Verifiable Credentials Data Model v2.0

W3C Candidate Recommendation Draft

More details about this document
This version:
https://www.w3.org/TR/2024/CRD-vc-data-model-2.0-20240505/
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
Implementation report:
https://w3c.github.io/vc-data-model-2.0-test-suite/
Editors:
Manu Sporny (Digital Bazaar) (v1.0, v1.1, v2.0)
Ted Thibodeau Jr (OpenLink Software) (v2.0)
Ivan Herman (W3C) (v2.0)
Michael B. Jones (Invited Expert) (v2.0)
Gabe Cohen (Block) (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)
Orie Steele (Transmute) (v2.0)
Oliver Terbu (Spruce Systems) (v2.0)
Authors:
Manu Sporny (Digital Bazaar)
Dave Longley (Digital Bazaar)
David Chadwick (Crossword Cybersecurity PLC)
Orie Steele (Transmute) (v2.0)
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/.

The Working Group is actively seeking implementation feedback for this specification. In order to exit the Candidate Recommendation phase, the Working Group has set the requirement of at least two independent implementations for each mandatory feature in the specification. Please see the implementation report for more details.

Comments regarding this specification are welcome at any time. Please file issues directly on GitHub, or, if that is not possible, send them to public-vc-comments@w3.org (subscribe, archives).

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

Publication as a Candidate Recommendation does not imply endorsement by W3C and its Members. A Candidate Recommendation Draft integrates changes from the previous Candidate Recommendation that the Working Group intends to include in a subsequent Candidate Recommendation Snapshot.

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 03 November 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:

The use cases and requirements that informed this specification can be found in Verifiable Credentials Use Cases [VC-USE-CASES].

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 8. 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 the truth of claims encoded therein. Rather, once the authenticity and currency of a verifiable credential or verifiable presentation are established, a verifier validates the included claims using their own business rules before relying on them. Such reliance only occurs after evaluating the issuer, the proof, the subject, and the claims, against one or more verifier policies.

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, verification material, and other relevant data, such as verifiable credential schemas, revocation registries, 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.

For a deeper exploration of the verifiable credentials ecosystem, along with a concrete lifecycle example, please refer to Verifiable Credentials Use Cases [VC-USE-CASES].

1.3 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, OPTIONAL, RECOMMENDED, REQUIRED, 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 a compacted JSON-LD document that complies with all of the relevant "MUST" statements in this specification. Specifically, the relevant normative "MUST" statements in Sections 4. Basic Concepts, 5. Advanced Concepts, and 6. Syntaxes of this document MUST be enforced. A conforming document is either a verifiable credential that MUST be serialized using the application/vc+ld+json media type or a verifiable presentation that MUST be serialized using the application/vp+ld+json media type. A conforming document MUST be secured by at least one securing mechanism as described in Section 4.9 Securing Mechanisms.

A conforming issuer implementation produces conforming documents, MUST include all required properties in the conforming documents that it produces, and MUST secure the conforming documents it produces using a securing mechanism as described in Section 4.9 Securing Mechanisms.

A conforming verifier implementation consumes conforming documents, MUST perform verification on a conforming document as described in Section 4.9 Securing Mechanisms, MUST check that each required property satisfies the normative requirements for that property, and MUST produce errors when non-conforming documents are detected.

This specification includes both required and optional properties. Optional properties MAY be ignored by conforming issuer implementations and/or conforming verifier implementations.

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.

Note: Human-readable texts in English are illustrative

Examples provided throughout this document include descriptive fields, such as name and description, with values in English to simplify the concepts in each example of the specification. These examples do not necessarily reflect the data structures needed for international use, which is described in more detail in Section 11. Internationalization Considerations.

2. Terminology

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. The definition of credential used in this specification differs from, NIST's definitions of credential.
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.
default graph
The graph containing all claims that are not explicitly part of a named graph.
entity
Anything that can be referenced in statements as an abstract or concrete noun. Entities include but are not limited to people, organizations, physical things, documents, abstract concepts, fictional characters, and arbitrary text. Any entity might perform roles in the ecosystem, if it is capable of doing so. Note that some entities fundamentally cannot take actions, e.g., the string "abc" cannot issue credentials.
graph
A set of claims, forming a network of information composed of subjects and their relationship to other subjects or data. Each claim is part of a graph; this is either explicit in the case of named graphs, or implicit for the default graph.
holder
A role an entity might perform by possessing one or more verifiable credentials and generating verifiable presentations from them. A holder is often, 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.
named graph
A graph associated with specific properties, such as verifiableCredential. These properties result in separate graphs that contain all claims defined in the corresponding JSON objects.
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.
unlinkable disclosure
A type of selective disclosure where presentations cannot be correlated between verifiers.
subject
A thing about which claims are made.
validation
The assurance that a claim from a specific issuer satisfies the business requirements of a verifier for a particular use. This specification defines how verifiers verify verifiable credentials and verifiable presentations.
It also specifies that verifiers validate claims in verifiable credentials before relying on them. However, the means for such validation vary widely and are outside the scope of this specification. Verifiers trust certain issuers for certain claims and apply their own rules to determine which claims in which credentials are suitable for use by their systems.
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, verification material, and other relevant data, such as verifiable credential schemas, revocation registries, 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 verification material, 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 current 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.
verification material
Information that is used to verify the security of cryptographically protected information. For example, a cryptographic public key used to verify a digital signature associated with a verifiable credential.
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, presentations, verifiable credentials, and verifiable presentations, which form the foundation of this specification.

Note: The difference between a credential and a verifiable credential

Readers might note that some concepts described in this section, such as credential and presentation, do not have media types defined by this specification. However, the concepts of a verifiable credential or a verifiable presentation are defined as conforming documents and do have associated media types. The concrete difference between these concepts — between credential and presentation vs. verifiable credential and verifiable presentation — is simply the fact that the "verifiable" objects are secured in a way that is cryptographically verifiable, and the others are not. For more details, see Section 4.9 Securing Mechanisms.

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, verification material, status information, and so on. A verifiable credential is a set of tamper-evident claims and metadata that cryptographically prove who issued it. Examples of verifiable credentials include, but are not limited to, digital employee identification cards, digital birth certificates, and digital educational certificates.

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

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 using an embedded proof based on Verifiable Credential Data Integrity. It is composed of at least two information graphs. The first of these information graphs, the verifiable credential graph (which is the default graph), expresses the verifiable credential itself, through credential metadata and other claims. The second information graph, referred to by the proof property, is the proof graph of the verifiable credential, and is a separate named graph. The proof graph expresses the digital proof, which, in this case, is a digital signature. Readers that are interested in the need for multiple information graphs can refer to Section 5.11 Verifiable Credential Graphs.

Diagram with a collections of
claims for a 'verifiable credential graph' on top
connected via a proof property (or predicate) to a 'verifiable credential proof
graph' on the bottom. The claims for a verifiable credential include 'Credential
123' as a subject with 4 properties: 'type' of value ExampleAlumniCredential,
'issuer' of Example University, 'validFrom' of 2010-01-01T19:23:24Z, and
credentialSubject of Pat, who also has an alumniOf property with value of
Example University.  The verifiable credential proof graph has an object
'Signature 456' subject with 5 properties: 'type' of DataIntegrityProof,
'verificationMethod' of Example University Public Key 7, 'created' of
2017-06-18T21:19:10Z, a 'nonce' of 34dj239dsj328, and 'proofValue' of
'zBavE110…3JT2pq'. The verifiable credential graph is also annotated with the
parenthetical remark '(the default graph)', the verifiable credential proof
graph is annotated with the parenthetical remark '(a named graph)'.
Figure 6 Information graphs associated with a basic verifiable credential, using an embedded proof based on Verifiable Credential Data Integrity [VC-DATA-INTEGRITY].

Figure 7 below shows the same verifiable credential as Figure 6, but using JOSE based on [VC-JOSE-COSE]. The payload contains a single information graph, that being the verifiable credential graph containing credential metadata and other claims.

Diagram with, on the left, a box, labeled as
'SD-JWT (Decoded)', and with three textual labels stacked vertically,
namely 'Header', 'Payload', and 'Signature'. The 'Header' label is
connected, with an arrow, to a separate rectangle on the right hand
side containing six text fields: 'kid: aB8J-_Z', 'alg: ES384', and
'cty: vc+ld+json', iss: https://example.com, iat: 1704690029, and typ:
vc+ld+json+sd-jwt The 'Payload' label on the left side is connected,
with an arrow, to a separate rectangle, containing a single graph. The
rectangle has a label: 'verifiable credential graph (serialized in
JSON)' The claims in the graph include 'Credential 123' as a subject
with 4 properties: 'type' with value 'ExampleAlumniCredential',
'issuer' with value 'Example University', 'validFrom' with value
'2010-01-01T19:23:24Z', and 'credentialSubject' with value 'Pat', who
also has an 'alumniOf' property with value 'Example University'.
Finally, the 'Signature' label on the left side is connected, with an
arrow, to a separate rectangle, containing a single text field:
'DtEhU3ljbEg8L38VWAfUA...'.
Figure 7 Information graphs associated with a basic verifiable credential, using an enveloping proof based on Securing Verifiable Credentials using JOSE and COSE [VC-JOSE-COSE].
Note

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

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 personas that are appropriate for given situations. 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 is created by a holder, can express data from multiple verifiable credentials, and can contain arbitrary additional data encoded as JSON-LD. They are used 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 8 Basic components of a verifiable presentation.

Figure 8 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 9 below shows a more complete depiction of a verifiable presentation using an embedded proof based on [VC-DATA-INTEGRITY]. It is composed of at least four information graphs. The first of these information graphs, the verifiable presentation graph (which is the default graph), expresses the verifiable presentation itself through presentation metadata. The verifiable presentation refers, via the verifiableCredential property, to a verifiable credential. This credential is a self-contained verifiable credential graph containing credential metadata and other claims. This credential refers to a verifiable credential proof graph via a proof property, expressing the proof (usually a digital signature) of the credential. This verifiable credential graph, and its linked proof graph, constitute the second and third information graphs, respectively, and each is a separate named graph. The presentation also refers, via the proof property, to the presentation's proof graph, which is the fourth information graph (another named graph). This presentation proof graph represents the digital signature of the verifiable presentation graph, the verifiable credential graph, and the proof graph linked from the verifiable credential graph.

Diagram with a
'verifiable presentation graph' on top connected via a 'proof' to
a 'verifiable presentation proof graph on the bottom.  The verifiable
presentation graph has and object 'Presentation ABC' with 3 properties: 'type'
of value VerifiablePresentation, 'termsOfUse' of value 'Do Not Archive'. The
graph is annotated with the parenthetical remark '(the default graph)'. This
graph is connected, through 'verifiableCredential', to the part of the figure
which is identical to Figure 6, except that the verifiable credential graph is
annotated to be a named graph instead of a default graph.
The verifiable presentation proof graph has an object with 'Signature 8910'
with 5 properties: 'type' with value 'DataIntegrityProof'; 'verificationMethod' with value 'Example
Presenter Public Key 11'; 'created' with value '2018-01-15T12:43:56Z';
'nonce' with value 'd28348djsj3239'; and 'proofValue' with value
'zp2KaZ...8Fj3K='. This graph is annotated with the parenthetical remark '(a
named graph)'
Figure 9 Information graphs associated with a basic verifiable presentation that is using an embedded proof based on Verifiable Credential Data Integrity [VC-DATA-INTEGRITY].

Figure 10 below shows the same verifiable presentation as Figure 9, but using an enveloping proof based on [VC-JOSE-COSE]. The payload contains only two information graphs: the verifiable presentation graph expressing the verifiable presentation itself through presentation metadata; and the corresponding verifiable credential graph, referred to by the verifiableCredential property. The verifiable credential graph contains a single EnvelopedVerifiableCredential instance referring, via a data: URL [RFC2397], to the verifiable credential secured via an enveloping proof shown on Figure 7.

