# zkFOCIL: SNARK-based Linkable Ring Signatures Ethereum's FOCIL (Fork-choice enforced Inclusion Lists) mechanism aims to enhance censorship resistance by allowing committees of validators to force-include transactions in blocks. However, the current design exposes validator identities, creating potential vulnerabilities to targeted attacks. The zkFOCIL approach proposes using privacy-enhancing cryptography to protect validator identities while maintaining FOCIL functionality. ### Goal Explore practical approaches for implementing privacy-preserving inclusion lists using zero-knowledge proofs, with a focus on SNARK-based Linkable Ring Signatures. ## Objectives ### Core objectives 1. Research SNARK-based approaches for implementing Linkable Ring Signatures in the context of zkFOCIL 2. Prototype and benchmark implementations to evaluate viability 3. Determine performance characteristics across different validator set sizes 4. Analyze security guarantees and potential vulnerabilities ### Secondary Objectives 1. Explore alternative schemes for snark based LRS constructions to identify tradeoffs 2. Investigate compatibility with future reward mechanisms 3. Evaluate scalability with growing validator sets 4. Identify potential networking layer improvements ## Scope ### Inclusions - Research on SNARK-based LRS approaches for zkFOCIL - Prototype implementation of selected approaches - Performance benchmarking and comparison - Security analysis of proposed approaches ### Possible - Integration into Ethereum clients - Networking layer privacy improvements ### Exclusions - Implementation of anonymous reward mechanisms - Changes to core FOCIL protocol beyond privacy enhancements ## Milestones ### Milestone 1: Research Phase - Survey existing LRS schemes and SNARK systems - Identify promising approaches for zkFOCIL Expected Delivery date: Q2 2025 ### Milestone 2: Prototype and Initial Benchmarking - Implement prototype of selected approach(es) - Conduct initial performance measurements Expected Delivery date: Q3 2025 ### Milestone 3: Analysis and Recommendations - Security and scalability analysis - Provide recommendations for full implementation - Publish research findings Expected Delivery date: Q4 2025 ## Why Now? As Ethereum continues to rely on specialized block builders, censorship resistance remains a critical concern. FOCIL represents a significant advancement in this area, and addressing its privacy limitations before widespread deployment is important for long-term security. The growing validator set also increases the need for privacy protections. ## Why PSE? PSE research areas involve zero-knowledge proof schemes and Ethereum's protocol enhancements (such as former zk-evm work) related to privacy and scalability, making it well-positioned to lead this research. PSE's focus on advancing privacy technology for public benefit aligns perfectly with improving FOCIL's privacy characteristics. ## Resources and Team Structure ### Team Members - Brechy ### External Collaboration - EF Robust Incentive Group (RIG) members working on FOCIL - EF Cryptography Research team - Execution and Consensus client teams if integrations become part of this project. ### Resource Requirements None ## Evaluation Criteria ### Success Metrics - Identification of viable approaches for zkFOCIL implementation - Prototype performance within practical bounds for Ethereum - Clear understanding of tradeoffs between different approaches ## Appendices ### Technical Background #### Core Concepts - Linkable Ring Signatures allow signers to prove membership in a group without revealing identity - Key images enable detection of double-signing while preserving anonymity - SNARK systems can provide efficient zero-knowledge proofs with various tradeoffs - Private lottery mechanisms can enhance validator privacy while maintaining fairness #### Key Requirements - Reasonable signature size for large validator sets - Efficient verification compatible with consensus timing - No additional key registration beyond existing BLS keys - Strong privacy guarantees against various attacks ## References - [zkFOCIL: Inclusion List Privacy using Linkable Ring Signatures](https://ethresear.ch/t/zkfocil-inclusion-list-privacy-using-linkable-ring-signatures/21688) - [EIP-7805: Fork-choice enforced Inclusion Lists (FOCIL)](https://eips.ethereum.org/EIPS/eip-7805) - [Efficient Linkable Ring Signatures: New Framework and Post-Quantum Instantiations](https://eprint.iacr.org/2024/553) - [Inclusion List Committee Selection in FOCIL](https://hackmd.io/@ttsao/il-committee-selection#3-Aggregator-approach) - [IncluderSelect: Leveraging External Incentives in FOCIL](https://mirror.xyz/julianma.eth/G15Gs2TGfnU93t8R7fuyFjTmZGIwwhRFhNhH_M0dgGE)