Decentralized Identifiers (DIDs) v1.0

Abstract

Decentralized identifiers (DIDs) are a new type of identifier that enables verifiable, decentralized digital identity. A DID identifies any subject (e.g., a person, organization, thing, data model, abstract entity, etc.) that the controller of the DID decides that it identifies. In contrast to typical, federated identifiers, DIDs have been designed so that they may be decoupled from centralized registries, identity providers, and certificate authorities. Specifically, while other parties might be used to help enable the discovery of information related to a DID, the design enables the controller of a DID to prove control over it without requiring permission from any other party. DIDs are URIs that associate a DID subject with a DID document allowing trustable interactions associated with that subject.

Each DID document can express cryptographic material, verification methods, or services, which provide a set of mechanisms enabling a DID controller to prove control of the DID. Services enable trusted interactions associated with the DID subject. A DID might provide the means to return the DID subject itself, if the DID subject is an information resource such as a data model.

This document specifies the DID syntax, a common data model, core properties, serialized representations, DID operations, and an explanation of the process of resolving DIDs to the resources that they represent.

1. Introduction

This section is non-normative.

As individuals and organizations, many of us use globally unique identifiers in a wide variety of contexts. They serve as communications addresses (telephone numbers, email addresses, usernames on social media), ID numbers (for passports, drivers licenses, tax IDs, health insurance), and product identifiers (serial numbers, barcodes, RFIDs). URIs (Uniform Resource Identifiers) are used for resources on the Web and each web page you view in a browser has a globally unique URL (Uniform Resource Locator).

The vast majority of these globally unique identifiers are not under our control. They are issued by external authorities that decide who or what they identify and when they can be revoked. They are useful only in certain contexts and recognized only by certain bodies not of our choosing. They might disappear or cease to be valid with the failure of an organization. They might unnecessarily reveal personal information. In many cases, they can be fraudulently replicated and asserted by a malicious third-party, which is more commonly known as "identity theft".

The Decentralized Identifiers (DIDs) defined in this specification are a new type of globally unique identifier. They are designed to enable individuals and organizations to generate their own identifiers using systems they trust. These new identifiers enable entities to prove control over them by authenticating using cryptographic proofs such as digital signatures.

Since the generation and assertion of Decentralized Identifiers is entity-controlled, each entity can have as many DIDs as necessary to maintain their desired separation of identities, personas, and interactions. The use of these identifiers can be scoped appropriately to different contexts. They support interactions with other people, institutions, or systems that require entities to identify themselves, or things they control, while providing control over how much personal or private data should be revealed, all without depending on a central authority to guarantee the continued existence of the identifier.

This specification does not presuppose any particular technology or cryptography to underpin the generation, persistence, resolution, or interpretation of DIDs. For example, implementers can create Decentralized Identifiers based on identifiers registered in federated or centralized identity management systems. Indeed, almost all types of identifier systems can add support for DIDs. This creates an interoperability bridge between the worlds of centralized, federated, and decentralized identifiers. This also enables implementers to design specific types of DIDs to work with the computing infrastructure they trust, such as distributed ledgers, decentralized file systems, distributed databases, and peer-to-peer networks.

This specification is for:

Anyone that wants to understand the core architectural principles that are the foundation for Decentralized Identifiers;
Software developers that want to produce and consume Decentralized Identifiers and their associated data formats;
Systems integrators that want to understand how to use Decentralized Identifiers in their software and hardware systems;
Specification authors that want to create new DID infrastructures, known as DID methods, that conform to the ecosystem described by this document.

1.1 A Simple Example

This section is non-normative.

A DID is a simple text string consisting of three parts: 1) the did URI scheme identifier, 2) the identifier for the DID method, and 3) the DID method-specific identifier.

A diagram showing the parts of a DID. The left-most letters spell 'did' in blue,
are enclosed in a horizontal bracket from above and a label that reads 'scheme'
above the bracket. A gray colon follows the 'did' letters. The middle letters
spell 'example' in magenta, are enclosed in a horizontal bracket from below and
a label that reads 'DID Method' below the bracket. A gray colon follows the
DID Method. Finally, the letters at the end read '123456789abcdefghijk' in
green, are enclosed in a horizontal bracket from below and a label that
reads 'DID Method Specific String' below the bracket. — Figure 1 A simple example of a decentralized identifier (DID)

The example DID above resolves to a DID document. A DID document contains information associated with the DID, such as ways to cryptographically authenticate a DID controller.

Example 1: A minimal DID document

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123456789abcdefghi",
  "authentication": [{
    // used to authenticate as did:...fghi
    "id": "did:example:123456789abcdefghi#keys-1",
    "type": "Ed25519VerificationKey2020",
    "controller": "did:example:123456789abcdefghi",
    "publicKeyMultibase": "zH3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
  }]
}

1.2 Design Goals

This section is non-normative.

Decentralized Identifiers are a component of larger systems, such as the Verifiable Credentials ecosystem [VC-DATA-MODEL], which influenced the design goals for this specification. The design goals for Decentralized Identifiers are summarized here.

Goal	Description
Decentralization	Eliminate the requirement for centralized authorities or single point failure in identifier management, including the registration of globally unique identifiers, public verification keys, services, and other information.
Control	Give entities, both human and non-human, the power to directly control their digital identifiers without the need to rely on external authorities.
Privacy	Enable entities to control the privacy of their information, including minimal, selective, and progressive disclosure of attributes or other data.
Security	Enable sufficient security for requesting parties to depend on DID documents for their required level of assurance.
Proof-based	Enable DID controllers to provide cryptographic proof when interacting with other entities.
Discoverability	Make it possible for entities to discover DIDs for other entities, to learn more about or interact with those entities.
Interoperability	Use interoperable standards so DID infrastructure can make use of existing tools and software libraries designed for interoperability.
Portability	Be system- and network-independent and enable entities to use their digital identifiers with any system that supports DIDs and DID methods.
Simplicity	Favor a reduced set of simple features to make the technology easier to understand, implement, and deploy.
Extensibility	Where possible, enable extensibility provided it does not greatly hinder interoperability, portability, or simplicity.

1.3 Architecture Overview

This section is non-normative.

This section provides a basic overview of the major components of Decentralized Identifier architecture.

DIDs and DID documents are recorded on a Verifiable Data Registry; DIDs resolve
to DID documents; DIDs identify DID subjects; a DID controller controls a DID
document; DID URLs contains a DID; DID URLs dereferenced to DID document
fragments or external resources. — Figure 2 Overview of DID architecture and the relationship of the basic components.

DIDs and DID URLs: A Decentralized Identifier, or DID, is a URI composed of three parts: the scheme did:, a method identifier, and a unique, method-specific identifier specified by the DID method. DIDs are resolvable to DID documents. A DID URL extends the syntax of a basic DID to incorporate other standard URI components such as path, query, and fragment in order to locate a particular resource—for example, a cryptographic public key inside a DID document, or a resource external to the DID document. These concepts are elaborated upon in § 3.1 DID Syntax and § 3.2 DID URL Syntax.
DID subjects: The subject of a DID is, by definition, the entity identified by the DID. The DID subject might also be the DID controller. Anything can be the subject of a DID: person, group, organization, thing, or concept. This is further defined in § 5.1.1 DID Subject.
DID controllers: The controller of a DID is the entity (person, organization, or autonomous software) that has the capability—as defined by a DID method—to make changes to a DID document. This capability is typically asserted by the control of a set of cryptographic keys used by software acting on behalf of the controller, though it might also be asserted via other mechanisms. Note that a DID might have more than one controller, and the DID subject can be the DID controller, or one of them. This concept is documented in § 5.1.2 DID Controller.
Verifiable data registries: In order to be resolvable to DID documents, DIDs are typically recorded on an underlying system or network of some kind. Regardless of the specific technology used, any such system that supports recording DIDs and returning data necessary to produce DID documents is called a verifiable data registry. Examples include distributed ledgers, decentralized file systems, databases of any kind, peer-to-peer networks, and other forms of trusted data storage. This concept is further elaborated upon in § 8. Methods.
DID documents: DID documents contain information associated with a DID. They typically express verification methods, such as cryptographic public keys, and services relevant to interactions with the DID subject. The generic properties supported in a DID document are specified in § 5. Core Properties. A DID document can be serialized to a byte stream (see § 6. Representations). The properties present in a DID document can be updated according to the applicable operations outlined in § 8. Methods.
DID methods: DID methods are the mechanism by which a particular type of DID and its associated DID document are created, resolved, updated, and deactivated. DID methods are defined using separate DID method specifications as defined in § 8. Methods.
DID resolvers and DID resolution: A DID resolver is a system component that takes a DID as input and produces a conforming DID document as output. This process is called DID resolution. The steps for resolving a specific type of DID are defined by the relevant DID method specification. The process of DID resolution is elaborated upon in § 7. Resolution.
DID URL dereferencers and DID URL dereferencing: A DID URL dereferencer is a system component that takes a DID URL as input and produces a resource as output. This process is called DID URL dereferencing. The process of DID URL dereferencing is elaborated upon in § 7.2 DID URL Dereferencing.

