Verifiable Credentials Data Model v2.0

W3C Working Draft

More details about this document
This version:
https://www.w3.org/TR/2023/WD-vc-data-model-2.0-20230730/
Latest published version:
https://www.w3.org/TR/vc-data-model-2.0/
Latest editor's draft:
https://w3c.github.io/vc-data-model/
History:
https://www.w3.org/standards/history/vc-data-model-2.0/
Commit history
Editors:
Manu Sporny (Digital Bazaar) (v1.0, v1.1, v2.0)
Orie Steele (Transmute) (v2.0)
Michael B. Jones (independent) (v2.0)
Gabe Cohen (Block) (v2.0)
Oliver Terbu (Spruce Systems, Inc.) (v2.0)
Former editors:
Grant Noble (ConsenSys) (v1.0)
Dave Longley (Digital Bazaar) (v1.0)
Daniel C. Burnett (ConsenSys) (v1.0)
Brent Zundel (Evernym) (v1.0)
Kyle Den Hartog (MATTR) (v1.1)
Authors:
Manu Sporny (Digital Bazaar)
Dave Longley (Digital Bazaar)
David Chadwick (Crossword Cybersecurity PLC)
Feedback:
GitHub w3c/vc-data-model (pull requests, new issue, open issues)

Abstract

Credentials are a part of our daily lives; driver's licenses are used to assert that we are capable of operating a motor vehicle, university degrees can be used to assert our level of education, and government-issued passports enable us to travel between countries. This specification provides a mechanism to express these sorts of credentials on the Web in a way that is cryptographically secure, privacy respecting, and machine-verifiable.

Status of This Document

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/.

Comments regarding this specification are welcome at any time. Please file issues directly on GitHub, or send them to public-vc-comments@w3.org (subscribe, archives).

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

Publication as a 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.

Credentials are a part of our daily lives; driver's licenses are used to assert that we are capable of operating a motor vehicle, university degrees can be used to assert our level of education, and government-issued passports enable us to travel between countries. These credentials provide benefits to us when used in the physical world, but their use on the Web continues to be elusive.

Currently it is difficult to express education qualifications, healthcare data, financial account details, and other sorts of third-party verified machine-readable personal information on the Web. The difficulty of expressing digital credentials on the Web makes it challenging to receive the same benefits through the Web that physical credentials provide us in the physical world.

This specification provides a standard way to express credentials on the Web in a way that is cryptographically secure, privacy respecting, and machine-verifiable.

For those unfamiliar with the concepts related to verifiable credentials, the following sections provide an overview of:

1.1 What is a Verifiable Credential?

This section is non-normative.

In the physical world, a credential might consist of:

A verifiable credential can represent all of the same information that a physical credential represents. The addition of technologies, such as digital signatures, makes verifiable credentials more tamper-evident and more trustworthy than their physical counterparts.

Holders of verifiable credentials can generate verifiable presentations and then share these verifiable presentations with verifiers to prove they possess verifiable credentials with certain characteristics.

Both verifiable credentials and verifiable presentations can be transmitted rapidly, making them more convenient than their physical counterparts when trying to establish trust at a distance.

While this specification attempts to improve the ease of expressing digital credentials, it also attempts to balance this goal with a number of privacy-preserving goals. The persistence of digital information, and the ease with which disparate sources of digital data can be collected and correlated, comprise a privacy concern that the use of verifiable and easily machine-readable credentials threatens to make worse. This document outlines and attempts to address a number of these issues in Section 7. Privacy Considerations. Examples of how to use this data model using privacy-enhancing technologies, such as zero-knowledge proofs, are also provided throughout this document.

The word "verifiable" in the terms verifiable credential and verifiable presentation refers to the characteristic of a credential or presentation as being able to be verified by a verifier, as defined in this document. Verifiability of a credential does not imply that the truth of claims encoded therein can be evaluated; however, the issuer can include values in the evidence property to help the verifier apply their business logic to determine whether the claims have sufficient veracity for their needs.

1.2 Ecosystem Overview

This section is non-normative.

This section describes the roles of the core actors and the relationships between them in an ecosystem where verifiable credentials are expected to be useful. A role is an abstraction that might be implemented in many different ways. The separation of roles suggests likely interfaces and protocols for standardization. The following roles are introduced in this specification:

holder
A role an entity might perform by possessing one or more verifiable credentials and generating verifiable presentations from them. Example holders include students, employees, and customers.
issuer
A role an entity performs by asserting claims about one or more subjects, creating a verifiable credential from these claims, and transmitting the verifiable credential to a holder. Example issuers include corporations, non-profit organizations, trade associations, governments, and individuals.
subject
An entity about which claims are made. Example subjects include human beings, animals, and things. In many cases the holder of a verifiable credential is the subject, but in certain cases it is not. For example, a parent (the holder) might hold the verifiable credentials of a child (the subject), or a pet owner (the holder) might hold the verifiable credentials of their pet (the subject). For more information about these special cases, see the Subject-Holder Relationships section in the Verifiable Credentials Implementation Guide [VC-IMP-GUIDE].
verifier
A role an entity performs by receiving one or more verifiable credentials, optionally inside a verifiable presentation, for processing. Example verifiers include employers, security personnel, and websites.
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. Example verifiable data registries include trusted databases, decentralized databases, government ID databases, and distributed ledgers. Often there is more than one type of verifiable data registry utilized in an ecosystem.
diagram showing how
               credentials flow from issuer to holder and
               presentations flow from holder to verifier where all
               three parties can use information from a logical
               verifiable data registry
Figure 1 The roles and information flows forming the basis for this specification.
Note

Figure 1 above provides an example ecosystem in which to ground the rest of the concepts in this specification. Other ecosystems exist, such as protected environments or proprietary systems, where verifiable credentials also provide benefit.

1.3 Use Cases and Requirements

This section is non-normative.

The Verifiable Credentials Use Cases document [VC-USE-CASES] outlines a number of key topics that readers might find useful, including:

As a result of documenting and analyzing the use cases document, the following desirable ecosystem characteristics were identified for this specification:

1.4 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, SHOULD, and SHOULD NOT 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.

A conforming document is any concrete expression of the data model that complies with the normative statements in this specification. Specifically, all relevant normative statements in Sections 4. Basic Concepts, 5. Advanced Concepts, and 6. Syntaxes of this document MUST be enforced. A serialization format for the conforming document MUST be deterministic, bi-directional, and lossless as described in Section 6. Syntaxes. The conforming document MAY be transmitted or stored in any such serialization format.

A conforming processor is any algorithm realized as software and/or hardware that generates or consumes a conforming document. Conforming processors MUST produce errors when non-conforming documents are consumed.

This specification makes no normative statements with regard to the conformance of roles in the ecosystem, such as issuers, holders, or verifiers, because the conformance of ecosystem roles are highly application, use case, and market vertical specific.

Digital proof mechanisms, a subset of which are digital signatures, are required to ensure the protection of a verifiable credential. Having and validating proofs, which may be dependent on the syntax of the proof (for example, using the JSON Web Signature of a JSON Web Token for proofing a key holder), are an essential part of processing a verifiable credential. At the time of publication, Working Group members had implemented verifiable credentials using at least three proof mechanisms:

Implementers are advised to note that not all proof mechanisms are standardized as of the publication date of this specification. The group expects some of these mechanisms, as well as new ones, to mature independently and become standardized in time. Given there are multiple valid proof mechanisms, this specification does not standardize on any single digital signature mechanism. One of the goals of this specification is to provide a data model that can be protected by a variety of current and future digital proof mechanisms. Conformance to this specification does not depend on the details of a particular proof mechanism; it requires clearly identifying the mechanism a verifiable credential uses.

This document also contains examples that contain characters that are invalid JSON, such as inline comments (//) and the use of ellipsis (...) to denote information that adds little value to the example. Implementers are cautioned to remove this content if they desire to use the information as a valid document.

2. Terminology

This section is non-normative.

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

claim
An assertion made about a subject.
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.
derived predicate
A verifiable, boolean assertion about the value of another attribute in a verifiable credential. These are useful in zero-knowledge-proof-style verifiable presentations because they can limit information disclosure. For example, if a verifiable credential contains an attribute for expressing a specific height in centimeters, a derived predicate might reference the height attribute in the verifiable credential demonstrating that the issuer attests to a height value meeting the minimum height requirement, without actually disclosing the specific height value. For example, the subject is taller than 150 centimeters.
entity
A thing with distinct and independent existence, such as a person, organization, or device that performs one or more roles in the ecosystem.
graph
A network of information composed of subjects and their relationship to other subjects or data.
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 provider
An identity provider, sometimes abbreviated as IdP, is a system for creating, maintaining, and managing identity information for holders, while providing authentication services to relying party applications within a federation or distributed network. In this case the holder is always the subject. Even if the verifiable credentials are bearer credentials, it is assumed the verifiable credentials remain with the subject, and if they are not, they were stolen by an attacker. This specification does not use this term unless comparing or mapping the concepts in this document to other specifications. This specification decouples the identity provider concept into two distinct concepts: the issuer and the holder.
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.
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.

3. Core Data Model

This section is non-normative.

The following sections outline core data model concepts, such as claims, credentials, and presentations, which form the foundation of this specification.

3.1 Claims

This section is non-normative.

A claim is a statement about a subject. A subject is a thing about which claims can be made. Claims are expressed using subject- property-value relationships.

subject has a property which
            has a value
Figure 2 The basic structure of a claim.

The data model for claims, illustrated in Figure 2 above, is powerful and can be used to express a large variety of statements. For example, whether someone graduated from a particular university can be expressed as shown in Figure 3 below.

Pat has an alumniOf
            property whose value is Example University
Figure 3 A basic claim expressing that Pat is an alumni of "Example University".

Individual claims can be merged together to express a graph of information about a subject. The example shown in Figure 4 below extends the previous claim by adding the claims that Pat knows Sam and that Sam is employed as a professor.

extends previous
            diagram with another property called knows whose value is
            Sam, and Sam has a property jobTitle whose value is Professor
Figure 4 Multiple claims can be combined to express a graph of information.

To this point, the concepts of a claim and a graph of information are introduced. To be able to trust claims, more information is expected to be added to the graph.

3.2 Credentials

This section is non-normative.

A credential is a set of one or more claims made by the same entity. Credentials might also include an identifier and metadata to describe properties of the credential, such as the issuer, the validity date and time period, a representative image, a public key to use for verification purposes, the revocation mechanism, and so on. The metadata might be signed by the issuer. A verifiable credential is a set of tamper-evident claims and metadata that cryptographically prove who issued it.

a Verifiable
               Credential contains Credential Metadata, Claim(s), and
               Proof(s)
Figure 5 Basic components of a verifiable credential.

Examples of verifiable credentials include digital employee identification cards, digital birth certificates, and digital educational certificates.

Note

Credential identifiers are often used to identify specific instances of a credential. These identifiers can also be used for correlation. A holder wanting to minimize correlation is advised to use a selective disclosure scheme that does not reveal the credential identifier.

Figure 5 above shows the basic components of a verifiable credential, but abstracts the details about how claims are organized into information graphs, which are then organized into verifiable credentials. Figure 6 below shows a more complete depiction of a verifiable credential, which is normally composed of at least two information graphs. The first graph expresses the verifiable credential itself, which contains credential metadata and claims. The second graph expresses the digital proof, which is usually a digital signature.

diagram with a
               Credential Graph on top connected via a proof to a
               Proof Graph on the bottom.  The Credential Graph has
               Credential 123 with 4 properties: 'type' of value
               ExampleAlumniCredential, 'issuer' of Example University,
               'validFrom' of 2010-01-01T19:23:24Z, and
               credentialSubject of Pat, who has an alumniOf property
               with value of Example University.  The Proof Graph has
               Signature 456 with 5 properties: 'type' of
               DataIntegrityProof, 'verificationMethod' of Example University
               Public Key 7, 'created' of 2017-06-18T21:19:10Z, and 'jws'
               of 'BavEll0...3JT24='
Figure 6 Information graphs associated with a basic verifiable credential.
Note

It is possible to have a credential, such as a marriage certificate, containing multiple claims about different subjects that are not required to be related.

Note

It is possible to have a credential that does not contain any claims about the entity to which the credential was issued. For example, a credential that only contains claims about a specific dog, but is issued to its owner.

3.3 Presentations

This section is non-normative.

Enhancing privacy is a key design feature of this specification. Therefore, it is important for entities using this technology to be able to express only the portions of their persona that are appropriate for a given situation. The expression of a subset of one's persona is called a verifiable presentation. Examples of different personas include a person's professional persona, their online gaming persona, their family persona, or an incognito persona.

A verifiable presentation can express data from multiple verifiable credentials and contain arbitrary additional data encoded as JSON-LD. They are used by a holder to present claims to a verifier. It is also possible to present verifiable credentials directly.

The data in a presentation is often about the same subject, but might have been issued by multiple issuers. The aggregation of this information typically expresses an aspect of a person, organization, or entity.

A Verifiable
            Presentation contains Presentation Metadata, Verifiable
            Credential(s), and Proof(s)
Figure 7 Basic components of a verifiable presentation.

Figure 7 above shows the components of a verifiable presentation, but abstracts the details about how verifiable credentials are organized into information graphs, which are then organized into verifiable presentations.

Figure 8 below shows a more complete depiction of a verifiable presentation, which is normally composed of at least four information graphs. The first of these information graphs, the Presentation Graph, expresses the verifiable presentation itself, which contains presentation metadata. The verifiableCredential property in the Presentation Graph refers to one or more verifiable credentials, each being one of the second information graphs, i.e., a self-contained Credential Graph, which in turn contains credential metadata and claims. The third information graph, the Credential Proof Graph, expresses the credential graph proof, which is usually a digital signature. The fourth information graph, the Presentation Proof Graph, expresses the presentation graph proof, which is usually a digital signature.

diagram with
               a Presentation Graph on top connected via a proof to a
               Presentation Proof Graph on the bottom.  The
               Presentation Graph has Presentation ABC with 3
               properties: 'type' of value VerifiablePresentation,
               'termsOfUse' of value Do Not Archive, and
               'verifiableCredential' whose value is Figure 6.  The
               Presentation Proof Graph has Signature 8910 with 5
               properties: 'type' of DataIntegrityProof, 'verificationMethod'
               of Example Presenter Public Key 11, 'created' of
               2018-01-15T12:43:56Z, 'challenge' of d28348djsj3239, and
               'jws' of 'p2KaZ...8Fj3K='
Figure 8 Information graphs associated with a basic verifiable presentation.
Note

It is possible to have a presentation, such as a business persona, which draws on multiple credentials about different subjects that are often, but not required to be, related.

3.4 Concrete Lifecycle Example

This section is non-normative.

The previous sections introduced the concepts of claims, verifiable credentials, and verifiable presentations using graphical depictions. This section provides a concrete set of simple but complete lifecycle examples of the data model expressed in one of the concrete syntaxes supported by this specification. The lifecycle of credentials and presentations in the Verifiable Credentials Ecosystem often take a common path:

  1. Issuance of one or more verifiable credentials.
  2. Storage of verifiable credentials in a credential repository (such as a digital wallet).
  3. Composition of verifiable credentials into a verifiable presentation for verifiers.
  4. Verification of the verifiable presentation by the verifier.

To illustrate this lifecycle, we will use the example of redeeming an alumni discount from a university. In the example below, Pat receives an alumni verifiable credential from a university, and Pat stores the verifiable credential in a digital wallet.