Diagram with, on the left, a box, labeled as
'JWT (Decoded)', and with three textual labels stacked vertically,
namely 'Header', 'Payload', and 'Signature'. The 'Header' label is
connected, with an arrow, to a separate rectangle on the right hand
side containing six text fields: 'kid: aB8J-_Z', 'alg: ES384', and
'cty: vc+ld+json', iss: https://example.com, iat: 1704690029, and typ:
vp+ld+json+sd-jwt The 'Payload' label of the left side is connected,
with an arrow, to a separate rectangle, consisting of two related
graphs (stacked vertically) connected by a an arrow labeled
'verifiableCredential'. The two graphs have each a label 'verifiable
presentation graph (serialized in JSON)' and 'verifiable credential
graph (serialized in JSON)', respectively. The top graph in the
rectangle has and object 'Presentation ABC' with 3 properties: 'type'
of value VerifiablePresentation, 'termsOfUse' of value 'Do Not
Archive'. The bottom graph includes
'data:application/vc+ld+json+sd-jwt;QzVjV...RMjU' as a subject with a
single property: 'type' of value `EnvelopedVerifiableCredential`.
Finally, the 'Signature' label on the left side is connected, with an
arrow, to a separate rectangle, containing a single text field:
'XaOOh4ljklxH7L99RTVSfOl...'.
Figure 10 Information graphs associated with a basic verifiable presentation that is using an enveloping proof based on JOSE [VC-JOSE-COSE]. The data: URL refers to the verifiable credential shown on Figure 7.
Note: Presentations can contain multiple verifiable credentials

It is possible to have a presentation, such as a collection of university credentials, which draws on multiple credentials about different subjects that are often, but not required to be, related. This is achieved by using the verifiableCredential property to refer to multiple verifiable credentials. See Appendix D. Additional Diagrams for Verifiable Presentations for more details.

Note: Presentations can be presented by issuers and verifiers

As described in Section 1.2 Ecosystem Overview, an entity can take on one or more roles as they step through a particular credential exchange. While a holder is typically expected to generate presentations, an issuer or verifier might generate a presentation to identify itself to a holder. This might occur if the holder needs higher assurance from the issuer or verifier before handing over sensitive information as part of a verifiable presentation.

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 section is non-normative.

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.

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 property of the credential subject. Once a developer has added a number of these property-value combinations, the modified object can be sent to the verifiable credential issuer software and a verifiable credential will be created for the developer. From a prototyping standpoint, that is all a developer needs to do.

Example 1: 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 5.2 Extensibility. Alternatively, developers can reuse existing vocabulary and context files that happen to fit their use case. They can explore the Verifiable Credentials 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 effectively by using the same language where the words they use, such as "name" and "website", mean the same thing to each individual. This is sometimes referred to as the context of a conversation. This specification uses a similar concept to achieve similar results for software systems by establishing a context in which to communicate.

Software systems that process verifiable credentials and verifiable presentations identify terminology by using URLs [URL] for each term. However, those URLs can be long and not very human-friendly, while short-form, human-friendly aliases can be more helpful. This specification uses the @context property to map such short-form aliases to the URLs.

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. Subsequent items in the ordered set MUST be composed of any combination of URLs and/or objects, where each is processable as a JSON-LD Context.
Example 2: 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": "did:example:2g55q912ec3476eba2l9812ecbfe",
  "validFrom": "2010-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "alumniOf": {
      "id": "did:example:c276e12ec21ebfeb1f712ebc6f1",
      "name": "Example University"
    }
  }
}

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

The second URL (https://www.w3.org/ns/credentials/examples/v2) is used 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 once and cached. For reference, a copy of the base context is provided in Appendix B.1 Base Context. 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 5.2 Extensibility.

Note: See JSON-LD for more information about @context.

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 1.1 [JSON-LD11] specification.

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. The id property expresses an identifier that others are expected to use when expressing statements about the specific thing identified by that identifier. Example id values include UUIDs (urn:uuid:0c07c1ce-57cb-41af-bef2-1b932b986873), HTTP URLs (https://id.example/things#123), and DIDs (did:example:1234abcd).

Note

Developers should remember that identifiers might be harmful in scenarios where pseudonymity is required. Developers are encouraged to read Section 8.4 Identifier-Based Correlation carefully when considering such scenarios. There are also other types of access and correlation mechanisms documented in Section 8. Privacy Considerations that create privacy concerns. Where privacy is a strong consideration, it is permissible to omit the id property. Some use cases do not need, or explicitly need to omit, the id property. Similarly, special attention is to be given to the choice between publicly resolvable URLs and other forms of identifiers. Publicly resolvable URLs can facilitate ease of verification and interoperability, yet they might also inadvertently grant access to potentially sensitive information if not used judiciously.

id
The id property is OPTIONAL. If present, the value of the id property MUST be a single URL, which MAY be dereferenceable. It is RECOMMENDED that the URL in the id be one which, if dereferenceable, results in a document containing machine-readable information about the id.
Example 3: 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, many verifiable credentials will use DIDs and software libraries implementing this specification will 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 object type information. This type information can be used during validation processes, as described in Appendix A. Validation.

Verifiable credentials and verifiable presentations MUST contain a type property with an associated value.

type
The value of the type property MUST be one or more terms and/or absolute URL strings. If more than one value is provided, the order does not matter.
Example 4: 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"]
credentialStatus object A valid credential status type. For example,
"type": "BitstringStatusListEntry"
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-LD11] and is detailed in Section 3.5: Specifying the Type and Section 9: JSON-LD Grammar. When using a JSON-LD context (see Section 5.2 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 SHOULD specify, or be associated with, additional more narrow types (like ExampleDegreeCredential, for example) so software systems can more easily detect and process this additional information.

When processing encapsulated objects defined in this specification, such as 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. Object types, and their associated values, are expected to be documented in at least a human-readable specification that can be found at the URL for the type. For example, the human-readable definition for the BitstringStatusList type can be found at https://www.w3.org/ns/credentials/status/#BitstringStatusList. It is also suggested that a machine-readable version be provided, through HTTP content negotiation, at the same URL.

Note: Creating new verifiable credential types

Explaining how to create new types of verifiable credentials is beyond the scope of this specification. Readers that are interested in doing so are advised to read the section on Creating New Credential Types in the Verifiable Credentials Implementation Guidelines 1.0.

4.5 Names and Descriptions

When displaying a credential, it can be useful to have text provided by the issuer that furnishes the credential with a name as well as a short description of its purpose. The name and description properties are meant to serve these purposes.

name
An OPTIONAL property that expresses the name of the credential. If present, the value of the name property MUST be a string or a language value object as described in 11.1 Language and Base Direction. Ideally, the name of a credential is concise, human-readable, and could enable an individual to quickly differentiate one credential from any other credentials that they might hold.
description
An OPTIONAL property that conveys specific details about a credential. If present, the value of the description property MUST be a string or a language value object as described in 11.1 Language and Base Direction. Ideally, the description of a credential is no more than a few sentences in length and conveys enough information about the credential to remind an individual of its contents without their having to look through the entirety of the claims.
Example 5: Usage of the name and description 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": "https://university.example/issuers/565049",
    "name": "Example University",
    "description": "A public university focusing on teaching examples."
  },
  "validFrom": "2015-05-10T12:30:00Z",
  "name": "Example University Degree",
  "description": "2015 Bachelor of Science and Arts Degree",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}

Names and descriptions also support expressing content in different languages. To express a string with language and base direction information, one can use an object that contains the @value, @language, and @direction properties to express the text value, language tag, and base direction, respectively. See 11.1 Language and Base Direction for further information.

Note

The @direction property in the examples below is not required for the associated single-language strings, as their default directions are the same as those set by the @direction value. We include the @direction property here for clarity of demonstration, and to make copy+paste+edit deliver functional results. Implementers are encouraged to read the section on JSON-LD String Internationalization in the JSON-LD 1.1 specification [JSON-LD11].

Example 6: Usage of the name and description 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": {
    "id": "https://university.example/issuers/565049",
    "name": [{
      "@value": "Example University",
      "@language": "en"
    }, {
      "@value": "Université Exemple",
      "@language": "fr"
    }, {
      "@value": "جامعة المثال",
      "@language": "ar",
      "@direction": "rtl"
    }],
    "description": [{
      "@value": "A public university focusing on teaching examples.",
      "@language": "en"
    }, {
      "@value": "Une université publique axée sur l'enseignement d'exemples.",
      "@language": "fr"
    }, {
      "@value": ".جامعة عامة تركز على أمثلة التدريس",
      "@language": "ar",
      "@direction": "rtl"
    }]
  },
  "validFrom": "2015-05-10T12:30:00Z",
  "name": [{
    "@value": "Example University Degree",
    "@language": "en"
  }, {
    "@value": "Exemple de Diplôme Universitaire",
    "@language": "fr"
  }, {
    "@value": "مثال الشهادة الجامعية",
    "@language": "ar",
    "@direction": "rtl"
  }],
  "description": [{
    "@value": "2015 Bachelor of Science and Arts Degree",
    "@language": "en"
  }, {
    "@value": "2015 Licence de Sciences et d'Arts",
    "@language": "fr"
  }, {
    "@value": "2015 بكالوريوس العلوم والآداب",
    "@language": "ar",
    "@direction": "rtl"
  }],
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": [{
        "@value": "Bachelor of Science and Arts Degree",
        "@language": "en"
      }, {
        "@value": "Licence de Sciences et d'Arts",
        "@language": "fr"
      }, {
        "@value": "بكالوريوس العلوم والآداب",
        "@language": "ar",
        "@direction": "rtl"
      }]
    }
  }
}

4.6 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 where each object MUST be the subject of one or more claims, which MUST be serialized inside the credentialSubject property. Each object MAY also contain an id to identify the subject, 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": "https://subject.example/subject/8675",
    "name": "Morgan Doe",
    "spouse": "https://subject.example/subject/7421"
  }]
}

4.7 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 whose value is a URL; in either case, the issuer selects this URL to identify itself in a globally unambiguous way. It is RECOMMENDED that the URL be one which, if dereferenced, results in a controller document, as defined in [VC-DATA-INTEGRITY] or [VC-JOSE-COSE], 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").

4.8 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.

When comparing dates and times, the calculation is done "temporally", which means that the string value is converted to a "temporal value" which exists as a point on a timeline. Temporal comparisons are then performed by checking to see where the date and time being compared is in relation to a particular point on the timeline.

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 or in the past. Note that this value represents the earliest point in time at which the information associated with the credentialSubject property becomes valid. If a validUntil value also exists, the validFrom value MUST express a datetime that is temporally the same or earlier than the datetime expressed by the validUntil value.
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 or in the future. 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 also exists, the validUntil value MUST express a datetime that is temporally the same or later than the datetime expressed by 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.

4.8.1 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 time zones, all time values expressed in conforming documents SHOULD be specified in dateTimeStamp format, either in Universal Coordinated Time (UTC), denoted by a Z at the end of the value, or with a time zone offset relative to UTC. Time values that are incorrectly serialized without an offset MUST be interpreted as UTC. Examples of valid time zone offsets relative to UTC include Z, +01:00, -08:00, and +14:00. See the regular expression at the end of this section for a formal definition of all acceptable values.

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))

4.9 Securing Mechanisms

This specification recognizes two classes of securing mechanisms: those that use enveloping proofs and those that use embedded proofs.

An enveloping proof is one that wraps a serialization of this data model. One such RECOMMENDED enveloping proof mechanism is defined in Securing Verifiable Credentials using JOSE and COSE [VC-JOSE-COSE].

An embedded proof is a mechanism where the proof is included in the serialization of the data model. One such RECOMMENDED embedded proof mechanism is defined in Verifiable Credential Data Integrity [VC-DATA-INTEGRITY].