1.4 Conformance

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

The key words MAY, MUST, MUST NOT, 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.

This document contains examples that contain JSON, CBOR, and JSON-LD content. Some of these examples contain characters that are invalid, 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 valid JSON, CBOR, or JSON-LD.

Some examples contain terms, both property names and values, that are not defined in this specification. These are indicated with a comment (// external (property name|value)). Such terms, when used in a DID document, are expected to be registered in the DID Specification Registries [DID-SPEC-REGISTRIES] with links to both a formal definition and a JSON-LD context.

Interoperability of implementations for DIDs and DID documents is tested by evaluating an implementation's ability to create and parse DIDs and DID documents that conform to this specification. Interoperability for producers and consumers of DIDs and DID documents is provided by ensuring the DIDs and DID documents conform. Interoperability for DID method specifications is provided by the details in each DID method specification. It is understood that, in the same way that a web browser is not required to implement all known URI schemes, conformant software that works with DIDs is not required to implement all known DID methods. However, all implementations of a given DID method are expected to be interoperable for that method.

A conforming DID is any concrete expression of the rules specified in § 3. Identifier which complies with relevant normative statements in that section.

A conforming DID document is any concrete expression of the data model described in this specification which complies with the relevant normative statements in § 4. Data Model and § 5. Core Properties. A serialization format for the conforming document is deterministic, bi-directional, and lossless, as described in § 6. Representations.

A conforming DID method is any specification that complies with the relevant normative statements in § 8. Methods.

A conforming producer is any algorithm realized as software and/or hardware that generates conforming DIDs or conforming DID Documents. A conforming producer MUST NOT produce non-conforming DIDs or DID documents.

A conforming consumer is any algorithm realized as software and/or hardware that consumes conforming DIDs or conforming DID documents. A conforming consumer MUST produce errors when consuming non-conforming DIDs or DID documents.

A conforming DID resolver is any algorithm realized as software and/or hardware that complies with the relevant normative statements in § 7.1 DID Resolution.

A conforming DID URL dereferencer is any algorithm realized as software and/or hardware that complies with the relevant normative statements in § 7.2 DID URL Dereferencing.

2. Terminology

This section is non-normative.

This section defines the terms used in this specification and throughout decentralized identifier infrastructure. A link to these terms is included whenever they appear in this specification.

authenticate

Authentication is a process by which an entity can prove it has a specific attribute or controls a specific secret using one or more verification methods. With DIDs, a common example would be proving control of the cryptographic private key associated with a public key published in a DID document.

binding

A concrete mechanism used by a caller to invoke a DID resolver or a DID URL dereferencer. This could be a local command line tool, a software library, or a network call such as an HTTPS request.

decentralized identifier (DID)

A globally unique persistent identifier that does not require a centralized registration authority and is often generated and/or registered cryptographically. The generic format of a DID is defined in § 3.1 DID Syntax. A specific DID scheme is defined in a DID method specification. Many—but not all—DID methods make use of distributed ledger technology (DLT) or some other form of decentralized network.

decentralized identity management

Identity management that is based on the use of decentralized identifiers. Decentralized identity management extends authority for identifier generation, registration, and assignment beyond traditional roots of trust such as X.500 directory services, the Domain Name System, and most national ID systems.

DID controller

An entity that has the capability to make changes to a DID document. A DID might have more than one DID controller. The DID controller(s) can be denoted by the optional controller property at the top level of the DID document. Note that a DID controller might be the DID subject.

DID delegate

An entity to whom a DID controller has granted permission to use a verification method associated with a DID via a DID document. For example, a parent who controls a child's DID document might permit the child to use their personal device in order to authenticate. In this case, the child is the DID delegate. The child's personal device would contain the private cryptographic material enabling the child to authenticate using the DID. However, the child might not be permitted to add other personal devices without the parent's permission.

DID document

A set of data describing the DID subject, including mechanisms, such as cryptographic public keys, that the DID subject or a DID delegate can use to authenticate itself and prove its association with the DID. A DID document might have one or more different representations as defined in § 6. Representations or in the W3C DID Specification Registries [DID-SPEC-REGISTRIES].

DID fragment

The portion of a DID URL that follows the first hash sign character (#). DID fragment syntax is identical to URI fragment syntax.

DID method

A definition of how a specific DID method scheme is implemented. A DID method is defined by a DID method specification, which specifies the precise operations by which DIDs and DID documents are created, resolved, updated, and deactivated. See § 8. Methods.

DID path

The portion of a DID URL that begins with and includes the first forward slash (/) character and ends with either a question mark (?) character, a fragment hash sign (#) character, or the end of the DID URL. DID path syntax is identical to URI path syntax. See § Path.

DID query

The portion of a DID URL that follows and includes the first question mark character (?). DID query syntax is identical to URI query syntax. See § Query.

DID resolution

The process that takes as its input a DID and a set of resolution options and returns a DID document in a conforming representation plus additional metadata. This process relies on the "Read" operation of the applicable DID method. The inputs and outputs of this process are defined in § 7.1 DID Resolution.

DID resolver

A DID resolver is a software and/or hardware component that performs the DID resolution function by taking a DID as input and producing a conforming DID document as output.

DID scheme

The formal syntax of a decentralized identifier. The generic DID scheme begins with the prefix did: as defined in § 3.1 DID Syntax. Each DID method specification defines a specific DID method scheme that works with that specific DID method. In a specific DID method scheme, the DID method name follows the first colon and terminates with the second colon, e.g., did:example:

DID subject

The entity identified by a DID and described by a DID document. Anything can be a DID subject: person, group, organization, physical thing, digital thing, logical thing, etc.

DID URL

A DID plus any additional syntactic component that conforms to the definition in § 3.2 DID URL Syntax. This includes an optional DID path (with its leading / character), optional DID query (with its leading ? character), and optional DID fragment (with its leading # character).

DID URL dereferencing

The process that takes as its input a DID URL and a set of input metadata, and returns a resource. This resource might be a DID document plus additional metadata, a secondary resource contained within the DID document, or a resource entirely external to the DID document. The process uses DID resolution to fetch a DID document indicated by the DID contained within the DID URL. The dereferencing process can then perform additional processing on the DID document to return the dereferenced resource indicated by the DID URL. The inputs and outputs of this process are defined in § 7.2 DID URL Dereferencing.

DID URL dereferencer

A software and/or hardware system that performs the DID URL dereferencing function for a given DID URL or DID document.

distributed ledger (DLT)

A non-centralized system for recording events. These systems establish sufficient confidence for participants to rely upon the data recorded by others to make operational decisions. They typically use distributed databases where different nodes use a consensus protocol to confirm the ordering of cryptographically signed transactions. The linking of digitally signed transactions over time often makes the history of the ledger effectively immutable.

public key description

A data object contained inside a DID document that contains all the metadata necessary to use a public key or a verification key.

resource

As defined by [RFC3986]: "...the term 'resource' is used in a general sense for whatever might be identified by a URI." Similarly, any resource might serve as a DID subject identified by a DID.

representation

As defined for HTTP by [RFC7231]: "information that is intended to reflect a past, current, or desired state of a given resource, in a format that can be readily communicated via the protocol, and that consists of a set of representation metadata and a potentially unbounded stream of representation data." A DID document is a representation of information describing a DID subject. See § 6. Representations.

services

Means of communicating or interacting with the DID subject or associated entities via one or more service endpoints. Examples include discovery services, agent services, social networking services, file storage services, and verifiable credential repository services.

service endpoint

A network address, such as an HTTP URL, at which services operate on behalf of a DID subject.

Uniform Resource Identifier (URI)

The standard identifier format for all resources on the World Wide Web as defined by [RFC3986]. A DID is a type of URI scheme.

verifiable credential

A standard data model and representation format for cryptographically-verifiable digital credentials as defined by the W3C Verifiable Credentials specification [VC-DATA-MODEL].

verifiable data registry

A system that facilitates the creation, verification, updating, and/or deactivation of decentralized identifiers and DID documents. A verifiable data registry might also be used for other cryptographically-verifiable data structures such as verifiable credentials. For more information, see the W3C Verifiable Credentials specification [VC-DATA-MODEL].

verifiable timestamp

A verifiable timestamp enables a third-party to verify that a data object existed at a specific moment in time and that it has not been modified or corrupted since that moment in time. If the data integrity could reasonably have been modified or corrupted since that moment in time, the timestamp is not verifiable.

verification method

A set of parameters that can be used together with a process to independently verify a proof. For example, a cryptographic public key can be used as a verification method with respect to a digital signature; in such usage, it verifies that the signer possessed the associated cryptographic private key.

"Verification" and "proof" in this definition are intended to apply broadly. For example, a cryptographic public key might be used during Diffie-Hellman key exchange to negotiate a shared symmetric key for encryption. This guarantees the integrity of the key agreement process. It is thus another type of verification method, even though descriptions of the process might not use the words "verification" or "proof."

verification relationship

An expression of the relationship between the DID subject and a verification method. An example of a verification relationship is § 5.3.1 Authentication.