Example 1: A simple example of a verifiable credential
{
  // set the context, which establishes the special terms we will be using
  // such as 'issuer' and 'alumniOf'.
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  // specify the identifier for the credential
  "id": "http://university.example/credentials/1872",
  // the credential types, which declare what data to expect in the credential
  "type": ["VerifiableCredential", "ExampleAlumniCredential"],
  // the entity that issued the credential
  "issuer": "https://university.example/issuers/565049",
  // when the credential was issued
  "validFrom": "2010-01-01T19:23:24Z",
  // claims about the subjects of the credential
  "credentialSubject": {
    // identifier for the only subject of the credential
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    // assertion about the only subject of the credential
    "alumniOf": {
      // identifier for the university
      "id": "did:example:c276e12ec21ebfeb1f712ebc6f1",
      // name of the university
      "name": "Example University"
  },
  // digital proof that makes the credential tamper-evident
  // see the NOTE at end of this section for more detail
  "proof": {
    // the type of embedded proof securing the verifiable credential
    "type": "DataIntegrityProof",
    // the name of the cryptographic signature suite
    "cryptosuite": "eddsa-2022",
    // the date the signature was created
    "created": "2023-06-18T21:19:10Z",
    // purpose of this proof
    "proofPurpose": "assertionMethod",
    // the identifier of the public key that can verify the signature
    "verificationMethod": "https://university.example/issuers/565049#key-123",
    // the digital signature value
    "proofValue": "zQeVbY4oey5q2M3XKaxup3tmzN4DRFTLVqpLMweBrSxMY2xHX5XTYV8nQA
      pmEcqaqA3Q1gVHMrXFkXJeV6doDwLWx"
  }
}

Pat then attempts to redeem the alumni discount. The verifier, a ticket sales system, states that any alumni of "Example University" receives a discount on season tickets to sporting events. Using a mobile device, Pat starts the process of purchasing a season ticket. A step in this process requests an alumni verifiable credential, and this request is routed to Pat's digital wallet. The digital wallet asks Pat if they would like to provide a previously issued verifiable credential. Pat selects the alumni verifiable credential, which is then composed into a verifiable presentation. The verifiable presentation is sent to the verifier and verified.

Example 2: A simple example of a verifiable presentation
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "type": "VerifiablePresentation",
  // the verifiable credential issued in the previous example
  "verifiableCredential": [{
    "@context": [
      "https://www.w3.org/ns/credentials/v2",
      "https://www.w3.org/ns/credentials/examples/v2"
    ],
    "id": "http://university.example/credentials/1872",
    "type": ["VerifiableCredential", "ExampleAlumniCredential"],
    "issuer": "https://university.example/issuers/565049",
    "validFrom": "2010-01-01T19:23:24Z",
    "credentialSubject": {
      "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
      "alumniOf": {
        "id": "did:example:c276e12ec21ebfeb1f712ebc6f1",
        "name": "Example University"
      }
    },
    "proof": {
      "type": "DataIntegrityProof",
      "cryptosuite": "eddsa-2022",
      "created": "2023-06-18T21:19:10Z",
      "proofPurpose": "assertionMethod",
      "verificationMethod": "https://university.example/issuers/565049#key-1",
      "proofValue": "zQeVbY4oey5q2M3XKaxup3tmzN4DRFTLVqpLMweBrSxMY2xHX5XTYV8nQA
        pmEcqaqA3Q1gVHMrXFkXJeV6doDwLWx"
    }
  }],
  // digital signature by Pat on the presentation
  // protects against replay attacks
  "proof": {
    "type": "DataIntegrityProof",
    "cryptosuite": "eddsa-2022",
    "created": "2018-09-14T21:19:10Z",
    "proofPurpose": "authentication",
    "verificationMethod": "did:example:ebfeb1f712ebc6f1c276e12ec21#keys-1",
    // 'challenge' and 'domain' protect against replay attacks
    "challenge": "1f44d55f-f161-4938-a659-f8026467f126",
    "domain": "4jt78h47fh47",
    "proofValue": "zqpLMweBrSxMY2xHX5XTYV8nQAJeV6doDwLWxQeVbY4oey5q2pmEcqaqA3Q1
      gVHMrXFkXM3XKaxup3tmzN4DRFTLV"
  }
}
Note

Implementers that are interested in understanding more about the proof mechanism used above can learn more in Section A.5 Proofs (Signatures) and by reading the following specifications: Data Integrity [VC-DATA-INTEGRITY] and the "Proofs" section of the Verifiable Credential Specifications Directory [VC-SPECS].

4. Basic Concepts

This section introduces some basic concepts for the specification, in preparation for Section 5. Advanced Concepts later in the document.

4.1 Getting Started

This specification is designed to ease the prototyping of new types of verifiable credentials. Developers can copy the template below and paste it into common verifiable credential tooling to start issuing, holding, and verifying prototype credentials.

It is expected that a developer will change MyPrototypeCredential below to the type of credential they would like to create. Since verifiable credentials talk about subjects, each property-value pair in the credentialSubject object expresses a particular attribute of the credential subject. Once a developer has added a number of these property-value combinations, the modified object can be sent to verifiable credential issuer sofware and a verifiable credential will be created for the developer. From a prototyping standpoint, that is all a developer needs to do.

Example 3: A template for creating prototype verifiable credentials
{
  "@context": ["https://www.w3.org/ns/credentials/v2"],
  "type": ["VerifiableCredential", "MyPrototypeCredential"],
  "credentialSubject": {
    "mySubjectProperty": "mySubjectValue"
  }
}

Once a developer has prototyped their credential to a point where they believe all of the credential properties are stable, it is advised that they generate vocabulary and context files for their application and publish them at stable URLs so that other developers can use the same vocabulary and context to achieve interoperability. This process is covered in Section 5.3 Extensibility. Alternatively, developers can reuse existing vocabulary and context files that happen to fit their use case. They can explore the Verifiable Credential Specifications Directory [VC-SPECS] for reusable resources.

4.2 Contexts

When two software systems need to exchange data, they need to use terminology that both systems understand. As an analogy, consider how two people communicate. Both people must use the same language and the words they use must mean the same thing to each other. This might be referred to as the context of a conversation.

Verifiable credentials and verifiable presentations have many attributes and values that are identified by URLs [URL]. However, those URLs can be long and not very human-friendly. In such cases, short-form human-friendly aliases can be more helpful. This specification uses the @context property to map such short-form aliases to the URLs required by specific verifiable credentials and verifiable presentations.

Note

In JSON-LD, the @context property can also be used to communicate other details, such as datatype information, language information, transformation rules, and so on, which are beyond the needs of this specification, but might be useful in the future or to related work. For more information, see Section 3.1: The Context of the [JSON-LD] specification.

Verifiable credentials and verifiable presentations MUST include a @context property.

@context
The value of the @context property MUST be an ordered set where the first item is a URL with the value https://www.w3.org/ns/credentials/v2. For reference, a copy of the base context is provided in Appendix B.1 Base Context. Subsequent items in the array MUST express context information and be composed of any combination of URLs or objects. It is RECOMMENDED that each URL in the @context be one which, if dereferenced, results in a document containing machine-readable information about the @context.
Note

This specification requires for a @context property to be present; this property is defined by [JSON-LD].

Example 4: Usage of the @context property
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://university.example/credentials/58473",
  "type": ["VerifiableCredential", "ExampleAlumniCredential"],
  "issuer": "https://university.example/issuers/565049",
  "validFrom": "2010-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "alumniOf": {
      "id": "did:example:c276e12ec21ebfeb1f712ebc6f1",
      "name": "Example University"
    }
  },
  "proof": { ... }
}

The example above uses the base context URL (https://www.w3.org/ns/credentials/v2) to establish that the conversation is about a verifiable credential. The second URL (https://www.w3.org/ns/credentials/examples/v2) establishes that the conversation is about examples.

Note

This document uses the example context URL (https://www.w3.org/ns/credentials/examples/v2) for the purpose of demonstrating examples. Implementations are expected to not use this URL for any other purpose, such as in pilot or production systems.

The data available at https://www.w3.org/ns/credentials/v2 is a static document that is never updated and SHOULD be downloaded and cached. The associated human-readable vocabulary document for the Verifiable Credentials Data Model is available at https://www.w3.org/2018/credentials/. This concept is further expanded on in Section 5.3 Extensibility.

4.3 Identifiers

When expressing statements about a specific thing, such as a person, product, or organization, it can be useful to use a globally unique identifier for that thing. Globally unique identifiers enable others to express statements about the same thing. This specification defines the optional id property for such identifiers. The id property allows for the expression of statements about specific things in the verifiable credential and is set by an issuer when expressing objects in a verifiable credential or a holder when expressing objects in a verifiable presentation. Example id values include UUIDs (urn:uuid:0c07c1ce-57cb-41af-bef2-1b932b986873), HTTP URLs (https://id.example/things#123), and DIDs (did:example:1234abcd).

If the id property is present:

Note

Developers should remember that identifiers might be harmful in scenarios where pseudonymity is required. Developers are encouraged to read Section 7.3 Identifier-Based Correlation carefully when considering such scenarios. There are also other types of correlation mechanisms documented in Section 7. Privacy Considerations that create privacy concerns. Where privacy is a strong consideration, the id property MAY be omitted. Some use cases do not require, or explicitly require omitting, the id property.

id
The value of the id property MUST be a single URL. It is RECOMMENDED that the URL in the id be one which, if dereferenced, results in a document containing machine-readable information about the id.
Example 5: Usage of the id property
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": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/565049",
  "validFrom": "2010-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}

The example above uses two types of identifiers. The first identifier is for the verifiable credential and uses an HTTP-based URL. The second identifier is for the subject of the verifiable credential (the thing the claims are about) and uses a decentralized identifier, also known as a DID.

Note

As of this publication, DIDs are a new type of identifier that are not necessary for verifiable credentials to be useful. Specifically, verifiable credentials do not depend on DIDs and DIDs do not depend on verifiable credentials. However, it is expected that many verifiable credentials will use DIDs and that software libraries implementing this specification will probably need to resolve DIDs. DID-based URLs are used for expressing identifiers associated with subjects, issuers, holders, credential status lists, cryptographic keys, and other machine-readable information associated with a verifiable credential.

4.4 Types

Software systems that process the kinds of objects specified in this document use type information to determine whether or not a provided verifiable credential or verifiable presentation is appropriate for the intended use case. This specification defines a type property for the expression of type information. This type information can be used during validation processes as described in Appendix A. Validation.

Verifiable credentials and verifiable presentations MUST have a type property. That is, any credential or presentation that does not have type property is not verifiable, so is neither a verifiable credential nor a verifiable presentation.

type
The value of the type property MUST be, or map to (through interpretation of the @context property), one or more URLs. If more than one URL is provided, the URLs MUST be interpreted as an unordered set. Syntactic conveniences SHOULD be used to ease developer usage. Such conveniences might include JSON-LD terms. It is RECOMMENDED that each URL in the type be one which, if dereferenced, results in a document containing machine-readable information about the type.
Example 6: Usage of the type property
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": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/565049",
  "validFrom": "2010-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}

With respect to this specification, the following table lists the objects that MUST have a type specified.

Object Type
Verifiable credential object VerifiableCredential and, optionally, a more specific verifiable credential type. For example,
"type": ["VerifiableCredential", "ExampleDegreeCredential"]
Verifiable presentation object VerifiablePresentation and, optionally, a more specific verifiable presentation type. For example,
"type": ["VerifiablePresentation", "ExamplePresentation"]
Proof object A valid proof type. For example,
"type": "DataIntegrityProof"
credentialStatus object A valid credential status type. For example,
"type": "StatusList2021Entry"
termsOfUse object A valid terms of use type. For example,
"type": "ExampleTermsPolicy")
evidence object A valid evidence type. For example,
"type": "ExampleEvidence"
Note

The type system for the Verifiable Credentials Data Model is the same as for [JSON-LD] and is detailed in Section 3.5: Specifying the Type and Section 9: JSON-LD Grammar. When using a JSON-LD context (see Section 5.3 Extensibility), this specification aliases the @type keyword to type to make the JSON-LD documents more easily understood. While application developers and document authors do not need to understand the specifics of the JSON-LD type system, implementers of this specification who want to support interoperable extensibility, do.

All credentials, presentations, and encapsulated objects MUST specify, or be associated with, additional more narrow types (like ExampleDegreeCredential, for example) so software systems can process this additional information.

When processing encapsulated objects defined in this specification, (for example, objects associated with the credentialSubject object or deeply nested therein), software systems SHOULD use the type information specified in encapsulating objects higher in the hierarchy. Specifically, an encapsulating object, such as a credential, SHOULD convey the associated object types so that verifiers can quickly determine the contents of an associated object based on the encapsulating object type.

For example, a credential object with the type of ExampleDegreeCredential, signals to a verifier that the object associated with the credentialSubject property contains the identifier for the:

This enables implementers to rely on values associated with the type property for verification purposes. The expectation of types and their associated properties should be documented in at least a human-readable specification, and preferably, in an additional machine-readable representation.

Note

The type system used in the data model described in this specification allows for multiple ways to associate types with data. Implementers and authors are urged to read the section on typing in the Verifiable Credentials Implementation Guidelines [VC-IMP-GUIDE].

4.5 Credential Subject

A verifiable credential contains claims about one or more subjects. This specification defines a credentialSubject property for the expression of claims about one or more subjects.

A verifiable credential MUST have a credentialSubject property.

credentialSubject
The value of the credentialSubject property is defined as a set of objects that MUST contain one or more claims that are each related to a subject of the verifiable credential. Each object MAY contain an id, as described in Section 4.3 Identifiers.
Example 7: Usage of the credentialSubject property
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": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/565049",
  "validFrom": "2010-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}

It is possible to express information related to multiple subjects in a verifiable credential. The example below specifies two subjects who are spouses. Note the use of array notation to associate multiple subjects with the credentialSubject property.

Example 8: Specifying multiple subjects in a verifiable credential
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "RelationshipCredential"],
  "issuer": "https://example.com/issuer/123",
  "validFrom": "2010-01-01T00:00:00Z",
  "credentialSubject": [{
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "name": "Jayden Doe",
    "spouse": "did:example:c276e12ec21ebfeb1f712ebc6f1"
  }, {
    "id": "did:example:c276e12ec21ebfeb1f712ebc6f1",
    "name": "Morgan Doe",
    "spouse": "did:example:ebfeb1f712ebc6f1c276e12ec21"
  }]
}

4.6 Issuer

This specification defines a property for expressing the issuer of a verifiable credential.

A verifiable credential MUST have an issuer property.

issuer
The value of the issuer property MUST be either a URL or an object containing an id property. It is RECOMMENDED that the URL in the issuer or its id be one which, if dereferenced, results in a document containing machine-readable information about the issuer that can be used to verify the information expressed in the credential.
Example 9: Usage of issuer property
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": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}

It is also possible to express additional information about the issuer by associating an object with the issuer property:

Example 10: Usage of issuer expanded property
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": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": {
    "id": "did:example:76e12ec712ebc6f1c221ebfeb1f",
    "name": "Example University"
  },
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}
Note

The value of the issuer property can also be a JWK (for example, "https://example.com/keys/foo.jwk") or a DID (for example, "did:example:abfe13f712120431c276e12ecab").

4.7 Validity Period

This specification defines the validFrom property to help an issuer to express the date and time when a credential becomes valid and the validUntil property for expressing the date and time when a credential ceases to be valid.

validFrom
If present, the value of the validFrom property MUST be an [XMLSCHEMA11-2] dateTimeStamp string value representing the date and time the credential becomes valid, which could be a date and time in the future. Note that this value represents the earliest point in time at which the information associated with the credentialSubject property becomes valid.
validUntil
If present, the value of the validUntil property MUST be an [XMLSCHEMA11-2] dateTimeStamp string value representing the date and time the credential ceases to be valid, which could be a date and time in the past. Note that this value represents the latest point in time at which the information associated with the credentialSubject property is valid. If a validFrom value exists, the validUntil value MUST be temporally greater than the validFrom value.
Example 11: Usage of validFrom and validUntil property
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": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "validUntil": "2020-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}
Note

If validFrom and validUntil are not present, the verifiable credential validity period is considered valid indefinitely. In such cases, the verifiable credential is assumed to be valid from the time the verifiable credential was created.

