Verifiable Credentials JSON Schema Specification 2023

Abstract

Among other things, the [VC-DATA-MODEL-2] specifies the models used for Verifiable Credentials, Verifiable Presentations, and explains the relationships between three parties: issuers, holders, and verifiers. Verifiability, extensibility, and semantic interoperability are critical pieces of functionality referenced throughout the [VC-DATA-MODEL-2]. This specification provides a mechanism to make use of a Credential Schema in Verifiable Credential, leveraging the existing Data Schemas concept.

This section is non-normative.

This specification provides a mechanism for the use of JSON Schemas with Verifiable Credentials. A significant part of the integrity of a Verifiable Credential comes from the ability to structure its contents so that all three parties — issuer, holder, verifier — may have a consistent mechanism of trust in interpreting the data that they are provided with. We introducing a new data model for an object to facilitate backing Credentials with JSON Schemas that we call a Credential Schema.

This specification provides a standardized way of creating Credential Schemas to be used in credentialing systems. Credential Schemas may apply to any portion of a Verifiable Credential. Multiple JSON Schemas may back a single Verifiable Credential, e.g. a schema for the credentialSubject and another for other credential properties.

This section is non-normative.

The following terms are used to describe concepts in this specification.

claim: An assertion made about a subject.
credential schema: The data model that this specification defines.
json schema: A declarative language that allows you to annotate and validate JSON documents.
credential: A set of one or more claims made by an issuer. The claims in a credential can be about different subjects.
data minimization: The act of limiting the amount of shared data strictly to the minimum necessary to successfully accomplish a task or goal.
decentralized identifier: A portable URL-based identifier, also known as a DID, associated with an entity. These identifiers are most often used in a verifiable credential and are associated with subjects such that a verifiable credential itself can be easily ported from one repository to another without the need to reissue the credential. An example of a DID is did:example:123456abcdef.
decentralized identifier document: Also referred to as a DID document, this is a document that is accessible using a verifiable data registry and contains information related to a specific decentralized identifier, such as the associated repository and public key information.
digital signature: A mathematical scheme for demonstrating the authenticity of a digital message.
entity: A thing with distinct and independent existence, such as a person, organization, or device that performs one or more roles in the ecosystem.
holder: A role an entity might perform by possessing one or more verifiable credentials and generating presentations from them. A holder is usually, but not always, a subject of the verifiable credentials they are holding. Holders store their credentials in credential repositories.
identity: The means for keeping track of entities across contexts. Digital identities enable tracking and customization of entity interactions across digital contexts, typically using identifiers and attributes. Unintended distribution or use of identity information can compromise privacy. Collection and use of such information should follow the principle of data minimization.
issuer: A role an entity can perform by asserting claims about one or more subjects, creating a verifiable credential from these claims, and transmitting the verifiable credential to a holder.
presentation: Data derived from one or more verifiable credentials, issued by one or more issuers, that is shared with a specific verifier.
repository: A program, such as a storage vault or personal verifiable credential wallet, that stores and protects access to holders' verifiable credentials.
selective disclosure: The ability of a holder to make fine-grained decisions about what information to share.
subject: A thing about which claims are made.
user agent: A program, such as a browser or other Web client, that mediates the communication between holders, issuers, and verifiers.
validation: The assurance that a verifiable credential or a verifiable presentation meets the needs of a verifier and other dependent stakeholders. This specification is constrained to verifying verifiable credentials and verifiable presentations regardless of their usage. Validating verifiable credentials or verifiable presentations is outside the scope of this specification.
verifiable credential: A verifiable credential is a tamper-evident credential that has authorship that can be cryptographically verified. Verifiable credentials can be used to build verifiable presentations, which can also be cryptographically verified.
verifiable data registry: A role a system might perform by mediating the creation and verification of identifiers, keys, and other relevant data, such as verifiable credential schemas, revocation registries, issuer public keys, and so on, which might be required to use verifiable credentials. Some configurations might require correlatable identifiers for subjects. Some registries, such as ones for UUIDs and public keys, might just act as namespaces for identifiers.
verifiable presentation: A verifiable presentation is a tamper-evident presentation encoded in such a way that authorship of the data can be trusted after a process of cryptographic verification. Certain types of verifiable presentations might contain data that is synthesized from, but do not contain, the original verifiable credentials (for example, zero-knowledge proofs).
verification: The evaluation of whether a verifiable credential or verifiable presentation is an authentic and timely statement of the issuer or presenter, respectively. This includes checking that: the credential (or presentation) conforms to the specification; the proof method is satisfied; and, if present, the status check succeeds. Verification of a credential does not imply evaluation of the truth of claims encoded in the credential..
verifier: A role an entity performs by receiving one or more verifiable credentials, optionally inside a verifiable presentation for processing. Other specifications might refer to this concept as a relying party.
URL: A Uniform Resource Locator, as defined by [URL]. URLs can be dereferenced such that they result in a resource, such as a document. The rules for dereferencing, or fetching, a URL are defined by the URL scheme. This specification does not use the term URI or IRI because those terms have been deemed to be confusing to Web developers.

