A Credential Proof Format is the technical specification that defines how a Verifiable Credential (VC) is cryptographically signed, serialized, and presented to a verifier. It is the concrete implementation of a proof, binding the credential's data to the issuer's cryptographic key. Common formats include JSON Web Tokens (JWT), JSON-LD with Linked Data Proofs (LD-Proofs), and SD-JWT (Selective Disclosure JWT). The choice of format dictates the underlying cryptography (e.g., EdDSA, ECDSA), the data model, and the mechanisms for selective disclosure and privacy preservation.
LABS
Glossary
Credential Proof Format
A Credential Proof Format is the technical specification defining the data serialization and cryptographic suite used to sign and verify a Verifiable Credential or Presentation.
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definition
DECENTRALIZED IDENTITY
What is a Credential Proof Format?
A Credential Proof Format is a standardized data structure that cryptographically packages and presents a Verifiable Credential for validation.
The format's primary role is to enable cryptographic verification. A verifier receives the credential in a specific proof format and uses the rules of that format to check the digital signature against the issuer's public key (often found in a Decentralized Identifier (DID) Document). This process proves the credential's authenticity and integrity—that it was issued by the claimed entity and has not been tampered with. Formats like LD-Proofs also enable zero-knowledge proofs (ZKPs) through BBS+ signatures, allowing a holder to prove statements about the credential without revealing the entire document.
Interoperability between different identity systems and wallets depends heavily on supporting common proof formats. For instance, the W3C Verifiable Credentials Data Model is a standard for the credential's content, but it does not mandate a specific proof format. Implementations must agree on formats like JWT-VC or LDP-VC to ensure credentials issued by one system can be understood and validated by another. This standardization is crucial for ecosystems like EU's Digital Identity Wallet (EUDIW) and OpenID for Verifiable Credentials (OID4VC).
Advanced proof formats incorporate features for enhanced user control and privacy. Selective Disclosure formats, such as SD-JWT and BBS+ signatures, allow the credential holder to reveal only specific attributes from a credential (e.g., proving they are over 21 without revealing their exact birthdate). Presentation formats, a related concept, define how multiple credentials and proofs are bundled into a single Verifiable Presentation. The evolution of these formats is central to moving beyond all-or-nothing data sharing towards minimal disclosure and user-centric data governance.
how-it-works
VERIFIABLE CREDENTIALS
How Credential Proof Formats Work
A credential proof format is the standardized data structure and cryptographic method used to encode and verify the authenticity and integrity of a digital credential, such as a diploma or identity document, without relying on a central authority.
At its core, a credential proof format defines the technical blueprint for creating a digital signature or zero-knowledge proof over a set of claims. This proof is cryptographically bound to the credential's data and the issuer's decentralized identifier (DID). Common formats include JSON Web Tokens (JWT), JSON-LD with Linked Data Proofs, and AnonCreds. The choice of format dictates the verification logic, the cryptographic primitives used (e.g., EdDSA, BBS+), and how the proof is serialized for transmission and storage.
The verification process is format-specific. A verifier, such as a website or employer, receives the credential and its attached proof. Using the rules of the specified format, the verifier checks the cryptographic signature against the issuer's public key (resolved from their DID) and ensures the credential data has not been tampered with. More advanced formats like W3C Verifiable Credentials Data Integrity or BBS+ signatures enable selective disclosure, allowing a holder to prove specific attributes (e.g., age > 21) without revealing the entire credential.
Interoperability between different ecosystems hinges on shared proof formats. For instance, a credential issued using the AnonCreds format in a Hyperledger Indy ecosystem must be translated or re-issued to be verifiable by a system that only supports W3C Data Integrity proofs. Standardization bodies like the W3C and Decentralized Identity Foundation (DIF) work to define and harmonize these formats. The proof format is therefore the critical technical layer that enables trust to be established in a decentralized, machine-readable manner across the web.
key-features
CREDENTIAL PROOF FORMAT
Key Features of Proof Formats
A credential proof format is a standardized structure for packaging and presenting cryptographic evidence that a set of claims is valid, enabling verifiable, privacy-preserving data exchange between parties.
01
Selective Disclosure
A core privacy feature that allows a holder to reveal only specific attributes from a credential without exposing the entire document. This is achieved using zero-knowledge proofs (ZKPs) or BBS+ signatures. For example, a digital driver's license credential could prove you are over 21 without revealing your exact birth date, name, or address.