4.7.1 Representing Time

Implementers are urged to understand that representing and processing time values is not as straight-forward as it might seem and have a variety of idiosyncrasies that are not immediately obvious nor uniformly observed in different regions of the world. For example:

  • Calendaring systems other than the Gregorian calendar are actively used by various regions.
  • When processing Daylight Saving/Summer Time, it is important to understand that 1) it is not observed in all regions, 2) it does not necessarily begin or end on the same day or at the same time of day, and 3) the amount or direction of the adjustment does not always match other similar regions.
  • Leap seconds might not be taken into account in all software systems, especially for dates and times that precede the introduction of the leap second. Leap seconds can affects highly sensitive systems that depend on the exact millisecond offset from the epoch. However, note that for most applications the only moment in time that is affected is the one second period of the leap second itself. That is, the moment after the most recent leap second can always be represented as the first moment of the next day (for example, 2023-01-01T00:00:00Z), regardless of whether the system in question understands leap seconds.

These are just a few examples that illustrate that the actual time of day, as would be seen on a clock on the wall, can exist in one region but not exist in another region. For this reason, implementers are urged to use time values that are more universal, such as values anchored to the Z time zone over values that are affected by Daylight Saving/Summer Time.

This specification attempts to increase the number of universally recognized combinations of dates and times, and reduce the potential for misinterpretation of time values, by utilizing the dateTimeStamp construction first established by the [XMLSCHEMA11-2] specification. In order to reduce misinterpretations between different regions, all times MUST be specified as offsets against Universal Coordinated Time (UTC).

Time zone definitions are occasionally changed by their governing body. When replacing or issuing new verifiable credentials, implementers are advised to ensure that changes to local time zone rules do not result in unexpected gaps in validity. For example, consider the zone America/Los_Angeles, which has a raw offset of UTC-8 and had voted to stop observing daylight savings time in the year 2024. A given verifiable credential that had a validUtil value of 2024-07-12T12:00:00-07:00, might be re-issued to have a validFrom value of 2024-07-12T12:00:00-08:00, which would create a gap of an hour where the verifiable credential would not be valid.

Implementers that desire to check dateTimeStamp values for validity can use the regular expression provided below, which is reproduced from the [XMLSCHEMA11-2] specification for convenience. To avoid doubt, the regular expression in [XMLSCHEMA11-2] is the normative definition. Implementers are advised that not all dateTimeStamp values that pass the regular expression below are valid moments in time. For example, the regular expression below allows for 31 days in every month, which allows for leap years, and leap seconds, as well as days in places where they do not exist. That said, modern system libraries that generate dateTimeStamp values are often error-free in their generation of valid dateTimeStamp values. The regular expression shown below (minus the whitespace included here for readability), is often adequate when processing library-generated dates and times on modern systems.

Example 12: Regular expression to detect a valid XML Schema 1.1: Part 2 dateTimeStamp
-?([1-9][0-9]{3,}|0[0-9]{3})
-(0[1-9]|1[0-2])
-(0[1-9]|[12][0-9]|3[01])
T(([01][0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9](\.[0-9]+)?|(24:00:00(\.0+)?))
(Z|(\+|-)((0[0-9]|1[0-3]):[0-5][0-9]|14:00))

4.8 Securing Verifiable Credentials

At least one securing mechanism, and the details necessary to evaluate it, MUST be expressed for a credential or presentation to be a verifiable credential or verifiable presentation; that is, to be verifiable.

This specification recognizes two classes of securing mechanisms: those that use external proofs and those that use embedded proofs. An external proof is one that wraps an expression of this data model, such as via a JSON Web Token, which is elaborated on in the Securing Verifiable Credentials using JSON Web Tokens [VC-JWT] specification. An embedded proof is a mechanism where the proof is included in the data model, such as a Data Integrity Proof, which is elaborated on in Verifiable Credential Data Integrity [VC-DATA-INTEGRITY].

It should be noted that these two classes of securing mechanisms are not mutually exclusive.

Methods of securing credentials or presentations that embed a proof in the data model MUST use the proof property.

Methods of securing credentials or presentations that use an external proof MAY use the proof property.

proof
One or more cryptographic proofs that can be used to detect tampering and verify the authorship of a credential or presentation. The specific method used for an embedded proof MUST be included using the type property.

Because the method used for a mathematical proof varies by representation language and the technology used, the set of name-value pairs that is expected as the value of the proof property will vary accordingly. For example, if digital signatures are used for the proof mechanism, the proof property is expected to have name-value pairs that include a signature, a reference to the signing entity, and a representation of the signing date. The example below uses Ed25519 digital signatures.

Example 13: Usage of the proof property on a verifiable credential
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://example.gov/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "proof": {
    "type": "Ed25519Signature2020",
    "created": "2021-11-13T18:19:39Z",
    "verificationMethod": "https://university.example/issuers/14#key-1",
    "proofPurpose": "assertionMethod",
    "proofValue": "z58DAdFfa9SkqZMVPxAQpic7ndSayn1PzZs6ZjWp1CktyGesjuTSwRdo
                   WhAfGFCF5bppETSTojQCrfFPP2oumHKtz"
  }
}
Note

As discussed in Section 1.4 Conformance, there are multiple viable proof mechanisms, and this specification does not standardize nor recommend any single proof mechanism for use with verifiable credentials. For more information about the proof mechanism, see the following specifications: Data Integrity [VC-DATA-INTEGRITY], Securing Verifiable Credentials using JSON Web Tokens [VC-JWT], and the "Proofs" section of the Verifiable Credential Specifications Directory [VC-SPECS].

4.9 Status

This specification defines the following credentialStatus property for the discovery of information about the current status of a verifiable credential, such as whether it is suspended or revoked.

credentialStatus
If present, the value of the credentialStatus property MUST include the following:

The precise content of the credential status information is determined by the specific credentialStatus type definition, and varies depending on factors such as whether it is simple to implement or if it is privacy-enhancing. It is expected that the value will provide enough information to determine the current status of the credential and that machine readable information will be retrievable from the URL. For example, the object could contain a link to an external document which notes whether or not the credential is suspended or revoked.

Example 14: Usage of the status property
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://w3id.org/vc/status-list/2021/v1"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "credentialStatus": {
    "id": "https://university.example/credentials/status/3#94567",
    "type": "StatusList2021Entry",
    "statusPurpose": "revocation",
    "statusListIndex": "94567",
    "statusListCredential": "https://university.example/credentials/status/3"
  }
}

Defining the data model, formats, and protocols for status schemes are out of scope for this specification. A Verifiable Credential Specifications Directory [VC-SPECS] exists that contains available status schemes for implementers who want to implement verifiable credential status checking.

4.10 Presentations

Verifiable presentations MAY be used to aggregate information from multiple verifiable credentials.

Verifiable presentations SHOULD be extremely short-lived, and bound to a challenge provided by a verifier. Details for accomplishing this depend on the securing mechanism, the transport protocol, and verifier policies. Unless additional requirements are defined by the particular securing mechanism or embedding protocol, a verifier cannot generally assume that the verifiable presentation has any correlation with the presented verifiable credentials.

The following properties are defined for a verifiable presentation:

id
The id property is optional. It MAY be used to provide a unique identifier for the verifiable presentation. If present, the normative guidance in Section 4.3 Identifiers MUST be followed.
type
The type property MUST be present. It is used to express the type of verifiable presentation. One value of this property MUST be VerifiablePresentation, but additional types MAY be included. The related normative guidance in Section 4.4 Types MUST be followed.
verifiableCredential
The verifiableCredential property MAY be present. The value MUST be an array of one or more verifiable credentials, or of data derived from verifiable credentials in a cryptographically verifiable format.
holder
The verifiable presentation MAY include a holder property. If present, the value MUST be either a URL or an object containing an id property. It is RECOMMENDED that the URL in the holder or its id be one which, if dereferenced, results in a document containing machine-readable information about the holder that can be used to verify the information expressed in the verifiable presentation. If the holder property is absent, information about the holder is expected to either be obtained via the securing mechanism, or to not pertain to the validation of the verifiable presentation.
proof
The verifiable presentation MAY include a proof property. If present, the value SHOULD be used to express a securing mechanism such as [VC-DATA-INTEGRITY]. A verifiable presentation MAY be secured using an external proof such as [VC-JWT]. For details related to the use of this property, see Section 4.8 Securing Verifiable Credentials.

The example below shows a verifiable presentation:

Example 15: Basic structure of a presentation
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:3978344f-8596-4c3a-a978-8fcaba3903c5",
  "type": ["VerifiablePresentation", "ExamplePresentation"],
  "verifiableCredential": [{ ... }],
  "proof": [{ ... }]
}

The contents of the verifiableCredential property shown above are verifiable credentials, as described by this specification. The contents of the proof property are proofs, as described by the Data Integrity [VC-DATA-INTEGRITY] specification. An example of a verifiable presentation using the JWT proof mechanism is provided in the Securing Verifiable Credentials using JSON Web Tokens [VC-JWT] specification.

4.10.1 Presentations Using Derived Credentials

Some zero-knowledge cryptography schemes might enable holders to indirectly prove they hold claims from a verifiable credential without revealing all claims in that verifiable credential. In these schemes, a verifiable credential might be used to derive presentable data, which is cryptographically asserted such that a verifier can trust the value if they trust the issuer.

Some selective disclosure schemes can share a subset of claims derived from a verifiable credential.

Note

For an example of a ZKP-style verifiable presentation containing derived data instead of directly embedded verifiable credentials, see Section 5.8 Zero-Knowledge Proofs.

Pat has a property
                 dateOfBirth whose value is 2010-01-01
Figure 9 A basic claim expressing that Pat's date of birth is January 1, 2010. Date encoding would be determined by the schema.

4.10.2 Presentations Including Holder Claims

A holder MAY use the verifiableCredential property in a verifiable presentation to include verifiable credentials from any issuer, including themselves. When the issuer of a verifiable credential is the holder, the claims in that verifiable credential are considered to be self-asserted. Such self-asserted claims can be secured by the same mechanism that secures the verifiable presentation in which they are included or by any mechanism usable for other verifiable credentials.

The subject(s) of these self-asserted claims are not limited, so these claims can include statements about the holder, one of the other included verifiable credentials, or even the verifiable presentation in which the self-asserted verifiable credential is included. In each case, the id property is used to identify the specific subject, in the object where the claims about it are made, just as it is done in verifiable credentials that are not self-asserted.

A verifiable presentation that includes a self-asserted verifiable credential that is only secured using the same mechanism as the verifiable presentation MUST include a holder property.

All of the normative requirements defined for verifiable credentials apply to self-asserted verifiable credentials.

When a self-asserted verifiable credential is secured using the same mechanism as the verifiable presentation, the value of the issuer property of the verifiable credential MUST be identical to the holder property of the verifiable presentation.

The example below shows a verifiable presentation that embeds a self-asserted verifiable credential that is secured using the same mechanism as the verifiable presentation.

Example 16: A verifiable presentation, secured with an embedded proof, with a self-asserted verifiable credential
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "type": ["VerifiablePresentation", "ExamplePresentation"],
  "holder": "did:example:12345678",
  "verifiableCredential": [{
    "@context": "https://www.w3.org/ns/credentials/v2",
    "type": ["VerifiableCredential", "ExampleFoodPreferenceCredential"],
    "issuer": "did:example:12345678",
    "credentialSubject": {
      "favoriteCheese": "Gouda"
    },
    { ... }
  }],
  "proof": [{ ... }]
}

The example below shows a verifiable presentation that embeds a self-asserted verifiable credential that holds claims about the verifiable presentation. It is secured using the same mechanism as the verifiable presentation.

Example 17: A verifiable presentation, secured with an embedded proof, with a self-asserted verifiable credential about the verifiable presentation
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "type": ["VerifiablePresentation", "ExamplePresentation"],
  "id": "urn:uuid:313801ba-24b7-11ee-be02-ff560265cf9b",
  "holder": "did:example:12345678",
  "verifiableCredential": [{
    "@context": "https://www.w3.org/ns/credentials/v2",
    "type": ["VerifiableCredential", "ExampleAssertCredential"],
    "issuer": "did:example:12345678",
    "credentialSubject": {
      "id": "urn:uuid:313801ba-24b7-11ee-be02-ff560265cf9b",
      "assertion": "This VP is submitted by the subject as evidence of a legal right to drive"
    },
    { ... }
  }],
  "proof": [{ ... }]
}

4.11 Data Schemas

Data schemas are useful when enforcing a specific structure on a given collection of data. There are at least two types of data schemas that this specification considers:

It is important to understand that data schemas serve a different purpose from the @context property, which neither enforces data structure or data syntax, nor enables the definition of arbitrary encodings to alternate representation formats.

This specification defines the following property for the expression of a data schema, which can be included by an issuer in the verifiable credentials that it issues:

credentialSchema

The value of the credentialSchema property MUST be one or more data schemas that provide verifiers with enough information to determine if the provided data conforms to the provided schema(s). Each credentialSchema MUST specify its type (for example, JsonSchema2023), and an id property that MUST be a URL identifying the schema file. The precise contents of each data schema is determined by the specific type definition.

If multiple schemas are present, validity is determined according to the processing rules outlined by each associated credentialSchema type property.

Note

The credentialSchema property provides an opportunity to annotate type definitions or lock them to specific versions of the vocabulary. Authors of verifiable credentials can include a static version of their vocabulary using credentialSchema that is locked to some content integrity protection mechanism. The credentialSchema property also makes it possible to perform syntactic checking on the credential and to use verification mechanisms such as JSON Schema [VC-JSON-SCHEMA-2023] validation.

Example 18: Usage of the credentialSchema property to perform JSON schema validation
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential", "ExamplePersonCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    },
    "alumniOf": {
      "name": "Example University"
    }
  },
  "credentialSchema": [{
    "id": "https://example.org/examples/degree.json",
    "type": "JsonSchema2023"
  },
  {
    "id": "https://example.org/examples/alumni.json",
    "type": "JsonSchema2023"
  }]
}

In the example above, the issuer is specifying a credentialSchema, which points to a [VC-JSON-SCHEMA-2023] file that can be used by a verifier to determine if the verifiable credential is well formed.

Note

For information about linkages to JSON Schema [VC-JSON-SCHEMA-2023] or other optional verification mechanisms, see the Verifiable Credentials Implementation Guidelines [VC-IMP-GUIDE] document.

Data schemas can also be used to specify mappings to other formats, such as those used to perform zero-knowledge proofs. For more information on using the credentialSchema property with zero-knowledge proofs, see Section 5.8 Zero-Knowledge Proofs.

Example 19: Usage of the credentialSchema property to perform zero-knowledge validation
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "credentialSchema": {
    "id": "https://example.org/examples/degree",
    "type": "ZkpExampleSchema2018"
  },
  "proof": { ... }
}

In the example above, the issuer is specifying a credentialSchema pointing to a means of transforming the input data into a format which can then be used by a verifier to determine if the proof provided with the verifiable credential is valid.

5. Advanced Concepts

Building on the concepts introduced in Section 4. Basic Concepts, this section explores more complex topics about verifiable credentials.

5.1 Lifecycle Details

This section is non-normative.

