Private Reputation

Enables credit-based lending in DeFi by allowing borrowers to prove a positive credit history or asset ownership without revealing their full financial profile. This reduces capital inefficiency compared to over-collateralized loans.

• Proof of Solvency: Users can generate a zero-knowledge proof (ZKP) that they have sufficient off-chain assets or a good repayment history.
• Risk-Based Pricing: Lenders can offer personalized interest rates based on verified, private reputation scores.
• Example: A user proves they have a high credit score from a traditional bureau via a ZKP to secure a larger loan with lower collateral.

Prevents vote manipulation in decentralized autonomous organizations (DAOs) and airdrops by using private credentials to prove unique personhood or past contributions.

• Proof of Personhood: Users verify they are a unique human via an attestation (e.g., from Worldcoin or BrightID) without linking that attestation to their on-chain voting address.
• Reputation-Weighted Voting: Voting power can be weighted by a privately verified history of positive contributions or expertise.
• Example: A DAO member uses a semaphore proof to vote, demonstrating they are an eligible, unique contributor without revealing their identity.

Allows users to build a verifiable record of professional skills, employment history, and project contributions that can be selectively disclosed to potential employers or collaborators in web3 ecosystems.

• Selective Disclosure: Prove specific claims (e.g., "worked at Project X for 2 years") using verifiable credentials without revealing the entire resume.
• Portable Identity: Reputation is user-owned and can be used across different platforms (e.g., freelance marketplaces, grant programs).
• Example: A developer proves they contributed significantly to a major protocol's GitHub repository to qualify for a grant, without exposing their full work history.

Enables users and institutions to satisfy Know Your Customer (KYC) and Anti-Money Laundering (AML) requirements for accessing regulated DeFi services while maintaining financial privacy.

• Minimal Disclosure: Prove you are from a whitelisted jurisdiction or are not on a sanctions list using a ZKP, without submitting full ID documents on-chain.
• Auditable Privacy: Regulators can receive cryptographic proofs of compliance without accessing all user transaction data.
• Example: A user accesses a licensed DeFi platform by providing a zero-knowledge proof that a trusted verifier has confirmed their KYC status.

Facilitates peer-to-peer transactions and services in decentralized marketplaces by allowing parties to prove trustworthiness derived from off-platform or historical on-chain behavior.

• Proof of Reliability: Sellers can prove a history of successful deliveries or high ratings from other platforms (e.g., eBay, Airbnb) privately.
• Collateral Reduction: Buyers with proven payment histories can participate in auctions or escrow services with reduced deposit requirements.
• Example: On a P2P NFT trading platform, a user proves a 100% completion rate from 50+ OpenSea trades to list an item without a full escrow lock.

Enables the formation of private groups, gated content, and incentive-aligned communities where membership or access rights are based on privately verified attributes or reputation.

• Gated Access: Prove you hold a specific credential (e.g., university degree, conference attendance) to join a private forum or Discord channel, without revealing the credential details.
• Reputation-Based Moderation: Community moderators can be selected based on a privately verified history of constructive contributions.
• Example: A research DAO grants access to a private library only to members who can prove they hold a PhD in a relevant field via a zk-proof of credential.

The foundational cryptographic primitive enabling private reputation. Zero-knowledge proofs allow a user (the prover) to convince a verifier that a statement is true without revealing any information beyond the validity of the statement itself. For reputation, this means proving attributes like "I have a credit score > 700" or "I am a verified member of this DAO" without disclosing the actual score or identity.

• Key Properties: Completeness, Soundness, Zero-Knowledge.
• Common Types: zk-SNARKs, zk-STARKs, Bulletproofs.

The user-controlled ability to reveal specific, minimal claims derived from a credential. Instead of showing an entire diploma, a user could prove they graduated from a specific university after 2020. This is often implemented using signature schemes with efficient protocols (e.g., BBS+ signatures) or ZKPs over committed credentials. It balances privacy with the need for verifiable information.

The standard data model (W3C) for expressing credentials in a way that is cryptographically secure, privacy-respecting, and machine-verifiable. A Verifiable Credential is a tamper-evident credential with a cryptographic signature from an issuer (e.g., a university, employer, or protocol). Private reputation systems use VCs as the signed source material, then employ ZKPs to generate privacy-preserving proofs from them.

Specific cryptographic protocols designed for anonymous signaling and reputation. Semaphore is a framework that allows users to prove membership in a group and send signals (e.g., votes, reviews) without revealing their identity. It uses ZK-SNARKs and Merkle trees for group membership. Similar constructs form the basis for private voting, anonymous attestation, and sybil-resistant reputation systems.

A critical distinction in the implementation of private reputation systems.

• Trusted Setup (e.g., zk-SNARKs): Requires a one-time, secure ceremony to generate public parameters. If compromised, privacy can be broken. Often more efficient.
• Trustless/Transparent (e.g., zk-STARKs, Bulletproofs): No trusted setup required, enhancing security assumptions. May have larger proof sizes or higher verification costs.