Universally Unique Identifier (UUID)

A type of globally unique identifier defined by [RFC4122]. UUIDs are similar to DIDs in that they do not require a centralized registration authority. UUIDs differ from DIDs in that they are not resolvable or cryptographically-verifiable.

In addition to the terminology above, this specification also uses terminology from the [INFRA] specification to formally define the data model. When [INFRA] terminology is used, such as string, set, and map, it is linked directly to that specification.

3. Identifier

This section describes the formal syntax for DIDs and DID URLs. The term "generic" is used to differentiate the syntax defined here from syntax defined by specific DID methods in their respective specifications.

3.1 DID Syntax

The generic DID scheme is a URI scheme conformant with [RFC3986]. The ABNF definition can be found below, which uses the syntax in [RFC5234] and the corresponding definitions for ALPHA and DIGIT. All other rule names not defined in the ABNF below are defined in [RFC3986]. All DIDs MUST conform to the DID Syntax ABNF Rules.

(Feature at Risk) Issue: Should DID syntax allow an empty 'method-specific-id'?

This ABNF does not currently permit an empty method-specific-id string. Some DID methods have expressed an interest in providing resolution of a DID with an empty method-specific-id string, for example to enable discovery of a DID document describing a verifiable data registry by resolving the DID method name alone. The Working Group is requesting feedback during the Candidate Recommendation stage on whether or not an empty method-specific-id string is of interest to implementers. This feature may change as a result of that feedback. See also Issue 34.

The DID Syntax ABNF Rules
did = "did:" method-name ":" method-specific-id method-name = 1method-char method-char = %x61-7A / DIGIT method-specific-id = ( idchar ":" ) 1idchar idchar = ALPHA / DIGIT / "." / "-" / "_"

For requirements on DID methods relating to the DID syntax, see Section § 8.1 Method Syntax.

3.2 DID URL Syntax

A DID URL is a network location identifier for a specific resource. It can be used to retrieve things like representations of DID subjects, verification methods, services, specific parts of a DID document, or other resources.

The following is the ABNF definition using the syntax in [RFC5234]. It builds on the did scheme defined in § 3.1 DID Syntax. The path-abempty, query, and fragment components are defined in [RFC3986]. All DID URLs MUST conform to the DID URL Syntax ABNF Rules. DID methods can further restrict these rules, as described in § 8.1 Method Syntax.

The DID URL Syntax ABNF Rules
did-url = did path-abempty [ "?" query ] [ "#" fragment ]

Note: Semicolon character is reserved for future use

Although the semicolon (;) character can be used according to the rules of the DID URL syntax, future versions of this specification may use it as a sub-delimiter for parameters as described in [MATRIX-URIS]]. To avoid future conflicts, developers ought to refrain from using it.

Path

A DID path is identical to a generic URI path and conforms to the path-abempty ABNF rule in RFC 3986, section 3.3.

Example 2

did:example:123456/path

Query

A DID query is identical to a generic URI query and conforms to the query ABNF rule in RFC 3986, section 3.4. This syntax feature is elaborated upon in § 3.2.1 DID Parameters.

Example 3

did:example:123456?versionId=1

Fragment

DID fragment syntax and semantics are identical to a generic URI fragment and conforms to the fragment ABNF rule in RFC 3986, section 3.5.

A DID fragment is used as a method-independent reference into a DID document or external resource. Some examples of DID fragment identifiers are shown below.

Example 4: A unique verification method in a DID Document

did:example:123#public-key-0

Example 5: A unique service in a DID Document

did:example:123#agent

Example 6: A resource external to a DID Document

did:example:123?service=agent&relativeRef=/credentials#degree

Note: Fragment semantics across representations

In order to maximize interoperability, implementers are urged to ensure that DID fragments are interpreted in the same way across representations (see § 6. Representations). For example, while JSON Pointer [RFC6901] can be used in a DID fragment, it will not be interpreted in the same way across non-JSON representations.

Additional semantics for fragment identifiers, which are compatible with and layered upon the semantics in this section, are described for JSON-LD representations in § B.2 application/did+ld+json. For information about how to dereference a DID fragment, see § 7.2 DID URL Dereferencing.

3.2.1 DID Parameters

The DID URL syntax supports a simple format for parameters based on the query component described in § Query. Adding a DID parameter to a DID URL means that the parameter becomes part of the identifier for a resource.

Example 7: A DID URL with a 'versionTime' DID parameter

did:example:123?versionTime=2021-05-10T17:00:00Z

Example 8: A DID URL with a 'service' and a 'relativeRef' DID parameter

did:example:123?service=files&relativeRef=/resume.pdf

Some DID parameters are completely independent of of any specific DID method and function the same way for all DIDs. Other DID parameters are not supported by all DID methods. Where optional parameters are supported, they are expected to operate uniformly across the DID methods that do support them. The following table provides common DID parameters that function the same way across all DID methods. Support for all DID Parameters is OPTIONAL.

Parameter Name	Description
`service`	Identifies a service from the DID document by service ID. If present, the associated value MUST be an ASCII string.
`relativeRef`	A relative URI reference according to RFC3986 Section 4.2 that identifies a resource at a service endpoint, which is selected from a DID document by using the `service` parameter. If present, the associated value MUST be an ASCII string and MUST use percent-encoding for certain characters as specified in RFC3986 Section 2.1.
`versionId`	Identifies a specific version of a DID document to be resolved (the version ID could be sequential, or a UUID, or method-specific). If present, the associated value MUST be an ASCII string.
`versionTime`	Identifies a certain version timestamp of a DID document to be resolved. That is, the DID document that was valid for a DID at a certain time. If present, the associated value MUST be an ASCII string which is a valid XML datetime value, as defined in section 3.3.7 of W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes [XMLSCHEMA11-2]. This datetime value MUST be normalized to UTC 00:00:00 and without sub-second decimal precision. For example: `2020-12-20T19:17:47Z`.
`hl`	A resource hash of the DID document to add integrity protection, as specified in [HASHLINK]. This parameter is non-normative. If present, the associated value MUST be an ASCII string.

Implementers as well as DID method specification authors might use additional DID parameters that are not listed here. For maximum interoperability, it is RECOMMENDED that DID parameters use the DID Specification Registries mechanism [DID-SPEC-REGISTRIES], to avoid collision with other uses of the same DID parameter with different semantics.

DID parameters might be used if there is a clear use case where the parameter needs to be part of a URL that references a resource with more precision than using the DID alone. It is expected that DID parameters are not used if the same functionality can be expressed by passing input metadata to a DID resolver. Additional considerations for processing these parameters are discussed in [DID-RESOLUTION].

Note: DID parameters and DID resolution

The DID resolution and the DID URL dereferencing functions can be influenced by passing input metadata to a DID resolver that are not part of the DID URL (see § 7.1.1 DID Resolution Options). This is comparable to HTTP, where certain parameters could either be included in an HTTP URL, or alternatively passed as HTTP headers during the dereferencing process. The important distinction is that DID parameters that are part of the DID URL should be used to specify what resource is being identified, whereas input metadata that is not part of the DID URL should be use to control how that resource is resolved or dereferenced.

3.2.2 Relative DID URLs

A relative DID URL is any URL value in a DID document that does not start with did:<method-name>:<method-specific-id>. More specifically, it is any URL value that does not start with the ABNF defined in § 3.1 DID Syntax. The URL is expected to reference a resource in the same DID document. Relative DID URLs MAY contain relative path components, query parameters, and fragment identifiers.

When resolving a relative DID URL reference, the algorithm specified in RFC3986 Section 5: Reference Resolution MUST be used. The base URI value is the DID that is associated with the DID subject, see § 5.1.1 DID Subject. The scheme is did. The authority is a combination of <method-name>:<method-specific-id>, and the path, query, and fragment values are those defined in § Path, § Query, and § Fragment, respectively.

Relative DID URLs are often used to reference verification methods and services in a DID Document without having to use absolute URLs. DID methods where storage size is a consideration might use relative URLs to reduce the storage size of DID documents.

Example 9: An example of a relative DID URL

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123456789abcdefghi",
  "verificationMethod": [{
    "id": "did:example:123456789abcdefghi#key-1",
    "type": "Ed25519VerificationKey2018", // external (property value)
    "controller": "did:example:123456789abcdefghi",
    "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
  }, ...],
  "authentication": [
    // a relative DID URL used to reference a verification method above
    "#key-1"
  ]
}

In the example above, the relative DID URL value will be transformed to an absolute DID URL value of did:example:123456789abcdefghi#key-1.

Data Type	Considerations
map	A finite ordered sequence of key/value pairs, with no key appearing twice as specified in [INFRA]. A map is sometimes referred to as an ordered map in [INFRA].
list	A finite ordered sequence of items as specified in [INFRA].
set	A finite ordered sequence of items that does not contain the same item twice as specified in [INFRA]. A set is sometimes referred to as an ordered set in [INFRA].
datetime	A date and time value that is capable of losslessly expressing all values expressible by a `dateTime` as specified in [XMLSCHEMA11-2].
string	A sequence of code units often used to represent human readable language as specified in [INFRA].
integer	A real number without a fractional component as specified in [XMLSCHEMA11-2]. To maximize interoperability, implementers are urged to heed the advice regarding integers in RFC8259, Section 6: Numbers.
double	A value that is often used to approximate arbitrary real numbers as specified in [XMLSCHEMA11-2]. To maximize interoperability, implementers are urged to heed the advice regarding doubles in RFC8259, Section 6: Numbers.
boolean	A value that is either true or false as defined in [INFRA].
null	A value that is used to indicate the lack of a value as defined in [INFRA].

