Verifiable Credentials JSON Schema Specification

JSON Schemas for Verifiable Credentials

W3C First Public Working Draft

More details about this document
This version:
https://www.w3.org/TR/2023/WD-vc-json-schema-20230807/
Latest published version:
https://www.w3.org/TR/vc-json-schema/
Latest editor's draft:
https://w3c.github.io/vc-json-schema/
History:
https://www.w3.org/standards/history/vc-json-schema/
Commit history
Editors:
Gabe Cohen (Block)
Orie Steele (Transmute)
Andres Uribe (Block)
Authors:
Gabe Cohen (Block)
Orie Steele (Transmute)
Feedback:
GitHub w3c/vc-json-schema (pull requests, new issue, open issues)
Related Documents
Verifiable Credentials Data Model

Copyright © 2023 World Wide Web Consortium. W3C® liability, trademark and permissive document license rules apply.

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.

Status of This Document

This is a preview

Do not attempt to implement this version of the specification. Do not reference this version as authoritative in any way. Instead, see https://w3c.github.io/vc-json-schema/ for the Editor's draft.

This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

Status of This Document

This document is experimental and is undergoing heavy development. It is inadvisable to implement the specification in its current form. An experimental implementation is available.

This document was published by the Verifiable Credentials Working Group as a First Public Working Draft using the Recommendation track.

Publication as a First Public Working Draft does not imply endorsement by W3C and its Members.

This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 12 June 2023 W3C Process Document.

1. Introduction

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.

1.1 Terminology

This section is non-normative.

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Cannot GET /uploads/mNDNdp/terms.html

1.2 Conformance

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, MUST NOT, RECOMMENDED, 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.

2. Data Model

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

Implementers may find use in packaging a JSON Schema as a verifiable credential when they wish to leverage features of the [VC-DATA-MODEL-2], answering questions such as:

2.1 JsonSchema

This term is part of the Verifiable Credentials Vocabulary v2.0.

JsonSchema is used for the validation of W3C Verifiable Credentials using JSON Schema. When dereferencing the id property associated with the JsonSchema type value the result is a valid JSON Schema document according to its specification version.

The specification 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 MUST be a URL that identifies the schema associated with the verifiable credential.
type The type property MUST be JsonSchema.

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

Example 1: Example JsonSchema 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/3732",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "emailAddress": "subject@example.com"
  },
  "credentialSchema": {
    "id": "https://example.com/schemas/email.json",
    "type": "JsonSchema"
  }
}

Upon dereferencing the value of the id https://example.com/schemas/email.json, a process also be referred to as schema resolution, the following JSON Schema document is returned:

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 JsonSchema",
  "type": "object",
  "properties": {
    "credentialSubject": {
      "type": "object",
      "properties": {
        "emailAddress": {
          "type": "string",
          "format": "email"
        }
      },
      "required": [
        "emailAddress"
      ]
    }
  }
}

2.2 JsonSchemaCredential

This term is part of the Verifiable Credentials Vocabulary v2.0.

JsonSchemaCredential is used for the validation of W3C Verifiable Credentials using JSON Schema, where the JSON Schema is contained with a verifiable credential. When dereferencing the id property associated with the JsonSchemaCredential type value the result is a valid verifiable credential. The resulting verifiable credential's credentialSubject property MUST contain a two properties:

The term definition for using the jsonSchema property within the credentialSubject of a verifiable credential is https://www.w3.org/ns/credentials#JsonSchema.

The specification 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 MUST be a URL that identifies the verifiable credential which contains a credential schema.
type The type property MUST be JsonSchemaCredential

An example of utilizing the VC Data Model's credentialSchema is provided below:
Example 3: Example JsonSchemaCredential 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/3733",
  "type": ["VerifiableCredential", "ExampleEmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "emailAddress": "subject@example.com"
  },
  "credentialSchema": {
    "id": "https://example.com/credentials/3734",
    "type": "JsonSchemaCredential"
  }
}

Upon dereferencing the value of the id https://example.com/credentials/3734, a process also be referred to as schema resolution, the following verifiable credential, representing a JSON Schema, is returned:

Example 4: Example Email Credential Schema 
{
  "@context": [
      "https://www.w3.org/ns/credentials/v2",
      "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/3734",
  "type": ["VerifiableCredential", "JsonSchemaCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "https://example.com/schemas/email-credential-schema.json",
    "type": "JsonSchema",
    "jsonSchema": {
       "$id": "https://example.com/schemas/email-credential-schema.json",
       "$schema": "https://json-schema.org/draft/2020-12/schema",
       "name": "EmailCredential",
       "description": "EmailCredential using JsonSchemaCredential",
       "type": "object",
       "properties": {
         "credentialSubject": {
           "type": "object",
           "properties": {
             "emailAddress": {
               "type": "string",
               "format": "email"
             }
           },
           "required": ["emailAddress"]
         }
       }
    }
  }
}

Issue 159: Language on nesting of credential schemas when using CredentialSchema2023 enhancementdiscusspre-cr

Add language about JsonSchemaCredential credentials having a credentialSchema property and the risks of nesting.

3. JSON Schema Specifications

The following section describes the allowed specifications for using a [JSON-Schema] with a credential schema.

To promote conformance and enable interoperability, implementers MUST provide support for JSON Schema specifications where, in the following table, the required column's value is yes.

JSON Schema Specification Date of Publication $schema URI Required
[JSON-SCHEMA-2020-12] 10 June 2022 https://json-schema.org/draft/2020-12/schema Yes
[JSON-SCHEMA-2019-09] 19 March 2020 https://json-schema.org/draft/2019-09/schema No
[JSON-SCHEMA-DRAFT-7] 20 September 2018 http://json-schema.org/draft-07/schema# No
Note: A stable JSON Schema specification is coming

A stable JSON Schema specification is in the works. When it's released, we intend to update this table to require the stable version.

3.1 Reserved Keywords

JSON Schema specifications reserve certain keywords that hold specific meanings and functions during the processing of JSON Schemas. It is crucial to avoid using conflicting keys when creating JSON Schemas. The specification document for each version of JSON Schema lists these reserved keywords, which can be found in the table provided above.

In the upcoming sections we list some keywords that possess unique significance and should not be used in conflicting ways.

Furthermore, we identify specific keywords, that are not explicitly defined by JSON Schema, but are emphasized in this specification to support widespread usage.

3.1.1 $id

Across JSON Schema specifications, the $id keyword identifies a schema resource with its canonical [RFC-6596] URI. The $id MUST be present and its value MUST represent a valid URI-reference [RFC-3986].

It is RECOMMENDED that the value of the $id property match the id value in the credentialSchema object of a verifiable credential, and that the value of the $id is a dereferenceable URL [URL].

3.1.2 $schema

Across JSON Schema specifications, the $schema keyword identifies a JSON Schema providing the feature set for a given JSON Schema specification. This property MUST be present in each schema. For example, when constructing a schema for Draft 2020-12 the value of the $schema identifier MUST be https://json-schema.org/draft/2020-12/schema.

3.1.3 name

It is RECOMMENDED that all JSON Schemas include a name property which provides a human-readable name that describes the schema.

3.1.4 description

JSON Schemas MAY choose to include an optional description property which provides a human-readable sentence describing the schema.

3.2 Representations of JSON Schema

Issue 142: Support YAML schema representations pre-cr

Write section on using different representations of JSON Schema, such as YAML.

4. Processing

This section details how to process Credential Schemas, which is commonly referred to as JSON schema validation.

There are many open source implementations of [JSON-SCHEMA] validators across many common programming languages. The OpenJS Foundation maintains a list of implementations as a part of the JSON Schema official documentation.

A common feature of a JSON Schema validator is the ability to detect the version of a JSON Schema document and select the validator for that specific version of [JSON-SCHEMA]. This is done by switching on the schema's $schema property and picking the corresponding validator. Schemas without a $schema property are not considered valid and MUST NOT be processed. Implementers SHOULD choose validators which possess this capability and are able to limit validation to the JSON Schema specifications supported by this document.