Section 1.2 Ecosystem Overview provided an overview of the verifiable credential ecosystem. This section provides more detail about how the ecosystem is envisaged to operate.

diagram showing how
         credentials flow from issuer to holder, and optionally
         from one holder to another; and how
         presentations flow from holder to verifier, where
         all parties can use information from a logical
         verifiable data registry
Figure 10 The roles and information flows for this specification.

The roles and information flows in the verifiable credential ecosystem are as follows:

Note

The order of the actions above is not fixed, and some actions might be taken more than once. Such action-recurrence might be immediate or at any later point.

The most common sequence of actions is envisioned to be:

  1. An issuer issues to a holder.
  2. The holder presents to a verifier.
  3. The verifier verifies.

This specification does not define any protocol for transferring verifiable credentials or verifiable presentations, but assuming other specifications do specify how they are transferred between entities, then this Verifiable Credential Data Model is directly applicable.

This specification also does not define an authorization framework nor the decisions that a verifier might make after verifying a verifiable credential or verifiable presentation, taking into account the holder, the issuers of the verifiable credentials, the contents of the verifiable credentials, and its own policies.

In particular, Sections 5.6 Terms of Use and the Subject-Holder Relationships section in the Verifiable Credentials Implementation Guide [VC-IMP-GUIDE] specify how a verifier can determine:

5.2 Trust Model

This section is non-normative.

The verifiable credentials trust model is as follows:

This trust model differentiates itself from other trust models by ensuring the:

By decoupling the trust between the identity provider and the relying party a more flexible and dynamic trust model is created such that market competition and customer choice is increased.

For more information about how this trust model interacts with various threat models studied by the Working Group, see the Verifiable Credentials Use Cases document [VC-USE-CASES].

Note

The data model detailed in this specification does not imply a transitive trust model, such as that provided by more traditional Certificate Authority trust models. In the Verifiable Credentials Data Model, a verifier either directly trusts or does not trust an issuer. While it is possible to build transitive trust models using the Verifiable Credentials Data Model, implementers are urged to learn about the security weaknesses introduced by broadly delegating trust in the manner adopted by Certificate Authority systems.

5.3 Extensibility

One of the goals of the Verifiable Credentials Data Model is to enable permissionless innovation. To achieve this, the data model needs to be extensible in a number of different ways. The data model is required to:

This approach to data modeling is often called an open world assumption, meaning that any entity can say anything about any other entity. While this approach seems to conflict with building simple and predictable software systems, balancing extensibility with program correctness is always more challenging with an open world assumption than with closed software systems.

The rest of this section describes, through a series of examples, how both extensibility and program correctness are achieved.

Let us assume we start with the verifiable credential shown below.

Example 20: A simple credential
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": "http://example.com/credentials/4643",
  "type": ["VerifiableCredential"],
  "issuer": "https://example.com/issuers/14",
  "validFrom": "2018-02-24T05:28:04Z",
  "credentialSubject": {
    "id": "did:example:abcdef1234567",
    "name": "Jane Doe"
  }
}

This verifiable credential states that the entity associated with did:example:abcdef1234567 has a name with a value of Jane Doe.

Now let us assume a developer wants to extend the verifiable credential to store two additional pieces of information: an internal corporate reference number, and Jane's favorite food.

The first thing to do is to create a JSON-LD context containing two new terms, as shown below.

Example 21: A JSON-LD context
{
  "@context": {
    "referenceNumber": "https://example.com/vocab#referenceNumber",
    "favoriteFood": "https://example.com/vocab#favoriteFood"
  }
}

After this JSON-LD context is created, the developer publishes it somewhere so it is accessible to verifiers who will be processing the verifiable credential. Assuming the above JSON-LD context is published at https://example.com/contexts/mycontext.jsonld, we can extend this example by including the context and adding the new properties and credential type to the verifiable credential.

Example 22: A verifiable credential with a custom extension
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2",
    "https://example.com/contexts/mycontext.jsonld"
  ],
  "id": "http://example.com/credentials/4643",
  "type": ["VerifiableCredential", "CustomExt12"],
  "issuer": "https://example.com/issuers/14",
  "validFrom": "2018-02-24T05:28:04Z",
  "referenceNumber": 83294847,
  "credentialSubject": {
    "id": "did:example:abcdef1234567",
    "name": "Jane Doe",
    "favoriteFood": "Papaya"
  }
}

This example demonstrates extending the Verifiable Credentials Data Model in a permissionless and decentralized way. The mechanism shown also ensures that verifiable credentials created in this way provide a mechanism to prevent namespace conflicts and semantic ambiguity.

A dynamic extensibility model such as this does increase the implementation burden. Software written for such a system has to determine whether verifiable credentials with extensions are acceptable based on the risk profile of the application. Some applications might accept only certain extensions while highly secure environments might not accept any extensions. These decisions are up to the developers of these applications and are specifically not the domain of this specification.

Developers are urged to ensure that extension JSON-LD contexts are highly available. Implementations that cannot dereference a context will produce an error. Strategies for ensuring that extension JSON-LD contexts are always available include using content-addressed URLs for contexts, bundling context documents with implementations, or enabling aggressive caching of contexts.

Implementers are advised to pay close attention to the extension points in this specification, such as in Sections A.5 Proofs (Signatures), 4.9 Status, 4.11 Data Schemas,5.5 Refreshing, 5.6 Terms of Use, and 5.7 Evidence. While this specification does not define concrete implementations for those extension points, the Verifiable Credential Specifications Directory [VC-SPECS] provides an unofficial, curated list of extensions that developers can use from these extension points.

5.3.1 Semantic Interoperability

  • JSON-LD-based processors MUST produce an error when a JSON-LD context redefines any term in the active context. The only way to change the definition of existing terms is to introduce a new term that clears the active context within the scope of that new term. Authors that are interested in this feature should read about the @protected feature in the JSON-LD 1.1 specification.

A human-readable document describing the expected order of values for the @context property is expected to be published by any implementer seeking interoperability. A machine-readable description (that is, a normal JSON-LD Context document) is expected to be published at the URL specified in the @context property by JSON-LD implementers seeking interoperability.

5.5 Refreshing

Issue: (AT RISK) Feature depends on demonstration of independent implementations

This feature is at risk and will be removed from the specification if at least two independent, interoperable implementations are not demonstrated for a single extension type by the end of the Candidate Recommendation Phase. If this feature is removed, the property will be included in Section 5.10 Reserved Extension Points, in anticipation of future implementation and inclusion in the specification.

It is useful for systems to enable the manual or automatic refresh of an expired verifiable credential. For more information about validity periods for verifiable credentials, see Section A.6 Validity Periods. This specification defines a refreshService property, which enables an issuer to include a link to a refresh service.

The issuer can include the refresh service as an element inside the verifiable credential if it is intended for either the verifier or the holder (or both), or inside the verifiable presentation if it is intended for the holder only. In the latter case, this enables the holder to refresh the verifiable credential before creating a verifiable presentation to share with a verifier. In the former case, including the refresh service inside the verifiable credential enables either the holder or the verifier to perform future updates of the credential.

The refresh service is only expected to be used when either the credential has expired or the issuer does not publish credential status information. Issuers are advised not to put the refreshService property in a verifiable credential that does not contain public information or whose refresh service is not protected in some way.

Note

Placing a refreshService property in a verifiable credential so that it is available to verifiers can remove control and consent from the holder and allow the verifiable credential to be issued directly to the verifier, thereby bypassing the holder.

refreshService
The value of the refreshService property MUST be one or more refresh services that provides enough information to the recipient's software such that the recipient can refresh the verifiable credential. Each refreshService value MUST specify its type (for example, ManualRefreshService2018) and its id, which is the URL of the service. There is an expectation that machine readable information needs to be retrievable from the URL. The precise content of each refresh service is determined by the specific refreshService type definition.
Example 25: Usage of the refreshService property by an issuer
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "refreshService": {
    "id": "https://university.example/refresh/3732",
    "type": "ManualRefreshService2018"
  }
}

In the example above, the issuer specifies a manual refreshService that can be used by directing the holder or the verifier to https://university.example/refresh/3732.

5.6 Terms of Use

Issue 1010: (AT RISK) Feature depends on demonstration of independent implementations conversationdirectorybefore-CR

This feature is at risk and will be removed from the specification if at least two independent, interoperable implementations are not demonstrated for a single extension type by the end of the Candidate Recommendation Phase. If this feature is removed, the property will be included in Section 5.10 Reserved Extension Points, in anticipation of future implementation and inclusion in the specification.

Terms of use can be utilized by an issuer or a holder to communicate the terms under which a verifiable credential or verifiable presentation was issued. The issuer places their terms of use inside the verifiable credential. The holder places their terms of use inside a verifiable presentation. This specification defines a termsOfUse property for expressing terms of use information.

The value of the termsOfUse property tells the verifier what actions it is required to perform (an obligation), not allowed to perform (a prohibition), or allowed to perform (a permission) if it is to accept the verifiable credential or verifiable presentation.

Note

Further study is required to determine how a subject who is not a holder places terms of use on their verifiable credentials. One way could be for the subject to request the issuer to place the terms of use inside the issued verifiable credentials. Another way could be for the subject to delegate a verifiable credential to a holder and place terms of use restrictions on the delegated verifiable credential.

termsOfUse
The value of the termsOfUse property MUST specify one or more terms of use policies under which the creator issued the credential or presentation. If the recipient (a holder or verifier) is not willing to adhere to the specified terms of use, then they do so on their own responsibility and might incur legal liability if they violate the stated terms of use. Each termsOfUse value MUST specify its type, for example, IssuerPolicy, and MAY specify its instance id. The precise contents of each term of use is determined by the specific termsOfUse type definition.
Example 26: Usage of the termsOfUse property by an issuer
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "termsOfUse": [{
    "type": "IssuerPolicy",
    "id": "http://example.com/policies/credential/4",
    "profile": "http://example.com/profiles/credential",
    "prohibition": [{
      "assigner": "https://university.example/issuers/14",
      "assignee": "AllVerifiers",
      "target": "http://university.example/credentials/3732",
      "action": ["Archival"]
    }]
  }]
  
}

In the example above, the issuer (the assigner) is prohibiting verifiers (the assignee) from storing the data in an archive.

Example 27: Usage of the termsOfUse property by a holder
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2",
    {
        "@protected": true,
        "VerifiablePresentationTermsOfUseExtension": {
          "@id": "https://www.w3.org/2018/credentials/examples#VerifiablePresentationExtension",
          "@context": {
            "@protected": true,
            "termsOfUse": {
              "@id": "https://www.w3.org/2018/credentials#termsOfUse",
              "@type": "@id"
            }
          }
        }
    }
  ],
  "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
  "type": ["VerifiablePresentation"],
  "verifiableCredential": [{
    "@context": [
      "https://www.w3.org/ns/credentials/v2",
      "https://www.w3.org/ns/credentials/examples/v2"
    ],
    "id": "http://university.example/credentials/3732",
    "type": ["VerifiableCredential", "ExampleDegreeCredential"],
    "issuer": "https://university.example/issuers/14",
    "validFrom": "2010-01-01T19:23:24Z",
    "credentialSubject": {
      "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
      "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
    },
    "proof": { ... }
  }],
  "termsOfUse": [{
    "type": "HolderPolicy",
    "id": "http://example.com/policies/credential/6",
    "profile": "http://example.com/profiles/credential",
    "prohibition": [{
      "assigner": "did:example:ebfeb1f712ebc6f1c276e12ec21",
      "assignee": "https://wineonline.example.org/",
      "target": "http://university.example/credentials/3732",
      "action": ["3rdPartyCorrelation"]
    }]
  }],
  "proof": [ ... ]
}

In the example above, the holder (the assigner), who is also the subject, expressed a term of use prohibiting the verifier (the assignee, https://wineonline.example.org) from using the information provided to correlate the holder or subject using a third-party service. If the verifier were to use a third-party service for correlation, they would violate the terms under which the holder created the presentation.

This feature is also expected to be used by government-issued verifiable credentials to instruct digital wallets to limit their use to similar government organizations in an attempt to protect citizens from unexpected usage of sensitive data. Similarly, some verifiable credentials issued by private industry are expected to limit usage to within departments inside the organization, or during business hours. Implementers are urged to read more about this rapidly evolving feature in the appropriate section of the Verifiable Credentials Implementation Guidelines [VC-IMP-GUIDE] document.

5.7 Evidence

Issue 870: (AT RISK) Feature depends on demonstration of independent implementations evidencebefore-CR

This feature is at risk and will be removed from the specification if at least two independent, interoperable implementations are not demonstrated for a single extension type by the end of the Candidate Recommendation Phase. If this feature is removed, the property will be included in Section 5.10 Reserved Extension Points, in anticipation of future implementation and inclusion in the specification.

Evidence can be included by an issuer to provide the verifier with additional supporting information in a verifiable credential. This could be used by the verifier to establish the confidence with which it relies on the claims in the verifiable credential.

For example, an issuer could check physical documentation provided by the subject or perform a set of background checks before issuing the credential. In certain scenarios, this information is useful to the verifier when determining the risk associated with relying on a given credential.

This specification defines the evidence property for expressing evidence information.

evidence
The value of the evidence property MUST be one or more evidence schemes providing enough information for a verifier to determine whether the evidence gathered by the issuer meets its confidence requirements for relying on the credential. Each evidence scheme is identified by its type. The id property is optional, but if present, SHOULD contain a URL that points to where more information about this instance of evidence can be found. The precise content of each evidence scheme is determined by the specific evidence type definition.
Note

For information about how attachments and references to credentials and non-credential data might be supported by the specification, see the Verifiable Credentials Implementation Guidelines [VC-IMP-GUIDE] document.

Example 28: Usage of the evidence property
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "evidence": [{
    "id": "https://university.example/evidence/f2aeec97-fc0d-42bf-8ca7-0548192d4231",
    "type": ["DocumentVerification"],
    "verifier": "https://university.example/issuers/14",
    "evidenceDocument": "DriversLicense",
    "subjectPresence": "Physical",
    "documentPresence": "Physical",
    "licenseNumber": "123AB4567"
  }],
  "proof": { ... }
}
Note

In this evidence example, the issuer is asserting that they physically matched the subject of the credential to a physical copy of a driver's license with the stated license number. This driver's license was used in the issuance process to verify that "Example University" verified the subject before issuance of the credential and how they did so (physical verification).

Note

The evidence property provides different and complementary information to the proof property. The evidence property is used to express supporting information, such as documentary evidence, related to the integrity of the verifiable credential. In contrast, the proof property is used to express machine-verifiable mathematical proofs related to the authenticity of the issuer and integrity of the verifiable credential. For more information about the proof property, see Section A.5 Proofs (Signatures).

5.8 Zero-Knowledge Proofs

Issue 863: ZKP Section Normative Changes pr existspending close

We plan to remove the normative requirements in this section if there are no active work items for securing verifiable credentials using zero knowledge proof mechanisms when we transition v2 of the data model to CR. Additionally, the remaining non-normative language will likely be moved to the Verifiable Credentials Implementation Guidelines [VC-IMP-GUIDE].

Zero-knowledge proofs are cryptographic methods which enable a user to prove knowledge of a value without disclosing the actual value. This data model supports being secured with the use of zero-knowledge proof mechanisms.

Some capabilities that are compatible with verifiable credentials which are made possible by zero-knowledge proof mechanisms:

Not all capabilities are supported in all zero-knowledge proof mechanisms. Specific details about the capabilities and techniques provided by a particular zero knowledge proof mechanism, along with any normative requirements for using them with verifiable credentials, would be found in a specification for securing verifiable credentials with that zero-knowledge proof mechanism.

We note that in most instances, for holder to make use of zero knowledge mechanisms with verifiable credentials requires an issuer to secure the verifiable credential in a manner that supports these capabilities.

There are two requirements for verifiable credentials when they are to be used in zero-knowledge proof systems.