5. Core Properties

A DID is associated with a DID document. DID documents are expressed using the data model and can be serialized into a representation. The following sections define the properties in a DID document, including whether these properties are required or optional. These properties describe relationships between the DID subject and the value of the property.

The following tables contain informative references for the core properties defined by this specification, with expected values, and whether or not they are required. The property names in the tables are linked to the normative definitions and more detailed descriptions of each property.

Note: Property names used in maps of different types

The property names id, type, and controller can be present in maps of different types with possible differences in constraints.

DID Document properties

Property	Required?	Value constraints
`id`	yes	A string that conforms to the rules in § 3.1 DID Syntax.
`alsoKnownAs`	no	A set of strings that conform to the rules of [RFC3986] for URIs.
`controller`	no	A string or a set of strings that conform to the rules in § 3.1 DID Syntax.
`verificationMethod`	no	A set of Verification Method maps that conform to the rules in § Verification Method properties.
`authentication`	no	A set of either Verification Method maps that conform to the rules in § Verification Method properties) or strings that conform to the rules in § 3.2 DID URL Syntax.
`assertionMethod`	no
`keyAgreement`	no
`capabilityInvocation`	no
`capabilityDelegation`	no
`service`	no	A set of Service Endpoint maps that conform to the rules in § Service properties.

Verification Method properties

Property	Required?	Value constraints
`id`	yes	A string that conforms to the rules in § 3.2 DID URL Syntax.
`controller`	yes	A string that conforms to the rules in § 3.1 DID Syntax.
`type`	yes	A string.
`publicKeyJwk`	no	A map representing a JSON Web Key that conforms to [RFC7517]. See definition of publicKeyJwk for additional constraints.
`publicKeyBase58`	no	A string that conforms to a base58btc encoded public key.

Service properties

Property	Required?	Value constraints
`id`	yes	A string that conforms to the rules of [RFC3986] for URIs.
`type`	yes	A string or a set of strings.
`serviceEndpoint`	yes	A string that conforms to the rules of [RFC3986] for URIs, a map, or a set composed of a one or more strings that conform to the rules of [RFC3986] for URIs and/or maps.

5.1 Identifiers

This section describes the mechanisms by which DID documents include identifiers for DID subjects and DID controllers.

5.1.1 DID Subject

The DID for a particular DID subject is expressed using the id property in the DID document.

id: The value of id MUST be a string that conforms to the rules in § 3.1 DID Syntax and MUST exist in the root map of the data model for the DID document.

Example 10

{
  "id": "did:example:123456789abcdefghijk"
}

The id property only denotes the DID of the DID subject when it is present in the topmost map of the DID document.

Note: Intermediate representations

DID method specifications can create intermediate representations of a DID document that do not contain the id property, such as when a DID resolver is performing DID resolution. However, the fully resolved DID document always contains a valid id property.

5.1.2 DID Controller

A DID controller is an entity that is authorized to make changes to a DID document. The process of authorizing a DID controller is defined by the DID method.

controller: The controller property is OPTIONAL. If present, the value MUST be a string or a set of strings that conform to the rules in § 3.1 DID Syntax. The corresponding DID document(s) SHOULD contain verification relationships that explicitly permit the use of certain verification methods for specific purposes.

When a controller property is present in a DID document, its value expresses one or more DIDs. Any verification methods contained in the DID documents for those DIDs SHOULD be accepted as authoritative, such that proofs that satisfy those verification methods are to be considered equivalent to proofs provided by the DID subject.

Example 11: DID document with a controller property

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123456789abcdefghi",
  "controller": "did:example:bcehfew7h32f32h7af3",
}

Note: Authorization vs authentication

Note that authorization provided by the value of controller is separate from authentication as described in § 5.3.1 Authentication. This is particularly important for key recovery in the case of cryptographic key loss, where the DID subject no longer has access to their keys, or key compromise, where the DID controller's trusted third parties need to override malicious activity by an attacker. See § 9. Security Considerations for information related to threat models and attack vectors.

5.1.3 Also Known As

(Feature at Risk) Issue: Implementation of alsoKnownAs

The DID Working Group is seeking implementer feedback regarding the alsoKnownAs feature. If there is not enough implementer interest in implementing this feature, it will be removed from this specification and placed into the DID Specification Registries [DID-SPEC-REGISTRIES] as an extension.

A DID subject can have multiple identifiers for different purposes, or at different times. The assertion that two or more DIDs (or other types of URI) identify the same DID subject can be made using the alsoKnownAs property.

alsoKnownAs: The alsoKnownAs property is OPTIONAL. If present, the value MUST be a set where each item in the set is a URI conforming to [RFC3986].; This relationship is a statement that the subject of this identifier is also identified by one or more other identifiers.

Note: Equivalence and alsoKnownAs

Applications might choose to consider two identifiers related by alsoKnownAs to be equivalent if the alsoKnownAs relationship is reciprocated in the reverse direction. It is best practice not to consider them equivalent in the absence of this inverse relationship. In other words, the presence of an alsoKnownAs assertion does not prove that this assertion is true. Therefore, it is strongly advised that a requesting party obtain independent verification of an alsoKnownAs assertion.

Given that the DID subject might use different identifiers for different purposes, an expectation of strong equivalence between the two identifiers, or merging the information of the two corresponding DID documents, is not necessarily appropriate, even with a reciprocal relationship.

5.2 Verification Methods

A DID document can express verification methods, such as cryptographic public keys, which can be used to authenticate or authorize interactions with the DID subject or associated parties. For example, a cryptographic public key can be used as a verification method with respect to a digital signature; in such usage, it verifies that the signer could use the associated cryptographic private key. Verification methods might take many parameters. An example of this is a set of five cryptographic keys from which any three are required to contribute to a cryptographic threshold signature.

verificationMethod

The verificationMethod property is OPTIONAL. If present, the value MUST be a set of verification methods, where each verification method is expressed using a map. The verification method map MUST include the id, type, controller, and specific verification material properties that are determined by the value of type and are defined in § 5.2.1 Verification Material. A verification method MAY include additional properties. Verification methods SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES].

id: The value of the id property for a verification method MUST be a string that conforms to the rules in Section § 3.2 DID URL Syntax.
type: The value of the type property MUST be a string that references exactly one verification method type. In order to maximize global interoperability, the verification method type SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES].
controller: The value of the controller property MUST be a string that conforms to the rules in § 3.1 DID Syntax.

Example 12: Example verification method structure

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123456789abcdefghi",
  ...
  "verificationMethod": [{
    "id": ...,
    "type": ...,
    "controller": ...,
    "publicKeyJwk": ...
  }, {
    "id": ...,
    "type": ...,
    "controller": ...,
    "publicKeyBase58": ...
  }]
}

Note: Verification method controller(s) and DID controller(s)

The semantics of the controller property are the same when the subject of the relationship is the DID document as when the subject of the relationship is a verification method, such as a cryptographic public key. Since a key can't control itself, and the key controller cannot be inferred from the DID document, it is necessary to explicitly express the identity of the controller of the key. The difference is that the value of controller for a verification method is not necessarily a DID controller. DID controllers are expressed using the controller property at the highest level of the DID document (the topmost map in the data model); see § 5.1.2 DID Controller.

5.2.1 Verification Material

Verification material is any information that is used by a process that applies a verification method. The type of a verification method is expected to be used to determine its compatibility with such processes. Examples of verification material properties are publicKeyJwk or publicKeyBase58. A verification suite definition is responsible for specifying the verification method type and its associated verification material. For example, see JSON Web Signature 2020 and Ed25519 Signature 2018. For all registered verification method types and associated verification material available for DIDs, please see the DID Specification Registries [DID-SPEC-REGISTRIES].

To increase the likelihood of interoperable implementations, this specification limits the number of formats for expressing verification material in a DID document. The fewer formats that implementers have to implement, the more likely it will be that they will support all of them. This approach attempts to strike a delicate balance between ease of implementation and supporting formats that have historically had broad deployment. Two supported verification material properties are listed below:

publicKeyBase58: The publicKeyBase58 property is OPTIONAL. This feature is non-normative. If present, the value MUST be a string representation of a [BASE58] encoded public key.

(Feature at Risk) Issue: publicKeyBase58 and publicKeyMultibase
The DID Working Group is seeking implementer feedback on the preference of the ecosystem with respect to using publicKeyBase58 [BASE58] or publicKeyMultibase [MULTIBASE]. The latter can be used for encoding more base-representation formats and provides a more future proof path. Depending on implementer feedback, one or both options might be included in the final specification, or migrated into the DID Specification Registries as an extension.
publicKeyJwk: The publicKeyJwk property is OPTIONAL. If present, the value MUST be a map representing a JSON Web Key that conforms to [RFC7517]. The map MUST NOT contain "d", or any other members of the private information class as described in Registration Template. It is RECOMMENDED that verification methods that use JWKs [RFC7517] to represent their public keys use the value of kid as their fragment identifier. It is RECOMMENDED that JWK kid values are set to the public key fingerprint [RFC7638]. See the first key in Example 13 for an example of a public key with a compound key identifier.

