonical transaction order is collectively determined. Furthermore, because the data availability function is integrated into this consensus process, the data required to verify the batch is guaranteed to be available upon finality, thus eliminating the need for a separate, trusted Data Availability Committee (DAC).
Parameters
- Byzantine Fault Tolerance → Up to one-third of nodes can be malicious or fail without compromising the system’s security or liveness, a foundational property inherited from the underlying BFT consensus model.
Outlook
This research establishes a new architectural blueprint for L2s, shifting the focus from simply optimizing transaction throughput to maximizing credible neutrality. The concept of a unified “arranger” will drive future research into mechanism design for shared sequencing networks, potentially enabling atomic composability across multiple rollups. In the long term, this theoretical framework could fundamentally restructure the MEV supply chain by decentralizing the block-building right away from a single entity, securing the L2 ecosystem’s integrity for the next generation of decentralized applications.
Verdict
The decentralized arranger and its reliance on Set Byzantine Consensus provide the necessary theoretical framework to resolve the core centralization risk in Layer 2 rollup architecture.