These two classes of securing mechanisms are not mutually exclusive. Additional securing mechanism specifications might also be defined according to the rules in Section 5.12 Securing Mechanism Specifications.

Example 13: A verifiable credential utilizing an embedded proof
{
  "@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": "did:example:6fb1f712ebe12c27cc26eebfe11",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "https://subject.example/subject/3921",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "proof": {
    "type": "DataIntegrityProof",
    "cryptosuite": "eddsa-rdfc-2022",
    "created": "2021-11-13T18:19:39Z",
    "verificationMethod": "https://university.example/issuers/14#key-1",
    "proofPurpose": "assertionMethod",
    "proofValue": "z58DAdFfa9SkqZMVPxAQp...jQCrfFPP2oumHKtz"
  }
}
Example 14: A verifiable credential that uses an enveloping proof in SD-JWT format
eyJhbGciOiJFUzM4NCIsImtpZCI6IkdOV2FBTDJQVlVVMkpJVDg5bTZxMGM3U3ZjNDBTLWJ2UjFTT0
Q3REZCb1UiLCJ0eXAiOiJ2YytsZCtqc29uK3NkLWp3dCIsImN0eSI6InZjK2xkK2pzb24ifQ
.
eyJAY29udGV4dCI6WyJodHRwczovL3d3dy53My5vcmcvbnMvY3JlZGVudGlhbHMvdjIiLCJodHRwcz
ovL3d3dy53My5vcmcvbnMvY3JlZGVudGlhbHMvZXhhbXBsZXMvdjIiXSwiaXNzdWVyIjoiaHR0cHM6
Ly91bml2ZXJzaXR5LmV4YW1wbGUvaXNzdWVycy81NjUwNDkiLCJ2YWxpZEZyb20iOiIyMDEwLTAxLT
AxVDE5OjIzOjI0WiIsImNyZWRlbnRpYWxTY2hlbWEiOnsiX3NkIjpbIlNFOHp4bmduZTNNbWEwLUNm
S2dlYW1rNUVqU1NfOXRaNlN5NDdBdTdxRWMiLCJjT3lySEVrSlZwdEtSdURtNkNZVTREajJvRkExd0
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.
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~
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~
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4.10 Status

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

If present, the value associated with the credentialStatus property is a single object or a set of one or more objects. The following properties are defined for every object:

id
The id property is OPTIONAL. It MAY be used to provide a unique identifier for the credential status object. If present, the normative guidance in Section 4.3 Identifiers MUST be followed.
type
The type property is REQUIRED. It is used to express the type of status information expressed by the object. The related normative guidance in Section 4.4 Types MUST be followed.

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. The value will provide enough information to determine the current status of the credential and whether 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 15: Usage of the status 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"
    }
  },
  "credentialStatus": {
    "id": "https://university.example/credentials/status/3#94567",
    "type": "BitstringStatusListEntry",
    "statusPurpose": "revocation",
    "statusListIndex": "94567",
    "statusListCredential": "https://university.example/credentials/status/3"
  }
}

It is possible for a credential to have more than one status associated with it, such as whether it has been revoked or suspended.

Example 16: Usage of multiple entries for the status property
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "http://license.example/credentials/9837",
  "type": ["VerifiableCredential", "ExampleDrivingLicenseCredential"],
  "issuer": "https://license.example/issuers/48",
  "validFrom": "2020-03-14T12:10:42Z",
  "credentialSubject": {
    "id": "did:example:f1c276e12ec21ebfeb1f712ebc6",
    "license": {
      "type": "ExampleDrivingLicense",
      "name": "License to Drive a Car"
    }
  },
  "credentialStatus": [{
    "id": "https://license.example/credentials/status/84#14278",
    "type": "BitstringStatusListEntry",
    "statusPurpose": "revocation",
    "statusListIndex": "14278",
    "statusListCredential": "https://license.example/credentials/status/84"
  }, {
    "id": "https://license.example/credentials/status/84#82938",
    "type": "BitstringStatusListEntry",
    "statusPurpose": "suspension",
    "statusListIndex": "82938",
    "statusListCredential": "https://license.example/credentials/status/84"
  }]
}

Implementers are cautioned that credentials with multiple status entries might contain conflicting information. Reconciling such conflicts is a part of the validation process, hence part of the verifier's business logic, and therefore out of scope for this specification.

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.

Specification authors that create status schemes are provided the following guideline:

4.11 Verifiable Credentials

Verifiable credentials are used to express properties of one or more subjects as well as properties of the credential itself. The following properties are defined in this specification for a verifiable credential:

@context
Defined in Section 4.2 Contexts.
id
Defined in Section 4.3 Identifiers.
type
Defined in Section 4.4 Types.
name
Defined in Section 4.5 Names and Descriptions.
description
Defined in Section 4.5 Names and Descriptions.
issuer
Defined in Section 4.7 Issuer.
validFrom
Defined in Section 4.8 Validity Period.
validUntil
Defined in Section 4.8 Validity Period.
status
Defined in Section 4.10 Status.
credentialSchema
Defined in Section 4.13 Data Schemas.
credentialSubject
Defined in Section 4.6 Credential Subject.

A verifiable credential can be extended to have additional properties through the extension mechanism defined in Section 5.2 Extensibility.

4.12 Verifiable 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 default graph of a verifiable presentation is also referred to as the verifiable presentation graph.

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 one or more verifiable credential and/or enveloped verifiable credential objects (to be clear, the values MUST NOT be non-object values such as numbers, strings, or URLs). These types of objects are called verifiable credential graphs and MUST express information that is secured using a securing mechanism. See Section 5.11 Verifiable Credential Graphs for further details.
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 either is obtained via the securing mechanism, or does not pertain to the validation of the verifiable presentation.

The example below shows a verifiable presentation:

Example 17: 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": [{ ... }]
}

The contents of the verifiableCredential property shown above are verifiable credential graphs, as described by this specification.

4.12.1 Enveloped Verifiable Credentials

It is possible for a verifiable presentation to include one or more verifiable credentials that have been secured using a securing mechanism that "envelopes" the payload, such as Securing Verifiable Credentials using JOSE and COSE [VC-JOSE-COSE]. This can be accomplished by associating the verifiableCredential property with an object that has a type of EnvelopedVerifiableCredential.

EnvelopedVerifiableCredential
Used to associate an object containing an enveloped verifiable credential with the verifiableCredential property in a verifiable presentation. The @context property of the object MUST be present and include a context, such as the base context for this specification, that defines at least the id, type, and EnvelopedVerifiableCredential terms as defined by the base context provided by this specification. The id value of the object MUST be a data: URL [RFC2397] that expresses a secured verifiable credential using an enveloping security scheme, such as Securing Verifiable Credentials using JOSE and COSE [VC-JOSE-COSE]. The type value of the object MUST be EnvelopedVerifiableCredential.

The example below shows a verifiable presentation that contains an enveloped verifiable credential:

Example 18: Basic structure of a presentation
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "type": ["VerifiablePresentation", "ExamplePresentation"],
  "verifiableCredential": [{
    "@context": "https://www.w3.org/ns/credentials/v2",
    "id": "data:application/vc+ld+json+sd-jwt;QzVjV...RMjU",
    "type": "EnvelopedVerifiableCredential"
  }]
}
Note: Processing enveloped content as RDF

It is possible that an implementer might want to process the object described in this section, and the enveloped presentation expressed by the id value, in an RDF environment and create linkages between the objects that are relevant to RDF. The desire and mechanisms for doing so are use case dependent and will, thus, be implementation dependent.

4.12.2 Enveloped Verifiable Presentations

It is possible to express a verifiable presentation that has been secured using a mechanism that "envelops" the payload, such as Securing Verifiable Credentials using JOSE and COSE [VC-JOSE-COSE]. This can be accomplished by using an object that has a type of EnvelopedVerifiablePresentation.

EnvelopedVerifiablePresentation
Used to express an enveloped verifiable presentation. The @context property of the object MUST be present and include a context, such as the base context for this specification, that defines at least the id, type, and EnvelopedVerifiablePresentation terms as defined by the base context provided by this specification. The id value of the object MUST be a data: URL [RFC2397] that expresses a secured verifiable presentation using an enveloping securing mechanism, such as Securing Verifiable Credentials using JOSE and COSE [VC-JOSE-COSE]. The type value of the object MUST be EnvelopedVerifiablePresentation.

The example below shows an enveloped verifiable presentation:

Example 19: Basic structure of an enveloped verifiable presentation
{
  "@context": "https://www.w3.org/ns/credentials/v2",
  "id": "data:application/vp+ld+json+jwt;eyJraWQiO...zhwGfQ",
  "type": "EnvelopedVerifiablePresentation"
}

4.12.3 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 5.7 Zero-Knowledge Proofs.

Pat has a property
                 overAge whose value is 21
Figure 11 A basic claim expressing that Pat is over the age of 21.

4.12.4 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 20: A verifiable presentation, secured with an embedded Data Integrity 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 21: A verifiable presentation, secured with an embedded Data Integrity 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": { ... }
  }],
  "proof": { ... }
}

4.13 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 whether the provided data conforms to the provided schema(s). Each credentialSchema MUST specify its type (for example, JsonSchema), 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] validation.

Example 22: 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": "JsonSchema"
  },
  {
    "id": "https://example.org/examples/alumni.json",
    "type": "JsonSchema"
  }]
}

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

Note

For information about linkages to JSON Schema [VC-JSON-SCHEMA] or other optional schema validation 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 5.7 Zero-Knowledge Proofs.

Example 23: 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"
  }
}

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 whether the proof provided with the verifiable credential is well-formed.

5. Advanced Concepts

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

5.1 Trust Model

This section is non-normative.

The verifiable credentials trust model is based on the following expectations:

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

By decoupling the expectations between the issuer and the verifier, 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 [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.

5.2 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 24: 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 25: 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 26: 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.6 Proofs (Signatures), 4.10 Status, 4.13 Data Schemas,5.4 Refreshing, 5.5 Terms of Use, and 5.6 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.

5.2.1 Semantic Interoperability

When defining new terms in an application-specific vocabulary, developers MUST use globally unambiguous URLs to identify the terms. Whenever possible, it is RECOMMENDED to re-use terms — and their corresponding URLs — defined by well-known, public vocabularies, such as DCMI Metadata Terms [DCTERMS] or Schema.org [schema-org]. If that is not possible, authors MUST define a new URL for each term. When doing so, the general guidelines for [LINKED-DATA] are expected to be followed, in particular:

  • Human-readable documentation MUST be published, describing the semantics of and the constraints on the use of each term.
  • It is RECOMMENDED to also publish the collection of all new terms as a machine-readable vocabulary using RDF Schema 1.1 [RDF-SCHEMA].
  • It SHOULD be possible to dereference the URL of a term, resulting in its description and/or formal definition.

Developers SHOULD follow the detailed checklist in Best Practices for Publishing Linked Data [LD-BP] when defining a new vocabulary.

Furthermore, a machine-readable description (that is, a JSON-LD Context document) MUST be published at the URL specified in the @context property for the vocabulary. This context MUST map each term to its corresponding URL, possibly accompanied by further constraints like the type of the property value. A human-readable document describing the expected order of values for the @context property is also expected to be published by any implementer seeking interoperability.

Note

When processing the active context defined by the base JSON-LD Context document defined in this specification, compliant JSON-LD-based processors produce an error when a JSON-LD context redefines any term. 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 keyword in the JSON-LD 1.1 specification.

The base JSON-LD Context file for this specification also includes an extra feature, using the @vocab keyword, which ensures that any undefined term in a verifiable credential or a verifiable presentation is automatically mapped to a URL prefixed with https://www.w3.org/ns/credentials/issuer-dependent#. This is to allow early experimentation with terms during the development phase, without requiring a formal definition in every cycle of that experimentation. Note that developers SHOULD NOT use this feature in production; this could lead to name clashes, yielding semantic ambiguities with other applications. Instead, they SHOULD define all the terms, as described earlier in this section, to achieve proper interoperability.