A verification method MUST NOT contain multiple verification material properties for the same material. For example, expressing key material in a verification method using both publicKeyJwk and publicKeyBase58 at the same time is prohibited.

An example of a DID document containing verification methods using both properties above is shown below.

Example 13: Verification methods using publicKeyJwk and publicKeyBase58

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123456789abcdefghi",
  ...
  "verificationMethod": [{
    "id": "did:example:123#_Qq0UL2Fq651Q0Fjd6TvnYE-faHiOpRlPVQcY_-tA4A",
    "type": "JsonWebKey2020", // external (property value)
    "controller": "did:example:123",
    "publicKeyJwk": {
      "crv": "Ed25519", // external (property name)
      "x": "VCpo2LMLhn6iWku8MKvSLg2ZAoC-nlOyPVQaO3FxVeQ", // external (property name)
      "kty": "OKP", // external (property name)
      "kid": "_Qq0UL2Fq651Q0Fjd6TvnYE-faHiOpRlPVQcY_-tA4A" // external (property name)
    }
  }, {
    "id": "did:example:123456789abcdefghi#keys-1",
    "type": "Ed25519VerificationKey2018", // external (property value)
    "controller": "did:example:pqrstuvwxyz0987654321",
    "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
  }],
  ...
}

5.2.2 Referring to Verification Methods

Verification methods can be embedded in or referenced from properties associated with various verification relationships as described in § 5.3 Verification Relationships. Referencing verification methods allows them to be used by more than one verification relationship.

If the value of a verification method property is a map, the verification method has been embedded and its properties can be accessed directly. However, if the value is a URL string, the verification method has been included by reference and its properties will need to be retrieved from elsewhere in the DID document or from another DID document. This is done by dereferencing the URL and searching the resulting resource for a verification method map with an id property whose value matches the URL.

Example 14: Embedding and referencing verification methods

{
...

  "authentication": [
    // this key is referenced and might be used by
    // more than one verification relationship
    "did:example:123456789abcdefghi#keys-1",
    // this key is embedded and may *only* be used for authentication
    {
      "id": "did:example:123456789abcdefghi#keys-2",
      "type": "Ed25519VerificationKey2018", // external (property value)
      "controller": "did:example:123456789abcdefghi",
      "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
    }
  ],

...
}

5.3 Verification Relationships

A verification relationship expresses the relationship between the DID subject and a verification method.

Different verification relationships enable the associated verification methods to be used for different purposes. It is up to a verifier to ascertain the validity of a verification attempt by checking that the verification method used is contained in the appropriate verification relationship property of the DID Document.

The verification relationship between the DID subject and the verification method is explicit in the DID document. Verification methods that are not associated with a particular verification relationship cannot be used for that verification relationship. For example, a verification method in the value of the authentication property cannot be used to engage in key agreement protocols with the DID subject—the value of the keyAgreement property needs to be used for that.

The DID document does not express revoked keys using a verification relationship. If a referenced verification method is not in the latest DID Document used to dereference it, then that verification method is considered invalid or revoked. Each DID method specification is expected to detail how revocation is performed and tracked.

The following sections define several useful verification relationships. A DID document MAY include any of these, or other properties, to express a specific verification relationship. In order to maximize global interoperability, any such properties used SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES].

5.3.1 Authentication

The authentication verification relationship is used to specify how the DID subject is expected to be authenticated, for purposes such as logging into a website or engaging in any sort of challenge-response protocol.

authentication: The authentication property is OPTIONAL. If present, the associated value MUST be a set of one or more verification methods. Each verification method MAY be embedded or referenced.

Example 15: Authentication property containing three verification methods

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123456789abcdefghi",
  ...
  "authentication": [
    // this method can be used to authenticate as did:...fghi
    "did:example:123456789abcdefghi#keys-1",
    // this method is *only* approved for authentication, it may not
    // be used for any other proof purpose, so its full description is
    // embedded here rather than using only a reference
    {
      "id": "did:example:123456789abcdefghi#keys-2",
      "type": "Ed25519VerificationKey2018",
      "controller": "did:example:123456789abcdefghi",
      "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
    }
  ],
  ...
}

If authentication is established, it is up to the DID method or other application to decide what to do with that information. A particular DID method could decide that authenticating as a DID controller is sufficient to, for example, update or delete the DID document. Another DID method could require different keys, or a different verification method entirely, to be presented in order to update or delete the DID document than that used to authenticate. In other words, what is done after the authentication check is out of scope for the data model; DID methods and applications are expected to define this themselves.

This is useful to any authentication verifier that needs to check to see if an entity that is attempting to authenticate is, in fact, presenting a valid proof of authentication. When a verifier receives some data (in some protocol-specific format) that contains a proof that was made for the purpose of "authentication", and that says that an entity is identified by the DID, then that verifier checks to ensure that the proof can be verified using a verification method (e.g., public key) listed under authentication in the DID Document.

Note that the verification method indicated by the authentication property of a DID document can only be used to authenticate the DID subject. To authenticate a different DID controller, the entity associated with the value of controller, as defined in § 5.1.2 DID Controller, needs to authenticate with its own DID document and associated authentication verification relationship.

5.3.2 Assertion

The assertionMethod verification relationship is used to specify how the DID subject is expected to express claims, such as for the purposes of issuing a Verifiable Credential [VC-DATA-MODEL].

assertionMethod: The assertionMethod property is OPTIONAL. If present, the associated value MUST be a set of one or more verification methods. Each verification method MAY be embedded or referenced.

This property is useful, for example, during the processing of a verifiable credential by a verifier. During verification, a verifier checks to see if a verifiable credential contains a proof created by the DID subject by checking that the verification method used to assert the proof is associated with the assertionMethod property in the corresponding DID document.

Example 16: Assertion method property containing two verification methods

{
"@context": "https://www.w3.org/ns/did/v1",
"id": "did:example:123456789abcdefghi",
...
"assertionMethod": [
  // this method can be used to assert statements as did:...fghi
  "did:example:123456789abcdefghi#keys-1",
  // this method is *only* approved for assertion of statements, it is not
  // used for any other verification relationship, so its full description is
  // embedded here rather than using a reference
  {
    "id": "did:example:123456789abcdefghi#keys-2",
    "type": "Ed25519VerificationKey2018", // external (property value)
    "controller": "did:example:123456789abcdefghi",
    "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
  }
],
...
}

5.3.3 Key Agreement

The keyAgreement verification relationship is used to specify how an entity can generate encryption material in order to transmit confidential information intended for the DID subject, such as for the purposes of establishing a secure communication channel with the recipient.

keyAgreement: The keyAgreement property is OPTIONAL. If present, the associated value MUST be a set of one or more verification methods. Each verification method MAY be embedded or referenced.

An example of when this property is useful is when encrypting a message intended for the DID subject. In this case, the counterparty uses the cryptographic public key information in the verification method to wrap a decryption key for the recipient.

Example 17: Key agreement property containing two verification methods

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123456789abcdefghi",
  ...
  "keyAgreement": [
    // this method can be used to perform key agreement as did:...fghi
    "did:example:123456789abcdefghi#keys-1",
    // this method is *only* approved for key agreement usage, it will not
    // be used for any other verification relationship, so its full description is
    // embedded here rather than using only a reference
    {
      "id": "did:example:123#zC9ByQ8aJs8vrNXyDhPHHNNMSHPcaSgNpjjsBYpMMjsTdS",
      "type": "X25519KeyAgreementKey2019", // external (property value)
      "controller": "did:example:123",
      "publicKeyBase58": "9hFgmPVfmBZwRvFEyniQDBkz9LmV7gDEqytWyGZLmDXE"
    }
  ],
  ...
}

5.3.4 Capability Invocation

The capabilityInvocation verification relationship is used to specify a verification method that might be used by the DID subject to invoke a cryptographic capability, such as the authorization to update the DID Document.

capabilityInvocation: The capabilityInvocation property is OPTIONAL. If present, the associated value MUST be a set of one or more verification methods. Each verification method MAY be embedded or referenced.

An example of when this property is useful is when a DID subject needs to access a protected HTTP API that requires authorization in order to use it. In order to authorize when using the HTTP API, the DID subject uses a capability that is associated with a particular URL that is exposed via the HTTP API. The invocation of the capability could be expressed in a number of ways, e.g., as a digitally signed message that is placed into the HTTP Headers.

The server providing the HTTP API is the verifier of the capability and it would need to verify that the verification method referred to by the invoked capability exists in the capabilityInvocation property of the DID document. The verifier would also check to make sure that the action being performed is valid and the capability is appropriate for the resource being accessed. If the verification is successful, the server has cryptographically determined that the invoker is authorized to access the protected resource.