When a holder has selectively disclosed a portion of a verifiable credential, it is important that the verifier check whether the information provided in the derived verifiable credential is compatible with the schema in the credentialSchema property provided by the issuer. It is also possible for the verifier to provide a schema to the holder as part of a request for the holder's data, and for the verifier to ensure that the derived verifiable credential is compatible with that schema as well. We do not define such a request schema in this specification, but an example of one method for doing so is [PRES-EX].

Note

credentialSchema implementers are encouraged to consider the implications of selective disclosure credentials and provide guidance for processing depending on the construction. If a schema is not formed with selective disclosure in mind, then validation is likely to fail.

The examples below highlight how the data model might be used to issue and present verifiable credentials in zero-knowledge.

Note

The provided examples will either be significantly re-written to demonstrate how to secure a verifiable credential using a normatively defined method that enable zero knowledge proofs, or they will be removed.

The following example shows one method of using verifiable credentials in zero-knowledge. It makes use of a Camenisch-Lysyanskaya Signature [CL-SIGNATURES], which allows the presentation of the verifiable credential in a way that supports the privacy of the holder and subject through the use of selective disclosure of the verifiable credential values. Some other cryptographic systems which rely upon zero-knowledge proofs to selectively disclose attributes can be found in the Verifiable Credential Specifications Directory [VC-SPECS] as well.

Example 29: A verifiable credential that supports CL Signatures
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "credentialSchema": {
    "id": "did:example:cdf:35LB7w9ueWbagPL94T9bMLtyXDj9pX5o",
    "type": "did:example:schema:22KpkXgecryx9k7N6XN1QoN3gXwBkSU8SfyyYQG"
  },
  "issuer": "did:example:Wz4eUg7SetGfaUVCn8U9d62oDYrUJLuUtcy619",
  "credentialSubject": {
    "givenName": "Jane",
    "familyName": "Doe",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts",
      "college": "College of Engineering"
    }
  },
  "proof": {
    "type": "CLSignature2019",
    "issuerData": "5NQ4TgzNfSQxoLzf2d5AV3JNiCdMaTgm...BXiX5UggB381QU7ZCgqWivUmy4D",
    "attributes": "pPYmqDvwwWBDPNykXVrBtKdsJDeZUGFA...tTERiLqsZ5oxCoCSodPQaggkDJy",
    "signature": "8eGWSiTiWtEA8WnBwX4T259STpxpRKuk...kpFnikqqSP3GMW7mVxC4chxFhVs",
    "signatureCorrectnessProof": "SNQbW3u1QV5q89qhxA1xyVqFa6jCrKwv...dsRypyuGGK3RhhBUvH1tPEL8orH"
  }
}

The example above provides the verifiable credential definition by using the credentialSchema property and a specific proof that is usable in the Camenisch-Lysyanskaya Zero-Knowledge Proof system.

The next example utilizes the verifiable credential above to generate a new derived verifiable credential with a privacy-preserving proof. The derived verifiable credential is then placed in a verifiable presentation, so that the verifiable credential discloses only the claims and additional credential metadata that the holder intended. To do this, all of the following requirements are expected to be met:

Example 30: A verifiable presentation that supports CL Signatures
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "type": "VerifiablePresentation",
  "verifiableCredential": [
    {
      "@context": [
        "https://www.w3.org/ns/credentials/v2",
        "https://www.w3.org/ns/credentials/examples/v2"
      ],
      "type": ["VerifiableCredential", "ExampleDegreeCredential"],
      "credentialSchema": {
        "id": "did:example:cdf:35LB7w9ueWbagPL94T9bMLtyXDj9pX5o",
        "type": "did:example:schema:22KpkXgecryx9k7N6XN1QoN3gXwBkSU8SfyyYQG"
      },
      "issuer": "did:example:Wz4eUg7SetGfaUVCn8U9d62oDYrUJLuUtcy619",
      "credentialSubject": {
        "degreeType": "ExampleBachelorDegree",
        "degreeSchool": "College of Engineering"
      },
      "proof": {
        "type": "AnonCredDerivedCredentialv1",
        "primaryProof": "cg7wLNSi48K5qNyAVMwdYqVHSMv1Ur8i...Fg2ZvWF6zGvcSAsym2sgSk737",
        "nonRevocationProof": "mu6fg24MfJPU1HvSXsf3ybzKARib4WxG...RSce53M6UwQCxYshCuS3d2h"
      }
  }],
  "proof": {
    "type": "AnonCredPresentationProofv1",
    "proofValue": "DgYdYMUYHURJLD7xdnWRinqWCEY5u5fK...j915Lt3hMzLHoPiPQ9sSVfRrs1D"
  }
}
Verifiable
            Credential 1 and Verifiable Credential 2 on the left map
            to Derived Credential 1 and Derived Credential 2 inside a
            Presentation on the right.  Verifiable Credential 1
            contains Context, Type, ID, Issuer, Issue Date, Expiration
            Date, CredentialSubject, and Proof, where
            CredentialSubject contains GivenName, FamilyName, and
            Birthdate and Proof contains Signature, Proof of
            Correctness, and Attributes.  Verifiable Credential 2
            contains Context, Type, ID, Issuer, Issue Date, Expiration
            Date, CredentialSubject, and Proof, where
            CredentialSubject contains University, which contains
            Department, which contains DegreeAwarded, and Proof contains Signature, Proof of
            Correctness, and Attributes.  The Presentation diagram on
            the right contains Context, Type, ID,
            VerifiableCredential, and Proof, where
            VerifiableCredential contains Derived Credential 1 and
            Derived Credential 2 and Proof contains Common Link
            Secret.  Derived Credential 1 contains Context, Type, ID,
            Issuer, Issue Date, CredentialSubject, and Proof, where
            CredentialSubject contains AgeOver18 and Proof contains
            Knowledge of Signature.  Derived Credential 2 contains
            Context, Type, ID, Issuer, Issue Date, CredentialSubject,
            and Proof, where CredentialSubject contains Degree and
            Proof contains Knowledge of Signature.  A line links
            Birthdate in Verifiable Credential 1 to AgeOver18 in
            Derived Credential 1.  A line links DegreeAwarded in
            Verifiable Credential 2 to Degree in Derived Credential 2.
Figure 11 A visual example of the relationship between credentials and derived credentials in a ZKP presentation.
Note

Important details regarding the format for the credential definition and of the proofs are omitted on purpose because they are outside of the scope of this document. The purpose of this section is to guide implementers who want to extend verifiable credentials and verifiable presentations to support zero-knowledge proof systems.

5.9 Authorization

This section is non-normative.

Verifiable credentials are intended as a means of reliably identifying subjects. While it is recognized that Role Based Access Controls (RBACs) and Attribute Based Access Controls (ABACs) rely on this identification as a means of authorizing subjects to access resources, this specification does not provide a complete solution for RBAC or ABAC. Authorization is not an appropriate use for this specification without an accompanying authorization framework.

The Working Group did consider authorization use cases during the creation of this specification and is pursuing that work as an architectural layer built on top of this specification.

5.10 Reserved Extension Points

This specification reserves a number of properties to serve as possible extension points. While some implementers signaled interest in these properties, their inclusion in this specification was considered to be premature; these extension points might be more formally defined in future versions of this specification. It is important to note that these properties are not defined by this specification and implementers are cautioned that usage of these properties is considered experimental.

Implementers MAY use these properties, but SHOULD expect them and/or their meanings to change during the process to normatively specify them. Implementers SHOULD NOT use these properties without a publicly disclosed specification describing their implementation.

In order to avoid collisions regarding how the following properties are used, implementations MUST specify a type property in the value associated with the reserved property. For more information related to adding type information, see Section 4.4 Types.

Issue: Extension points under consideration by the Working Group

The working group is discussing if additional extension points will be reserved in https://www.w3.org/ns/credentials/v2.
The working group currently plans to only reserve extension points that have at least a draft specification that is being incubated in a community group.

Reserved Property Description
evidence A property used for specifying the evidence that was presented in order to issue the credential. The associated vocabulary URL MUST be https://www.w3.org/2018/credentials#evidence.
Issue: (AT RISK) Reservation depends on implementations

This property reservation might be deleted in favor of an existing section in the specification if at least one specification with two independent implementations are demonstrated by the end of the Candidate Recommendation Phase. If that does not occur, this reservation will remain, but the existing section in the specification will be removed.

refreshService A property used for specifying how a credential can be refreshed. The associated vocabulary URL MUST be https://www.w3.org/2018/credentials#refreshService.
Issue: (AT RISK) Reservation depends on implementations

This property reservation might be deleted in favor of an existing section in the specification if at least one specification with two independent implementations are demonstrated by the end of the Candidate Recommendation Phase. If that does not occur, this reservation will remain, but the existing section in the specification will be removed.

renderMethod A property used for specifying how to render a credential into a visual, auditory, or haptic format. The associated vocabulary URL MUST be https://www.w3.org/2018/credentials#renderMethod.
Issue: (AT RISK) Reservation depends on implementations

This reserved property is at risk and will be removed from the specification if at least one specification with two independent implementations are not demonstrated by the end of the Candidate Recommendation Phase.

termsOfUse A property used for specifying the terms of use for a credential. The associated vocabulary URL MUST be https://www.w3.org/2018/credentials#termsOfUse.
Issue: (AT RISK) Reservation depends on implementations

This property reservation might be deleted in favor of an existing section in the specification if at least one specification with two independent implementations are demonstrated by the end of the Candidate Recommendation Phase. If that does not occur, this reservation will remain, but the existing section in the specification will be removed.

An unofficial list of specifications that are associated with the extension points defined in this specification, as well as the reserved extension points defined in this section, can be found in the Verifiable Credentials Specifications Directory [VC-SPECS]. Items in the directory that refer to reserved extension points SHOULD be treated as experimental.

6. Syntaxes

The data model as described in Sections 3. Core Data Model, 4. Basic Concepts, and 5. Advanced Concepts is the canonical structural representation of a verifiable credential or verifiable presentation. All serializations are representations of that data model in a specific format. This section specifies how the data model is realized in JSON-LD for application/vc+ld+json, the base media type for Verifiable Credentials. Although syntactic mappings are only provided for JSON-LD, applications and services can use any other data representation syntax (such as XML, YAML, or CBOR) that is capable of being mapped back to application/vc+ld+json. As the verification and validation requirements are defined in terms of the data model, all serialization syntaxes have to be deterministically translated to the data model for processing, validation, or comparison.

The expected arity of the property values in this specification, and the resulting datatype which holds those values, can vary depending on the property. If present, the following properties are represented as a single value:

All other properties, if present, are represented as either a single value or an array of values.

6.1 JSON-LD

[JSON-LD] is a JSON-based format used to serialize Linked Data. The syntax is designed to easily integrate into deployed systems already using JSON, and provides a smooth upgrade path from JSON to [JSON-LD]. It is primarily intended to be a way to use Linked Data in Web-based programming environments, to build interoperable Web services, and to store Linked Data in JSON-based storage engines.

[JSON-LD] is useful when extending the data model described in this specification. Instances of the data model are encoded in JSON-LD compact form [JSON-LD] and include the @context property. The JSON-LD context is described in detail in the [JSON-LD] specification and its use is elaborated on in Section 5.3 Extensibility.

Multiple contexts MAY be used or combined to express any arbitrary information about verifiable credentials in idiomatic JSON. The JSON-LD context, available at https://www.w3.org/ns/credentials/v2, is a static document that is never updated and can therefore be downloaded and cached client side. The associated vocabulary document for the Verifiable Credentials Data Model is available at https://www.w3.org/2018/credentials.

This specification restricts the usage of JSON-LD representations of the data model. JSON-LD compact document form MUST be utilized for all representations of the data model in the base media type, application/vc+ld+json.

6.1.1 Syntactic Sugar

In general, the data model and syntaxes described in this document are designed such that developers can copy and paste examples to incorporate verifiable credentials into their software systems. The design goal of this approach is to provide a low barrier to entry while still ensuring global interoperability between a heterogeneous set of software systems. This section describes some of these approaches, which will likely go unnoticed by most developers, but whose details will be of interest to implementers. The most noteworthy syntactic sugars provided by [JSON-LD] are:

  • The @id and @type keywords are aliased to id and type respectively, enabling developers to use this specification as idiomatic JSON.
  • Data types, such as integers, dates, units of measure, and URLs, are automatically typed to provide stronger type guarantees for use cases that require them.
  • The verifiableCredential and proof properties are treated as graph containers. That is, mechanisms used to isolate sets of data asserted by different entities. This ensures, for example, proper cryptographic separation between the data graph provided by each issuer and the one provided by the holder presenting the verifiable credential to ensure the provenance of the information for each graph is preserved.
  • The @protected properties feature of [JSON-LD] 1.1 is used to ensure that terms defined by this specification cannot be overridden. This means that as long as the same @context declaration is made at the top of a verifiable credential or verifiable presentation, interoperability is guaranteed for all terms understood by users of the data model whether or not they use a [JSON-LD] processor.

6.2 Media Types

Media types, as defined in [RFC6838], identify the syntax used to express a verifiable credential as well as other useful processing guidelines.

Syntaxes used to express the data model in this specification SHOULD be identified by a media type, and conventions outlined in this section SHOULD be followed when defining or using media types with verifiable credentials.

There are two media types associated with the core data model, which are listed in the Section C. IANA Considerations: application/vc+ld+json and application/vp+ld+json.

The application/vc+ld+json and application/vp+ld+json media types do not imply any particular securing mechanism, but are intended to be used in conjunction with securing mechanisms. A securing mechanism needs to be applied to protect the integrity of these media types. Do not assume security of content regardless of the media type used to communicate it.

6.2.1 Media Type Precision

This section is non-normative.

At times, developers or systems might use lower precision media types to convey verifiable credentials or verifiable presentations. Some of the reasons for use of lower precision media types include:

  • A web server defaults to text/plain or application/octet-stream when a file extension is not available and it cannot determine the media type.
  • A developer adds a file extension that leads to a media type that is less specific than the content of the file. For example, .json could result in a media type of application/json and .jsonld might result in a media type of application/ld+json.
  • A protocol requires a less precise media type for a particular transaction; for example, application/json instead of application/vp+ld+json,

Implementers are urged to not raise errors when it is possible to determine the intended media type from a payload, provided that the media type used is acceptable in the given protocol. For example, if an application only accepts payloads that conform to the rules associated with the application/vc+ld+json media type, but the payload is tagged with application/json or application/ld+json instead, the application might perform the following steps to determine whether the payload also conforms to the higher precision media type:

  1. Parse the payload as a JSON document.
  2. Ensure that the first element of the @context field matches https://www.w3.org/2018/credentials/v2.
  3. Assume an application/vp+ld+json media type if the JSON document contains a top-level type field containing a VerifiablePresentation element. Additional subsequent checks are still expected to be performed (according to this specification) to ensure the payload expresses a conformant Verifiable Presentation.
  4. Assume an application/vc+ld+json media type if the JSON document contains a top-level type field containing a VerifiableCredential element. Additional subsequent checks are still expected to be performed (according to this specification) to ensure the payload expresses a conformant Verifiable Credential.

Whenever possible, implementers are advised to use the most precise (the highest precision) media type for all payloads defined by this specification. Implementers are also advised to recognize that a payload tagged with a lower precision media type does not mean that the payload does not meet the rules necessary to tag it with a higher precision type. Similarly, a payload tagged with a higher precision media type does not mean that the payload will meet the requirements associated with the media type. Receivers of payloads, regardless of their associated media type, are expected to perform appropriate checks to ensure that payloads conform with the requirements for their use in a given system.