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY, MUST, and SHOULD in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

The following sections outline the data models for this document, of which there are two: JsonSchema2023 for usage of a [JSON-Schema] directly in a credentialSchema property, and CredentialSchema2023 for usage of a [JSON-Schema] represented as a verifiable credential.

This term definition is https://www.w3.org/ns/credentials#JsonSchema2023.

JsonSchema2023 is for the validation of W3C Verifiable Credentials, based on JSON Schema. The version of [JSON-Schema] can be any version noted in the section on JSON Schema Specifications.

Property	Description
id	The constraints on the `id` property are listed in the Verifiable Credentials Data Model specification [VC-DATA-MODEL-2]. The value is expected to be a URL that identifies the schema associated with the verifiable credential.
type	The `type` property MUST be JsonSchema2023.

An example of utilizing the VC Data Model's credentialSchema is provided below:

Example 1: Example JsonSchema2023

{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://example.edu/credentials/3732",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21"
    "email": "subject@example.com"
  },
  "credentialSchema": {
    "id": "https://example.com/schemas/email.json",
    "type": "JsonSchema2023"
  }
}

Example 2: Example Email JSON Schema

{
  "$id": "https://example.com/schemas/email.json"
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "name": "EmailCredential",
  "description": "EmailCredential using JsonSchema2023",
  "type": "object",
  "properties": {
    "credentialSubject": {
      "type": "object",
      "properties": {
        "emailAddress": {
          "type": "string",
          "format": "email"
        }
      },
      "required": [
        "emailAddress"
      ]
    }
  }
}

This term definition is https://www.w3.org/ns/credentials#CredentialSchema2023.

CredentialSchema2023 is for the validation of W3C Verifiable Credentials, based on representing JSON Schema in a verifiable credential. The version of [JSON-Schema] can be any version noted in the section on JSON Schema Specifications.

Property	Description
id	The constraints on the `id` property are listed in the Verifiable Credentials Data Model specification [VC-DATA-MODEL-2]. The value is expected to be a URL that identifies the credential schema associated with the verifiable credential.
type	The `type` property MUST be CredentialSchema2023

An example of utilizing the VC Data Model's credentialSchema is provided below:

Example 3: Example CredentialSchema2023

{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://example.edu/credentials/3733",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21"
    "email": "subject@example.com"
  },
  "credentialSchema": {
    "id": "https://example.com/schemas/email-credential-schema.json",
    "type": "CredentialSchema2023"
  }
}

Example 4: Example Email Credential Schema

{
  "@context": [
      "https://www.w3.org/ns/credentials/v2",
      "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://example.edu/credentials/3734",
  "type": ["VerifiableCredential", "CredentialSchema2023"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "$id": "https://example.com/schemas/email-credential-schema.json",
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "name": "EmailCredential",
    "description": "EmailCredential using CredentialSchema2023",
    "type": "object",
    "properties": {
      "credentialSubject": {
        "type": "object",
        "properties": {
          "emailAddress": {
            "type": "string",
            "format": "email"
          }
        },
        "required": ["emailAddress"]
      }
    }
  }
}