02
Cryptographic Binding
The mechanism that cryptographically links the proof to the credential issuer and the holder's decentralized identifier (DID). This ensures the proof's authenticity and prevents tampering. Common methods include:
- Digital Signatures (e.g., Ed25519, ES256K)
- Linked Data Proofs (e.g., Ed25519Signature2020)
- BBS+ Signatures for selective disclosure
03
Standardized Data Model
Proofs follow a defined schema to ensure interoperability across different systems and verifiers. Key standards include:
- W3C Verifiable Credentials Data Model: The foundational standard.
- JSON-LD (Linked Data): Adds semantic meaning, enabling machines to understand the data's context.
- JWT (JSON Web Token): A compact, URL-safe representation often used for Verifiable Presentations.
04
Proof Types & Algorithms
Different cryptographic suites enable various security and privacy properties. Common types include:
- Signature Proofs: Simple verification of an issuer's signature (e.g., Ed25519Signature2018).
- Zero-Knowledge Proofs (ZKPs): Enable complex predicate logic (e.g., "age > 18") without revealing underlying data, using schemes like zk-SNARKs or zk-STARKs.
- BBS+ Signatures: Support deriving multiple, unlinkable selective disclosure proofs from a single master signature.
05
Presentation Exchange
The process where a holder presents a proof (a Verifiable Presentation) to a verifier. The format defines how the proof is packaged, which includes:
- The proof itself.
- Metadata about the presentation.
- Optional holder binding proofs. Frameworks like WACI (Wallet and Credential Interactions) and OpenID for Verifiable Credentials (OIDC4VC) standardize this request-response flow.
06
Revocation & Status
Mechanisms to invalidate a proof if the underlying credential is revoked. Formats must support status checks without compromising privacy. Common approaches are:
- Revocation Lists (e.g., Status List 2021): A cryptographically signed list of revoked credential indices.
- Accumulators: A cryptographic data structure (like a Merkle tree) where non-revoked credentials can prove membership without revealing which specific credential they hold.
TECHNICAL SPECS
Comparison of Major Credential Proof Formats
A technical comparison of the primary cryptographic proof formats used for verifiable credentials, focusing on their underlying mechanisms, standardization, and typical use cases.
| Feature / Attribute | JSON Web Token (JWT) | JSON Web Proof (JWP) | Data Integrity Proof (e.g., LD-Proofs) |
|---|---|---|---|
Cryptographic Foundation | Digital Signatures (JWS) | Digital Signatures & Key Binding (JWP) | Linked Data Signatures (e.g., Ed25519Signature2020) |
Primary Standard | RFC 7519 (IETF) | Draft RFC (IETF) | W3C Verifiable Credentials Data Model |
Data Model | Compact, encoded payload | JSON-based, selective disclosure | Linked Data / JSON-LD |
Selective Disclosure | |||
Schema Binding & Validation | |||
Typical Proof Size | ~1-2 KB | ~2-5 KB | ~5-15 KB |
Common Use Case | API authentication, simple claims | Privacy-preserving credentials | Interoperable, semantically-rich credentials |
examples
CREDENTIAL PROOF FORMAT
Common Proof Format Examples
A credential proof format is the standardized data structure and cryptographic method used to package and verify a verifiable credential's authenticity and integrity. These formats define how claims, metadata, and digital signatures are serialized for interoperability across different systems.
technical-details
CREDENTIAL PROOF FORMAT
Technical Details: Serialization & Cryptography
A credential proof format is a standardized data structure that cryptographically binds a set of claims to a verifiable credential, enabling secure, privacy-preserving verification without revealing the underlying credential data.
A credential proof format defines the serialization and cryptographic methods used to create a verifiable presentation from a verifiable credential. This format specifies how to generate a digital signature or a zero-knowledge proof over a selected subset of claims, allowing a holder to prove they possess a valid credential from an issuer without disclosing the credential in its entirety. Common proof types include JSON Web Tokens (JWT), JSON-LD with Linked Data Proofs, and W3C Data Integrity Proofs, each with different trade-offs in complexity, interoperability, and cryptographic agility.
The core cryptographic operation in a proof format is the creation of a cryptographic suite signature. This involves taking the credential's claims, a proof-specific nonce or challenge from the verifier to prevent replay attacks, and other metadata, then signing this payload with the holder's private key. For advanced privacy, formats like BBS+ signatures enable selective disclosure, where a holder can prove a single attribute (e.g., "I am over 21") without revealing their birthdate or other credential contents. The resulting proof is a compact, self-contained package that can be transmitted and validated.