6.3 Proof Formats

The data model described in this specification is designed to be proof format agnostic. This specification does not normatively require any particular digital proof or signature format. While the data model is the canonical representation of a credential or presentation, the proofing mechanisms for these are often tied to the syntax used in the transmission of the document between parties. As such, each proofing mechanism has to specify whether the verification of the proof is calculated against the state of the document as transmitted, against the possibly transformed data model, or against another form. At the time of publication, at least two proof formats are being actively utilized by implementers and the Working Group felt that documenting what these proof formats are and how they are being used would be beneficial to implementers. The sections detailing the current proof formats being actively utilized to issue verifiable credentials are:

7. Privacy Considerations

This section is non-normative.

This section details the general privacy considerations and specific privacy implications of deploying the Verifiable Credentials Data Model into production environments.

7.1 Spectrum of Privacy

This section is non-normative.

It is important to recognize there is a spectrum of privacy ranging from pseudonymous to strongly identified. Depending on the use case, people have different comfort levels about what information they are willing to provide and what information can be derived from what is provided.

Horizontal bar with
            red on the left, orange in the middle, and green on the
            right.  The red has the text 'Highly correlatable (global
            IDs), e.g., government ID, shipping address, credit card
            number'.  The orange has the text 'Correlatable via collusion
            (personally identifiable info), e.g., name, birthday, zip
            code'.  The green has the text 'Non-correlatable
            (pseudonyms), e.g., age over 21'.
Figure 12 Privacy spectrum ranging from pseudonymous to fully identified.

For example, most people probably want to remain anonymous when purchasing alcohol because the regulatory check required is solely based on whether a person is above a specific age. Alternatively, for medical prescriptions written by a doctor for a patient, the pharmacy fulfilling the prescription is required to more strongly identify the medical professional and the patient. Therefore there is not one approach to privacy that works for all use cases. Privacy solutions are use case specific.

Note

Even for those wanting to remain anonymous when purchasing alcohol, photo identification might still be required to provide appropriate assurance to the merchant. The merchant might not need to know your name or other details (other than that you are over a specific age), but in many cases just proof of age might still be insufficient to meet regulations.

The Verifiable Credentials Data Model strives to support the full privacy spectrum and does not take philosophical positions on the correct level of anonymity for any specific transaction. The following sections provide guidance for implementers who want to avoid specific scenarios that are hostile to privacy.

7.2 Personally Identifiable Information

This section is non-normative.

Data associated with verifiable credentials stored in the credential.credentialSubject field is susceptible to privacy violations when shared with verifiers. Personally identifying data, such as a government-issued identifier, shipping address, and full name, can be easily used to determine, track, and correlate an entity. Even information that does not seem personally identifiable, such as the combination of a birthdate and a postal code, has very powerful correlation and de-anonymizing capabilities.

Implementers are strongly advised to warn holders when they share data with these kinds of characteristics. Issuers are strongly advised to provide privacy-protecting verifiable credentials when possible. For example, issuing ageOver verifiable credentials instead of date of birth verifiable credentials when a verifier wants to determine if an entity is over the age of 18.

Because a verifiable credential often contains personally identifiable information (PII), implementers are strongly advised to use mechanisms while storing and transporting verifiable credentials that protect the data from those who should not access it. Mechanisms that could be considered include Transport Layer Security (TLS) or other means of encrypting the data while in transit, as well as encryption or data access control mechanisms to protect the data in a verifiable credential while at rest.

7.3 Identifier-Based Correlation

This section is non-normative.

Subjects of verifiable credentials are identified using the credential.credentialSubject.id field. The identifiers used to identify a subject create a greater risk of correlation when the identifiers are long-lived or used across more than one web domain.

Similarly, disclosing the credential identifier (credential.id) leads to situations where multiple verifiers, or an issuer and a verifier, can collude to correlate the holder. If holders want to reduce correlation, they should use verifiable credential schemes that allow hiding the identifier during verifiable presentation. Such schemes expect the holder to generate the identifier and might even allow hiding the identifier from the issuer, while still keeping the identifier embedded and signed in the verifiable credential.

If strong anti-correlation properties are a requirement in a verifiable credentials system, it is strongly advised that identifiers are either:

7.4 Signature-Based Correlation

This section is non-normative.

The contents of verifiable credentials are secured using the credential.proof field. The properties in this field create a greater risk of correlation when the same values are used across more than one session or domain and the value does not change. Examples include the verificationMethod, created, proofPurpose, and jws fields.

If strong anti-correlation properties are required, it is advised that signature values and metadata are regenerated each time using technologies like third-party pairwise signatures, zero-knowledge proofs, or group signatures.

Note

Even when using anti-correlation signatures, information might still be contained in a verifiable credential that defeats the anti-correlation properties of the cryptography used.

7.5 Long-Lived Identifier-Based Correlation

This section is non-normative.

Verifiable credentials might contain long-lived identifiers that could be used to correlate individuals. These types of identifiers include subject identifiers, email addresses, government-issued identifiers, organization-issued identifiers, addresses, healthcare vitals, verifiable credential-specific JSON-LD contexts, and many other sorts of long-lived identifiers.

Organizations providing software to holders should strive to identify fields in verifiable credentials containing information that could be used to correlate individuals and warn holders when this information is shared.

7.6 Device Fingerprinting

This section is non-normative.

There are mechanisms external to verifiable credentials that are used to track and correlate individuals on the Internet and the Web. Some of these mechanisms include Internet protocol (IP) address tracking, web browser fingerprinting, evercookies, advertising network trackers, mobile network position information, and in-application Global Positioning System (GPS) APIs. Using verifiable credentials cannot prevent the use of these other tracking technologies. Also, when these technologies are used in conjunction with verifiable credentials, new correlatable information could be discovered. For example, a birthday coupled with a GPS position can be used to strongly correlate an individual across multiple websites.

It is recommended that privacy-respecting systems prevent the use of these other tracking technologies when verifiable credentials are being used. In some cases, tracking technologies might need to be disabled on devices that transmit verifiable credentials on behalf of a holder.

7.7 Favor Abstract Claims

This section is non-normative.

To enable recipients of verifiable credentials to use them in a variety of circumstances without revealing more PII than necessary for transactions, issuers should consider limiting the information published in a credential to a minimal set needed for the expected purposes. One way to avoid placing PII in a credential is to use an abstract property that meets the needs of verifiers without providing specific information about a subject.

For example, this document uses the ageOver property instead of a specific birthdate, which constitutes much stronger PII. If retailers in a specific market commonly require purchasers to be older than a certain age, an issuer trusted in that market might choose to offer a verifiable credential claiming that subjects have met that requirement instead of offering verifiable credentials containing claims about specific birthdates. This enables individual customers to make purchases without revealing specific PII.

7.8 The Principle of Data Minimization

This section is non-normative.

Privacy violations occur when information divulged in one context leaks into another. Accepted best practice for preventing such violations is to limit the information requested, and received, to the absolute minimum necessary. This data minimization approach is required by regulation in multiple jurisdictions, including the Health Insurance Portability and Accountability Act (HIPAA) in the United States and the General Data Protection Regulation (GDPR) in the European Union.

With verifiable credentials, data minimization for issuers means limiting the content of a verifiable credential to the minimum required by potential verifiers for expected use. For verifiers, data minimization means limiting the scope of the information requested or required for accessing services.

For example, a driver's license containing a driver's ID number, height, weight, birthday, and home address is a credential containing more information than is necessary to establish that the person is above a certain age.

It is considered best practice for issuers to atomize information or use a signature scheme that allows for selective disclosure. For example, an issuer of driver's licenses could issue a verifiable credential containing every attribute that appears on a driver's license, as well as a set of verifiable credentials where every verifiable credential contains only a single attribute, such as a person's birthday. It could also issue more abstract verifiable credentials (for example, a verifiable credential containing only an ageOver attribute). One possible adaptation would be for issuers to provide secure HTTP endpoints for retrieving single-use bearer credentials that promote the pseudonymous usage of verifiable credentials. Implementers that find this impractical or unsafe, should consider using selective disclosure schemes that eliminate dependence on issuers at proving time and reduce temporal correlation risk from issuers.

Verifiers are urged to only request information that is absolutely necessary for a specific transaction to occur. This is important for at least two reasons. It:

Note

While it is possible to practice the principle of minimum disclosure, it might be impossible to avoid the strong identification of an individual for specific use cases during a single session or over multiple sessions. The authors of this document cannot stress how difficult it is to meet this principle in real-world scenarios.

7.9 Bearer Credentials

This section is non-normative.

A bearer credential is a privacy-enhancing piece of information, such as a concert ticket, which entitles the holder of the bearer credential to a specific resource without divulging sensitive information about the holder. Bearer credentials are often used in low-risk use cases where the sharing of the bearer credential is not a concern or would not result in large economic or reputational losses.

Verifiable credentials that are bearer credentials are made possible by not specifying the subject identifier, expressed using the id property, which is nested in the credentialSubject property. For example, the following verifiable credential is a bearer credential:

Example 31: Usage of issuer properties
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": "http://university.example/credentials/temporary/28934792387492384",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2017-10-22T12:23:48Z",
  "credentialSubject": {
    // note that the 'id' property is not specified for bearer credentials
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}

While bearer credentials can be privacy-enhancing, they must be carefully crafted so as not accidentally divulge more information than the holder of the bearer credential expects. For example, repeated use of the same bearer credential across multiple sites enables these sites to potentially collude to unduly track or correlate the holder. Likewise, information that might seem non-identifying, such as a birthdate and postal code, can be used to statistically identify an individual when used together in the same bearer credential or session.

Issuers of bearer credentials should ensure that the bearer credentials provide privacy-enhancing benefits that:

Holders should be warned by their software if bearer credentials containing sensitive information are issued or requested, or if there is a correlation risk when combining two or more bearer credentials across one or more sessions. While it might be impossible to detect all correlation risks, some might certainly be detectable.

Verifiers should not request bearer credentials that can be used to unduly correlate the holder.

7.10 Validity Checks

This section is non-normative.

When processing verifiable credentials, verifiers are expected to perform many of the checks listed in Appendix A. Validation as well as a variety of specific business process checks. Validity checks might include checking:

The process of performing these checks might result in information leakage that leads to a privacy violation of the holder. For example, a simple operation such as checking a revocation list can notify the issuer that a specific business is likely interacting with the holder. This could enable issuers to collude and correlate individuals without their knowledge.

Issuers are urged to not use mechanisms, such as credential revocation lists that are unique per credential, during the verification process that could lead to privacy violations. Organizations providing software to holders should warn when credentials include information that could lead to privacy violations during the verification process. Verifiers should consider rejecting credentials that produce privacy violations or that enable bad privacy practices.

7.11 Storage Providers and Data Mining

This section is non-normative.

When a holder receives a verifiable credential from an issuer, the verifiable credential needs to be stored somewhere (for example, in a credential repository). Holders are warned that the information in a verifiable credential is sensitive in nature and highly individualized, making it a high value target for data mining. Services that advertise free storage of verifiable credentials might in fact be mining personal data and selling it to organizations wanting to build individualized profiles on people and organizations.

Holders need to be aware of the terms of service for their credential repository, specifically the correlation and data mining protections in place for those who store their verifiable credentials with the service provider.

Some effective mitigations for data mining and profiling include using:

7.12 Aggregation of Credentials

This section is non-normative.

Holding two pieces of information about the same subject almost always reveals more about the subject than just the sum of the two pieces, even when the information is delivered through different channels. The aggregation of verifiable credentials is a privacy risk and all participants in the ecosystem need to be aware of the risks of data aggregation.

For example, if two bearer credentials, one for an email address and then one stating the holder is over the age of 21, are provided across multiple sessions, the verifier of the information now has a unique identifier as well as age-related information for that individual. It is now easy to create and build a profile for the holder such that more and more information is leaked over time. Aggregation of credentials can also be performed across multiple sites in collusion with each other, leading to privacy violations.

From a technological perspective, preventing aggregation of information is a very difficult privacy problem to address. While new cryptographic techniques, such as zero-knowledge proofs, are being proposed as solutions to the problem of aggregation and correlation, the existence of long-lived identifiers and browser tracking techniques defeats even the most modern cryptographic techniques.

The solution to the privacy implications of correlation or aggregation tends not to be technological in nature, but policy driven instead. Therefore, if a holder does not want information about them to be aggregated, they must express this in the verifiable presentations they transmit.

7.13 Usage Patterns

This section is non-normative.

Despite the best efforts to assure privacy, actually using verifiable credentials can potentially lead to de-anonymization and a loss of privacy. This correlation can occur when:

In part, it is possible to mitigate this de-anonymization and loss of privacy by:

It is understood that these mitigation techniques are not always practical or even compatible with necessary usage. Sometimes correlation is a requirement.

For example, in some prescription drug monitoring programs, usage monitoring is a requirement. Enforcement entities need to be able to confirm that individuals are not cheating the system to get multiple prescriptions for controlled substances. This statutory or regulatory need to correlate usage overrides individual privacy concerns.

Verifiable credentials will also be used to intentionally correlate individuals across services, for example, when using a common persona to log in to multiple services, so all activity on each of those services is intentionally linked to the same individual. This is not a privacy issue as long as each of those services uses the correlation in the expected manner.

Privacy risks of credential usage occur when unintended or unexpected correlation arises from the presentation of credentials.

7.14 Sharing Information with the Wrong Party

This section is non-normative.

When a holder chooses to share information with a verifier, it might be the case that the verifier is acting in bad faith and requests information that could be used to harm the holder. For example, a verifier might ask for a bank account number, which could then be used with other information to defraud the holder or the bank.

Issuers should strive to tokenize as much information as possible such that if a holder accidentally transmits credentials to the wrong verifier, the situation is not catastrophic.

For example, instead of including a bank account number for the purpose of checking an individual's bank balance, provide a token that enables the verifier to check if the balance is above a certain amount. In this case, the bank could issue a verifiable credential containing a balance checking token to a holder. The holder would then include the verifiable credential in a verifiable presentation and bind the token to a credit checking agency using a digital signature. The verifier could then wrap the verifiable presentation in their digital signature, and hand it back to the issuer to dynamically check the account balance.

Using this approach, even if a holder shares the account balance token with the wrong party, an attacker cannot discover the bank account number, nor the exact value in the account. And given the validity period for the counter-signature, does not gain access to the token for more than a few minutes.

7.15 Frequency of Claim Issuance

This section is non-normative.

As detailed in Section 7.13 Usage Patterns, usage patterns can be correlated into certain types of behavior. Part of this correlation is mitigated when a holder uses a verifiable credential without the knowledge of the issuer. Issuers can defeat this protection however, by making their verifiable credentials short lived and renewal automatic.

For example, an ageOver verifiable credential is useful for gaining access to a bar. If an issuer issues such a verifiable credential with a very short validity period and an automatic renewal mechanism, then the issuer could possibly correlate the behavior of the holder in a way that negatively impacts the holder.

Organizations providing software to holders should warn them if they repeatedly use credentials with short lifespans, which could result in behavior correlation. Issuers should avoid issuing credentials in a way that enables them to correlate usage patterns.

7.16 Prefer Single-Use Credentials

This section is non-normative.

An ideal privacy-respecting system would require only the information necessary for interaction with the verifier to be disclosed by the holder. The verifier would then record that the disclosure requirement was met and forget any sensitive information that was disclosed. In many cases, competing priorities, such as regulatory burden, prevent this ideal system from being employed. In other cases, long-lived identifiers prevent single use. The design of any verifiable credentials ecosystem, however, should strive to be as privacy-respecting as possible by preferring single-use verifiable credentials whenever possible.

