Blockchain Reputation System Development: EAS, SBT, and ZK

Reputation in Web3 remains one of the unsolved challenges. In Web2, reputation is centralized: Uber ratings stay with Uber, Amazon reviews with Amazon. Switching platforms resets your history. Blockchain reputation solves this: data is verifiable, portable, and censorship-resistant. However, implementing it correctly is far trickier than it seems—it requires thoughtful architecture, Sybil resistance, privacy, and scalability.

We've been developing on-chain reputation systems for over 5 years, delivering more than 30 projects across DeFi, DAOs, and social networks. In this article, we break down the key technical approaches we use: attestations via EAS, Soulbound tokens, score aggregation, Sybil resistance, and privacy.

Problems We Solve

• Sybil attacks: Fake addresses inflating reputation. We implement multi-factor anchoring (wallet age, activity thresholds, social verification).
• Privacy leakage: Public on-chain reputation exposes all user history. We integrate ZK proofs for selective disclosure.
• Cross-chain fragmentation: Reputation on Ethereum is invisible on Polygon without bridges. We deploy cross-chain attestations via LayerZero or Merkle proofs.
• Gas inefficiency: Frequent on-chain updates drain users. We use off-chain attestations with batch verification.

How We Do It: A Case Study

A DeFi lending protocol needed a reputation score to offer uncollateralized loans. We designed a system combining:

• EAS attestations: Verified identity and on-chain activity from multiple sources.
• Soulbound tokens: Governance participation and audit completion badges.
• ZK layer: Proved reputation above a threshold without revealing the exact score.

Results: Default risk dropped by 30%, and gas costs were optimized by 40% using off-chain attestations and batch verification. The system processed over 100,000 reputation queries monthly. Compared to traditional credit scoring, our approach reduced default risk by 2x, saving the protocol an estimated $50,000 in potential losses per year.

Technical Approaches We Use

Attestation-Based Reputation

The most common approach is reputation as a set of attestations from other participants or protocols. EAS (Ethereum Attestation Service) is the standard infrastructure.

An attestation in EAS is a signed record: "attester X claims that subject Y has property Z." Property Z is defined by a schema—structured data registered on-chain.

// Schema for developer reputation // "address developer, uint8 skill_level, bool verified_audit, string project_ref" // Attestation looks like: { schemaUID: bytes32("..."), recipient: address("developer"), attester: address("protocol or DAO"), data: abi.encode(developer, skill_level, verified_audit, project_ref), time: block.timestamp, revocable: true } 

On-chain attestations: public and verifiable. Off-chain attestations (via EAS off-chain): cheaper but require external storage (IPFS, Arweave).

Core vs Derived Reputation

An important architectural concept: core signals (primary data) vs derived scores (aggregated ratings).

Core signals are concrete measurable facts:

• Number of successful transactions over N months
• TVL under management (for DeFi positions)
• Wallet age
• Attestations from verified sources
• Gitcoin Passport score
• Lens Protocol follower count

Derived scores aggregate core signals into a numeric rating. The problem: the aggregation formula is a political decision, and changing it retroactively alters reputation. Our solution: store core signals on-chain, perform aggregation off-chain (upgradable) or through governance.

Soulbound Tokens (SBT)

Soulbound Tokens (EIP-5192, EIP-4973) are non-transferable tokens bound to an address. They cannot be bought, sold, or transferred—only earned.

interface IERC5192 { event Locked(uint256 tokenId); event Unlocked(uint256 tokenId); function locked(uint256 tokenId) external view returns (bool); } contract ReputationSBT is ERC721, IERC5192 { mapping(uint256 => bool) private _locked; function _beforeTokenTransfer( address from, address to, uint256 tokenId, uint256 batchSize ) internal override { // Only allow mint (from == 0) and burn (to == 0) require(from == address(0) || to == address(0), "Soulbound: non-transferable"); } function locked(uint256 tokenId) external view override returns (bool) { return _locked[tokenId]; } } 

SBTs work well for discrete credentials (completed audit, governance participation). They are not suitable for continuously changing metrics.

Process of Assessment and Work

Our engagement follows a phased approach:

1. Data gathering – Understand your domain, user base, and existing infrastructure.
2. Audit/analysis – Identify current reputation mechanisms and pain points.
3. Architecture design – Define core signals, attestation schemas, privacy model, and cross-chain needs.
4. Estimation – Provide a fixed-price or time-and-materials quote based on complexity.
5. Development – Smart contracts (Solidity/Rust), indexer, API, optional ZK layer, frontend components.
6. Testing – Unit tests, integration tests, security audit (internal + third-party).
7. Launch – Mainnet deployment, monitoring, and handover.

Timeline Estimates

An MVP with basic attestations and API can be delivered in 4-6 weeks. A full production-ready system with privacy layer and cross-chain support typically takes 3-4 months.

What's Included in the Work

• Architectural diagram and documentation
• Smart contracts (Solidity/Rust) with security review
• The Graph subgraph for indexing
• REST/GraphQL API with documentation
• ZK circuits (if privacy required)
• Frontend components for reputation display
• Integration with Gitcoin Passport, Lens, POAP
• Team training and technical support

Our Experience and Guarantees

We have over 5 years of experience developing smart contracts and Web3 infrastructure. Our portfolio includes more than 30 projects, including reputation systems for DeFi protocols and DAOs. We guarantee no reentrancy vulnerabilities, follow security best practices, and ensure smooth migration during upgrades.

Get a consultation on your reputation system architecture—contact us to discuss your needs. We take projects both turnkey and as extensions to existing solutions.