Conformant implementers MUST support JSON Schema specification versions marked as required in the table defined in the JSON Schema specifications section of this document. Implementers MAY support JSON Schema specification versions not marked as required.

4.1 Integrity Validation

Credential Schemas MAY be packaged as verifiable credentials as defined by usage of the JsonSchemaCredential type. The credential containing a credential schema may include a proof, either embedded according to [VC-DATA-INTEGRITY] or packaged as a [VC-JWT].

Secured credentials representing credential schemas SHOULD first be validated according to the rules set out in the aforementioned securing specifications before proceeding with additional processing.

Issue 143: Add examples of validating VC-JWT and Linked Data Proof credentials pre-cr

Provide examples for Data Integrity and VC-JWT Credential Schemas

Credential Schemas of type JsonSchema MAY be annotated with integrity information by adding the digestSRI property to the credentialSchema value in the Verifiable Credential which contains the schema, using the method specified in Subresource Integrity. Validation of the integrity of the schema MUST be done before evaluation.

An example of such usage is provided below:

Example 5: Example Verifiable Credential JsonSchema with Integrity Information 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/3733",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "emailAddress": "subject@example.com"
  },
  "credentialSchema": {
    "id": "https://example.com/schemas/email.json",
    "type": "JsonSchema",
    "digestSRI": "sha384-dNwyy/Zs/YjPor8aoOgnaCqb+PH24QcNFxbxM1XoBOxdbgnpQcVaGYH8QunXww2U",
  }
}

4.2 Evaluation

Validation of a given credential against a schema is to be performed according to its associated [JSON-SCHEMA] specification. Validation MUST result in one of the following three possible outcomes:

Examples for the Success and Failure possible outcomes are provided below.

Example 6: 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 JsonSchema",
  "type": "object",
  "properties": {
    "credentialSubject": {
      "type": "object",
      "properties": {
        "emailAddress": {
          "type": "string",
          "format": "email"
        }
      },
      "required": [
        "emailAddress"
      ]
    }
  }
}

Validation according to the spec [JSON-schema-2020-12] yields Success when applying it to the VC below.

Example 7: Example Verifiable Credential - validations Success
Verifiable CredentialSecured with Data IntegritySecured with VC-JWT
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/3732",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "emailAddress": "subject@example.com"
  },
  "credentialSchema": {
    "id": "https://example.com/schemas/email.json",
    "type": "JsonSchema"
  }
}

Validation according to the spec [JSON-schema-2020-12] yields Failure when applying it to the VC below.

Example 8: Example Verifiable Credential - validation Failure
Verifiable CredentialSecured with Data IntegritySecured with VC-JWT
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/3732",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "emailAddress": "not an email"
  },
  "credentialSchema": {
    "id": "https://example.com/schemas/email.json",
    "type": "JsonSchema"
  }
}

Assuming that the implementer does not support [JSON-SCHEMA-2019-09], an example of Indeterminate evaluation is provided below.

Example 9: Example Email JSON Schema using unsupported JSON Schema version 
{
  "$id": "https://example.com/schemas/email.json",
  "$schema": "https://json-schema.org/draft/2019-09/schema",
  "name": "EmailCredential",
  "description": "EmailCredential using JsonSchema",
  "type": "object",
  "properties": {
    "credentialSubject": {
      "type": "object",
      "properties": {
        "emailAddress": {
          "type": "string",
          "format": "email"
        }
      },
      "required": [
        "emailAddress"
      ]
    }
  }
}
Example 10: Example Verifiable Credential - validation Indeterminate
Verifiable CredentialSecured with Data IntegritySecured with VC-JWT
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/3732",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/issuers/14",
  "issuanceDate": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "emailAddress": "not an email"
  },
  "credentialSchema": {
    "id": "https://example.com/schemas/email.json",
    "type": "JsonSchema"
  }
}

5. Implementation Considerations

This section is non-normative.

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

5.1 Validation of Specific Properties in a Credential

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

5.2 Additional Properties

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

5.3 Versioning

This section is non-normative.