Using single-use verifiable credentials provides several benefits. The first benefit is to verifiers who can be sure that the data in a verifiable credential is fresh. The second benefit is to holders, who know that if there are no long-lived identifiers in the verifiable credential, the verifiable credential itself cannot be used to track or correlate them online. Finally, there is nothing for attackers to steal, making the entire ecosystem safer to operate within.

7.17 Private Browsing

This section is non-normative.

In an ideal private browsing scenario, no PII will be revealed. Because many credentials include PII, organizations providing software to holders should warn them about the possibility of revealing this information if they wish to use credentials and presentations while in private browsing mode. As each browser vendor handles private browsing differently, and some browsers might not have this feature at all, it is important for implementers to be aware of these differences and implement solutions accordingly.

7.18 Issuer Cooperation Impacts on Privacy

This section is non-normative.

It cannot be overstated that verifiable credentials rely on a high degree of trust in issuers. The degree to which a holder might take advantage of possible privacy protections often depends strongly on the support an issuer provides for such features. In many cases, privacy protections which make use of zero-knowledge proofs, data minimization techniques, bearer credentials, abstract claims, and protections against signature-based correlation, require the issuer to actively support such capabilities and incorporate them into the verifiable credentials they issue.

It should also be noted that, in addition to a reliance on issuer participation to provide verifiable credential capabilities that help preserve holder and subject privacy, holders rely on issuers to not deliberately subvert privacy protections. For example, an issuer might sign verifiable credentials using a signature scheme that protects against signature-based correlation. This would protect the holder from being correlated by the signature value as it is shared among verifiers. However, if the issuer creates a unique key for each issued credential, it might be possible for the issuer to track presentations of the credential, regardless of a verifier's inability to do so.

8. Security Considerations

This section is non-normative.

There are a number of security considerations that issuers, holders, and verifiers 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.

While this section attempts to highlight a broad set of security considerations, it is not a complete list. Implementers are urged to seek the advice of security and cryptography professionals when implementing mission critical systems using the technology outlined in this specification.

8.1 Cryptography Suites and Libraries

This section is non-normative.

Some aspects of the data model described in this specification can be protected through the use of cryptography. It is important for implementers to understand the cryptography suites and libraries used to create and process credentials and presentations. Implementing and auditing cryptography systems generally requires substantial experience. Effective red teaming can also help remove bias from security reviews.

Cryptography suites and libraries have a shelf life and eventually fall to new attacks and technology advances. Production quality systems need to take this into account and ensure mechanisms exist to easily and proactively upgrade expired or broken cryptography suites and libraries, and to invalidate and replace existing credentials. Regular monitoring is important to ensure the long term viability of systems processing credentials.

8.2 Content Integrity Protection

This section is non-normative.

Verifiable credentials often contain URLs to data that resides outside of the verifiable credential itself. Linked content that exists outside a verifiable credential, such as images, JSON-LD Contexts, and other machine-readable data, are often not protected against tampering because the data resides outside of the protection of the proof on the verifiable credential. For example, the following highlighted links are not content-integrity protected but probably should be:

While this specification does not recommend any specific content integrity protection, document authors who want to ensure links to content are integrity protected are advised to use URL schemes that enforce content integrity. Two such schemes are the [HASHLINK] specification and the [IPFS]. The example below transforms the previous example and adds content integrity protection to the JSON-LD Contexts using the [HASHLINK] specification, and content integrity protection to the image by using an [IPFS] link.

Note

It is debatable whether the JSON-LD Contexts above need protection because production implementations are expected to ship with static copies of important JSON-LD Contexts.

While the example above is one way to achieve content integrity protection, there are other solutions that might be better suited for certain applications. Implementers are urged to understand how links to external machine-readable content that are not content-integrity protected could result in successful attacks against their applications.

8.3 Unsigned Claims

This section is non-normative.

This specification allows credentials to be produced that do not contain signatures or proofs of any kind. These types of credentials are often useful for intermediate storage, or self-asserted information, which is analogous to filling out a form on a web page. Implementers should be aware that these types of credentials are not verifiable because the authorship either is not known or cannot be trusted.

8.4 Token Binding

This section is non-normative.

A verifier might need to ensure it is the intended recipient of a verifiable presentation and not the target of a man-in-the-middle attack. Approaches such as token binding [RFC8471], which ties the request for a verifiable presentation to the response, can secure the protocol. Any unsecured protocol is susceptible to man-in-the-middle attacks.

8.5 Bundling Dependent Claims

This section is non-normative.

It is considered best practice for issuers to atomize information in a credential, or use a signature scheme that allows for selective disclosure. In the case of atomization, if it is not done securely by the issuer, the holder might bundle together different credentials in a way that was not intended by the issuer.

For example, a university might issue two verifiable credentials to a person, each containing two properties, which must be taken together to designate the "role" of that person in a given "department", such as "Staff Member" in the "Department of Computing", or "Post Graduate Student" in the "Department of Economics". If these verifiable credentials are atomized to put only one of these properties into each credential , then the university would issue four credentials to the person, each containing one of the following designations: "Staff Member", "Post Graduate Student", "Department of Computing", and "Department of Economics". The holder might then transfer the "Staff Member" and "Department of Economics" verifiable credentials to a verifier, which together would comprise a false claim.

8.6 Highly Dynamic Information

This section is non-normative.

When verifiable credentials are issued for highly dynamic information, implementers should ensure the validity periods are set appropriately. Validity periods longer than the timeframe where the verifiable credential is meant for use might create exploitable security vulnerabilities. Validity periods shorter than the timeframe where the information expressed by the verifiable credential is expected to be used creates a burden on holders and verifiers. It is therefore important to set validity periods for verifiable credentials that are appropriate to the use case and the expected lifetime for the information contained in the verifiable credential.

8.7 Device Theft and Impersonation

This section is non-normative.

When verifiable credentials are stored on a device and that device is lost or stolen, it might be possible for an attacker to gain access to systems using the victim's verifiable credentials. Ways to mitigate this type of attack include:

9. 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 implementation of any web standard or protocol, ignoring accessibility issues makes this information unusable by a large subset of the population. It is important to follow accessibility guidelines and standards, such as [WCAG21], to ensure that 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.

This section details the general accessibility considerations to take into account when utilizing this data model.

9.1 Data First Approaches

This section is non-normative.

Many physical credentials in use today, such as government identification cards, have poor accessibility characteristics, including, but not limited to, small print, reliance on small and high-resolution images, and no affordances for people with vision impairments.

When utilizing this data model to create verifiable credentials, it is suggested that data model designers use a data first approach. For example, given the choice of using data or a graphical image to depict a credential, designers should express every element of the image, such as the name of an institution or the professional credential, in a machine-readable way instead of relying on a viewer's interpretation of the image to convey this information. Using a data first approach is preferred because it provides the foundational elements of building different interfaces for people with varying abilities.

10. Internationalization Considerations

This section is non-normative.

Implementers are advised to be aware of a number of internationalization considerations 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 limits the applicability of the specification and significantly diminishes its value as a standard.

Implementers are strongly advised to read the Strings on the Web: Language and Direction Metadata document [STRING-META], published by the W3C Internationalization Activity, which elaborates on the need to provide reliable metadata about text to support internationalization. For the latest information on internationalization considerations, implementers are also urged to read the Verifiable Credentials Implementation Guidelines [VC-IMP-GUIDE] document.

This section outlines general internationalization considerations to take into account when utilizing this data model and is intended to highlight specific parts of the Strings on the Web: Language and Direction Metadata document [STRING-META] that implementers might be interested in reading.

10.1 Language and Base Direction

This section is non-normative.

Data publishers are strongly encouraged to read the section on Cross-Syntax Expression in the Strings on the Web: Language and Direction Metadata document [STRING-META] to ensure that the expression of language and base direction information is possible across multiple expression syntaxes, such as [JSON-LD], [JSON], and CBOR [RFC7049].

The general design pattern is to use the following markup template when expressing a text string that is tagged with a language and, optionally, a specific base direction.

Example 34: Design pattern for natural language strings
"property": {
  "value": "The string value",
  "lang": "LANGUAGE"
  "dir": "DIRECTION"
}

Using the design pattern above, the following example expresses the title of a book in the English language without specifying a text direction.

Example 35: Expressing natural language text as English
"title": {
  "value": "HTML and CSS: Designing and Creating Websites",
  "lang": "en"
}

The next example uses a similar title expressed in the Arabic language with a base direction of right-to-left.

Example 36: Arabic text with a base direction of right-to-left
"title": {
  "value": "HTML و CSS: تصميم و إنشاء مواقع الويب",
  "lang": "ar"
  "dir": "rtl"
}
Note

The text above would most likely be rendered incorrectly as left-to-right without the explicit expression of language and direction because many systems use the first character of a text string to determine text direction.

Implementers utilizing JSON-LD are strongly urged to extend the JSON-LD Context defining the internationalized property and use the Scoped Context feature of JSON-LD to alias the @value, @language, and @direction keywords to value, lang, and dir, respectively. An example of a JSON-LD Context snippet doing this is shown below.

Example 37: Specifying scoped aliasing for language information
"title": {
  "@context": {"value": "@value", "lang": "@language", "dir": "@direction"},
  "@id": "https://www.w3.org/2018/credentials/examples#title"
}

10.2 Complex Language Markup

This section is non-normative.

When multiple languages, base directions, and annotations are used in a single natural language string, more complex mechanisms are typically required. It is possible to use markup languages, such as HTML, to encode text with multiple languages and base directions. It is also possible to use the rdf:HTML datatype to encode such values accurately in JSON-LD.

Despite the ability to encode information as HTML, implementers are strongly discouraged from doing this because it:

If implementers feel they must use HTML, or other markup languages capable of containing executable scripts, to address a specific use case, they are advised to analyze how an attacker would use the markup to mount injection attacks against a consumer of the markup and then deploy mitigations against the identified attacks.

A. Validation

This section is non-normative.

While this specification does not provide conformance criteria for the process of the validation of verifiable credentials or verifiable presentations, readers might be curious about how the information in this data model is expected to be utilized by verifiers during the process of validation. This section captures a selection of conversations held by the Working Group related to the expected usage of the data fields in this specification by verifiers.

A.1 Credential Type

This section is non-normative.

When a verifier requests one or more verifiable credentials from a holder, they can specify the type of credential(s) that they would like to receive. The type of a credential is expressed via the type property. A verifiable credential of a specific type is expected to contain specific properties that can be used to determine whether or not the presentation meets a set of processing rules that the verifier is executing. By requesting verifiable credentials of a particular type, the verifier is able to gather specific information from the holder, which originated with the issuer of each verifiable credential, that will enable it to determine the next stage of an interaction with a holder.

A.2 Credential Subject

This section is non-normative.

In the verifiable credentials presented by a holder, the value associated with the id property for each credentialSubject is expected to identify a subject to the verifier. If the holder is also the subject, then the verifier could authenticate the holder if they have public key metadata related to the holder. The verifier could then authenticate the holder using a signature generated by the holder contained in the verifiable presentation. The id property is optional. Verifiers could use other properties in a verifiable credential to uniquely identify a subject.

Note

For information on how authentication and WebAuthn might work with verifiable credentials, see the Verifiable Credentials Implementation Guidelines [VC-IMP-GUIDE] document.

A.3 Issuer

This section is non-normative.

The value associated with the issuer property is expected to identify an issuer that is known to and trusted by the verifier.

Relevant metadata about the issuer property is expected to be available to the verifier. For example, an issuer can publish information containing the public keys it uses to digitally sign verifiable credentials that it issued. This metadata is relevant when checking the proofs on the verifiable credentials.

A.4 Issuance Date

This section is non-normative.

The validFrom is expected to be within an expected range for the verifier. For example, a verifier can check that the start of the validity period for a verifiable credential is not in the future.

A.5 Proofs (Signatures)

This section is non-normative.

The cryptographic mechanism used to prove that the information in a verifiable credential or verifiable presentation was not tampered with is called a proof. There are many types of cryptographic proofs including, but not limited to, digital signatures and zero-knowledge proofs. In general, when verifying proofs, implementations are expected to ensure:

Some proofs are digital signatures. In general, when verifying digital signatures, implementations are expected to ensure:

Note

The digital signature provides a number of protections, other than tamper resistance, which are not immediately obvious. For example, a Linked Data Signature created property establishes a date and time before which the credential should not be considered verified. The verificationMethod property specifies, for example, the public key that can be used to verify the digital signature. Dereferencing a public key URL reveals information about the controller of the key, which can be checked against the issuer of the credential. The proofPurpose property clearly expresses the purpose for the proof and ensures this information is protected by the signature. A proof is typically attached to a verifiable presentation for authentication purposes and to a verifiable credential as a method of assertion.

A.6 Validity Periods

This section is non-normative.

The validFrom and validUntil properties are expected to be within an expected range for the verifier. For example, a verifier can check that the end of the validity period of a verifiable credential is not in the past.

A.7 Status

This section is non-normative.

If the credentialStatus property is available, the status of a verifiable credential is expected to be evaluated by the verifier according to the credentialStatus type definition for the verifiable credential and the verifier's own status evaluation criteria. For example, a verifier can ensure the status of the verifiable credential is not "withdrawn for cause by the issuer".

A.8 Schema

This section is non-normative.

If the credentialSchema property is available, the schema of a verifiable credential is expected to be evaluated by the verifier according to the credentialSchema type definition for the verifiable credential and the verifier's own schema evaluation criteria. For example, if the credentialSchema's type value is [VC-JSON-SCHEMA-2023], then a verifier can ensure a credential's data is valid against the given JSON Schema.

A.9 Fitness for Purpose

This section is non-normative.

Fitness for purpose is about whether the custom properties in the verifiable credential are appropriate for the verifier's purpose. For example, if a verifier needs to determine whether a subject is older than 21 years of age, they might rely on a specific birthdate property, or on more abstract properties, such as ageOver.

The issuer is trusted by the verifier to make the claims at hand. For example, a franchised fast food restaurant location trusts the discount coupon claims made by the corporate headquarters of the franchise. Policy information expressed by the issuer in the verifiable credential should be respected by holders and verifiers unless they accept the liability of ignoring the policy.

B. Contexts, Vocabularies, Types, and Credential Schemas

This section is non-normative.

B.1 Base Context

Issue: (AT RISK) Hash values might change during Candidate Recommendation

This section lists cryptographic hash values that might change during the Candidate Recommendation phase based on implementer feedback that requires the referenced files to be modified.

Implementations MUST ensure that the base context value, located at https://www.w3.org/ns/credentials/v2, matches the following SHA-384 digest of the value computed and encoded according to the [SRI] definition of digest: lHKDHh0msc6pRx8PhDOMkNtSI8bOfsp4giNbUrw71nXXLf13nTqNJoRp3Nx+ArVK. The base context value matching the digest previously stated can be used to implement a local cached copy. It is possible to confirm the SHA-384 digest by running the following command from a modern Unix command interface line: curl -s https://www.w3.org/ns/credentials/v2 | openssl dgst -sha384 -binary | openssl base64 -A.

Issue 1177: Provide guidance for when hash values do not match specification text before-CR

The Working Group is currently discussing what a processor should do if a hash value differs from one that is listed in the specification.

More details regarding this hash encoding method may be found in the integrity metadata section of [SRI]. It is strongly advised that all JSON-LD Contexts used in an application utilize a similar mechanism to ensure end-to-end security.

This section serves as a reminder of the importance of ensuring that, when verifying verifiable credentials and verifiable presentations, the verifier has information that is consistent with what the issuer or holder had when securing the credential or presentation. This information might include at least:

  1. The contents of the credential itself, which is secured in verifiable credentials and verifiable presentations by using mechanisms such as [VC-JWT] and [VC-DATA-INTEGRITY].
  2. The content in a credential whose meaning depends on a link to an external URL, such as a JSON-LD Context, which can be secured by using a local static copy, or a cryptographic digest of the file.

