Sedna: Sharding transactions in multiple concurrent proposer blockchains

2025-12-18

AI Summary

Multi-proposer (MCP) blockchains enhance censorship resistance and decentralization but face a fundamental censorship–latency–cost trilemma in transaction dissemination: full broadcast wastes bandwidth and exacerbates MEV, while targeted forwarding undermines censorship resistance and latency guarantees. This paper introduces the first user-centric, verifiable rateless coding protocol for MCP blockchains. It combines symbolic transaction splitting, zero-knowledge verifiable distribution, and an *until-decode* privacy mechanism to achieve confidentiality, deterministic decoding, and consensus-agnostic incremental deployment. Theoretically, it approaches the information-theoretic lower bound on bandwidth overhead and requires zero consensus-layer modifications. Compared to naive replication, it improves bandwidth efficiency by 2–3×, substantially mitigates MEV opportunities, and strictly guarantees liveness, censorship resistance, and bounded end-to-end latency.

Technology Category

• Multiagent Systems: Mechanism Design
• Cognitive Modeling & Cognitive Systems: Neural Spike Coding
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• Security and Privacy: Blockchains and distributed ledgers
• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Economics, Online Markets and Human Computation: Economic aspects of blockchain and cryptocurrencies

Abstract

Modern blockchains increasingly adopt multi-proposer (MCP) consensus to remove single-leader bottlenecks and improve censorship resistance. However, MCP alone does not resolve how users should disseminate transactions to proposers. Today, users either naively replicate full transactions to many proposers, sacrificing goodput and exposing payloads to MEV, or target few proposers and accept weak censorship and latency guarantees. This yields a practical trilemma among censorship resistance, low latency, and reasonable cost (in fees or system goodput). We present Sedna, a user-facing protocol that replaces naive transaction replication with verifiable, rateless coding. Users privately deliver addressed symbol bundles to subsets of proposers; execution follows a deterministic order once enough symbols are finalized to decode. We prove Sedna guarantees liveness and emph{until-decode privacy}, significantly reducing MEV exposure. Analytically, the protocol approaches the information-theoretic lower bound for bandwidth overhead, yielding a 2-3x efficiency improvement over naive replication. Sedna requires no consensus modifications, enabling incremental deployment.

Problem

• Resolves transaction dissemination trilemma in multi-proposer blockchains.
• Reduces MEV exposure with verifiable rateless coding for privacy.
• Minimizes bandwidth overhead approaching information-theoretic lower bounds.

Innovation

• Verifiable rateless coding replaces naive replication
• Private symbol bundles to subsets of proposers
• No consensus modifications for incremental deployment