lambda-prize/prizes/LP-0016.md

LP-0016: Anonymous Forum with Threshold Moderation and Membership Revocation [OPEN]

Status: Open Logos Circle: N/A

Overview

This prize is for a protocol for anonymous, moderated forums. Members post without revealing their identity and their posts are unlinkable to one another — yet a coordinated group of moderators can act on individual pieces of content, and a member who accumulates too many moderation strikes loses their membership.

All forum activity and moderation happens off-chain using the Logos stack — nothing goes on-chain until a member reaches the revocation threshold and a slash is submitted. This keeps the common path free of transaction costs while preserving trustless enforcement at the point of revocation.

The deliverable has two required parts: a forum-agnostic moderation library (a standalone SDK for threshold moderation and cryptographic membership revocation, making no assumptions about forum content or structure) and an end application (a working Logos Basecamp app of any forum shape built on top of the library).

Motivation

The Pseudonymity Problem

Most forums that present themselves as "anonymous" are in practice pseudonymous: users pick a persistent handle, and that handle accumulates a social history. Over time, a pseudonym becomes an identity in its own right. Other participants form impressions of the author before reading the content — they up-vote familiar handles, dismiss posts from accounts they distrust, and calibrate their interpretation of every new message through the lens of prior interactions. The same argument lands differently depending on whether it comes from a long-standing respected member or a newcomer. Bias and reputation are inseparable from the username.

This social accumulation is not a bug in pseudonymous systems — it is a direct consequence of linking posts together under a persistent identifier. Participants who want to be judged purely on the content of their ideas, without carrying the weight of prior interactions, have no recourse. Minority viewpoints expressed early may suppress further participation from that account. And for anyone operating in a context where prior association is a liability — whistleblowers, dissidents, participants in contested debates — pseudonymity offers far weaker protection than it appears.

True anonymity means each post is evaluated entirely on its own merits. Enabling a marketplace of ideas. No post is linkable to any other post from the same person. There is no username to pre-judge, no history to hold against an author, no accumulated reputation to exploit or to be penalised for. Every contribution stands alone. This prize targets the cryptographic building blocks that make true anonymity compatible with a moderated forum.

The Case for Moderation

A persistent pseudonym is one way to implement reputation — but not the only one. Forums that rely on reputation, by whatever mechanism, to surface good content and suppress bad behaviour form a distinct design domain. This prize does not address that domain.

This prize targets forums where content quality is maintained by a designated moderation team. Moderation is a first-class primitive. Every forum instance defines its own rules and its own moderator set. The cryptographic protocol enforces those rules consistently: a member who accumulates enough violations is revoked, regardless of who argues for leniency. Moderators cannot selectively enforce rules against members they dislike without leaving a public audit trail. No single moderator can act alone. The cryptographic machinery is not a substitute for human judgement about acceptable content — it is a substrate for enforcing that judgement fairly and without unilateral power.

Forum Competition and Moderation Quality

Each forum instance is independently parameterised and governed. Different instances will develop different characters — shaped by their topic, community, rules, and moderation team. Users are not locked in. They can observe the moderation record of a forum — all certificates are publicly auditable off-chain — and choose instances whose moderation philosophy matches their needs.

Forum success depends on many factors: topic relevance, network effects, content quality, community norms. Moderation is one of them. What this protocol adds is that moderation behaviour is falsifiable: because the audit trail is public and cryptographically verifiable, a community dissatisfied with how a forum is run has the information needed to make that case — and the ability to fork the instance and try to do better.

What This Prize Delivers

The deliverable is not a forum — it is a set of building blocks. The moderation library is forum-agnostic: it handles membership, proof generation, N-of-M moderation, and revocation without making assumptions about content or social structure. Any team building a forum on these primitives can make their own choices about content types, interaction models, and governance — while inheriting strong anonymity and fair moderation guarantees from the underlying protocol.

