A ZK-Badge is a cryptographic token that leverages zero-knowledge proofs (ZKPs) to enable verifiable claims about an individual or entity. Unlike traditional attestations, it allows a user to prove they possess a certain credential—such as being over 18, holding a specific NFT, or having completed a course—without disclosing their identity, wallet address, or any other extraneous information. This mechanism separates the proof of a claim from the data behind it, enabling selective disclosure and minimizing data exposure.
LABS
Glossary
ZK-Badge
A ZK-Badge is a non-transferable, privacy-preserving attestation of a trait or achievement, represented as a verifiable credential using zero-knowledge proofs.
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definition
DIGITAL CREDENTIAL
What is a ZK-Badge?
A ZK-Badge is a privacy-preserving, self-sovereign digital credential that proves specific attributes or achievements without revealing the underlying personal data.
The core technical components of a ZK-Badge typically involve an issuer (who signs the credential), a holder (who receives and stores it, often in a digital wallet), and a verifier (who requests proof). When a verifier asks for proof of a claim, the holder's wallet generates a zk-SNARK or zk-STARK proof. This proof cryptographically demonstrates that the holder possesses a valid, unrevoked credential signed by a trusted issuer, satisfying the verifier's query without transmitting the credential itself. This process is often managed through decentralized identity standards like Verifiable Credentials (VCs).
ZK-Badges enable critical use cases in web3 that require both trust and privacy. Common applications include sybil-resistant governance (proving unique personhood via tools like Worldcoin without revealing identity), gated access to exclusive content or DAOs based on asset ownership or reputation, and compliance (proving KYC status to a DeFi protocol without linking that status to all transactions). They transform opaque on-chain activity into a rich, reusable graph of verifiable attributes while preserving user autonomy.
The implementation and verification of ZK-Badges rely on specific infrastructure. Projects like Sismo and Orange Protocol provide modular tooling for issuing and managing these badges. From a user perspective, interacting with a ZK-Badge often involves connecting a wallet to an application, which then requests a zero-knowledge proof for a specific claim. The user's wallet software handles the proof generation locally, ensuring the private data never leaves their device, and then submits only the cryptographic proof for verification on-chain or off-chain.
Compared to Soulbound Tokens (SBTs), which are non-transferable but fully transparent NFTs, ZK-Badges offer a fundamentally different privacy model. While an SBT's metadata and holder address are publicly visible on-chain, a ZK-Badge's existence and contents are private by default, revealed only through generated proofs. This makes ZK-Badges better suited for sensitive personal data, allowing users to build a pluralistic identity—compiling credentials from multiple sources—and present tailored facets of their identity to different applications without creating a centralized, correlatable profile.
how-it-works
MECHANISM
How a ZK-Badge Works
A technical breakdown of the cryptographic and on-chain processes that enable ZK-Badges to function as privacy-preserving, verifiable credentials.
A ZK-Badge is a privacy-preserving, non-transferable credential that uses zero-knowledge proofs (ZKPs) to allow a user to cryptographically prove they possess certain attributes or have completed specific actions without revealing the underlying data. The core mechanism involves a prover (the user) generating a succinct proof, often a zk-SNARK or zk-STARK, that attests to the validity of a private statement (e.g., "my wallet balance was > X on date Y") against a public set of rules defined in a circuit. This proof is then verified by a verifier, typically a smart contract on-chain, which only needs the proof and the public inputs to confirm its truth.
The workflow begins with credential issuance. An issuer, such as a protocol or community, defines the attestation logic and publishes the corresponding verification key or smart contract. When a user qualifies (e.g., by holding an NFT, having a transaction history, or completing a task), they can generate a proof locally in their wallet using a prover key. This process keeps all sensitive data—like the specific wallet address, transaction amounts, or personal identifiers—entirely private and never leaves the user's device. The resulting cryptographic proof is the essence of the ZK-Badge.
Finally, the user presents the proof for verification. In most implementations, the proof is submitted to a verifier contract on a blockchain like Ethereum or a Layer 2. The contract runs a deterministic verification function; if the proof is valid, it updates a public registry or emits an event, cryptographically attesting that the anonymous holder meets the criteria. This allows the badge holder to participate in gated communities, claim rewards, or access services based on reputation—all while maintaining pseudonymity and preventing the creation of a centralized database of user activity.
key-features
CORE MECHANICS
Key Features of ZK-Badges
ZK-Badges are non-transferable, privacy-preserving attestations that leverage zero-knowledge proofs to verify credentials without revealing underlying data.