Serialization is a critical component, determining how the proof and its associated data are encoded for transmission. Lightweight formats like Compact Serialization used in SD-JWT (Selective Disclosure JWT) are designed for constrained environments like mobile wallets and QR codes, while JSON-LD provides rich semantic context for machine readability. The choice of format impacts verifier performance, holder wallet complexity, and ecosystem interoperability, making it a foundational decision in verifiable credential system architecture.
ecosystem-usage
CREDENTIAL PROOF FORMAT
Ecosystem Usage & Standards
A Credential Proof Format is a standardized data structure and serialization method for cryptographically verifying claims about an entity, such as identity attributes, permissions, or reputation scores, without revealing the underlying data. These formats enable interoperability across decentralized identity (DID) systems, verifiable credentials (VCs), and zero-knowledge proof applications.
security-considerations
CREDENTIAL PROOF FORMAT
Security & Interoperability Considerations
A credential proof format is a standardized data structure for cryptographically verifying claims about an entity. These formats define how proofs are encoded, signed, and validated across different systems.
01
Verifiable Credentials (VCs)
The foundational W3C standard model for expressing credentials on the web in a way that is cryptographically secure, privacy-respecting, and machine-verifiable. A VC is a set of claims made by an issuer about a subject.
- Core Components: Issuer, subject, claims, proof, and optional status information.
- Key Property: The credential is tamper-evident and the authorship is verifiable.
- Example: A digital driver's license issued by a state DMV, containing your name, date of birth, and license class.
02
JSON Web Tokens (JWT)
A compact, URL-safe token format defined in RFC 7519, widely used as a proof format for VCs. JWTs encode claims in a JSON object which is then digitally signed or MACed.
- Structure: Header (algorithm & type), Payload (claims), and Signature.
- Common Use: Used in OpenID Connect and many decentralized identity implementations.
- Verification: Relies on checking the signature against the issuer's public key, often found in a DID Document.
03
JSON-LD & Linked Data Proofs
A method for encoding VCs using JSON-LD (Linked Data) and associated cryptographic suites like Ed25519Signature2020. This approach emphasizes semantic interoperability.
- Linked Data: Data is linked to globally unambiguous contexts, making its meaning clear to machines.
- Proof Suites: Define the exact cryptographic primitives (e.g., hash function, signature type) used.
- Benefit: Enables advanced features like selective disclosure through BBS+ signatures, where you can reveal only specific claims from a credential.
04
Selective Disclosure & Zero-Knowledge Proofs
Advanced proof formats that allow a holder to prove a claim without revealing the underlying credential data. This is critical for privacy.
- Selective Disclosure: Revealing only specific attributes from a VC (e.g., proving you are over 21 without revealing your birthdate).
- Zero-Knowledge Proof (ZKP): A cryptographic method where one party (the prover) can prove to another (the verifier) that a statement is true, without conveying any information beyond the validity of the statement itself.
- Formats: BBS+ signatures and zk-SNARKs/zk-STARKs are used to construct these privacy-preserving proofs.
05
Presentation Exchange & Holder Binding
Protocols that define how a verifier requests proofs and how a holder presents them. Holder binding ensures the person presenting the proof is its legitimate owner.
- Presentation Request: A verifier specifies the type and constraints of credentials required.
- Holder Binding: Achieved through challenge-response mechanisms where the holder must sign a unique nonce with a key they control, proving possession of the Decentralized Identifier (DID) linked to the credential.
- Prevents: Replay attacks and presentation of stolen credentials.
06
Interoperability Challenges
Despite standards, fragmentation in proof formats, signature suites, and DID methods creates interoperability hurdles.
- Format Proliferation: JWT, JSON-LD, AnonCreds, and custom formats may not be natively compatible.
- Signature Suite Support: Verifiers must support the specific cryptographic suite used by the issuer.
- Resolver Dependence: Verifying a proof often requires resolving the issuer's DID to a DID Document to fetch public keys, introducing latency and dependency on DID resolvers and Verifiable Data Registries.
CREDENTIAL PROOF FORMAT
Frequently Asked Questions
A Credential Proof Format is a standardized data structure for cryptographically verifying claims about an entity, such as identity, reputation, or authorization, without revealing the underlying data. These FAQs cover its core components, technical workings, and applications in decentralized systems.
A Credential Proof Format is a standardized data structure that packages cryptographically verifiable claims, such as a user's age or membership status, into a portable, privacy-preserving digital document. It works by allowing a holder (the user) to present a verifiable credential issued by an issuer (a trusted entity) to a verifier (a service), proving a claim is true without revealing the underlying raw data. Common formats include W3C Verifiable Credentials (VCs) and JSON Web Tokens (JWTs), which use digital signatures, zero-knowledge proofs, or selective disclosure mechanisms to enable trust and interoperability across different systems.
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