5.4 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 5.9 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.7 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. The precise content of each refresh service is determined by the specific refreshService type definition.
Example 29: Usage of the refreshService property by an issuer
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2",
    "https://w3id.org/vc-refresh-service/v1"
  ],
  "id": "http://university.example/credentials/3732",
  "type": ["VerifiableCredential", "ExampleDegreeCredential"],
  "issuer": "https://university.example/issuers/14",
  "validFrom": "2020-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "ExampleBachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "refreshService": {
    "type": "VerifiableCredentialRefreshService2021",
    "url": "https://university.example/workflows/refresh-degree",
    "validFrom": "2021-09-01T19:23:24Z",
    "validUntil": "2022-02-01T19:23:24Z"
  }
}

In the example above, the issuer specifies an automatic refreshService that can be used by directing the holder to https://university.example/workflows/refresh-degree.

5.5 Terms of Use

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 might be used to tell the verifier any or all of the following, among other things:

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 30: 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": "urn:did:123456",
  "type": [
    "VerifiableCredential",
    "EbsiTermsOfUseExample"
  ],
  "issuer": "did:ebsi:zz7XsC9ixAXuZecoD9sZEM1",
  "validFrom": "2021-11-01T00:00:00Z",
  "validUntil": "2021-10-30T00:00:00Z",
  "credentialSubject": {
    "id": "did:key:z2dmzD81cgPx8Vki7JbuuMmFYrWPgYoytykUZ3eyqht1j9KbrDt4zxXoDrBWYFiATYZ8G9JMeEXC7Kki24fbTwtsJbGe5qcbkYFunSzcDokMRmj8UJ1PbdCGh33mf97K3To89bMzd15qrYq3VkDztoZqfmujkJVpvTbqoXWXqxmzNDbvMJ",
    "personalIdentifier": "IT/DE/1234",
    "familyName": "Castafiori",
    "firstName": "Bianca",
    "dateOfBirth": "1930-10-01"
  },
  "credentialSchema": {
    "id": "https://api-test.ebsi.eu/trusted-schemas-registry/v2/schemas/z3MgUFUkb722uq4x3dv5yAJmnNmzDFeK5UC8x83QoeLJM",
    "type": "JsonSchema"
  },
  "termsOfUse": {
    "id": "https://api-test.ebsi.eu/trusted-issuers-registry/v4/issuers/did:ebsi:zz7XsC9ixAXuZecoD9sZEM1/attributes/7201d95fef05f72667f5454c2192da2aa30d9e052eeddea7651b47718d6f31b0",
    "type": "IssuanceCertificate"
  }
}

In the example above, the issuer is asserting that as a European Blockchain Services Infrastructure (EBSI) accredited issuer, it complies with the EBSI policies as an accredited issuer and is registered in the EBSI register of trusted issuers. The termsOfUse id can be resolved by the verifier to confirm that the issuer has been issued an accreditation VC (in JWT format) by a trusted issuer higher in the EBSI trust chain [?EBSI].

Example 31: 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"
      }
    }
  }],
  "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"]
    }]
  }]
}

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.

5.6 Evidence

Issue 1303: (AT RISK) Feature depends on demonstration of independent implementations pending closebefore-PR

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 5.9 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 32: 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"
  }
}
Example 33: Example of evidence supporting a skill achievement credential
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2",
    "https://purl.imsglobal.org/spec/ob/v3p0/context-3.0.3.json"
  ],
  "id": "http://1edtech.edu/credentials/3732",
  "type": [
    "VerifiableCredential",
    "OpenBadgeCredential"
  ],
  "issuer": {
    "id": "https://1edtech.edu/issuers/565049",
    "type": "Profile"
  },
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "type": "AchievementSubject",
    "name": "Alice Smith",
    "activityEndDate": "2023-12-02T00:00:00Z",
    "activityStartDate": "2023-12-01T00:00:00Z",
    "awardedDate": "2024-01-01T00:00:00Z",
    "achievement": [{
      "id": "urn:uuid:d46e8ef1-c647-419b-be18-5e045d1c4e64",
      "type": ["Achievement"],
      "name": "Basic Barista Training",
      "criteria": {
        "narrative": "Team members are nominated for this badge by their supervisors, after passing the Basic Barista Training course."
      },
      "description": "This achievement certifies that the bearer is proficient in basic barista skills."
    }]
  },
  "evidence": [{
      // url to an externally hosted evidence file/artifact
      "id": "https://videos.example.com/training/alice-espresso.mp4",
      "type": ["Evidence"],
      "name": "Talk-aloud video of double espresso preparation",
      "description": "This is a talk-aloud video of Alice demonstrating preparation of a double espresso drink.",
      // digest hash of the mp4 video file
      "digestSRI": "sha384-zNNbQTWCSUSi0bbz7dbua...OHdzwELMYO9Mz68M26"
    }
  ]
}
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 information that is different from and information to the securing mechanism utilized. The evidence property is used to express supporting information, such as documentary evidence, related to the integrity of the verifiable credential. In contrast, the securing mechanism 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 securing mechanisms, see Section 4.9 Securing Mechanisms.

5.7 Zero-Knowledge Proofs

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.

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 diagram below highlights how the data model might be used to issue and present verifiable credentials in zero-knowledge.

Issue

Examples of leveraging vc-di-bbs, will be added here in the future, or this section will be removed.

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 12 A visual example of the relationship between credentials and derived credentials in a ZKP presentation.

The following guideline is provided for authors who create securing mechanisms specifications that provide unlinkability:

5.8 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.

5.9 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. Some of these extension points were originally defined in previous versions of this specification, while others were not. It is important to note that none of these properties are defined by this specification. Consequently, implementers are cautioned that use of these properties is considered experimental.

Implementers MAY use these properties, but SHOULD expect them and/or their meanings to change during the process of normatively specifying 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
confidenceMethod A property used for specifying one or more methods that a verifier might use to increase their confidence that the value of a property in or of a verifiable credential or verifiable presentation is accurate, including but not limited to properties such as initialRecipient (a/k/a issuee), presenter, authorizedPresenter, holder, etc. The associated vocabulary URL MUST be https://www.w3.org/2018/credentials#confidenceMethod.
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. See Verifiable Credential Confidence Methods.

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 one or more methods 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. See Verifiable Credential Rendering Methods.

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.

5.10 Ecosystem Compatibility

There are a number of digital credential formats that do not natively use the data model provided in this document, but are aligned with a number of concepts in this specification. At the time of publication, examples of these digital credential formats include JSON Web Tokens (JWTs), CBOR Web Tokens (CWTs), ISO-18013-5:2021 (mDLs), AnonCreds, Gordian Envelopes, and Authentic Chained Data Containers (ACDCs).

If conceptually aligned digital credential formats can be transformed into a conforming document according to the rules provided in this section, they are considered "compatible with the W3C Verifiable Credentials ecosystem". Specification authors are advised to adhere to the following rules when documenting transformations that enable compatibility with the Verifiable Credentials ecosystem. The transformation specification —

Note: What constitutes a verifiable credential?

Readers are advised that a digital credential is only considered compatible with the W3C Verifiable Credentials ecosystem if it is a conforming document and it utilizes at least one securing mechanism, as described by their respective requirements in this specification. While some communities might call some digital credential formats that are not conforming documents "verifiable credentials", doing so does NOT make that digital credential compliant to this specification.

5.11 Verifiable Credential Graphs

When expressing verifiable credentials (for example in a presentation), it is important to ensure that data in one verifiable credential is not mistaken to be the same data in another verifiable credential. For example, if one has two verifiable credentials, each containing an object of the following form: {"type": "Person", "name": "Jane Doe"}, it is not possible to tell if one object is describing the same person as the other object. In other words, merging data between two verifiable credentials without confirming that they are discussing the same entities and/or properties, can lead to a corrupted data set.

To ensure that data from different verifiable credentials are not accidentally co-mingled, the concept of a verifiable credential graph is used to encapsulate each verifiable credential. For simple verifiable credentials, i.e., when the JSON-LD document contains a single credential with, possibly, associated proofs, this graph is the default graph. For presentations, each value associated with the verifiableCredential property of the presentation is a separate named graph of type VerifiableCredentialGraph which contains a single verifiable credential or an enveloped verifiable credential.

Using these graphs has a concrete effect when performing JSON-LD processing, which properly separates graph node identifiers in one graph from those in another graph. Implementers that limit their inputs to application-specific JSON-LD documents will also need to keep this in mind if they merge data from one verifiable credential with data from another, such as when the credentialSubject.id is the same in both verifiable credentials, but the object might contain objects of the "Jane Doe" form described in the previous paragraph. It is important to not merge objects that seem to have similar properties but do not contain an id property that uses a global identifier, such as a URL.

5.12 Securing Mechanism Specifications

As described in Section 4.9 Securing Mechanisms, there are multiple strategies that an implementer can use when securing a conforming document. In order to maximize utility and interoperability, specification authors that desire to author new ways of securing conforming documents are provided with the guidance in this section.

Securing mechanism specifications MUST document normative algorithms that provide content integrity protection for conforming documents. The algorithms MAY be general in nature and MAY be used to secure data other than conforming documents.

Securing mechanism specifications MUST provide a verification mechanism that returns only the information in the conforming document that has been secured, without any securing mechanism information included, such as proof or JOSE/COSE header parameters and signatures. Specifications MAY provide additional mechanisms to convey other information that might be helpful (for example, during validation or for debugging purposes), such as securing mechanism data. A securing mechanism's verification algorithm MUST provide an interface that receives inputs of a media type (string inputMediaType) paired with either a sequence of bytes (byte sequence inputBytes) or a document (map inputDocument), and returns a verification result with at least the following items:

boolean status
A verification status whose value is true if the verification succeeded and false if it did not.
map document
A document that only contains information that was successfully secured.
string mediaType
A media type as defined in [RFC6838].
(Feature at Risk) Issue: Controller document reference might change

The Working Group is currently attempting to align the definitions of a controller document between Decentralized Identifiers (DIDs) v1.0, Verifiable Credential Data Integrity, and Securing Verifiable Credentials using JOSE and COSE. The goal is to have one specification that each of the previously stated specifications, and this specification, can reference for the normative statements related to controller documents. The normative references to controller documents are expected to change during the Candidate Recommendation phase.

Securing mechanism specifications SHOULD provide integrity protection for any information referenced by a URL that is critical to validation. Mechanisms that can achieve this protection are discussed in Section 5.3 Integrity of Related Resources and Section B.1 Base Context.

Securing mechanism specifications that create new types of embedded proofs MUST specify a property for securing both verifiable credentials and verifiable presentations. The requirements for the property used by the embedded securing mechanism are as follows:

Securing mechanism specifications SHOULD register the securing mechanism in the Securing Mechanisms section of the Verifiable Credentials Specifications Directory [VC-SPECS].

Note: Choice of securing mechanism is use-case dependent

There are multiple acceptable securing mechanisms, and this specification does not mandate any particular securing mechanism for use with verifiable credentials or verifiable presentations. The Working Group that produced this specification did standardize two securing mechanism options, which are: Verifiable Credential Data Integrity [VC-DATA-INTEGRITY] and Securing Verifiable Credentials using JOSE and COSE [VC-JOSE-COSE]. Other securing mechanisms that are known to the community can be found in the Securing Mechanisms section of the Verifiable Credentials Specifications Directory [VC-SPECS].