The choice impacts the security model and practicality of the system.

A core challenge that private reputation must solve. The system must prevent a single entity from creating multiple fake identities (Sybil attacks) to amass reputation illegitimately. Solutions often involve:

• Proof of Personhood: Anonymous yet unique biometrics (e.g., Worldcoin's Proof of Personhood).
• Costly Signaling: Requiring a bond or stake that is economically prohibitive to duplicate.
• Social Graph Analysis: Using web-of-trust models where attestations are themselves privately verifiable.

Users control exactly what information is shared. Instead of exposing a full transaction history, a user can prove specific, bounded claims:

• "I have > 1 ETH in my wallet" (for a loan)
• "My account is > 2 years old" (for trust)
• "I completed 50 trades on Uniswap v3" (for airdrop) This principle limits the attack surface for profiling and data aggregation.

A key challenge is preventing Sybil attacks (creating many fake identities) while maintaining user privacy. Solutions often involve:

• Attestations from trusted, known entities (KYC providers, DAOs).
• Bounded linkability using stealth addresses or semaphore-style group signatures, allowing a user to prove membership in a group without revealing which member they are.
• Balancing proof-of-personhood with privacy.

Where and how reputation data is stored critically impacts security.

• On-Chain: Public, immutable, but risks exposing pattern analysis.
• Off-Chain (Client-Side): User holds data (e.g., in a wallet), maximizing control but risking loss.
• Off-Chain (Custodial): Held by an issuer or platform, creating a central point of failure. Hybrid models using verifiable credentials (W3C standard) stored off-chain with on-chain revocation registries are common.

Mechanisms must exist to invalidate compromised or outdated credentials without compromising privacy.

• Revocation Registries: A private, updatable commitment (often on-chain) that allows verifiers to check if a credential is still valid.
• Key Rotation: Ability to update the cryptographic keys associated with an identity to recover from key compromise, without losing reputation history. Failure here can lead to permanent, unusable credentials.

Private reputation shifts trust from the public ledger to the issuers of credentials. Security depends on:

• Issuer Integrity: Is the attestation source honest and competent?
• Issuer Security: Can the issuer's signing keys be compromised?
• Collusion: Can issuers and verifiers collude to de-anonymize users? Systems must be designed to minimize and distribute these trust assumptions.

A cryptographic method allowing one party (the prover) to prove to another (the verifier) that a statement is true without revealing any information beyond the validity of the statement itself. This is the core technology enabling private reputation.

• Key Types: zk-SNARKs (Succinct Non-Interactive Arguments of Knowledge) and zk-STARKs (Scalable Transparent Arguments of Knowledge).
• Application: A user can prove they have a high credit score or own a specific NFT without revealing the score value or the NFT's token ID.

A user-controlled, portable digital identity that does not depend on a centralized registry, identity provider, or certificate authority. It forms the basis for a sovereign reputation system.

• Standard: W3C Decentralized Identifiers (DIDs).
• Components: A DID (a unique identifier) and associated Verifiable Credentials (VCs) that contain attestations about the identity holder.
• Connection to Reputation: Private reputation scores or badges can be issued as Verifiable Credentials to a user's DID.

A tamper-evident digital credential whose authorship can be cryptographically verified. They are the standard format for issuing and holding claims about a subject (like a person or entity).

• Structure: Contains claims (e.g., "has reputation score > 750"), metadata, and proofs.
• Issuers: Trusted entities (oracles, protocols, communities) sign VCs.
• Holder's Control: The user (holder) stores VCs in a digital wallet and presents only the necessary proofs, enabling selective disclosure for private reputation.

The ability for a user to reveal only specific, necessary attributes from a credential or data set, rather than the entire document. This is fundamental to privacy-preserving systems.

• Mechanism: Enabled by zero-knowledge proofs or cryptographic blinding.
• Example: Proving you are over 21 from a driver's license VC without revealing your birth date, address, or license number.
• Reputation Use Case: Proving your reputation is above a protocol's threshold without revealing the exact score.

Cryptographically signed statements made by one entity about another. They are the atomic unit of reputation data.

• On-Chain vs. Off-Chain: Can be recorded on a blockchain (e.g., Ethereum Attestation Service) or held off-chain as VCs.
• Examples: A protocol attesting a user completed a transaction, a DAO attesting membership, a lender attesting a loan was repaid.
• Aggregation: Multiple attestations are aggregated and computed to generate a composite reputation score.

The property of a system to resist Sybil attacks, where a single adversary creates many fake identities to gain disproportionate influence. Effective reputation systems must be Sybil-resistant.

• Common Mechanisms: Proof-of-Work, Proof-of-Stake, proof of unique humanity (e.g., biometrics), or cost-of-identity systems.
• Private Reputation Link: A private reputation score is only valuable if it is tied to a Sybil-resistant identity. Otherwise, users could trivially create infinite high-reputation identities.