Briefing
The core problem is the architectural central point of failure and censorship risk inherent in Layer 2 rollups’ reliance on a single, centralized sequencer. This research introduces the Decentralized Arranger service, a novel mechanism that unifies the sequencer and Data Availability Committee (DAC) roles using a modified Byzantine Fault Tolerance protocol called Set Byzantine Consensus (SBC). SBC enables a committee of nodes to reach consensus on a set of proposed transaction batches, not just a single block, thereby achieving a fully decentralized and fault-tolerant ordering and data availability solution. The most important implication is the foundational unlocking of truly trustless and censorship-resistant Layer 2 scaling solutions by resolving their core decentralization bottleneck.
Context
The prevailing architectural limitation in Layer 2 scaling solutions, such as Optimistic and ZK-Rollups, is the “decentralization bottleneck” caused by the single, centralized sequencer. This centralized entity is responsible for ordering transactions and posting compressed data to Layer 1, creating a single point of trust susceptible to censorship, liveness failures (halting the L2), and malicious ordering influence. This structural vulnerability prevents L2s from achieving full architectural decentralization, despite their computational offloading benefits.
Analysis
The core mechanism is the Set Byzantine Consensus (SBC) protocol, which is an extension of traditional BFT consensus. Classic Byzantine Fault Tolerance protocols agree on a single value; the SBC extension mandates agreement on a subset of all proposed transaction sets. This allows multiple replicas to propose sets of transaction requests or batch hashes. The protocol then achieves consensus on a subset of the union of all proposed sets, ensuring all included transactions are valid and available.
This is crucial because it merges the decentralized ordering of transactions (sequencing) and the cryptographic certification of data availability (DAC) into a single, cohesive, fault-tolerant service → the Arranger. The approach guarantees correctness as long as more than two-thirds of the replicas are honest.
Parameters
- Consensus Fault Tolerance → Two-thirds plus one honest replica. A successful consensus requires the honest majority to exceed two-thirds of the total arranger committee.
- Arranger Unification → Sequencer and Data Availability Committee (DAC). The new service formally defines and merges these two distinct roles into a single decentralized primitive.
Outlook
This foundational work opens a new research avenue for mechanism design in Layer 2 architectures, shifting focus from simply scaling computation to securing the sequencing layer. The immediate application is the deployment of fully decentralized Validiums and Optimiums, which currently rely on centralized or semi-decentralized arrangers. In the next three to five years, this primitive could be adapted to create shared, neutral sequencing layers across multiple rollups, fundamentally securing the entire Layer 2 ecosystem against centralized transaction ordering and censorship risks.
Verdict
The Set Byzantine Consensus primitive fundamentally re-architects Layer 2 rollups, resolving the critical centralization risk in transaction ordering and data availability.