01
Selective Disclosure
A ZK-Badge allows a user to prove they hold a specific credential (e.g., 'is over 18', 'has a degree') without revealing the credential's details or any other personal data. This is achieved using zero-knowledge proofs (ZKPs), which generate cryptographic proof of a statement's truth. For example, a user can prove they are a resident of a country without disclosing their passport number or exact address.
02
Non-Transferable (Soulbound)
ZK-Badges are typically implemented as Soulbound Tokens (SBTs), meaning they are permanently bound to a single cryptographic identity (e.g., a wallet address) and cannot be sold or transferred. This ensures the attestation represents a persistent property of the holder, not a tradable asset. It creates a verifiable, on-chain reputation system resistant to Sybil attacks.
03
Minimal On-Chain Footprint
To preserve privacy and scalability, the sensitive data behind a ZK-Badge is stored off-chain (e.g., in a decentralized storage network or a verifier's private database). Only the essential cryptographic commitments and the ZK-proof are published on-chain. This approach minimizes gas costs and keeps personal data private while maintaining public verifiability of the proof's validity.
04
Composability & Aggregation
Multiple ZK-Badges and proofs can be composed or aggregated into a single, more complex proof. This allows a user to satisfy a multi-faceted requirement (e.g., 'Prove you are over 18 AND a citizen of Country X AND have completed Course Y') by generating one succinct proof, rather than sharing several individual credentials. This enhances both privacy and efficiency.
05
Revocation & Expiry
ZK-Badge systems incorporate mechanisms to manage credential lifecycle. Common patterns include:
- On-Chain Revocation Registries: A smart contract or merkle tree that lists revoked badge identifiers.
- Time-Based Expiry: Proofs can be designed to be valid only until a certain block timestamp.
- Verifier-Controlled Status: The original issuer can update an off-chain status, requiring fresh proofs to reflect the current state.
06
Sybil Resistance
By binding non-transferable attestations to a persistent identity, ZK-Badges are a foundational tool for Sybil resistance. Applications can gate access or allocate resources based on proven, unique human attributes (like a verified phone number or government ID) without forcing users to publicly link those sensitive credentials to their on-chain activity. This enables fair airdrops, governance, and access to exclusive communities.
primary-use-cases
ZK-BADGE
Primary Use Cases
ZK-Badges are non-transferable, privacy-preserving attestations that prove specific credentials or achievements without revealing underlying personal data. Their primary applications leverage zero-knowledge proofs to enable trustless verification across decentralized systems.
03
Reputation Portability
Users can aggregate and prove their reputation or history across different platforms without starting from zero. A ZK-Badge can attest to a user's on-chain history (e.g., "Top 10% trader on Uniswap V3") or off-chain achievements (e.g., "Verified GitHub contributor"). This enables:
- Trust Minimization: New protocols can bootstrap trust using verified reputation from other sources.
- User Sovereignty: Reputation is user-owned and portable, not locked into a single platform.
04
Compliance & Regulatory Proofs
ZK-Badges allow users to prove compliance with regulations like AML/KYC or eligibility criteria (e.g., citizenship for airdrops) while maintaining privacy. A trusted issuer (like a regulated entity) can attest to a user's status, and the user can generate a ZK-proof that they hold a valid attestation without revealing the underlying documents. This facilitates privacy-preserving DeFi and access to real-world asset markets.
05
Selective Disclosure for Airdrops
Project teams can design fair airdrops by requiring ZK-Badges that prove specific, hard-to-fake user behaviors. This targets rewards to genuine users and mitigates airdrop farming. For example, a badge could prove:
- Historical Activity: "Active user prior to token launch" without revealing all transaction history.
- Contribution Proof: "Made at least 5 commits to the project's GitHub repo."
- Exclusion Proofs: Prove you are not on a blocklist (e.g., associated with an exploit) without revealing your address.
06
Cross-Chain Identity & Interoperability
ZK-Badges issued on one blockchain can be verified on another, enabling a unified cross-chain identity layer. This is achieved through verification libraries deployed on multiple chains or bridging attestations via canonical messaging systems. Use cases include:
- Consistent Access: Use the same "Gold Tier Trader" badge to access perks on both Ethereum and Arbitrum.
- State Bridging: Securely port reputation or achievement states across different execution environments.