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-LD11] is a JSON-based format used to serialize Linked Data. Linked Data is modeled using Resource Description Framework (RDF). RDF [RDF11-CONCEPTS] is a technology for modeling graphs of statements. Each statement is a single subject→property→value (also known as entity→attribute→value) relationship, which is referred to as a claim in this specification. JSON-LD [JSON-LD11] is a technology that enables the expression of RDF using idiomatic JSON, enabling developers familiar with JSON to write applications that consume RDF as JSON. In general, subjects are expressed as JSON objects with each property and value of the subject as a JSON key and value, respectively. A special affordance is made to express an identifier of a subject, if necessary, using the id key in this specification. See Relationship of JSON-LD to RDF for more details.

[JSON-LD11] is useful when extending the data model described in this specification. Instances of the data model are encoded in JSON-LD compacted form [JSON-LD11] and include the @context property. The JSON-LD context is described in detail in the [JSON-LD11] specification and its use is elaborated on in Section 4.2 Contexts and Section 5.2 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 compacted document form MUST be utilized for all representations of the data model in the base media type, application/vc+ld+json.

As elaborated upon in Section 6.3 Type-Specific Credential Processing, some software applications might not perform generalized JSON-LD processing. Authors of conforming documents are advised that interoperability might be reduced if JSON-LD keywords in the @context value are used to globally affect values in a verifiable credential or verifiable presentation, such as by globally setting the @base keyword. For example, globally setting these values might trigger a failure in a mis-implemented JSON Schema check on the @context value in an implementation that is performing type-specific credential processing and not expecting the @base value to be expressed in the @context value.

In order to increase interoperability, conforming document authors are urged to not use JSON-LD features that are not easily detected when performing type-specific credential processing. These features include:

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-LD11] 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 property is defined as a JSON-LD 1.1 graph container. This requires the creation of named graphs, 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-LD11] 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-LD11] processor.

6.1.2 Lists and Arrays

Lists, arrays, and even lists of lists, are possible when using [JSON-LD11] 1.1. We encourage those who want RDF semantics in use cases requiring lists and arrays to follow the guidance on lists in JSON-LD 1.1.

In general, a JSON array is ordered, while a JSON-LD array is not ordered unless that array uses the @list keyword.

Note

While it is possible to use this data model without any JSON-LD processing, those who do so and make use of arrays need to be aware that unless the above guidance is followed, the order of items in an array cannot be guaranteed in JSON-LD. This might lead to unexpected behavior.

If JSON structure or ordering is important to your application, we recommend you mark such elements as @json via an @context.

Example 34: A @context file that defines a matrix as an embedded JSON data structure
{
  "@context":
    {
      "matrix": {
        "@id": "https://website.example/vocabulary#matrix",
        "@type": "@json"
      }
    }
}
Example 35: A verifiable credential with an embedded JSON data structure
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2",
    "https://website.example/matrix/v1"
  ],
  "id": "http://university.example/credentials/1872",
  "type": [
    "VerifiableCredential",
    "ExampleMatrixCredential"
  ],
  "issuer": "https://university.example/issuers/565049",
  "validFrom": "2010-01-01T19:23:24Z",
  "credentialSubject": {
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "matrix": [
      [1,2,3,4,5,6,7,8,9,10,11,12],
      [1,1,1,1,1,1,1,1,0,0,0,0],
      [0,0,1,1,1,1,1,1,1,0,0,0]
    ]
  }
}

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.

6.2.2 HTTP

This section is non-normative.

HTTP clients and servers use media types associated with verifiable credentials and verifiable presentations in accept headers and when indicating content types.

Nonetheless, HTTP servers might ignore the accept header and return another content type, or return an error code such as 415 Unsupported Media Type.

6.3 Type-Specific Credential Processing

This section is non-normative.

As JSON can be used to express different kinds of information, a consumer of a particular JSON document can only properly interpret the author's intent if they possess information that contextualizes and disambiguates it from other possible expressions. Information to assist with this interpretation can either be wholly external to the JSON document or linked from within it. Compacted JSON-LD documents include a @context property that internally expresses or links to contextual information to express claims. These features enable generalized processors to be written to convert JSON-LD documents from one context to another, but this is not needed when consumers receive JSON-LD documents that already use the context and shape that they expect. Authors of JSON-LD documents, such as issuers of verifiable credentials, are required to provide proper JSON-LD contexts and follow these rules in order to facilitate interoperability.

The text below helps consumers understand how to ensure a JSON-LD document is expressed in a context and shape that their application already understands such that they do not need to transform it in order to consume its contents. Notably, this does not mean that consumers do not need to understand any context at all; rather, consuming applications only need to understand a chosen set of contexts and document shapes to work with and not others. Issuers can publish contexts and information about their verifiable credentials to aid consumers who do not use generalized processors, just as can be done with any other JSON-formatted data.

General JSON-LD processing is defined as a mechanism that utilizes a JSON-LD software library to process a conforming document by performing various transformations. Type-specific credential processing is defined as a lighter-weight mechanism for processing conforming documents, that doesn't require a JSON-LD software library. Some consumers of verifiable credentials only need to consume credentials with specific types. These consumers can use type-specific credential processing instead of generalized processing. Scenarios where type-specific credential processing can be desirable include, but are not limited to, the following:

That is, type-specific credential processing is allowed as long as the document being consumed or produced is a conforming document. If this type of processing is desired, an implementer is advised to follow this rule:

Using static context files with a JSON Schema is one acceptable approach to implementing the rule above. This can ensure proper term identification, typing, and order, when performing type-specific credential processing.

The rule above guarantees semantic interoperability between the two processing mechanisms for mapping literal JSON keys to URIs via the @context mechanism. While general JSON-LD processing can use previously unseen @context values provided in its algorithms to verify that all terms are correctly specified, implementations that perform type-specific credential processing only accept specific @context values which the implementation is engineered ahead of time to understand, resulting in the same semantics without invoking any JSON-LD APIs. In other words, the context in which the data exchange happens is explicitly stated for both processing mechanisms by using @context in a way that leads to the same conforming document semantics.

7. Algorithms

This section contains algorithms that can be used by implementations to perform common operations, such as verification. Conformance requirements phrased as algorithms utilize normative concepts from the Infra Standard [INFRA]. See the section on Conformance in the Infra Standard for more guidance on implementation requirements.

(Feature at Risk) Issue: Issues need resolution before Candidate Recommendation

There is one issue that is associated with this section that will need to be resolved before the Working Group can enter the Candidate Recommendation phase. This entire section is at risk until those issues are resolved.

Issue 1377: Rewrite verification algorithm in a way that does not cause layer violations pr existsbefore-CR

Both @selfissued and @OR13 raised architectural layering concerns around the way that the verification algorithm is written. This issue is being raised to track their concerns.

Note: Implementers can include additional checks, warnings, and errors.

Implementers are advised that the algorithms in this section contain the bare minimum set of checks used by implementations to test conformance to this specification. Implementations are expected to provide additional checks that report helpful warnings for developers to help debug potential issues. Similarly, implementations are likely to provide additional checks that could result in new types of errors being reported in order to stop harmful content. Any of these additional checks might be integrated into future versions of this specification.

7.1 Verification

This section contains an algorithm that conforming verifier implementations MUST run when verifying a verifiable credential or a verifiable presentation. This algorithm takes inputs of a media type (string inputMediaType) paired with either a sequence of bytes (byte sequence inputBytes) or a document (map inputDocument), and returns a map that contains the following:

The verification algorithm is as follows:

  1. Ensure that the securing mechanism has properly protected the conforming document by performing the following steps:
    1. Set the verifyProof function by using the inputMediaType and the Securing Mechanisms section of the Verifiable Credentials Specifications Directory [VC-SPECS], or other mechanisms known to the implementation, to determine the cryptographic suite to use when verifying the securing mechanism. The verifyProof function MUST implement the interface described in 4.9 Securing Mechanisms.
      Issue: Mechanism for 'determining' is being detailed
      At present, the Working Group is concerned that the algorithm for "determining" might need to be more formally defined. At present, no implementation has had an issue determining the proper verifyProof algorithm to use, but the Working Group is attempting to see if saying more here would be worthwhile. Additional example language could be added that says that an implementation might have an allow list of acceptable cryptosuites — and these will be used as inputs for finding matching proofs to be verified.
    2. Set result to the result of passing inputBytes and inputMediaType to the verifyProof function. If the call was successful, result will contain the status, document, mediaType, controller, controllerDocument, warnings, and errors properties.
    3. If result.status is set to false, add a CRYPTOGRAPHIC_SECURITY_ERROR to result.errors.
  2. If result.status is set to true, ensure that result.document is a conforming document. If it is not, set result.status to false, remove the document property from result, and add at least one MALFORMED_VALUE_ERROR to result.errors. Other warnings and errors MAY be included to aid any debugging process.
  3. Return result.

The steps for verifying the state of the securing mechanism and verifying that the input document is a conforming document MAY be performed in a different order than that provided above as long as the implementation returns errors for the same invalid inputs. Implementations MAY produce different errors than described above.

7.2 Problem Details

When an implementation detects an anomaly while processing a document, a ProblemDetails object can be used to report the issue to other software systems. The interface for these types of objects follows [RFC9457] to encode the data. A ProblemDetails object consists of the following properties:

type
The type property MUST be present and its value MUST be a URL identifying the type of problem.
code
The code property is OPTIONAL. present, its value MUST be an integer that identifies the type of the problem. Integer codes are useful in systems that only provide integer return values.
title
The title property MUST be present and its value SHOULD provide a short but specific human-readable string for the problem.
detail
The detail property MUST be present and its value SHOULD provide a longer human-readable string for the problem.

The following problem description types and codes are defined by this specification:

https://www.w3.org/TR/vc-data-model#PARSING_ERROR (-64)
There was an error while parsing input.
https://www.w3.org/TR/vc-data-model#CRYPTOGRAPHIC_SECURITY_ERROR (-65)
The securing mechanism for the document has detected a modification in the contents of the document since it was created; potential tampering detected. See Section 7.1 Verification.
https://www.w3.org/TR/vc-data-model#MALFORMED_VALUE_ERROR (-66)
The value associated with a particular property is malformed. The name of the property and the path to the property SHOULD be provided in the ProblemDetails object. See Section 7.1 Verification.
https://www.w3.org/TR/vc-data-model#RANGE_ERROR (-67)
A provided value is outside of the expected range of an associated value, such as a given index value for an array being larger than the current size of the array.

Implementations MAY extend the ProblemDetails object by specifying additional types, codes, or properties. See the Extension Member section in [RFC9457] for further guidance on using this mechanism.

8. 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.

8.1 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 13 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.

8.2 Software Trust Boundaries

This section is non-normative.

A variety of trust relationships exist in the ecosystem described by this specification. An individual using a web browser trusts the web browser, also known as a user agent, to preserve that trust by not uploading their personal information to a data broker; similarly, entities filling the roles in the ecosystem described by this specification trust the software that operates on behalf of each of those roles. Examples include the following:

The examples above are not exhaustive, and the users in these roles can also expect a variety of other things from the software they use to achieve their goals. In short, the software is expected to operate in the best interests of the user, and a violation of that expectation is a violation of trust that will result in the software being replaced by something that does not violate that trust. Implementers are strongly advised to write software that does not violate the trust of the users it will serve. Implementers are also advised to provide auditing features in the software that they create such that the users, or trusted third parties, can check whether the software is indeed behaving in their best interests.

Readers are advised that some software, such as a website that provides services to a single verifier and multiple holders, might operate as a user agent to both roles, but might not always be able to simultaneously operate in the best interests of all parties. For example, if that website detects an attempt at fraudulent verifiable credential use among multiple holders, it might report such an anomaly to the verifier, which might be considered to not be in the best interest of the holder committing the violation, but would be in the best interest of the verifier as well as any holders not committing such a violation. It is strongly advised that when software operates in this manner, that it is made clear in whose best interest the software is operating through mechanisms such as a website usage policy.

8.3 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 to be personally identifiable, such as the combination of a birthdate and a postal code, has very powerful correlation and de-anonymization capabilities.