Versioning is not provided as an explicit feature of this specification. Implementers are advised to make backwards compatabile changes to schemas, should they be adjusted. Otherwise, it is advised that new credential schemas be created with unique identifiers to avoid processing conflicts.

5.4 Content Integrity Protection

This section is non-normative.

It is important to make sure that credential schemas have not been tampered with before processing. When making use of the JsonSchemaCredential2023 representation of a schema, the credential's associated integrity protection mechanism can be used to detect mutations of a credential schema via its digital signature.

As an alternative, the aforementioned [SRI] scheme may be used to provide content integrity protection, ensuring that the underlying credential schema resource has not been tampered with.

5.5 Storage

This section is non-normative.

Credential schemas can be stored on any number of storage media such as a distributed ledger, traditional database, or decentralized file storage. For more robust availability guarantees, the same schema could be replicated across multiple file stores.

5.6 Multiple Schemas

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 13: 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",
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "name": "Name schema",
      "description": "A schema capturing a human name",
      "type": "object",
      "properties": {
        "credentialSubject": {
          "type": "object",
          "properties": {
            "name": {
              "type": "object",
              "properties": {
                "firstName": {
                  "type": "string"
                },
                "lastName": {
                  "type": "string"
                },
                "additionalProperties": false
              },
              "required": [
                "firstName",
                "lastName"
              ]
            }
          }
        }
      }
    },
    {
      "$id": "email-schema-1.0",
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "name": "Email schema",
      "description": "A schema requiring an email address.",
      "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 14: 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": "JsonSchemaCredential"
    },
    "proof": { ... }
}

Issue 136: Add warning for improperly formed schemes using multiple schemas enhancementpre-cr

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

5.7 Validity of a Verifiable Credential

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.

5.8 Relationship to Verifiable Credential Type Property

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 15: Verifiable Credential with Schema Type 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "https://example.com/credentials/email-credential",
  "type": ["VerifiableCredential", "EmailCredential"],
  "issuer": "https://example.com/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": "JsonSchema"
  }
}

Example 16: Schema with Matching Type Name 
{
  "$id": "https://example.com/schemas/email.json",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "name": "Email Credential",
  "description": "Email Credential Schema for usage in JsonSchema",
  "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.

6. Privacy Considerations

This section is non-normative.

This section details the general privacy considerations and specific privacy implications of deploying this specification into production environments.

6.1 Personally Identifiable Information

Data associated with schemas and verifiable credentials are susceptible to privacy violations when shared. Personally identifying data, such as a government-issued identifier, address, or name, can be used to track and correlate entities. Even less overt personal data such as a birthdate or postal code has the ability to result in correlation and de-anonymization.

Implementers are strongly advised to avoid constructing schemas with any personally identifiable information (PII).

If such personally identifiable information is necessary in a schema, or a credential schema, implementers are strongly advised to use mechanisms while storing and transporting verifiable credentials that protect the data from those who should not access it such as Transportation Layer Security (TLS) or other means of encrypting the data whether in transit or at rest.

6.2 Verifier Caching

Since schemas are immutable, they are highly cachable. It is possible for verifiers to increase the privacy of the holder whose verifiable credential is being checked by caching schemas that have been fetched from remote servers. By caching the content locally, less correlatable information can be inferred from verifier-based access patterns on the schema.

6.3 Content Distribution Networks

The use of content distribution networks by issuers can increase the privacy of holders by reducing or eliminating requests for the schemas lists from the issuer. Often, a request for a schema list will be served by an edge device and thus be faster and reduce the load on the server as well as cloaking verifiers and holders from issuers.

7. Security Considerations

This section is non-normative.

There are a number of security considerations that implementers should be aware of when processing data described by this specification. Ignoring or not understanding the implications of this section can result in security vulnerabilities.

7.1 Issuer Impersonation

It is possible for a schema to become authoritative, such as schemas provided by a recognized industry group like a consoritum of financial companies. To avoid confusion as to the authorship of credential schemas it is advised that they are packaged as secured verifiable credentials.

8. Accessibility Considerations

This section is non-normative.

