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---
id: <leave blank -- will be assigned by reviewers>
title: SoK: Proposer-Builder Separation and Beyond
team: Oriol SAGUILLO, Prerna AROTE, Lucianna KIFFER (IMDEA Networks Institute)
created: <date created on, in yyyy-mm-dd format>
---

## Background and Problem Statement

Proposer–Builder Separation (PBS) [7][11][5], together with MEV-Boost, represents the first widely adopted approach for decoupling block construction from
block proposal in Ethereum. These mechanisms have enabled a more efficient and competitive market for block building and MEV extraction [2][28][1]. However,
their current realization relies predominantly on off-chain relayers, introducing non-trivial trust assumptions and creating centralization pressures
within the block production pipeline [27][11][10].

In response to these limitations, a broad spectrum of alternative designs and protocol-level enhancements has been proposed. These include (but are
not limited to):
• Enshrined PBS[20][14]
• Encrypted and Privacy-preserving block building [13][23][12]
• MEV burn mechanisms [8]
• Execution tickets [4],
• Execution auctions [3],
• Inclusion lists (FOCIL, AUCIL, COMIS, etc.) [26][24][25],
• Cross-domain PBS architectures [19][18][16]

Each class of design targets distinct challenges of the existing PBS model, such as reducing relayer dependence,
mitigating censorship and liveness risks, improving incentive alignment across participants, and strengthening security guarantees for validators and order-flow
providers.

However, discussions of these designs, including their security assumptions and trade-offs are fragmented across blog posts, research articles, and forum
discussions. As a result, there is no single, comprehensive resource that systematically compares these approaches or clearly outlines their shared objectives,
design trade-offs, and remaining open challenges.

The goal of this project is to compile and systematize existing PBS-related
designs across different layers of the blockchain protocol. The project will identify and categorize the desired properties of proposer–builder separation mech-
anisms, analyze known and potential attack vectors— Sandwich attack, Frontrunning attack [7][9], Back-running attack[21], Free-option problem[15], Timing
game[22], Equivocation attacks [17], Bribery attack[6], etc. , and highlight open research questions. By providing a unified framework for understanding current
proposals and their limitations across both industry and academia, this work aims to serve as a reference for researchers, protocol designers, and the broader
blockchain community.

## Plan and Deliverables

The study will proceed in the following steps:

• Compile and review existing literature on Proposer–Builder Separation (PBS), including current implementations and proposed alternative de-
signs related to any step in the workflow from transaction submission to block validation.
• Formalize the key properties required for a secure, efficient, and decentralized block-building system.
• Analyze known and potential attack vectors that obstruct the realization of these properties, and discuss their implications for different PBS de-
signs.
• Synthesize the above analysis into a unified taxonomy of PBS design trade-offs, highlighting open problems and directions for future research

## References

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tralization in execution tickets. arXiv preprint arXiv:2408.11255, 2024.
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