Example 18: Capability invocation property containing two verification methods

{
  "@context": "https://www.w3.org/ns/did/v1", "id":
  "did:example:123456789abcdefghi",
  ...
  "capabilityInvocation": [
    // this method can be used to invoke capabilities as did:...fghi
    "did:example:123456789abcdefghi#keys-1",
    // this method is *only* approved for capability invocation usage, it will not
    // be used for any other verification relationship, so its full description is
    // embedded here rather than using only a reference
    {
    "id": "did:example:123456789abcdefghi#keys-2",
    "type": "Ed25519VerificationKey2018", // external (property value)
    "controller": "did:example:123456789abcdefghi",
    "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
    }
  ],
  ...
}

5.3.5 Capability Delegation

The capabilityDelegation verification relationship is used to specify a mechanism that might be used by the DID subject to delegate a cryptographic capability to another party, such as delegating the authority to access a specific HTTP API to a subordinate.

capabilityDelegation: The capabilityDelegation property is OPTIONAL. If present, the associated value MUST be a set of one or more verification methods. Each verification method MAY be embedded or referenced.

An example of when this property is useful is when a DID controller chooses to delegate their capability to access a protected HTTP API to a party other than themselves. In order to delegate the capability, the DID subject would use a verification method associated with the capabilityDelegation verification relationship to cryptographically sign the capability over to another DID subject. The delegate would then use the capability in a manner that is similar to the example described in § 5.3.4 Capability Invocation.

Example 19: Capability Delegation property containing two verification methods

{
  "@context": "https://www.w3.org/ns/did/v1", "id":
  "did:example:123456789abcdefghi",
  ...
  "capabilityDelegation": [
    // this method can be used to perform capability delegation as did:...fghi
    "did:example:123456789abcdefghi#keys-1",
    // this method is *only* approved for granting capabilities; it will not
    // be used for any other verification relationship, so its full description is
    // embedded here rather than using only a reference
    {
    "id": "did:example:123456789abcdefghi#keys-2",
    "type": "Ed25519VerificationKey2018", // external (property value)
    "controller": "did:example:123456789abcdefghi",
    "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
    }
  ],
  ...
}

5.4 Services

Services are used in DID documents to express ways of communicating with the DID subject or associated entities. A service can be any type of service the DID subject wants to advertise, including decentralized identity management services for further discovery, authentication, authorization, or interaction.

Due to privacy concerns, revealing public information through services, such as social media accounts, personal websites, and email addresses, is discouraged. Further exploration of privacy concerns can be found in § 10.1 Keep Personal Data Private and § 10.6 Service Privacy. The information associated with services is often service specific. For example, the information associated with an encrypted messaging service can express how to initiate the encrypted link before messaging begins.

Services are expressed using the service property, which is described below:

service

The service property is OPTIONAL. If present, the associated value MUST be a set of services, where each service is described by a map. Each service map MUST contain id, type, and serviceEndpoint properties. Each service extension MAY include additional properties and MAY further restrict the properties associated with the extension.

id: The value of the id property MUST be a URI conforming to [RFC3986]. A conforming producer MUST NOT produce multiple service entries with the same id. A conforming consumer MUST produce an error if it detects multiple service entries with the same id.
type: The value of the type property MUST be a string or a set of strings. In order to maximize interoperability, the verification method type and its associated properties SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES].
serviceEndpoint: The value of the serviceEndpoint property MUST be a string, a map, or a set composed of one or more strings and/or maps. All string values MUST be valid URIs conforming to [RFC3986] and normalized according to the Normalization and Comparison rules in RFC3986 and to any normalization rules in its applicable URI scheme specification.

For more information regarding privacy and security considerations related to services see § 10.6 Service Privacy, § 10.1 Keep Personal Data Private, § 10.3 DID Document Correlation Risks, and § 9.3 Authentication Service Endpoints.

Example 20: Usage of the service property

{
  "service": [{
    "id":"did:example:123#linked-domain",
    "type": "LinkedDomains", // external (property value)
    "serviceEndpoint": "https://bar.example.com"
  }]
}

6. Representations

A concrete serialization of a DID document in this specification is called a representation. A representation is created by serializing the data model through a process called production. A representation is transformed into the data model through a process called consumption. The production and consumption processes enable the conversion of information from one representation to another. This specification defines representations for JSON, JSON-LD, and CBOR, and developers can use any other representation, such as XML or YAML, that is capable of expressing the data model. The following sections define the general rules for production and consumption, as well as the JSON, JSON-LD, and CBOR representations.

6.1 Production and Consumption

In addition to the representations defined in this specification, implementers can use other representations, providing each such representation is properly specified (including rules for interoperable handling of properties not listed in the DID Specification Registries [DID-SPEC-REGISTRIES]). See § 4.1 Extensibility for more information.

The requirements for all representations are as follows:

A representation MUST define deterministic production and consumption rules for all data types specified in § 4. Data Model.
A representation MUST be uniquely associated with an IANA-registered Media Type.
A representation MUST define fragment processing rules for its Media Type that are conformant with the fragment processing rules defined in § Fragment.
A representation SHOULD use the lexical representation of data model data types. For example, JSON and JSON-LD use the XML Schema dateTime lexical serialization to represent datetimes. A representation MAY choose to serialize the data model data types using a different lexical serializations as long as the consumption process back into the data model is lossless. For example, some CBOR-based representations express datetime values using integers to represent the number of seconds since the Unix epoch.
A representation MAY define representation-specific entries that are stored in a representation-specific entries map for use during the production and consumption process. These entries are used when consuming or producing to aid in ensuring lossless conversion.
In order to maximize interoperability, representation specification authors SHOULD register their representation in the DID Specification Registries [DID-SPEC-REGISTRIES].

The requirements for all conforming producers are as follows:

A conforming producer MUST take a DID document data model and a representation-specific entries map as input into the production process. The conforming producer MAY accept additional options as input into the production process.
A conforming producer MUST serialize all entries in the DID document data model, and the representation-specific entries map, that do not have explicit processing rules for the representation being produced using only the representation's data type processing rules and return the serialization after the production process completes.
A conforming producer MUST return the Media Type string associated with the representation after the production process completes.

The requirements for all conforming consumers are as follows:

A conforming consumer MUST take a representation and Media Type string as input into the consumption process. A conforming consumer MAY accept additional options as input into the consumption process.
A conforming consumer MUST determine the representation of a DID document using the Media Type input string.
A conforming consumer MUST detect any representation-specific entry across all known representations and place the entry into a representation-specific entries map which is returned after the consumption process completes. A list of all known representation-specific entries is available in the DID Specification Registries [DID-SPEC-REGISTRIES].
A conforming consumer MUST add all non-representation-specific entries that do not have explicit processing rules for the representation being consumed to the DID document data model using only the representation's data type processing rules and return the DID document data model after the consumption process completes.

Note: Conversion between representations

An implementation is expected to convert between representations by using the consumption rules on the source representation resulting in the data model and then using the production rules to serialize data model to the target representation, or any other mechanism that results in the same target representation.

6.2 JSON

This section defines the production and consumption rules for the JSON representation.

6.2.1 Production

The DID document, DID document data structures, and representation-specific entries map MUST be serialized to the JSON representation according to the following production rules:

Data Type	JSON Representation Type
map	A JSON Object, where each entry is serialized as a member of the JSON Object with the entry key as a JSON String member name and the entry value according to its type, as defined in this table.
list	A JSON Array, where each element of the list is serialized, in order, as a value of the array according to its type, as defined in this table.
set	A JSON Array, where each element of the set is added, in order, as a value of the array according to its type, as defined in this table.
datetime	A JSON String serialized as an XML Datetime normalized to UTC 00:00:00 and without sub-second decimal precision. For example: `2020-12-20T19:17:47Z`.
string	A JSON String.
integer	A JSON Number without a decimal or fractional component.
double	A JSON Number with a decimal and fractional component.
boolean	A JSON Boolean.
null	A JSON null literal.

All implementers creating conforming producers that produce JSON representations are advised to ensure that their algorithms are aligned with the JSON serialization rules in the [INFRA] specification and the precision advisements regarding Numbers in the JSON [RFC8259] specification.

All entries of a DID document MUST be included in the root JSON Object. Entries MAY contain additional data substructures subject to the value representation rules in the list above. When serializing a DID document, a conforming producer MUST specify a media type of application/did+json to downstream applications such as described in § 7.1.2 DID Resolution Metadata.

Example 21: Example DID document in JSON representation

{
	"id": "did:example:123456789abcdefghi",
	"authentication": [{
		"id": "did:example:123456789abcdefghi#keys-1",
		"type": "Ed25519VerificationKey2018",
		"controller": "did:example:123456789abcdefghi",
		"publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
	}]
}

6.2.2 Consumption

The DID document and DID document data structures JSON representation MUST be deserialized into the data model according to the following consumption rules:

JSON Representation Type	Data Type
JSON Object	A map, where each member of the JSON Object is added as an entry to the map. Each entry key is set as the JSON Object member name. Each entry value is set by converting the JSON Object member value according to the JSON representation type as defined in this table. Since order is not specified by JSON Objects, no insertion order is guaranteed.
JSON Array where the data model entry value is a list or unknown	A list, where each value of the JSON Array is added to the list in order, converted based on the JSON representation type of the array value, as defined in this table.
JSON Array where the data model entry value is a set	A set, where each value of the JSON Array is added to the set in order, converted based on the JSON representation type of the array value, as defined in this table.
JSON String where data model entry value is a datetime	A datetime.
JSON String, where the data model entry value type is string or unknown	A string.
JSON Number without a decimal or fractional component	An integer.
JSON Number with a decimal and fractional component, or when entry value is a double regardless of inclusion of fractional component	A double.
JSON Boolean	A boolean.
JSON null literal	A null value.