COMPARISON
ZK-Badge vs. Soulbound Tokens vs. Verifiable Credentials
A technical comparison of three distinct mechanisms for representing identity, reputation, and attestations on-chain.
| Feature | ZK-Badge | Soulbound Token (SBT) | Verifiable Credential (VC) |
|---|---|---|---|
Core Data Model | On-chain token with private metadata | On-chain, non-transferable token | Off-chain JSON-LD document with proofs |
Privacy & Selective Disclosure | |||
Native On-Chain Verifiability | |||
Token Transferability | Revocable & non-transferable by default | Permanently non-transferable | Not a token; credential is presented |
Primary Storage Location | On-chain state with private data proofs | On-chain token ledger | Holder's off-chain wallet (e.g., SSI) |
Revocation Mechanism | On-chain verifier registry or nullifier | Issuer burn function or expiry | Status list or on-chain registry |
Primary Use Case | Private, verifiable on-chain membership & reputation | Public, permanent on-chain affiliation & history | Portable, interoperable off-chain identity attestations |
Typical Issuance Cost | High (ZK proof generation + gas) | Medium (gas cost only) | Low (off-chain signing) |
ecosystem-usage
ZK-BADGE
Ecosystem Usage & Protocols
A ZK-Badge is a non-transferable, soulbound token (SBT) that uses zero-knowledge proofs to verify specific user attributes or credentials without revealing the underlying private data.
01
Core Mechanism & Privacy
A ZK-Badge is a non-transferable token (often an SBT) that leverages zero-knowledge proofs (ZKPs). It allows a user to prove they possess a specific credential (e.g., KYC status, DAO membership, event attendance) without exposing the raw data used to generate it. This enables selective disclosure and privacy-preserving verification on-chain.
02
Primary Use Cases
ZK-Badges enable a wide range of privacy-focused applications:
- Gated Access: Grant entry to token-gated communities or content based on verified, private traits.
- Sybil Resistance: Prove unique personhood or membership in a group for fair airdrops or governance without a public identity ledger.
- Reputation Systems: Build portable, private reputation scores based on on-chain activity or off-chain achievements.
- Compliance: Demonstrate regulatory compliance (e.g., KYC/AML) to protocols while keeping personal data off-chain.
03
Technical Implementation
Issuance typically involves an off-chain verifier (like an issuer's server) that signs a claim about a user. The user then generates a ZK-SNARK or ZK-STARK proof that they possess a valid signature for a specific claim. This proof is verified by a smart contract when minting the badge or accessing a gated function. The badge itself is often a minimal ERC-1155 or ERC-721 token with a locked transfer function.
05
Benefits Over Traditional Badges
ZK-Badges solve critical limitations of standard NFTs or on-chain records:
- Privacy: The user's underlying data never touches the blockchain.
- Composability: Proofs from multiple sources can be aggregated into a single, verifiable badge.
- Security: Reduces attack surface by not storing sensitive data on-chain.
- User Sovereignty: Users control which attributes to prove and to whom, moving away from custodial identity models.
06
Challenges & Considerations
Adoption faces several hurdles:
- Issuer Trust: The system's security depends on the honesty and security of the off-chain issuer.
- Proof Generation Cost: Creating ZK proofs can be computationally expensive for end-user devices.
- Standardization: Lack of universal standards for claim schemas and verification contracts.
- Revocation: Mechanisms for revoking a badge if the underlying credential is invalidated are complex in a privacy-preserving system.
technical-components
ZK-BADGE
Core Technical Components
A ZK-Badge is a non-transferable, privacy-preserving credential that uses zero-knowledge proofs to verify a user's attributes or membership without revealing the underlying data.
01
Non-Transferable Token (SBT)
A ZK-Badge is a specialized form of a Soulbound Token (SBT). Unlike fungible or standard NFTs, it is permanently bound to a user's wallet, representing persistent identity, reputation, or attestations. This prevents credential trading or sybil attacks while enabling persistent on-chain identity graphs.
02
Zero-Knowledge Proof Core
The badge's privacy is enabled by zero-knowledge proofs (ZKPs), specifically zk-SNARKs or zk-STARKs. A user generates a proof that they hold a valid credential (e.g., is over 18, holds a specific NFT) without revealing the credential itself or their wallet address, enabling selective disclosure.
03
Selective Disclosure & Verification
Users can prove specific claims derived from their credentials. For example:
- Prove you are a "Gold Member" without showing transaction history.
- Prove your country of residence is within an allowed list.
- Prove you completed a task without revealing your identity. A verifier contract checks the ZKP's validity on-chain.