Implementers of software used by holders 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 dateOfBirth verifiable credentials for use when a verifier wants to determine whether 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.

In general, individuals are advised to assume that a verifiable credential, like most physical credentials, will leak personally identifiable information when shared. To combat this leakage, the verifiable credential, and the securing mechanism, need to be specifically designed to avoid correlation. Verifiable credentials that are specifically designed to prevent the leakage of personally identifiable information do exist. Individuals and implementers are urged to prefer these types of credentials over ones that are not designed to protect personally identifiable information.

8.4 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, and many other sorts of long-lived identifiers. Implementers of software used by holders are advised to strive to detect identifiers in verifiable credentials containing information that could be used to correlate individuals and warn holders when they are getting ready to share this information. The rest of this section elaborates on guidance related to the use of long-lived identifiers.

Subjects of verifiable credentials are identified using the id property, as defined in Section 4.3 Identifiers, and are used in places such as the credentialSubject.id property. 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. Other types of identifiers that fall into this category are email addresses, government-issued identifiers, and organization-issued identifiers.

Similarly, disclosing the credential identifier (such as in Example 3) 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 are advised to use verifiable credentials from issuers that allow selectively disclosing correlating identifiers in a verifiable presentation. Such approaches expect the holder to generate the identifier and might even allow hiding the identifier from the issuer through the use of techniques like blind signatures, while still keeping the identifier embedded and signed in the verifiable credential.

Securing mechanism specification authors are advised to avoid enabling identifier-based correlation by designing their technologies, when possible, to avoid the use of correlating identifiers that cannot be selectively disclosed.

If strong anti-correlation properties are a requirement in a verifiable credentials system, it is strongly advised that identifiers are one or more of the following:

8.5 Signature-Based Correlation

This section is non-normative.

The contents of a verifiable credential are secured using a securing mechanism. Values used to represent the securing mechanism 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 of these sorts of values include the following:

If strong anti-correlation properties are required, it is advised that issuers produce verifiable credentials where the signature values and metadata can be regenerated for each verifiable presentation using technologies that support unlinkable disclosure, such as the Data Integrity BBS Cryptosuites v1.0 specification. It is advised that, if possible, verifiers prefer verifiable presentations that use this technology in order to enhance the privacy for holders and subjects.

Note: Unlinkability is not a complete solution

Even when using unlinkable signatures, information might still be contained in a verifiable credential that defeats the anti-correlation properties of the cryptography used. See Sections 8.3 Personally Identifiable Information, 8.4 Identifier-Based Correlation, 8.6 Metadata-based Correlation, 8.11 Correlation During Validation, and most of the other subsections of Section 8. Privacy Considerations.

8.6 Metadata-based Correlation

This section is non-normative.

The use of different extension points described in Section 4. Basic Concepts and Section 5. Advanced Concepts can serve as an unintentional or unwanted correlation mechanism if the number of issuers using a specific extension type or combination of types is relatively small. For example, the use of certain types of cryptography that are only used by particular nation states, or revocation formats used by specific jurisdictions, or credential types used by specific localities, can be used as a mechanism to reduce the pseudonymity that a holder might expect to have when performing a selective disclosure of information to a verifier.

Issuers are urged to reduce metadata-based correlation possibilities when issuing verifiable credentials that are expected to be used in a pseudonymous fashion by reducing the types of extensions that can be used to narrow the pseudonymity of the holder. Using credential types, extensions, and technology profiles that have global use is preferred over ones that have national use, which are preferred over ones that only have local use.

8.7 Device Tracking and 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.

The Oblivious HTTP protocol [OHTTP] is one mechanism that implementers might consider using when fetching external resources that are associated with a verifiable credential or a verifiable presentation. Oblivious HTTP allows a client to make multiple requests to an origin server without that server being able to link those requests to that client or even to identify those requests as having come from a single client, while placing only limited trust in the nodes used to forward the messages. Hence, Oblivious HTTP is one privacy-preserving mechanism that can be used to reduce the possibility of device tracking and fingerprinting. Concrete examples for how Oblivious HTTP can benefit ecosystem participants are included below.

8.8 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 are advised to limit the information published in a verifiable credential to a minimal set needed for the expected purposes. One way to avoid placing PII in a verifiable credential is to use an abstract property that meets the needs of verifiers without providing overly-specific information about a subject.

For example, this document uses the ageOver property instead of a specific birthdate, which represents more sensitive 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 verifiable credentials claiming that subjects have met that requirement instead of offering verifiable credentials containing claims about the customers' birthdays. This enables individual customers to make purchases without revealing more PII than necessary.

8.9 The Principle of Data Minimization

This section is non-normative.

Privacy violations occur when information divulged in one context leaks into another. One accepted best practice for preventing such a violation is for verifiers to limit the information requested, and received, to the absolute minimum necessary for a particular transaction. This data minimization approach is required by regulations 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 expressed as a verifiable credential contains 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 securing mechanism that allows for selective disclosure. For example, an issuer of driver's licenses could issue a verifiable credential containing every property that appears on a driver's license and allow each property to be selectively disclosed by the holder. It could also issue more abstract verifiable credentials (for example, a verifiable credential containing only an ageOver property). 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, might 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:

Implementers of software used by holders are urged to disclose what information is being requested by a verifier, such that a holder can push back on the over-collection of information that is unnecessary for the transaction.

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.

8.10 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 36: 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.

8.11 Correlation During Validation

This section is non-normative.

When processing verifiable credentials, verifiers evaluate any relevant claims before relying upon them. This evaluation might be done in any manner desired, as long as it satisfies the requirements of the verifier doing the validation. Many verifiers will perform the checks listed in Appendix A. Validation as well as a variety of specific business process checks such as:

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 an improperly configured revocation list, can notify the issuer that a specific business is likely interacting with the holder. This could enable issuers to collude to 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.

8.12 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:

In addition to the mitigations above, the participation of civil society and regulators in the analysis and auditing of vendors can also ensure that there are legal protections in place, and enforced, for individuals affected by practices that are not aligned with their best interests.

8.13 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.

8.14 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 violations of verifiable credential usage occur when unintended or unexpected correlation arises from the presentation of those verifiable credentials.

8.15 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.

8.16 Data Theft

This section is non-normative.

The data expressed in verifiable credentials and verifiable presentations are valuable since they contain authentic statements made by trusted third parties, such as issuers, or individuals, such as holders and subjects. The storage and acessibility of this data can inadvertently create honeypots of sensitive data for malicious actors. These adversaries often seek to exploit such resevoirs of sensitive information, aiming to acquire and exchange that data for financial gain.

Issuers are advised to retain the minimum amount of data necessary to issue verifiable credentials to holders and manage the status and revocation of those credentials. Similarly, issuers are advised to avoid the practice of creating publicly resolvable credentials that include personally identifiable information (PII) or other sensitive data. Software implementers are advised to safeguard verifiable credentials using robust consent and access control measures, ensuring that they remain inaccessible to unauthorized entities.

Holders are advised to use implementations that appropriately encrypt their data both in transit and at rest, and protect sensitive material (such as cryptographic secrets) in ways that cannot be easily extracted from hardware devices. Furthermore, it is suggested that holders store and manipulate their data only on devices that they control, away from centralized systems, to reduce the likelihood of attack on their data, or large-scale theft if an attack is successful. Furthermore, holders are encouraged to rigorously control access to their credentials and presentations, allowing access only to those with explicit authorization.

Verifiers are advised to only ask for data necessary for a particular transaction and to not retain any data beyond the needs of any particular transaction.

Regulators are advised to rethink audit requirements such that more privacy-preserving mechanisms can be used to achieve similar levels of enforcement and audit capabilities. For example, audit-focused regulations that insist on collection and long-term retention of personally identifiable information can cause harm to individuals and organizations if that same information is compromised and accessed by an attacker. The technologies described by this specification enable holders to more-readily prove properties about themselves and others, reducing the need for long-term data retention by verifiers. Alternatives include keeping logs that the information was collected and checked, as well as random tests to ensure that compliance regimes are operating as expected.

8.17 Frequency of Claim Issuance

This section is non-normative.

As detailed in Section 8.14 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.

8.18 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.

8.19 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.

8.20 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.

In addition to previously described privacy protections an issuer might use, issuers need to also be aware of data they leak associated with identifiers and claim types they use when issuing credentials. One example of this would be an issuer issuing drivers licenses which reveal both the location(s) in which they have jurisdiction and the location of the subject's residence. Verifiers might take advantage of this by requesting a credential to check that the subject is licensed to drive, when in fact they are interested in metadata about the credential, such as which issuer issued the credential, and tangential information that might have been leaked by the issuer, such as the subject's home address. To mitigate such leakage, issuers might choose to use common identifiers to mask specific location information or other sensitive metadata; for example, a shared issuer identifier at a state or nation level, instead of at the level of a county, city, town, or other smaller municipality. Further, holder attestation mechanisms can be used by verifiers to preserve privacy, by providing proofs that an issuer exists in a set of trusted entities, without needing to disclose the exact issuer.

9. 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.

9.1 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.

9.2 Key Management

This section is non-normative.

The security of most digital signature algorithms, which are used to secure verifiable credentials and verifiable presentations, is dependent on the quality and protection of their private signing keys. Guidance in the management of cryptographic keys is a large subject and the reader is referred to [NIST-SP-800-57-Part-1] for more extensive recommendations and discussion. As strongly recommended in both [FIPS-186-5] and [NIST-SP-800-57-Part-1], a private signing key is not to be used for multiple purposes, e.g., a private signing key is not to be used for encryption as well as signing.

[NIST-SP-800-57-Part-1] strongly advises that private signing keys and public verification keys have limited cryptoperiods, where a cryptoperiod is "the time span during which a specific key is authorized for use by legitimate entities or the keys for a given system will remain in effect." [NIST-SP-800-57-Part-1] gives extensive guidance on cryptoperiods for different key types under different situations, and generally recommends a 1-3 year cryptoperiod for a private signing key.

To deal with potential private key compromises, [NIST-SP-800-57-Part-1] provides recommendations for protective measures, harm reduction, and revocation. Although this section focuses primarily on the security of the private signing key, [NIST-SP-800-57-Part-1] also highly recommends confirmation of the validity of all verification material before using it.

9.3 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 extension contexts, JSON Schemas, and other machine-readable data, are not protected by default against tampering because the data resides outside of the protection of the securing mechanism on the verifiable credential.

This specification provides an optional mechanism, contained in Section 5.3 Integrity of Related Resources, that is capable of ensuring content integrity for external resources. While this mechanism need not be utilized for external resources that do not affect the security of the verifiable credential, it is strongly suggested for external resources that could result in a security issue if the external content changes.

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, and utilize the content integrity protection mechanism provided by this specification if a security issue could occur if the external resource is changed.

9.4 Unsigned Claims

This section is non-normative.

This specification allows credentials to be produced that are not secured by 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.

9.5 Man-in-the-Middle (MITM), Replay, and Cloning Attacks

This section is non-normative.

The data model does not inherently prevent Man-in-the-Middle (MITM), replay, and spoofing attacks. Both online and offline use cases might be susceptible to these types of attacks, where an adversary intercepts, modifies, re-uses, and/or replicates the verifiable credential data during transmission or storage.

9.5.1 Man-in-the-Middle (MITM) Attack

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. Some securing mechanisms, like [VC-JOSE-COSE] or [VC-DATA-INTEGRITY], provide an option to specify the intended audience or domain of a presentation, which can help reduce this risk.

Alternate 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.

9.5.2 Replay Attack

A verifier might wish to ensure that a verifiable presentation is not used more than a certain number of times. For example, a verifiable credential representing an event ticket, might allow entry to multiple individuals if presented multiple times, undermining the purpose of the ticket from the perspective of its issuer. To prevent against such attacks, holders can make use of techniques such as including a nonce during presentation, or adding an expiry timestamp to reduce the window of attack.