All implementers creating conforming consumers that produce JSON representations are advised to ensure that their algorithms are aligned with the JSON conversion rules in the [INFRA] specification and the precision advisements regarding Numbers in the JSON [RFC8259] specification.

If media type information is available to a conforming consumer and the media type value is application/did+json, then the data structure being consumed is a DID document, and the root element MUST be a JSON Object where all members of the object are entries of the DID document. A conforming consumer for a JSON representation that is consuming a DID document with a root element that is not a JSON Object MUST report an error.

6.3 JSON-LD

JSON-LD [JSON-LD11] is a JSON-based format used to serialize Linked Data. This section defines the production and consumption rules for the JSON-LD representation.

The JSON-LD representation defines the following representation-specific entries:

@context: The JSON-LD Context is either a string or a list containing any combination of strings and/or ordered maps.

6.3.1 Production

The DID document, DID document data structures, and representation-specific entries map MUST be serialized to the JSON-LD representation according to the JSON representation production rules as defined in § 6.2 JSON.

In addition to using the JSON representation production rules, JSON-LD production MUST include the representation-specific @context entry. The serialized value of @context MUST be the JSON String https://www.w3.org/ns/did/v1, or a JSON Array where the first item is the JSON String https://www.w3.org/ns/did/v1 and the subsequent items are serialized according to the JSON representation production rules.

Example 22: A valid serialization of a simple @context entry

{
  "@context": "https://www.w3.org/ns/did/v1",
  ...
}

Example 23: A valid serialization of a layered @context entry

{
  "@context": [
    "https://www.w3.org/ns/did/v1",
    "https://did-method-extension.example/v1"
  ],
  ...
}

All implementers creating conforming producers that produce JSON-LD representations are advised to ensure that their algorithms produce valid JSON-LD [JSON-LD11] documents. Invalid JSON-LD documents will cause JSON-LD processors to halt and report errors.

In order to achieve interoperability across different representations, all JSON-LD Contexts and their terms SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES].

A conforming producer that generates a JSON-LD representation SHOULD NOT produce a DID document that contains terms not defined via the @context as conforming consumers are expected to remove unknown terms. When serializing a JSON-LD representation of a DID document, a conforming producer MUST specify a media type of application/did+ld+json to downstream applications such as described in § 7.1.2 DID Resolution Metadata.

(Feature at Risk) Issue: IETF did+ld+json media type registration

Use of the media type application/did+ld+json is pending clarification over the registration of media types with multiple suffixes. The alternative will be to use application/ld+json with an expected profile parameter of https://www.w3.org/ns/did/json-ld-profile if multiple suffixes cannot be registered by the time the rest of DID Core is ready for W3C Proposed Recommendation. See also Issue 208.

6.3.2 Consumption

The DID document and any DID document data structures expressed by a JSON-LD representation MUST be deserialized into the data model according to the JSON representation consumption rules as defined in § 6.2 JSON.

All implementers creating conforming consumers that consume JSON-LD representations are advised to ensure that their algorithms only accept valid JSON-LD [JSON-LD11] documents. Invalid JSON-LD documents will cause JSON-LD processors to halt and report errors.

Conforming consumers that process a JSON-LD representation SHOULD drop all terms from a DID document that are not defined via the @context.

6.4 CBOR

This section defines the production and consumption rules for the CBOR representation.

(Feature at Risk) Issue

The Working Group is seeking volunteers to write tests for, and at least two independent and interoperable implementations of, the CBOR representation during the Candidate Recommendation phase. If these goals are not met, this section will be removed from this specification.

6.4.1 Production

The DID document, DID document data structures, and representation-specific entries map MUST be serialized to the CBOR representation according to the following production rules:

Data Type	CBOR Representation Type
map	A CBOR map (major type 5), where each entry is represented as a member of the CBOR map. The entry key is expressed as a CBOR string (major type 3) as the key, and the entry value according to its type, as defined in this table.
list	A CBOR array (major type 4), where each element of the list is added, in order, as a value of the array according to its type, as defined in this table.
set	A CBOR array (major type 4), where each element of the list is added, in order, as a value of the array according to its type, as defined in this table.
datetime	A CBOR string (major type 3) formatted as an XML Datetime normalized to UTC 00:00 and without sub-second decimal precision. For example: `2020-12-20T19:17:47Z`.
string	A CBOR string (major type 3).
integer	A CBOR integer (major type 0 or 1), choosing the shortest byte representation.
double	A CBOR floating-point number (major type 7). All floating point values MUST be encoded as 64-bits (additional type value 27), even for integral values.
boolean	A CBOR simple value (major type 7, subtype 24) with a simple value of 21 (true) or 20 (false).
null	A CBOR simple value (major type 7, subtype 24) with a simple value of 22 (null).

In addition to the data type production rules above, the following rules apply for conforming producers that serialize CBOR representations:

Indefinite-length items are not allowed and MUST be made a CBOR definite length.
All CBOR tags MUST be retained regardless of whether they are optional.
All four Canonical CBOR rules listed in [RFC8949] MUST be applied to all relevant data types.

All entries of a DID document MUST be included in the root CBOR map (major type 5). Entries MAY contain additional data substructures subject to the value representation rules in the list above. When serializing a DID document to its CBOR representation, a conforming producer MUST specify a media type of application/did+cbor to downstream applications such as described in § 7.1.2 DID Resolution Metadata.

The following examples express the CBOR representation of a DID document in hexidecimal notation, and in CBOR diagnostic notation:

Example 24: DID Document encoded as CBOR (hexadecimal)

A2626964781E6469643A6578616D706C653A313233343536373839616263
6465666768696E61757468656E7469636174696F6E81A462696478256469
643A6578616D706C653A313233343536373839616263646566676869236B
6579732D316474797065781A45643235353139566572696669636174696F
6E4B6579323031386A636F6E74726F6C6C6572781E6469643A6578616D70
6C653A3132333435363738396162636465666768696F7075626C69634B65
79426173653538782C483343324156764C4D7636676D4D4E616D33755641
6A5A70666B634A437744776E5A6E367A3377586D715056

Example 25: DID Document encoded as CBOR (diagnostic notation)

A2                                   # map(2)
62                                   # text(2)
   6964                              # "id"
78 1E                                # text(30)
   6469643A6578616D706C653A313233343536373839616263646566676869 # "did:example:123456789abcdefghi"
6E                                   # text(14)
   61757468656E7469636174696F6E      # "authentication"
81                                   # array(1)
   A4                                # map(4)
      62                             # text(2)
         6964                        # "id"
      78 25                          # text(37)
         6469643A6578616D706C653A313233343536373839616263646566676869236B6579732D31 # "did:example:123456789abcdefghi#keys-1"
      64                             # text(4)
         74797065                    # "type"
      78 1A                          # text(26)
         45643235353139566572696669636174696F6E4B657932303138 # "Ed25519VerificationKey2018"
      6A                             # text(10)
         636F6E74726F6C6C6572        # "controller"
      78 1E                          # text(30)
         6469643A6578616D706C653A313233343536373839616263646566676869 # "did:example:123456789abcdefghi"
      6F                             # text(15)
         7075626C69634B6579426173653538 # "publicKeyBase58"
      78 2C                          # text(44)
         483343324156764C4D7636676D4D4E616D337556416A5A70666B634A437744776E5A6E367A3377586D715056 # "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"

6.4.2 Consumption

The DID document and any DID document data structures expressed by the data model MUST be deserialized into the data model according to the following consumption rules:

CBOR Representation Type	Data Type
CBOR map (major type 5)	A map, where each data item of the CBOR map is added as an entry to the map with the entry key being the data item name and the value converted based on the CBOR type and, if available, entry definition, as defined here; as no order can be enforced for general CBOR maps, no insertion order is guaranteed.
CBOR array (major type 4), where the data model entry value is a list or unknown	A list, where each value of the CBOR array is added to the list in order, converted based on the CBOR type of the array value, as defined in this table.
CBOR array (major type 4), where the data model entry value is a set	A set, where each value of the CBOR array is added to the set in order, converted based on the CBOR type of the array value as defined in this table.
CBOR string (major type 3) where the data model entry value is a datetime	A datetime.
CBOR string (major type 3), where the data model entry value type is string or unknown	A string.
CBOR integer (major type 0 or 1), choosing the shortest byte representation	An integer.
CBOR floating-point number (major type 7)	A double.
CBOR simple value (major type 7, subtype 24) with a simple value of 21 (True) or 20 (False)	A boolean.
CBOR simple value (major type 7, subtype 24) with a simple value of 22 (Null)	A null value.

