Sedna: Sharding transactions in multiple concurrent proposer blockchains

TL;DR

Sedna introduces a protocol using verifiable rateless coding for efficient, privacy-preserving transaction dissemination in multi-proposer blockchains, improving bandwidth efficiency and reducing MEV exposure without modifying consensus.

Contribution

Sedna's novel rateless coding approach enhances transaction privacy and efficiency in multi-proposer blockchains, addressing the censorship-latency-goodput trade-off.

Findings

Achieves 2-3x efficiency over naive replication

Guarantees until-decode privacy, reducing MEV exposure

Approaches information-theoretic bandwidth lower bound

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.