Core Mechanism

Goals

Each forum is an independent instance with its own membership registry, moderator set, and parameters: how many moderation strikes revoke membership (K) and how many moderators must agree to issue one strike (N-of-M).

Anonymous posting: Members register with a private identity. Each post carries a proof that the author is a registered, non-revoked member — without revealing which member. Posts from the same author are unlinkable to any observer — including moderators — until the slash threshold is reached. The anonymity set is the full set of non-revoked registered members.

N-of-M moderation: When N out of M designated moderators agree that a piece of content violates forum rules, they jointly issue a moderation certificate against the author. Fewer than N moderators cannot act — no single moderator has unilateral power. Certificates are recorded off-chain using the Logos stack, publicly auditable without any on-chain transaction.

Slashing: Once a member has accumulated K moderation certificates, any moderator, or even party, can submit a single on-chain slash transaction. The membership registry verifies the accumulated evidence, revokes the membership, and claims the stake. Future posts from that identity are rejected. No gas is spent until this final step.

Success Criteria

Functionality

• A member can register in a forum instance with a stake and subsequently publish posts with valid anonymous proofs of membership. Posts from the same member are unlinkable to any observer — including moderators — for as long as the member remains below the slash threshold.
• Upon slash, the reconstructed secret enables retroactive linkability of the slashed member's prior posts. No other member's anonymity is affected. This property is explicitly documented in docs/protocol.md.
• N-of-M moderators can jointly produce a valid moderation certificate off-chain using the Logos stack. Fewer than N moderation cannot produce a certificate.
• When K moderation certificates are accumulated for the same member, any moderator, or potentially members, can submit a single slash transaction to the membership registry. The registry verifies the off-chain evidence and revokes the membership.
• A slashed commitment is added to the revocation list. Subsequent posts with a membership proof tied to that commitment are rejected.
• The protocol is parameterisable: forum instances can independently set K (revocation threshold) and N-of-M.
• A standalone, forum-agnostic moderation library exposing well-documented APIs for: membership registration, encrypted proof generation and verification, moderation certificate construction, and slash submission. The library operates on abstract content identifiers, makes no assumptions about forum content structure, and uses the Logos stack for all off-chain activity.
• A working Logos Basecamp app, built using the library without modifying it. The app allows anyone to create a new forum instance, post, moderate it, and set moderators. The specific forum functionality (text posts, image board, comments, reactions, etc.) is at the applicant's discretion. The app demonstrates the full moderation lifecycle: instance creation, registration, publishing content, moderation, and revocation. The app must be usable by a non-technical user: core actions (posting, moderating, viewing moderation history) must complete within a reasonable time frame and without requiring CLI interaction or manual transaction crafting.
• End-to-end demonstration on LEZ testnet with at least two independent forum instances using different K and N-of-M parameters.

Usability

• Provide the moderation library as a module/SDK with a documented API that any Logos application can import to build a moderated forum without modifying the library.
• Provide an IDL for the membership registry LEZ program, using the SPEL framework.

Reliability

• Proof generation failures surface a clear error to the member and allow a retry without consuming the member's nullifier.
• A partial moderation certificate (fewer than N moderators) cannot be submitted on-chain — the library enforces the threshold client-side before any on-chain interaction.
• The application handles transient Logos stack failures (storage or messaging unavailability) gracefully: pending posts and moderation actions are queued and retried rather than silently dropped.

Performance

• ZK membership proof generation takes less than 10 seconds on a standard laptop (already captured in Scope; surfaced here as a measurable criterion).
• Document the compute unit (CU) cost of each on-chain operation (registration, slash submission) on LEZ devnet/testnet. Note: LEZ's per-transaction compute budget may change during testnet.

