JWT VC

A JWT Verifiable Credential (JWT VC) is a digital, machine-verifiable attestation issued by an issuer to a holder, encoded as a JSON Web Token. It is a specific implementation of the W3C Verifiable Credentials Data Model, where the credential's claims and metadata are packaged into a signed JWT structure. This format provides a compact, URL-safe means of representing claims that can be digitally verified by any verifier possessing the issuer's public key, ensuring the credential's authenticity and integrity.

The structure of a JWT VC follows the standard JWT components: a header specifying the token type and cryptographic algorithm, a payload containing the credential subject's claims and VC-specific metadata (like @context, type, and issuer), and a signature created by the issuer. This signature is the core of its verifiability, binding the credential data to the issuer's cryptographic key. Common signing algorithms include EdDSA (like Ed25519) and ES256K, aligning with decentralized identity systems.

JWT VCs are a foundational technology for Decentralized Identity (DID) and Self-Sovereign Identity (SSI) ecosystems. They enable portable, user-controlled credentials that can be presented for access control, KYC processes, or proof of qualifications without relying on a central database. Their interoperability stems from the universal support for JWT libraries across programming languages and platforms, making them a pragmatic choice for integrating verifiable credentials into existing web and mobile applications.

When a holder presents a JWT VC to a verifier—often as part of a Verifiable Presentation (VP), which can also be a JWT—the verifier performs several checks. These include validating the JWT signature against the issuer's DID document, checking for revocation status (e.g., via a revocation list), and ensuring the credential has not expired. This process allows for trustless verification, where the verifier need only trust the issuer's public key, not a centralized intermediary.

Compared to other VC formats like JSON-LD Signatures (LD-Proofs), JWT VCs offer simplicity and computational efficiency but with less inherent semantic interoperability. They are best suited for use cases requiring straightforward claim structures and high-performance verification. The standard is formally defined in the W3C VC-JWT specification, ensuring consistency across implementations and promoting their adoption for digital driver's licenses, employee badges, and educational certificates.

A JWT Verifiable Credential (JWT VC) is a W3C Verifiable Credential encoded as a JSON Web Token (JWT). This format leverages the JWT's established structure—a header, payload, and signature—to package credential data, metadata, and proof. The issuer (e.g., a university) cryptographically signs the JWT, creating a verifiable data integrity proof. This signature, typically using Elliptic Curve Digital Signature Algorithm (ECDSA) or EdDSA, allows any verifier to confirm the credential's authenticity and that it hasn't been altered since issuance.

The core data resides in the JWT's payload, which contains the credential subject (the holder's identifier, often a Decentralized Identifier (DID)), the issuer's DID, the issuance date, and the credential claims themselves (e.g., "degree":"Bachelor of Science"). This payload is wrapped within the standard JWT VC structure defined by the W3C, ensuring interoperability. The resulting signed JWT is then presented by the holder to a verifier. The verifier's process involves decoding the JWT, checking the issuer's signature against their public key (resolved from their DID), and validating the credential's status and expiration.

A key advantage of the JWT VC format is its compatibility with existing web infrastructure, as JWTs are natively supported by many libraries and APIs. It is often paired with JWT Verifiable Presentations (JWT VP), where a holder can present one or more VCs, optionally adding their own signature for holder binding. This mechanism is fundamental to Self-Sovereign Identity (SSI) architectures and decentralized trust models, enabling selective disclosure of attributes without relying on a central database for verification.

The JWT VC structure is a specific encoding of a W3C Verifiable Credential (VC) using the compact, URL-safe JSON Web Token (JWT) format, defined in the W3C VC Data Model JWT representation. In this structure, the credential's core claims—such as iss (issuer), sub (subject), vc (the credential data), and nbf (valid from)—are packaged into a JSON object, which is then cryptographically signed to produce a JWT. This creates a self-contained, proof-carrying token where the signature serves as the cryptographic proof, enabling verification without querying the issuer's backend.

The anatomy of a JWT VC consists of three Base64Url-encoded segments separated by dots: the Header, Payload, and Signature. The Header specifies the token type (JWT) and the signing algorithm (e.g., EdDSA or ES256K). The Payload contains the actual Verifiable Credential claims. The Signature is generated by signing the encoded Header and Payload, binding them together. This structure is inherently portable and suitable for HTTP headers or QR codes, making it a common choice for OpenID Connect Verifiable Credentials (OIDC4VC) and other stateless, bearer-token authentication flows.

A key advantage of the JWT VC format is its selective disclosure capability when combined with JSON Web Proof (JWP) or SD-JWT (Selective Disclosure for JWTs). These extensions allow the holder to reveal only specific claims from the credential while still providing a valid cryptographic proof, enhancing privacy. However, a limitation is that the credential data is opaque when encrypted; the structure itself does not natively support zero-knowledge proofs on the plaintext claims, a feature more inherent to Linked Data Proof (LDP) formats.

When a verifier receives a JWT VC, the verification process involves decoding the token, validating the JWT signature using the issuer's public key (often resolved via a DID in the iss claim), and then checking the contained VC data for validity and expiration. The vc claim within the payload is a JSON object conforming to the W3C VC data model, containing the credentialSubject, issuanceDate, and optional credentialSchema. This dual-layer structure—JWT wrapper and VC payload—provides a standardized method for interoperability across systems that already support JWT libraries.

In practice, the JWT VC structure is contrasted with the Linked Data Proof (LDP) format. While LDPs sign the credential's JSON-LD normalized data, embedding the proof directly within the credential JSON, JWT VCs are a detached proof format where the signature envelope is separate. The choice between them often depends on ecosystem requirements: JWT is favored for its library support and compactness in API-driven environments, whereas LDP is preferred for semantic web compatibility and advanced ZKP (Zero-Knowledge Proof) use cases. Both are valid representations per the W3C standard.