There are a number of accessibility considerations implementers should be aware of when processing data described in this specification. As with any web standards or protocols implementation, ignoring accessibility issues makes this information unusable to a large subset of the population. It is important to follow accessibility guidelines and standards, such as [WCAG21], to ensure all people, regardless of ability, can make use of this data. This is especially important when establishing systems utilizing cryptography, which have historically created problems for assistive technologies.

JSON Schemas are designed to be a machine-readable format which provides static validation. As such, human readability is a secondary concern. When using a verifiable credential to represent a schema, we recommend following the guidance in the VC Data Model.

9. Internationalization Considerations

This section is non-normative.

There are a number of internationalization considerations implementers should be aware of when publishing data described in this specification. As with any web standards or protocols implementation, ignoring internationalization makes it difficult for data to be produced and consumed across a disparate set of languages and societies, which would limit the applicability of the specification and significantly diminish its value as a standard.

JSON Schemas are JSON text intended primarily for machines to read, since they are used for strict static validation of data. Language and text direction concerns are addressed by the noted specification documents for JSON Schema itself.

When using a verifiable credential to represent a schema, we recommend following the guidance in the VC Data Model.

A. References

A.1 Normative references

[JSON-Schema]
JSON Schema: A Media Type for Describing JSON Documents. OpenJS Foundation. URL: https://json-schema.org/specification.html
[JSON-SCHEMA-2019-09]
JSON Schema 2019-09 Release Notes. OpenJS Foundation. URL: https://json-schema.org/draft/2019-09/release-notes.html
[JSON-SCHEMA-2020-12]
JSON Schema 2020-12 Release Notes. OpenJS Foundation. URL: https://json-schema.org/draft/2020-12/release-notes.html
[JSON-SCHEMA-DRAFT-7]
JSON Schema Draft-07 Release Notes. OpenJS Foundation. URL: https://json-schema.org/draft-07/json-schema-release-notes.html
[RFC-3986]
Uniform Resource Identifier (URI): Generic Syntax. T. Berners-Lee; R. Fielding; L. Masinter. January 2005. URL: https://www.rfc-editor.org/rfc/rfc3986
[RFC-6596]
The Canonical Link Relation. M. Ohye; J. Kupke. April 2012. URL: https://www.rfc-editor.org/rfc/rfc6596
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc2119
[RFC8174]
Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words. B. Leiba. IETF. May 2017. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc8174
[sri]
Subresource Integrity. Devdatta Akhawe; Frederik Braun; Francois Marier; Joel Weinberger. W3C. 23 June 2016. W3C Recommendation. URL: https://www.w3.org/TR/SRI/
[URL]
URL Standard. Anne van Kesteren. WHATWG. Living Standard. URL: https://url.spec.whatwg.org/
[VC-DATA-INTEGRITY]
Verifiable Credential Data Integrity 1.0. David Longley; Manu Sporny. W3C Verifiable Credentials Working Group. Working Draft. URL: https://www.w3.org/TR/vc-data-integrity/
[VC-DATA-MODEL-2]
Verifiable Credentials Data Model v2.0. Manu Sporny; Dave Longley; Grant Noble; Dan Burnett; Ted Thibodeau; Brent Zundel; David Chadwick; Kyle Den Hartog. W3C Verifiable Credentials Working Group. Working Draft. URL: https://www.w3.org/TR/vc-data-model-2.0/
[VC-JWT]
Securing Verifiable Credentials using JSON Web Tokens. Orie Steele; Michael Jones; Michael Prorock. W3C. URL: https://www.w3.org/TR/vc-jwt/

A.2 Informative references

[vc-data-model]
Verifiable Credentials Data Model v1.1. Manu Sporny; Grant Noble; Dave Longley; Daniel Burnett; Brent Zundel; Kyle Den Hartog. W3C. 3 March 2022. W3C Recommendation. URL: https://www.w3.org/TR/vc-data-model/
[WCAG21]
Web Content Accessibility Guidelines (WCAG) 2.1. Andrew Kirkpatrick; Joshue O'Connor; Alastair Campbell; Michael Cooper. W3C. 5 June 2018. W3C Recommendation. URL: https://www.w3.org/TR/WCAG21/