Verifiers are warned that other data that is referenced from within a credential, such as resources that are linked to via URLs, are not cryptographically protected by default. It is considered a best practice to ensure that the same sorts of protections are provided for any URL that is critical to the security of the credential through the use of permanently cached files and/or cryptographic hashes. See the Content Integrity section of the Verifiable Credential Implementation Guide for further information. Ultimately, knowing the cryptographic digest of any linked external content enables a verifier to confirm that the content is the same as what the issuer or holder intended.

B.2 Vocabularies

Issue: (AT RISK) URL values might change during Candidate Recommendation

This section lists URL values that might change during the Candidate Recommendation phase based on migration of documents to the W3C Technical Reports namespace and implementer feedback that requires the referenced URLs to be modified.

Implementations MUST ensure that the following vocabulary URLs used in the base context ultimately resolve to the following files, which are normative:

URL Media Type Content
https://www.w3.org/2018/credentials# text/html https://www.w3.org/2018/credentials/index.html
https://www.w3.org/2018/credentials# application/ld+json https://www.w3.org/2018/credentials/index.jsonld
https://schema.org/ text/html https://schema.org/
https://schema.org/ application/ld+json https://schema.org/version/latest/schemaorg-current-https.jsonld
https://w3id.org/security# text/html https://w3c.github.io/vc-data-integrity/vocab/security/vocabulary.html
https://w3id.org/security# application/ld+json https://w3c.github.io/vc-data-integrity/vocab/security/vocabulary.jsonld
Issue: w3c.github.io links expected to change

The URLs listed above that start with https://w3c.github.io/vc-data-integrity/vocab/security/ are expected to change to https://www.w3.org/ns/security/ or an equally normative and archived location under W3C control.

Issue: How to normatively refer to vocabulary files

The Working Group is currently discussing how it might want to normatively refer to the vocabulary files that are under the control of the Working Group. Current options are: inclusion of the files directly into the specification or publishing the files in W3C TR space and referring to them by using a cryptographic hash.

B.3 Differences between Contexts, Types, and CredentialSchemas

This section is non-normative.

The verifiable credential and verifiable presentation data models leverage a variety of underlying technologies including [JSON-LD] and [VC-JSON-SCHEMA-2023]. This section will provide a comparison of the @context, type, and credentialSchema properties, and cover some of the more specific use cases where it is possible to use these features of the data model.

The type property is used to uniquely identify the type of the verifiable credential in which it appears, i.e., to indicate which set of claims the verifiable credential contains. This property, and the value VerifiableCredential within the set of its values, are mandatory. Whilst it is good practice to include one additional value depicting the unique subtype of this verifiable credential, it is permitted to either omit or include additional type values in the array. Many verifiers will request a verifiable credential of a specific subtype, then omitting the subtype value could make it more difficult for verifiers to inform the holder which verifiable credential they require. When a verifiable credential has multiple subtypes, listing all of them in the type property is sensible. The usage of the type property in a [JSON-LD] representation of a verifiable credential enables to enforce the semantics of the verifiable credential because the machine is able to check the semantics. With [JSON-LD], the technology is not only describing the categorization of the set of claims, the technology is also conveying the structure and semantics of the sub-graph of the properties in the graph. In [JSON-LD], this represents the type of the node in the graph which is why some [JSON-LD] representations of a verifiable credential will use the type property on many objects in the verifiable credential.

The primary purpose of the @context property, from a [JSON-LD] perspective, is to convey the meaning of the data and term definitions of the data in a verifiable credential, in a machine readable way. The @context property is used to map the globally unique URLs for properties in verifiable credentials and verifiable presentations into short-form alias names, making [JSON-LD] representations more human-friendly to read. From a [JSON-LD] perspective, this mapping also allows the data in a credential to be modeled in a network of machine-readable data, by enhancing how the data in the verifiable credential or verifiable presentation relates to a larger machine-readable data graph. This is useful for telling machines how to relate the meaning of data to other data in an ecosystem where parties are unable to coordinate. This property, with the first value in the set being https://www.w3.org/ns/credentials/v2, is mandatory.

Since the @context property is used to map data to a graph data model, and the type property in [JSON-LD] is used to describe nodes within the graph, the type property becomes even more important when using the two properties in combination. For example, if the type property is not included within the resolved @context resource using [JSON-LD], it could lead to claims being dropped and/or their integrity no longer being protected during production and consumption of the verifiable credential. Alternatively, it could lead to errors being raised during production or consumption of a verifiable credential. This will depend on the design choices of the implementation and both paths are used in implementations today, so it's important to pay attention to these properties when using a [JSON-LD] representation of a verifiable credential or verifiable presentation.

The primary purpose of the credentialSchema property is to define the structure of the verifiable credential, and the datatypes for the values of each property that appears. A credentialSchema is useful for defining the contents and structure of a set of claims in a verifiable credential, whereas [JSON-LD] and a @context in a verifiable credential are best used only for conveying the semantics and term definitions of the data, and can be used to define the structure of the verifiable credential as well.

While it is possible to use some [JSON-LD] features to allude to the contents of the verifiable credential, it's not generally suggested to use @context to constrain the data types of the data model. For example, "@type": "@json" is useful for leaving the semantics open-ended and not strictly defined. This can be dangerous if the implementer is looking to constrain the data type of the claims in the credential, and is expected not to be used.

When the credentialSchema and @context properties are used in combination, both producers and consumers can be more confident about the expected contents and data types of the verifiable credential and verifiable presentation.

C. IANA Considerations

This section is non-normative.

This section will be submitted to the Internet Engineering Steering Group (IESG) for review, approval, and registration with IANA.

C.1 application/vc+ld+json

This specification registers the application/vc+ld+json Media Type specifically for identifying documents conforming to the Verifiable Credentials format.

Type name: application
Subtype name: vc+ld+json
Required parameters: None
Encoding considerations: Resources that use the "application/vc+ld+json" Media Type are required to conform to all of the requirements for the "application/ld+json" Media Type and are therefore subject to the same encoding considerations specified in Section 11 of [RFC7159].
Security considerations: As defined in this specification.
Contact: W3C Verifiable Credentials Working Group public-vc-wg@w3.org

Note that while the Verifiable Credentials format uses JSON-LD conventions, there are a number of constraints and additional requirements for Verifiable Credential implementations that justify the use of a specific media type.

This media type can be used with credentials secured using an external proof.

A [JSON-LD] context is expected to be present in the body of the document, and as indicated by the presence of ld+json in the media type, the credential is expected to be a valid JSON-LD document.

C.2 application/vp+ld+json

This specification registers the application/vp+ld+json Media Type specifically for identifying documents conforming to the Verifiable Presentations format.

Type name: application
Subtype name: vp+ld+json
Required parameters: None
Encoding considerations: Resources that use the "application/vp+ld+json" Media Type are required to conform to all of the requirements for the "application/ld+json" Media Type and are therefore subject to the same encoding considerations specified in Section 11 of [RFC7159].
Security considerations: As defined in this specification.
Contact: W3C Verifiable Credentials Working Group public-vc-wg@w3.org

Note that while the Verifiable Credentials format uses JSON-LD conventions, there are a number of constraints and additional requirements for Verifiable Credential implementations that justify the use of a specific media type.

This media type can be used with presentations secured using an external proof.

A [JSON-LD] context is expected to be present in the body of the document, and as indicated by the presence of ld+json in the media type, the credential is expected to be a valid JSON-LD document.

D. Revision History

This section contains the substantive changes that have been made to this specification over time.

Changes since the v1.1 Recommendation:

Changes since the v1.0 Recommendation:

E. Acknowledgements

This section is non-normative.

The Working Group thanks the following individuals not only for their contributions toward the content of this document, but also for yeoman's work in this standards community that drove changes, discussion, and consensus among a sea of varied opinions: Matt Stone, Gregg Kellogg, Ted Thibodeau Jr, Oliver Terbu, Joe Andrieu, David I. Lehn, Matthew Collier, and Adrian Gropper.

Work on this specification has been supported by the Rebooting the Web of Trust community facilitated by Christopher Allen, Shannon Appelcline, Kiara Robles, Brian Weller, Betty Dhamers, Kaliya Young, Manu Sporny, Drummond Reed, Joe Andrieu, Heather Vescent, Kim Hamilton Duffy, Samantha Chase, and Andrew Hughes. The participants in the Internet Identity Workshop, facilitated by Phil Windley, Kaliya Young, Doc Searls, and Heidi Nobantu Saul, also supported the refinement of this work through numerous working sessions designed to educate about, debate on, and improve this specification.

The Working Group also thanks our Chairs, Dan Burnett, Matt Stone, Brent Zundel, Wayne Chang, and Kristina Yasuda as well as our W3C Staff Contacts, Kazuyuki Ashimura and Ivan Herman, for their expert management and steady guidance of the group through the W3C standardization process.

Portions of the work on this specification have been funded by the United States Department of Homeland Security's Science and Technology Directorate under contract HSHQDC-17-C-00019. The content of this specification does not necessarily reflect the position or the policy of the U.S. Government and no official endorsement should be inferred.

The Working Group would like to thank the following individuals for reviewing and providing feedback on the specification (in alphabetical order):

Christopher Allen, David Ammouial, Joe Andrieu, Bohdan Andriyiv, Ganesh Annan, Kazuyuki Ashimura, Tim Bouma, Pelle Braendgaard, Dan Brickley, Allen Brown, Jeff Burdges, Daniel Burnett, ckennedy422, David Chadwick, Chaoxinhu, Kim (Hamilton) Duffy, Lautaro Dragan, enuoCM, Ken Ebert, Eric Elliott, William Entriken, David Ezell, Nathan George, Reto Gmür, Ryan Grant, glauserr, Adrian Gropper, Joel Gustafson, Amy Guy, Lovesh Harchandani, Daniel Hardman, Dominique Hazael-Massieux, Jonathan Holt, David Hyland-Wood, Iso5786, Renato Iannella, Richard Ishida, Ian Jacobs, Anil John, Tom Jones, Rieks Joosten, Gregg Kellogg, Kevin, Eric Korb, David I. Lehn, Michael Lodder, Dave Longley, Christian Lundkvist, Jim Masloski, Pat McBennett, Adam C. Migus, Liam Missin, Alexander Mühle, Anthony Nadalin, Clare Nelson, Mircea Nistor, Grant Noble, Darrell O'Donnell, Nate Otto, Matt Peterson, Addison Phillips, Eric Prud'hommeaux, Liam Quin, Rajesh Rathnam, Drummond Reed, Yancy Ribbens, Justin Richer, Evstifeev Roman, RorschachRev, Steven Rowat, Pete Rowley, Markus Sabadello, Kristijan Sedlak, Tzviya Seigman, Reza Soltani, Manu Sporny, Orie Steele, Matt Stone, Oliver Terbu, Ted Thibodeau Jr, John Tibbetts, Mike Varley, Richard Varn, Heather Vescent, Christopher Lemmer Webber, Benjamin Young, Kaliya Young, Dmitri Zagidulin, and Brent Zundel.

F. References

F.1 Normative references

[JSON-LD]
JSON-LD 1.1: A JSON-based Serialization for Linked Data. Gregg Kellogg; Manu Sporny; Dave Longley; Markus Lanthaler; Pierre-Antoine Champin; Niklas Lindström. W3C JSON-LD 1.1 Working Group. W3C Working Draft. URL: https://www.w3.org/TR/json-ld11/
[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
[RFC6838]
Media Type Specifications and Registration Procedures. N. Freed; J. Klensin; T. Hansen. IETF. January 2013. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc6838
[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. Manu Sporny; Dave Longley; Mike Prorock. Verifiable Credentials Working Group. W3C Working Draft. URL: https://www.w3.org/TR/vc-data-integrity/
[vc-imp-guide]
Verifiable Credentials Implementation Guidelines 1.0. Andrei Sambra. W3C. 24 September 2019. W3C Working Group Note. URL: https://www.w3.org/TR/vc-imp-guide/
[VC-JWT]
Securing Verifiable Credentials using JSON Web Tokens. Orie Steele; Michael Jones. W3C Verifiable Credentials Working Group. W3C Editor's Draft. URL: https://w3c.github.io/vc-jwt/
[VC-SPECS]
Verifiable Credentials Specifications Directory. Manu Sporny. W3C Verifiable Credentials Working Group. W3C Editor's Draft. URL: https://w3c.github.io/vc-specs-dir/
[XMLSCHEMA11-2]
W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes. David Peterson; Sandy Gao; Ashok Malhotra; Michael Sperberg-McQueen; Henry Thompson; Paul V. Biron et al. W3C. 5 April 2012. W3C Recommendation. URL: https://www.w3.org/TR/xmlschema11-2/

F.2 Informative references

[CL-SIGNATURES]
A Signature Scheme with Efficient Protocols. Jan Camenisch; Anna Lysyanskaya. IBM Research. Peer Reviewed Paper. URL: https://www.researchgate.net/publication/220922101_A_Signature_Scheme_with_Efficient_Protocols
[DEMOGRAPHICS]
Simple Demographics Often Identify People Uniquely. Latanya Sweeney. Data Privacy Lab. URL: https://dataprivacylab.org/projects/identifiability/paper1.pdf
Cryptographic Hyperlinks. Manu Sporny. Internet Engineering Task Force (IETF). Internet-Draft. URL: https://datatracker.ietf.org/doc/draft-sporny-hashlink/
[IPFS]
InterPlanetary File System (IPFS). Wikipedia. URL: https://en.wikipedia.org/wiki/InterPlanetary_File_System
[JSON]
The JavaScript Object Notation (JSON) Data Interchange Format. T. Bray, Ed.. IETF. December 2017. Internet Standard. URL: https://www.rfc-editor.org/rfc/rfc8259
[LINKED-DATA]
Linked Data Design Issues. Tim Berners-Lee. W3C. 27 July 2006. W3C-Internal Document. URL: https://www.w3.org/DesignIssues/LinkedData.html
[PRES-EX]
Presentation Exchange 2.0.0. Daniel Buchner; Brent Zundel; Martin Riedel; Kim Hamilton Duffy. Decentralized Identity Foundation. DIF Ratified Specification. URL: https://identity.foundation/presentation-exchange/spec/v2.0.0/
[RFC7049]
Concise Binary Object Representation (CBOR). C. Bormann; P. Hoffman. IETF. October 2013. Proposed Standard. URL: https://www.rfc-editor.org/rfc/rfc7049
[RFC7159]
The JavaScript Object Notation (JSON) Data Interchange Format. T. Bray, Ed.. IETF. March 2014. Proposed Standard. URL: https://www.rfc-editor.org/rfc/rfc7159
[RFC8471]
The Token Binding Protocol Version 1.0. A. Popov, Ed.; M. Nystroem; D. Balfanz; J. Hodges. IETF. October 2018. Proposed Standard. URL: https://www.rfc-editor.org/rfc/rfc8471
[STRING-META]
Strings on the Web: Language and Direction Metadata. Addison Phillips; Richard Ishida. Internationalization Working Group. W3C Working Draft. URL: https://www.w3.org/TR/string-meta/
[VC-JSON-SCHEMA-2023]
Verifiable Credentials JSON Schema 2023. Gabe Cohen; Orie Steele. W3C Verifiable Credentials Working Group. FPWD. URL: https://www.w3.org/TR/vc-json-schema/
[VC-USE-CASES]
Verifiable Credentials Use Cases. Shane McCarron; Joe Andrieu; Matt Stone; Tzviya Siegman; Gregg Kellogg; Ted Thibodeau. W3C. 24 September 2019. W3C Working Group Note. URL: https://www.w3.org/TR/vc-use-cases/
[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/