9.5.3 Spoofing Attack

A verifier has a vested interest in knowing that a holder is authorized to present the claims inside of a verifiable presentation. While the data model outlines the structure and data elements necessary for a verifiable credential, it does not include a mechanism to ascertain the authorization of presented credentials. To address this concern, implementers might need to explore supplementary methods, such as binding verifiable credentials to strong authentication mechanisms or using additional properties in verifiable presentations to enable proof of control.

9.6 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.

9.7 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.

9.8 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:

Furthermore, instances of impersonation can manifest in various forms, including situations where an entity attempts to disavow their actions. Elevating the level of trust and security within the realm of verifiable credentials entails more than just averting impersonation; it involves the implementation of non-repudiation mechanisms. These mechanisms solidify an entity's responsibility for their actions or transactions, thereby reinforcing accountability and deterring malicious behaviors. The attainment of non-repudiation is a multifaceted endeavor, encompassing an array of techniques ranging from securing mechanisms, proofs of possession, and authentication schemes in a variety of protocols designed to foster trust and reliability.

9.9 Acceptable Use

This section is non-normative.

Ensuring that there is alignment between an entity's actions, such as presentation, and the intended purpose of those actions, is of importance. It involves having the authorization to make use of verifiable credentials as well as using credentials in a manner that adheres to their designated scope(s) and objective(s). Two critical aspects that arise within this context are Unauthorized Use and Inappropriate Use.

9.9.1 Unauthorized Use

Any attempt by entities to make use of verifiable credentials and verifiable presentations outside of their intended use can be seen as unauthorized. One class of unauthorized use is a confidentiality violation. Consider an example where a holder shares a verifiable presentation with a verifier to establish their age and residency status. If the verifier then proceeds to exploit the holder's data without proper consent, such as by selling the data to a data broker, that would constitute an unauthorized use of the data, violating an expectation of privacy that the holder might have in the transaction.

Similarly, an issuer could make use of a termsOfUse property to stipulate how and when a credential might be used. A holder using credentials outside of the scopes defined in the termsOfUse would be considered unauthorized use.

Note

Further study is required to determine how a holder can assert and enforce authorized use of their data after presentation.

9.9.2 Inappropriate Use

While valid cryptographic signatures and successful status checks signify the reliability of credentials, they do not signify that all credentials are interchangeable for all contexts. It is crucial that verifiers also validate any claims which might be relevant, considering the source and nature of the claim as well as privilege or service for which the credential is presented.

For instance, in scenarios where a certified medical diagnosis is required, a self-asserted credential carrying the necessary data might not suffice because it lacks validity from an authoritative medical source. To ensure the propriety of credential use, stakeholders are urged to assess the credential's relevance and authority within the specific context of their intended application.

9.10 Code Injection

This section is non-normative.

It is possible for data in verifiable credentials to include executable code or scripting languages. Authors of verifiable credentials are advised to avoid doing so, unless necessary, and the risks have been mitigated to the extent possible.

For example, when a single natural language string contains multiple languages or annotations, the contents of the string might require additional structure or markup in order to be presented correctly. It is possible to use markup languages, such as HTML, to label spans of text in different languages or to supply string-internal markup needed for the proper display of bidirectional text. 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 so, for the following reasons:

If implementers feel they need to 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 could use the markup to mount injection attacks against a consumer of the markup, and then deploy mitigations against the identified attacks, such as running the HTML rendering engine in a sandbox with no ability to access the network.

10. 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.

10.1 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.

11. 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.

11.1 Language and Base Direction

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-LD11], [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 37: Design pattern for natural language strings
"myProperty": {
  "@value": "The string value",
  "@language": "LANGUAGE"
  "@direction": "DIRECTION"
}

When the language value object is used in place of a string value, the object MUST contain a @value property whose value is a string, and SHOULD contain a @language property whose value is a string containing a well-formed Language-Tag as defined by [BCP47], and MAY contain a @direction property whose value is a base direction string defined by the @direction property in [JSON-LD11]. The language value object MUST NOT include any other keys beyond @value, @language, and @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 38: Expressing natural language text as English
"title": {
  "@value": "HTML and CSS: Designing and Creating Websites",
  "@language": "en"
}

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

Example 39: Arabic text with a base direction of right-to-left
"title": {
  "@value": "HTML و CSS: تصميم و إنشاء مواقع الويب",
  "@language": "ar",
  "@direction": "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 its base direction.

Multiple language value objects MAY be provided as an array value for the property:

Example 40: Multiple language texts provided for title
"title": [
  {
    "@value": "HTML and CSS: Designing and Creating Websites",
    "@language": "en"
  },
  {
    "@value": "HTML و CSS: تصميم و إنشاء مواقع الويب",
    "@language": "ar",
    "@direction": "rtl"
  }
]

11.2 Providing Default Language and Direction

The language and base direction of each natural language string property value SHOULD be provided, either via the language value structure for each property value, or via a default language and base direction for all values in the entire credential. Using the per-value language value structure is preferred, because using document defaults can result in a requirement that downstream processors perform JSON-LD expansion-based transformation which is otherwise optional. See the String Internationalization section of the [JSON-LD11] specification for more information. Natural language string values that do not have a language associated with them SHOULD be treated as if the language value is undefined (language tag "und"). Natural language string values that do not have a base direction associated with them SHOULD be treated as if the direction value is "auto".

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. Credential types, as well as validation schemas for each type and each of their claims, are defined by specification authors and are published in places like the Verifiable Credentials Specifications Directory.

The type of a credential is expressed via the type property. A verifiable credential of a specific type contains specific properties (which might be deeply nested) that can be used to determine whether or not the presentation satisfies a set of processing rules that the verifier executes. 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 the verifier to determine the next stage of an interaction with a holder.

When a verifier requests a verifiable credential of a specific type, there will be a set of mandatory and optional claims that are associated with that type. A verifier's validation of a verifiable credential will fail when mandatory claims are not included, and any claim that is not associated with the specific type will be ignored. In other words, a verifier will perform input validation on the verifiable credential it receives and will reject malformed input based on the credential type specification.

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 identifies a subject to the verifier. If the holder is also the subject, then the verifier could authenticate the holder if they have verification 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 identifies an issuer to the verifier.

Metadata related to the issuer property is available to the verifier through the verification algorithm as defined in Section 7.1 Verification. This metadata includes identification of the verified controller of the verification method used by the securing mechanism to secure each verifiable credential or verifiable presentation, of which the controller is typically the respective issuer or holder.

Some ecosystems might have more complex relationships between issuers and controllers of verification methods and might use lists of verified issuers in addition to, or instead of, the mapping described above.

A.4 Holder

This section is non-normative.

The value associated with the holder property is used to identify the holder to the verifier.

Often relevant metadata about the holder, as identified by the value of the holder property, is available to, or retrievable by, the verifier. For example, a holder can publish information containing the verification material used to secure verifiable presentations. This metadata is used when checking proofs on verifiable presentations. Some cryptographic identifiers contain all necessary metadata in the identifier itself. In those cases, no additional metadata is required. Other identifiers use verifiable data registries where such metadata is automatically published for use by verifiers, without any additional action by the holder.

See the Verifiable Credentials Implementation Guidelines 1.0 and Verifiable Credentials Use Cases for additional examples related to subject and holder.

Note

Validation is the process by which verifiers apply business rules to evaluate the propriety of a particular use of a verifiable credential.

A verifier might need to validate a given verifiable presentation against complex business rules; for example, the verifier might need confidence that the holder is the same entity as a subject of a verifiable credential. In such a situation, the following factors can provide a verifier with reasonable confidence that the claims expressed regarding that identifier, in included verifiable credentials, are, in fact, about the current presenter:

A.5 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.6 Proofs (Signatures)

This section is non-normative.

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

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

A.7 Validity Periods

This section is non-normative.

The verifier expects that the validFrom and validUntil properties will be within a certain range. For example, a verifier can check that the end of the validity period of a verifiable credential is not in the past. Because some credentials can be useful for secondary purposes even if their original validity period has expired, validity period, as expressed using the validFrom and validUntil properties, is always considered a component of validation, which is performed after verification.

A.8 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.9 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], then a verifier can ensure a credential's data is valid against the given JSON Schema.

A.10 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

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.

The Working Group is expecting all of the terms and URLs supplied in the JSON-LD Context to be either stabilized, or removed, before the publication of this specification as a Proposed Recommendation. While that means that this specification could be delayed if dependencies such as [VC-DATA-INTEGRITY], [VC-JOSE-COSE], SD-JWT, [VC-JSON-SCHEMA], or status list do not enter the Proposed Recommendation phase around the same time frame, the Working Group is prepared to remove the dependencies if an undue burden is placed on transitioning to the Recommendation phase. This is a calculated risk that the Working Group is taking and has a mitigation strategy in place to ensure the timely transition of this specification to a Recommendation.

Implementations MUST treat the base context value, located at https://www.w3.org/ns/credentials/v2, as already retrieved; the following value is the SHA-384 digest of the resource computed and encoded according to the [SRI] definition of digest: vxRgTREj3/ZmDabpiTX+Au4UXY8GDhyCSFNw+UQtdtISDyO/znDUY+FTg8rNsGXJ. It is strongly advised that all JSON-LD Context URLs used by an application utilize the same mechanism, or a functionally equivalent mechanism, to ensure end-to-end security. Implementations are expected to throw errors if a cryptographic hash value for a resource does not match the expected hash value.

Implementations that apply the base context above, as well as other contexts and values in any @context property, during operations such as JSON-LD Expansion or transformation to RDF, are expected to do so without experiencing any errors. If such operations are performed and result in an error, the verifiable credential or verifiable presentation MUST result in a verification failure.

It is possible to confirm the SHA-384 digest above 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

More details regarding this hash encoding method can be found in the integrity metadata section of [SRI].

Note: See errata if hash value changes are detected

It is extremely unlikely that the files that have associated cryptographic hash values in this specification will change. However, if critical errata are found in the specification and corrections are required to ensure ecosystem stability the cryptographic hash values might change. As such, the HTTP cache times for the files are not set to infinity and implementers are advised to check for errata if a cryptographic hash value change is detected.

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-JOSE-COSE] 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 verifiable 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 time-stamped locations, migration of documents to the W3C Technical Reports namespace, and/or implementer feedback that requires the referenced URLs to be modified.

Implementations that depend on RDF vocabulary processing MUST ensure that the following vocabulary URLs used in the base context ultimately resolve to the following files when loading the JSON-LD serializations, which are normative. Other semantically equivalent serializations of the vocabulary files MAY be used by implementations. A cryptographic hash is provided for each JSON-LD document to ensure that developers can verify that the content of each file is correct.

URL JSON-LD Documents and Hashes
https://www.w3.org/2018/credentials# https://www.w3.org/2018/credentials/index.jsonld

sha256: z52TgKqh2nqTCuACI8lCvhRdjwxQjeVmuOMCDCEijq4=

https://w3id.org/security# https://w3c.github.io/vc-data-integrity/vocab/security/vocabulary.jsonld

sha256: LEaoTyf796eTaSlYWjfPe3Yb+poCW9TjWYTbFDmC0tc=

It is possible to confirm the cryptographic digests listed above by running a command like the following, replacing <DOCUMENT_URL> with the appropriate value, through a modern UNIX-like OS command line interface: curl -sL -H "Accept: application/ld+json" <DOCUMENT_URL> | openssl dgst -sha256 -binary | openssl base64 -nopad -a

Note: schema.org changes regularly, but is considered stable

Implementers and document authors might note that cryptographic digests for schema.org are not provided. This is because the schema.org vocabulary undergoes regular changes; any digest provided would be out of date within weeks of publication. The Working Group discussed this concern and concluded that the vocabulary terms from schema.org, that are used by this specification, have been stable for years and are highly unlikely to change in their semantic meaning.

