> For the complete documentation index, see [llms.txt](https://docs.empe.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.empe.io/develop/issuer/references-and-standards.md).

# References and Standards

The Issuer Service is built on open, standards-based specifications so that the credentials it issues remain interoperable with third-party wallets and verifiers. The references below cover the credential data models, identifier methods, issuance and presentation protocols, and query languages the service implements.

## Credential data models and formats

* **W3C Verifiable Credentials Data Model**: <https://www.w3.org/TR/vc-data-model/> The underlying data model for verifiable credentials. The service issues **JWT-VC-JSON** credentials (`jwt-vc-json` / `jwt_vc_json`) that follow this model.
* **SD-JWT VC (Selective Disclosure JWT Verifiable Credentials)**: <https://datatracker.ietf.org/doc/draft-ietf-oauth-sd-jwt-vc/> The format used for **SD-JWT VC** credentials (`vc+sd-jwt` / `sd-jwt-vc`). Each SD-JWT VC carries a `vct` (Verifiable Credential Type) and supports selective disclosure of individual claims. For example, a schema named `EmployeeBadge` at version `1.0` yields the credential configuration `EmployeeBadge@1.0:sd-jwt`.
* **Selective Disclosure for JWTs (SD-JWT)**: <https://datatracker.ietf.org/doc/draft-ietf-oauth-selective-disclosure-jwt/> The underlying mechanism that lets a holder reveal only selected claims when presenting an SD-JWT VC. A schema's `disclosureFrame` declares which claims are selectively disclosable.

## Identifiers

* **DID Core Specification**: <https://www.w3.org/TR/did-core/> The base specification for Decentralized Identifiers and DID documents.
* **DID Method: `did:web`**: <https://w3c-ccg.github.io/did-method-web/> HTTPS-resolvable DIDs. The service hosts the DID document itself and serves it at `/{uuid}/did.json` (also at `/{uuid}/.well-known/did.json`).
* **DID Method: `did:key`**: <https://w3c-ccg.github.io/did-method-key/> Self-contained DIDs (Ed25519) that encode the public key directly in the identifier, requiring no network lookup.

## Issuance and presentation protocols

* **OpenID for Verifiable Credential Issuance (OpenID4VCI)**: <https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html> The protocol the Issuer Service uses to deliver credentials to wallets. The service implements the pre-authorized code flow with an optional PIN.
* **OpenID for Verifiable Presentations (OpenID4VP)**: <https://openid.net/specs/openid-4-verifiable-presentations-1_0.html> The protocol used to request and receive verifiable presentations from wallets when a credential is later presented to a verifier. Authorization requests can target versions `v1`, `v1.draft21`, or `v1.draft24`.

## Presentation query languages

* **DIF Presentation Exchange v2**: <https://identity.foundation/presentation-exchange/> Describes the credentials a verifier requires in a presentation request.
* **DCQL (Digital Credentials Query Language)**: <https://openid.net/specs/openid-4-verifiable-presentations-1_0.html#name-digital-credentials-query-l> The OpenID4VP-native query language, supported as an alternative to DIF Presentation Exchange.

## Ecosystem context

For the `did:empe` method and the EMPE blockchain, see [Terminology and Concepts](/develop/issuer/terminology-and-concepts.md).


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