04
On-Chain vs. Off-Chain Issuance
Issuance can occur on-chain via a smart contract (e.g., for completing an on-chain action) or off-chain by a trusted entity (e.g., a DAO, university). The credential is often stored off-chain (like in a zk-Ceremony or Semaphore group), with only the cryptographic commitment stored on-chain for verification.
05
Semaphore & zk-Ceremonies
Common technical implementations include:
- Semaphore: A framework for creating anonymous signaling groups. A ZK-Badge can represent anonymous group membership.
- zk-Ceremonies: Trusted setups where issuers cryptographically attest to user attributes, enabling private proof generation. These form the foundational layer for many badge systems.
06
Primary Use Cases
ZK-Badges enable privacy-focused applications:
- Gated Access: Private entry to DAOs, events, or token-gated content.
- Sybil-Resistant Governance: One-person-one-vote systems without doxxing.
- Credit Scoring: Proving creditworthiness without exposing financial history.
- Proof-of-Humanity: Anonymous verification of unique personhood.
security-considerations
SECURITY & TRUST CONSIDERATIONS
ZK-Badge
ZK-Badges are privacy-preserving, non-transferable attestations that leverage zero-knowledge proofs to verify claims without revealing underlying data. This section details their core security mechanisms and trust models.
01
Privacy-Preserving Verification
A ZK-Badge uses zero-knowledge proofs (ZKPs) to allow a user to prove they hold a specific credential (e.g., being over 18, holding a certain NFT) without revealing the credential itself or any identifying information. This prevents data aggregation and profiling, a key privacy enhancement over traditional attestations.
02
Non-Transferability & Sybil Resistance
ZK-Badges are cryptographically bound to a user's wallet or identity, making them non-transferable. This property is crucial for Sybil resistance, ensuring that a single entity cannot amass multiple badges to unfairly influence governance, airdrops, or access controls. Binding is typically achieved via digital signatures or linkable proofs.
04
Selective Disclosure & Minimization
Beyond simple proof of possession, advanced ZK-Badges enable selective disclosure. A user can prove a derived property (e.g., 'age > 21') from a private datum (e.g., a birth date), adhering to data minimization principles. This reduces the attack surface and potential value of any compromised proof.
05
Revocation Mechanisms
A critical security consideration is how to revoke a ZK-Badge if the underlying credential is invalidated. Common mechanisms include:
- On-chain revocation registries (e.g., a smart contract storing revocation status).
- Accumulator-based schemes (e.g., cryptographic accumulators that allow efficient proof of non-revocation).
- Time-bound attestations with automatic expiration.
06
Verifier Trust & On-Chain vs. Off-Chain
The verifier (e.g., a dApp) must trust the correctness of the ZKP verification logic and the integrity of the attester's public key or on-chain registry. On-chain verification (in a smart contract) provides strong guarantees but is costly. Off-chain verification is efficient but requires the verifier's client-side code to be trusted.
ZK-BADGE
Common Misconceptions
ZK-Badges are a powerful primitive for decentralized identity and reputation, but their technical nature leads to frequent misunderstandings. This section clarifies what they are, what they are not, and how they truly function.
No, a ZK-Badge is fundamentally different from a standard NFT. While both can be represented as tokens on-chain, a ZK-Badge is a verifiable credential that proves specific claims about its holder without revealing their identity. An NFT is a simple record of ownership. A ZK-Badge uses zero-knowledge proofs (ZKPs) to cryptographically attest that the holder meets predefined criteria (e.g., "voted in DAO proposal #42" or "has >1000 governance tokens") while keeping the holder's wallet address and other data private. The badge itself can be soulbound or transferable, but its core value is the provable, private claim it represents.
ZK-BADGE
Frequently Asked Questions
ZK-Badges are a privacy-preserving credential system built on zero-knowledge proofs. This FAQ addresses their core technology, use cases, and how they differ from traditional NFTs and SBTs.
A ZK-Badge is a non-transferable, privacy-preserving digital credential that uses zero-knowledge proofs (ZKPs) to allow a user to cryptographically prove they possess certain attributes or have completed specific actions without revealing the underlying data or their identity. It works by having an issuer (like a protocol or DAO) sign a claim about a user's wallet (e.g., "completed 100 transactions"). The user can then generate a ZK-SNARK or ZK-STARK proof that they hold a valid signature for that claim from a trusted issuer. This proof, the ZK-Badge, can be presented to verifiers (like a dApp's gated community) to access services while keeping the user's wallet address and specific claim details private.
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