The following base classes are defined in this specification for processors and other specifications that benefit from such definitions:

Base Class Purpose
CredentialEvidence Serves as a superclass for specific evidence types that are placed into the evidence property. This superclass is at risk and will be removed if at least two independent implementations for the superclass are not identified by the end of the Candidate Recommendation phase.
CredentialSchema Serves as a superclass for specific schema types that are placed into the credentialSchema property.
CredentialStatus Serves as a superclass for specific credential status types that are placed into the credentialStatus property.
ConfidenceMethod Serves as a superclass for specific confidence method types that are placed into the confidenceMethod property. This superclass is at risk and will be removed if at least two independent implementations for the superclass are not identified by the end of the Candidate Recommendation phase.
RefreshService Serves as a superclass for specific refresh service types that are placed into the credentialRefresh property. This superclass is at risk and will be removed if at least two independent implementations for the superclass are not identified by the end of the Candidate Recommendation phase.
RenderMethod Serves as a superclass for specific render method types that are placed into the renderMethod property. This superclass is at risk and will be removed if at least two independent implementations for the superclass are not identified by the end of the Candidate Recommendation phase.
TermsOfUse Serves as a superclass for specific terms of use types that are placed into the termsOfUse property. This superclass is at risk and will be removed if at least two independent implementations for the superclass are not identified by the end of the Candidate Recommendation phase.

B.3 Datatypes

This section defines datatypes that are used by this specification.

B.3.1 The sriString Datatype

The string provides the integrity information for a resource using the method specified in the [SRI] specification.

The sriString datatype is defined as follows:

The URL denoting this datatype
https://www.w3.org/2018/credentials#sriString
The lexical space
See the ABNF grammar, defining the integrity attribute in the [SRI] specification, for the restrictions on the string format.
The value space
A (possibly empty) list of (alg,val) pairs, where alg identifies a hash function, and val is an integer as a standard mathematical concept.
The lexical-to-value mapping
Any element of the lexical space is mapped to the value space by following the parse metadata algorithm based on the ABNF grammar in the [SRI] specification.
The canonical mapping
The canonical mapping consists of the lexical-to-value mapping.

B.4 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-LD11] and [VC-JSON-SCHEMA]. 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-LD11] 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-LD11], 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-LD11], this represents the type of the node in the graph which is why some [JSON-LD11] 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-LD11] 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-LD11] representations more human-friendly to read. From a [JSON-LD11] 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-LD11] 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-LD11], 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-LD11] 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-LD11] 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-LD11] 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 for credentials secured using an enveloping proof.

A [JSON-LD11] 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 for presentations secured using an enveloping proof.

A [JSON-LD11] 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. Additional Diagrams for Verifiable Presentations

This section is non-normative.

Figure 14 below is a variant of Figure 9: a verifiable presentation referring to two verifiable credentials, and using embedded proofs based on [VC-DATA-INTEGRITY]. Each verifiable credential graph is connected to its own separate proof graph; the verifiableCredential property is used to connect the verifiable presentation to the verifiable credential graphs. The presentation proof graph represents the digital signature of the verifiable presentation graph, both verifiable credential graphs, and the proof graphs linked from the verifiable credential graphs. The complete verifiable presentation consists, in this case, of six information graphs.


Diagram with a 'verifiable presentation graph' on top, connected via a
'proof' to a 'verifiable presentation proof graph' on the bottom. The
verifiable presentation graph has an object, 'Presentation ABC', with 3
properties: 'type' with value 'VerifiablePresentation'; 'termsOfUse' with
value 'Do Not Archive'; and two instances of 'verifiableCredential',
detailed below. This graph is annotated with a parenthetical remark, '(the
default graph)'. This graph is connected, through 'verifiableCredential',
to the part of the figure that consists two variants of Figure 6 (one is
identical; the other has minor differences in the labels referring to
validity dates, the name of the person, and the values for the nonce and
the signature), except that these verifiable credential graphs are
annotated to be named graphs instead of a default graph. The verifiable
presentation proof graph has an object labeled 'Signature 8920' with 5
properties: 'type' with value 'DataIntegrityProof'; 'verificationMethod'
with value 'Example Presenter Public Key 11'; 'created' with value
'2024-01-02T12:43:56Z'; 'nonce' with value 'hasdkyruod87j'; and
'proofValue' with value 'zpewJHoan87='. This graph is annotated with the
parenthetical remark '(a named graph)'
Figure 14 A variant of Figure 9: information graphs associated with a verifiable presentation referring to two verifiable credentials, using an embedded proof based on Verifiable Credential Data Integrity [VC-DATA-INTEGRITY].

Figure 15 below shows the same verifiable presentation as Figure 14, but using an enveloping proof based on [VC-JOSE-COSE]. Each verifiable credential graph contains a single EnvelopedVerifiableCredential instance, referring, via a data: URL [RFC2397], to a verifiable credential secured via an enveloping proof.


Diagram with, on the left, a box, labeled as 'JWT (Decoded)', and with
three textual labels stacked vertically, namely 'Header', 'Payload', and
'Signature'. The 'Header' label is connected, with an arrow, to a
separate rectangle on the right hand side containing six text fields:
'kid: aB8J-_Z', 'alg: ES384', and 'cty: vc+ld+json', iss:
https://example.com, iat: 1704690029, and typ: vp+ld+json+sd-jwt The
'Payload' label of the left side is connected, with an arrow, to a
separate rectangle, consisting of three related graphs (stacked
vertically) connected by two arrows labeled 'verifiableCredential'
starting from the top graph and connecting it to the two other graphs,
respectively. The top graph has a label 'verifiable presentation graph
(serialized in JSON)'; the other two are both labeled by 'verifiable
credential graph (serialized in JSON)'. The top graph in the rectangle
has and object 'Presentation ABC' with 3 properties: 'type' of value
VerifiablePresentation, 'termsOfUse' of value 'Do Not Archive'. One of
the the bottom graphs includes
'data:application/vc+ld+json+sd-jwt;QzVjV...RMjU' as a subject with a
single property: 'type' of value `EnvelopedVerifiableCredential`. The
last bottom graph is identical other, except for the subject which is
labeled as 'data:application/vc+ld+json+sd-jwt;RkOyT...KjOl'. Finally,
the 'Signature' label on the left side is connected, with an arrow, to a
separate rectangle, containing a single text field:
'cYjaSdfIoJH45NIqw3MYnasGIba...'.
Figure 15 A variant of Figure 10: information graphs associated with a verifiable presentation referring to two verifiable credentials using enveloping proofs based on JOSE [VC-JOSE-COSE].

E. 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:

F. 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.

G. References

G.1 Normative references

[i18n-glossary]
Internationalization Glossary. Richard Ishida; Addison Phillips. W3C. 22 April 2024. W3C Working Group Note. URL: https://www.w3.org/TR/i18n-glossary/
[INFRA]
Infra Standard. Anne van Kesteren; Domenic Denicola. WHATWG. Living Standard. URL: https://infra.spec.whatwg.org/
[JSON-LD11]
JSON-LD 1.1. Gregg Kellogg; Pierre-Antoine Champin; Dave Longley. W3C. 16 July 2020. W3C Recommendation. URL: https://www.w3.org/TR/json-ld11/
[JSON-LD11-API]
JSON-LD 1.1 Processing Algorithms and API. Gregg Kellogg; Dave Longley; Pierre-Antoine Champin. W3C. 16 July 2020. W3C Recommendation. URL: https://www.w3.org/TR/json-ld11-api/
[LINKED-DATA]
Linked Data Design Issues. Tim Berners-Lee. W3C. 27 July 2006. W3C-Internal Document. URL: https://www.w3.org/DesignIssues/LinkedData.html
[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
[RFC2397]
The "data" URL scheme. L. Masinter. IETF. August 1998. Proposed Standard. URL: https://www.rfc-editor.org/rfc/rfc2397
[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
[RFC9457]
Problem Details for HTTP APIs. M. Nottingham; E. Wilde; S. Dalal. IETF. July 2023. Proposed Standard. URL: https://www.rfc-editor.org/rfc/rfc9457
[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-JOSE-COSE]
Securing Verifiable Credentials using JOSE and COSE. Michael Jones; Michael Prorock; Gabe Cohen. W3C. 25 April 2024. W3C Candidate Recommendation. URL: https://www.w3.org/TR/vc-jose-cose/
[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/

G.2 Informative references

[BCP47]
Tags for Identifying Languages. A. Phillips, Ed.; M. Davis, Ed.. IETF. September 2009. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc5646
[DCTERMS]
DCMI Metadata Terms. DCMI Usage Board. DCMI. 20 January 2020. DCMI Recommendation. URL: https://www.dublincore.org/specifications/dublin-core/dcmi-terms/
[DEMOGRAPHICS]
Simple Demographics Often Identify People Uniquely. Latanya Sweeney. Data Privacy Lab. URL: https://dataprivacylab.org/projects/identifiability/paper1.pdf
[DID-CORE]
Decentralized Identifiers (DIDs) v1.0. Manu Sporny; Amy Guy; Markus Sabadello; Drummond Reed. W3C. 19 July 2022. W3C Recommendation. URL: https://www.w3.org/TR/did-core/
[FIPS-186-5]
FIPS PUB 186-5: Digital Signature Standard (DSS). U.S. Department of Commerce/National Institute of Standards and Technology. 3 February 2023. National Standard. URL: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-5.pdf
[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
[LD-BP]
Best Practices for Publishing Linked Data. Bernadette Hyland; Ghislain Auguste Atemezing; Boris Villazón-Terrazas. W3C. 9 January 2014. W3C Working Group Note. URL: https://www.w3.org/TR/ld-bp/
[NIST-SP-800-57-Part-1]
Recommendation for Key Management: Part 1 – General. Elaine Barker. National Institute of Standards and Technology. May 2020. URL: https://doi.org/10.6028/NIST.SP.800-57pt1r5
[OHTTP]
Oblivious HTTP . Martin Thomson; Christopher A. Wood. IETF Oblivious HTTP Application Intermediation. Working Group Draft. URL: https://datatracker.ietf.org/doc/html/draft-ietf-ohai-ohttp
[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/
[RDF-SCHEMA]
RDF Schema 1.1. Dan Brickley; Ramanathan Guha. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/rdf-schema/
[RDF11-CONCEPTS]
RDF 1.1 Concepts and Abstract Syntax. Richard Cyganiak; David Wood; Markus Lanthaler. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/rdf11-concepts/
[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
[RFC7231]
Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content. R. Fielding, Ed.; J. Reschke, Ed.. IETF. June 2014. Proposed Standard. URL: https://httpwg.org/specs/rfc7231.html
[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
[schema-org]
Schema.org. W3C Schema.org Community Group. W3C. 6.0. URL: https://schema.org/
[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-DI-BBS]
Data Integrity BBS Cryptosuites v1.0. Greg Bernstein; Manu Sporny. W3C. 28 April 2024. W3C Candidate Recommendation. URL: https://www.w3.org/TR/vc-di-bbs/
[VC-IMP-GUIDE]
Verifiable Credentials Implementation Guidelines 1.0. Andrei Sambra; Manu Sporny. Credentials Community Group. W3C Editor's Draft. URL: https://w3c.github.io/vc-imp-guide/
[VC-JSON-SCHEMA]
Verifiable Credentials JSON Schema Specification. Gabe Cohen; Orie Steele. W3C Verifiable Credentials Working Group. FPWD. URL: https://www.w3.org/TR/vc-json-schema/
[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/
[VC-USE-CASES]
Verifiable Credentials Use Cases. Shane McCarron; Joe Andrieu; Matt Stone; Tzviya Siegman; Gregg Kellogg; Ted Thibodeau Jr. 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. Michael Cooper; Andrew Kirkpatrick; Joshue O'Connor; Alastair Campbell. W3C. 21 September 2023. W3C Recommendation. URL: https://www.w3.org/TR/WCAG21/