JSON Schema Specification	Date of Publication	References
draft-bhutton-json-schema-01	10 June 2022	• JSON Schema: A Media Type for Describing JSON Documents • JSON Schema Validation: A Vocabulary for Structural Validation of JSON • Relative JSON Pointers
Draft 2020-12, draft-bhutton-json-schema-00	11 June 2021	• JSON Schema: A Media Type for Describing JSON Documents • JSON Schema Validation: A Vocabulary for Structural Validation of JSON • Relative JSON Pointers
Draft 2019-09, Draft 8	19 March 2020	• JSON Schema: A Media Type for Describing JSON Documents • JSON Schema Validation: A Vocabulary for Structural Validation of JSON • JSON Hyper-Schema: A Vocabulary for Hypermedia Annotation of JSON

This section is non-normative.

This section details some issues implementers of the specification may consider.

This section is non-normative.

Implementers may wish to validate certain sections of a verifiable credential. To do this, credential schemas can be constructed to specify application to subsets of a given credential.

One example of such a construction would be to validate the presence of certain top-level properties in a verifiable credential. The following example demonstrates a schema which enforces that a credential issued against it has an validUntil property and includes evidence.

Example 5: ValidUntil and Evidence Credential Schema

{
  "$id": "validuntil-and-evidence-schema",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "description": "Schema requiring validUntil and evidence properties",
  "type": "object",
  "properties": {
    "validUntil": {
      "type": "object"
    },
    "evidence": {
      "type": "object"
    }
  },
  "required": ["validUntil", "evidence"]
}

This section is non-normative.

In using [JSON-Schema] it is advised that implementers avoid setting the additionalProperties to false. Doing so could inadvertently exclude properties in a credential from passing validation.

As an example, consider a credential schema that is intended to validate the credentialSubject property of a credential. It is common for the credentialSubject property to include an id, denoting the identifier the subject. Not including this id property in a given schema would result in validation failure. The simple alternative is to avoid setting additionalProperties to false.

Example 6: Example Name Credential Schema

{
  "$id": "name-schema",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "description": "Name",
  "type": "object",
  "properties": {
    "credentialSubject": {
      "type": "object",
      "properties": {
        "name": {
          "type": "object",
          "properties": {
            "firstName": {
              "type": "string"
            },
            "lastName": {
              "type": "string"
            },
            "additionalProperties": false
          },
          "required": [
            "firstName",
            "lastName"
          ]
        }
      }
    }
  }
}

This section is non-normative.

Versioning is not provided as an explicit feature of this specification. It is advised to make backwards compatabile changes to schemas, should they be adjusted. Otherwise, it is advised that a new credential schema is created with a unique identifier.

Issue 120: Consider adding language on schema immutability v2

Add language on enabling schema immutability/versioning, such as making use of hashlinks.

This section is non-normative.

Credential schemas MAY be created and made available as immutable objects. They can be stored on any number of storage mediums such as a distributed ledger, traditional database, or decentralized file storage. The same schema could be replicated across multiple file stores with the same identifier.

Immutability is key to enabling a consistent source of truth for usage with verifiable credentials which are tamper-evident by design.

This section is non-normative.

Issue 19: Example of the credentialSchema.id resolution to schema v2

Add section on schema resolution.

This section is non-normative.

A common use case is to include multiple schemas to validate against which a single verifiable Credential. One such use case is to utilize the JSON Schema defined by the [VC-DATA-MODEL-2] in addition to a schema to validate a specific property in the credential, such as the credentialSubject. Multiple schemas MAY be combined using native constructs from the [JSON-SCHEMA] specification, through utilizing properties such as oneOf, anyOf, or allOf.

