> 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/verifier/references-and-standards.md).

# References and Standards

The references below cover the protocols, query formats, credential formats, and identifier methods the Verifier implements.

## Protocols

* **OpenID for Verifiable Presentations (OpenID4VP)**: The protocol the Verifier uses to request, receive, and validate Verifiable Presentations. The Verifier supports the `v1`, `v1.draft21`, and `v1.draft24` versions, selectable per authorization request. <https://openid.net/specs/openid-4-verifiable-presentations-1_0.html>

## Query Formats

* **DCQL (Digital Credentials Query Language)**: A compact, credential-centric query format for describing the credentials and claims a presentation must contain. Defined as part of the OpenID4VP specification. <https://openid.net/specs/openid-4-verifiable-presentations-1_0.html>
* **DIF Presentation Exchange v2**: A standard, vendor-neutral way to express credential requirements using input descriptors, JSONPath `path` expressions, and JSON Schema `filter` constraints. Each authorization request carries exactly one of a `dcqlQuery` or a `presentationDefinition`. <https://identity.foundation/presentation-exchange/spec/v2.0.0/>

## Credential Formats

* **W3C Verifiable Credentials Data Model**: The foundational data model for Verifiable Credentials and Verifiable Presentations. <https://www.w3.org/TR/vc-data-model/>
* **SD-JWT VC (Selective Disclosure JWT Verifiable Credentials)**: A JWT-based credential format that supports **selective disclosure**, so a holder can reveal only the claims a verifier requests (`dc+sd-jwt`). <https://datatracker.ietf.org/doc/draft-ietf-oauth-sd-jwt-vc/>
* **JWT-VC-JSON**: A JWT-based W3C Verifiable Credential (`jwt_vc_json`), following the W3C VC Data Model. <https://www.w3.org/TR/vc-data-model/>

## Identifiers

* **Decentralized Identifier (DID) Core**: The core specification defining DIDs and DID Documents, which carry the public keys and service endpoints used to establish trust. <https://www.w3.org/TR/did-core/>
* **`did:web` Method**: A DID method whose DID Document is resolved over HTTPS at a domain. A verifier can sign its authorization requests with a `did:web` identifier. <https://w3c-ccg.github.io/did-method-web/>
* **`did:key` Method**: A self-contained DID method in which the public key is encoded directly in the identifier, requiring no external resolution. <https://w3c-ccg.github.io/did-method-key/>
* **`did:jwk` Method**: A self-contained DID method in which a JSON Web Key (JWK) is encoded directly in the identifier, so it resolves without any external lookup. <https://github.com/quartzjer/did-jwk/blob/main/spec.md>


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