Supportability

• The membership registry program is deployed and tested on LEZ devnet/testnet.
• End-to-end integration tests run against a LEZ sequencer (standalone mode) and are included in CI.
• CI must be green on the default branch.
• A README documents end-to-end usage: deployment steps, program addresses, and step-by-step instructions for creating a forum instance, registering, posting, moderating, and triggering a slash via the Basecamp app.
• A reproducible end-to-end demo script is provided and works against a real local sequencer with RISC0_DEV_MODE=0.
• A recorded video demo is included in the submission. The builder must narrate and walk through the architecture, key implementation decisions, and the full end-to-end flow — not merely screen-record a silent run. The recording must show terminal output (including proof generation) to confirm RISC0_DEV_MODE=0 was active.

Scope

In Scope

• Membership registry LEZ program: commitment registration, staking, revocation list, and slash verification.
• ZK membership proof circuit: proves commitment is in the registry and not revoked, without revealing which commitment. It takes less than 10 seconds to generate a message proof.
• Moderation library: a standalone, forum-agnostic SDK for threshold moderation and cryptographic membership revocation. It operates on abstract content identifiers, makes no assumptions about the shape of forum content, and uses the Logos stack for all off-chain activity. It handles threshold decryption coordination, certificate construction, share aggregation, and slash transaction submission. Must be importable by any application regardless of forum type.
• Slash verifier: verifies accumulated off-chain certificates and submits a valid on-chain slash transaction.
• End application: a Logos Basecamp app built using the moderation library. The app must allow users to create new forum instances. Forum content and moderation are handled off-chain via the Logos stack. The specific forum functionality — content types, interaction model, layout — is left entirely to the applicant. The application must not require changes to the library to function.
• Documentation covering: library API reference, integration guide, unlinkability analysis (including anonymity set size and the retroactive deanonymization property upon slash), moderator trust model, and threat model.

Out of Scope

• Discovery, search, feeds, or social graph features.
• Reputation tiers or rate limits on posting frequency.
• Multi-forum identity linking or cross-forum revocation.
• End-to-end encryption of forum content — applicants may implement it but it is not required.
• Hosted infrastructure beyond what is required to run the Logos Basecamp app.

Prize Structure

• Total Prize: $1,200
• Effort: Large

Eligibility

Open to any individual or team. Submissions must be original work. Teams must hold the rights to all submitted code and agree to license it under MIT or Apache-2.0.

Submission Requirements

• Public repository (MIT or Apache-2.0) containing:
  • LEZ program (membership registry with slash verification),
  • ZK membership proof circuit,
  • moderation library (forum-agnostic, standalone package) with public API, documentation, and usage examples,
  • slash verifier,
  • Logos Basecamp app built on the library without modifying it — forum functionality at applicant's discretion,
  • tests covering: valid registration, valid post proof, moderation certificate construction and verification, strike accumulation, slash submission, post rejection after revocation.
• Protocol specification (docs/protocol.md) covering: unlinkability argument, moderator trust assumptions, revocation mechanism, and threat model.
• End-to-end demo video walkthrough in which the builder explains what they built and why, walks through the architecture and key implementation decisions, and demonstrates the full lifecycle: registration, posting, N-of-M moderation, strike accumulation, slash, and post rejection. A screencast without narration or explanation is not sufficient.
• Two live forum instances on LEZ testnet with different K and N-of-M parameters and verified program IDs.

Evaluation Process

By default, submissions are evaluated first-come-first-served against the success criteria. The first submission that meets all criteria wins.

Evaluators will independently clone the repository and run the demo script from a clean environment; the script must succeed without modification. Evaluators may also ask technical follow-up questions to verify authorship and understanding of the implementation.

The following policies apply to all prizes (see evaluation policies):

• Submissions: each builder (or team) is allowed a maximum of 3 submissions per prize, with at most one submission/review per week.
• Feedback: initial evaluation feedback is limited to a pass/fail indication against the success criteria.

Resources

• Logos Execution Zone repo
• Semaphore — group membership and ZK proofs
• Shamir's Secret Sharing — foundational scheme for threshold reconstruction of the nullifier
• Threshold decryption overview — Boneh et al.
• LP-0001 — Private NFT Ownership Proof (ZK membership proof patterns)
• LP-0003 — Private Allowlist (nullifier and commitment scheme reference)