An example of how to construct such a schema using the [JSON-SCHEMA] property allOf is provided below, combining schemas for a verifiable credential, name, and email address:

Example 7: Multiple Schema Credential Schema Example

{
  "allOf": [
    {
      "$ref": "https://raw.githubusercontent.com/w3c/vc-data-model/main/schema/verifiable-credential/verifiable-credential-schema.json"
    },
    {
      "$id": "name-schema",
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "description": "Name",
      "type": "object",
      "properties": {
        "credentialSubject": {
          "type": "object",
          "properties": {
            "name": {
              "type": "object",
              "properties": {
                "firstName": {
                  "type": "string"
                },
                "lastName": {
                  "type": "string"
                },
                "additionalProperties": false
              },
              "required": [
                "firstName",
                "lastName"
              ]
            }
          }
        }
      }
    },
    {
      "$id": "email-schema-1.0",
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "description": "Email",
      "type": "object",
      "properties": {
        "credentialSubject": {
          "type": "object",
          "properties": {
            "email": {
              "type": "object",
              "properties": {
                "emailAddress": {
                  "type": "string",
                  "format": "email"
                }
              },
              "required": ["emailAddress"]
            }
          }
        }
      }
    }
  ]
}

The example above is used to validate every property in the following verifiable credential:

Example 8: Multiple Schema Verifiable Credential Example

{
    "@context": ["https://www.w3.org/ns/credentials/v2"],
    "id": "4995c86c-851f-43a6-9dd2-03dc891091fd",
    "type": ["VerifiableCredential"],
    "issuer": "did:example:1234",
    "validFrom": "2023-01-01T05:05:05Z",
    "credentialSubject": {
        "firstName": "Alice",
        "lastName": "Bobertson",
        "emailAddress": "alice@bobertson.com"
    },
    "credentialSchema": {
        "id": "multiple-credential-schema-test",
        "type": "CredentialSchema2023"
    },
    "proof": { ... }
}

Issue 136: Add warning for improperly formed schemes using multiple schemas enhancement

Add warning for improperly formed schemas and risks associated with using multiple schemas.

This section is non-normative.

Validation against a [JSON-SCHEMA] may be confused with validation or verification of a Verifiable Credential. A valid credential according to a [JSON-SCHEMA] refers only to the structure of the claims comprising a Verifiable Credential. This idea of validity does not imply anything about the validity of the Verifiable Credential itself. It's possible for a Verifiable Credential to be considered valid by one verifier, while another verifier would not consider it valid.

This section is non-normative.

It is common to define a credential schema that will be set for Verifiable Credentials whose type property contains a specific type. In this scenario, it is advised to use the value of the specific type in the id or in a name or description property. of a [JSON-Schema].

The example below illustrates this for EmailCredential:

Example 9: Verifiable Credential with Schema Type

{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://example.edu/credentials/3732",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.edu/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "emailAddress": "tester@example.com",
  },
  "credentialSchema": {
    "id": "https://example.org/examples/email.json",
    "type": "JsonSchema2023"
  }
}

Example 10: Schema with Matching Type Name

{
 "$id": "https://example.org/examples/email.json",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "name": "EmailCredential",
  "description": "Email Credential Schema for usage in JsonSchema2023",
  "type": "object",
  "properties": {
    "credentialSubject": {
      "type": "object",
      "properties": {
        "emailAddress": {
          "type": "string",
          "format": "email"
        }
      },
      "required": [
        "emailAddress"
      ]
    }
  }
}

It is important to note that a credential schema enables issuers to communicate how to process the structure of data inside a verifiable credential, whereas the type property of a verifiable credential lets issuers communicate the semantics of the data. It is advised to associate all properties that have a semantic mapping with a property in a credential schema.

Verifiable Credentials JSON Schema Specification 2023

JSON Schemas for Verifiable Credentials

Abstract

Status of This Document

Status of This Document

1. Introduction

1.1 Terminology

1.2 Conformance

2. Data Model

2.1 JsonSchema2023

2.2 CredentialSchema2023

3. JSON Schema Specifications

4. Processing

4.1 Integrity Validation

4.2 Evaluation

5. Implementation Considerations

5.1 Validation of Specific Properties in a Credential

5.2 Additional Properties

5.3 Versioning

5.4 Storage

5.5 Resolution

5.6 Multiple Schemas

5.7 Validity of a Verifiable Credential

5.8 Relationship to Verifiable Credential Type Property

6. Privacy Considerations

6.1 Verifier Caching

6.2 Content Distribution Networks

7. Security Considerations

7.1 Issuer Impersonation

8. Accessibility Considerations

9. Internationalization Considerations

A. References

A.1 Normative references

A.2 Informative references