In addition to the data type consumption rules above, the following rules apply for conforming consumers that deserialize CBOR representations:

CBOR indefinite-length items are not allowed and MUST produce an error.
A duplicate key in the same CBOR map MUST produce an error.
All CBOR tags MUST be retained for CBOR production regardless of whether they are optional.

If media type information is available to a conforming consumer and the media type value is application/did+cbor, then the data structure being consumed is a DID document, and the root element MUST be a CBOR map (major type 5) where all members of the object are entries of the DID document. A conforming consumer for a CBOR representation that is consuming a DID document with a root element that is not a CBOR map (major type 5) MUST report an error.

7. Resolution

(Feature at Risk) Issue: Concerns regarding testability of DID Resolution and Dereferencing

The Working Group is unsure if there will be enough implementation experience for the DID Resolution section. We are seeking feedback from the implementation community as to whether they prefer to do all of this work now, or if they would prefer that this section is, or parts of the section are, rewritten to be non-normative, or published as a NOTE and taken up in a future W3C DID Resolution Working Group. If there is support for rewriting a subset of the DID Resolution section, or publishing any part of it as a NOTE during the W3C Candidate Recommendation process, this section will be modified and/or published as a NOTE appropriately before the DID Core specification proceeds to the W3C Proposed Recommendation stage. See also Issue 549.

This section defines the inputs and outputs of DID resolution and DID URL dereferencing. Their exact implementation is out of scope for this specification, but some considerations for implementors are discussed in [DID-RESOLUTION].

All conformant DID resolvers MUST implement the DID resolution functions for at least one DID method and MUST be able to return a DID document in at least one conformant representation.

7.1 DID Resolution

The DID resolution functions resolve a DID into a DID document by using the "Read" operation of the applicable DID method as described in § 8.2 Method Operations. The details of how this process is accomplished are outside the scope of this specification, but all conforming DID resolvers implement the functions below, which have the following abstract forms:

resolve(did, resolutionOptions) →
   « didResolutionMetadata, didDocument, didDocumentMetadata »

resolveRepresentation(did, resolutionOptions) →
   « didResolutionMetadata, didDocumentStream, didDocumentMetadata »

The resolve function returns the DID document in its abstract form (a map). The resolveRepresentation function returns a byte stream of the DID Document formatted in the corresponding representation. The input variables of the resolve and resolveRepresentation functions are as follows:

did: This is the DID to resolve. This input is REQUIRED and the value MUST be a conformant DID as defined in § 3.1 DID Syntax.
resolutionOptions: A metadata structure containing properties defined in § 7.1.1 DID Resolution Options. This input is REQUIRED, but the structure MAY be empty.

These functions each return multiple values, and no limitations are placed on how these values are returned together. The return values of resolve are didResolutionMetadata, didDocument, and didDocumentMetadata. The return values of resolveRepresentation are didResolutionMetadata, didDocumentStream, and didDocumentMetadata. These values are described below:

didResolutionMetadata: A metadata structure consisting of values relating to the results of the DID resolution process which typically changes between invocations of the resolve and resolveRepresentation functions, as it represents data about the resolution process itself. This structure is REQUIRED, and in the case of an error in the resolution process, this MUST NOT be empty. This metadata is defined by § 7.1.2 DID Resolution Metadata. If resolveRepresentation was called, this structure MUST contain a contentType property containing the Media Type of the representation found in the didDocumentStream. If the resolution is not successful, this structure MUST contain an error property describing the error.
didDocument: If the resolution is successful, and if the resolve function was called, this MUST be a DID document abstract data model (a map) as described in § 4. Data Model that is capable of being transformed into a conforming DID Document (representation), using the production rules specified by the representation. The value of id in the resolved DID document MUST match the DID that was resolved. If the resolution is unsuccessful, this value MUST be empty.
didDocumentStream: If the resolution is successful, and if the resolveRepresentation function was called, this MUST be a byte stream of the resolved DID document in one of the conformant representations. The byte stream might then be parsed by the caller of the resolveRepresentation function into a data model, which can in turn be validated and processed. If the resolution is unsuccessful, this value MUST be an empty stream.
didDocumentMetadata: If the resolution is successful, this MUST be a metadata structure. This structure contains metadata about the DID document contained in the didDocument property. This metadata typically does not change between invocations of the resolve and resolveRepresentation functions unless the DID document changes, as it represents metadata about the DID document. If the resolution is unsuccessful, this output MUST be an empty metadata structure. Properties defined by this specification are in § 7.1.3 DID Document Metadata.

Conforming DID resolver implementations do not alter the signature of these functions in any way. DID resolver implementations might map the resolve and resolveRepresentation functions to a method-specific internal function to perform the actual DID resolution process. DID resolver implementations might implement and expose additional functions with different signatures in addition to the resolve and resolveRepresentation functions specified here.

7.1.1 DID Resolution Options

The possible properties within this structure and their possible values are registered in the DID Specification Registries [DID-SPEC-REGISTRIES]. This specification defines the following common properties.

accept: The Media Type of the caller's preferred representation of the DID document. The Media Type MUST be expressed as an ASCII string. The DID resolver implementation SHOULD use this value to determine the representation contained in the returned didDocumentStream if such a representation is supported and available. This property is OPTIONAL for the resolveRepresentation function and MUST NOT be used with the resolve function.

7.1.2 DID Resolution Metadata

contentType

The Media Type of the returned didDocumentStream. This property is REQUIRED if resolution is successful and if the resolveRepresentation function was called. This property MUST NOT be present if the resolve function was called. The value of this property MUST be an ASCII string that is the Media Type of the conformant representations. The caller of the resolveRepresentation function MUST use this value when determining how to parse and process the didDocumentStream returned by this function into the data model.

error

The error code from the resolution process. This property is REQUIRED when there is an error in the resolution process. The value of this property MUST be a single keyword ASCII string. The possible property values of this field SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES]. This specification defines the following common error values:

invalidDid: The DID supplied to the DID resolution function does not conform to valid syntax. (See § 3.1 DID Syntax.)
notFound: The DID resolver was unable to find the DID document resulting from this resolution request.
representationNotSupported: This error code is returned if the representation requested via the accept input metadata property is not supported by the DID method and/or DID resolver implementation.

7.1.3 DID Document Metadata

The possible properties within this structure and their possible values SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES]. This specification defines the following common properties.

created

DID document metadata SHOULD include a created property to indicate the timestamp of the Create operation. The value of the property MUST be a string formatted as an XML Datetime normalized to UTC 00:00:00 and without sub-second decimal precision. For example: 2020-12-20T19:17:47Z.

updated

DID document metadata SHOULD include an updated property to indicate the timestamp of the last Update operation for the document version which was resolved. The value of the property MUST follow the same formatting rules as the created property. The updated property is omitted if an Update operation has never been performed on the DID document. If an updated property exists, it can be the same value as the created property when the difference between the two timestamps is less than one second.

deactivated

If a DID has been deactivated, DID document metadata MUST include this property with the boolean value true. If a DID has not been deactivated, this property is OPTIONAL, but if included, MUST have the boolean value false.

nextUpdate

(Feature at Risk) Issue

The DID Working Group is seeking implementer feedback on this feature. If there is not enough implementation experience with this feature at the end of the Candidate Recommendation period, it will be removed from the specification.

DID document metadata MAY include a nextUpdate property if the resolved document version is not the latest version of the document. It indicates the timestamp of the next Update operation. The value of the property MUST follow the same formatting rules as the created property.

versionId

DID document metadata SHOULD include a versionId property to indicate the version of the last Update operation for the document version which was resolved. The value of the property MUST be an ASCII string.

nextVersionId

(Feature at Risk) Issue

DID document metadata MAY include a nextVersionId property if the resolved document version is not the latest version of the document. It indicates the version of the next Update operation. The value of the property MUST be an ASCII string.

equivalentId

(Feature at Risk) Issue

A DID Method can define different forms of a DID that are logically equivalent. An example is when a DID takes one form prior to registration in a verifiable data registry and another form after such registration. In this case, the DID Method specification might need to express one or more DIDs that are logically equivalent to the resolved DID as a property of the DID document. This is the purpose of the equivalentId property.

The value of equivalentId MUST be a set where each item is a string that conforms to the rules in Section § 3.1 DID Syntax. The relationship is a statement that each equivalentId value is logically equivalent to the id property value and thus identifies the same DID subject. Each equivalentId DID value MUST be produced by, and a form of, the same DID Method as the id property value. (e.g., did:example:abc == did:example:ABC)

A conforming DID Method specification MUST guarantee that each equivalentId value is logically equivalent to the id property value.

A requesting party is expected to retain the values from the id and equivalentId properties to ensure any subsequent interactions with any of the values they contain are correctly handled as logically equivalent (e.g. retain all variants in a database so an interaction with any one maps to the same underlying account).

Note: Stronger equivalence

equivalentId is a much stronger form of equivalence than alsoKnownAs because the equivalence MUST be guaranteed by the governing DID method. equivalentId represents a full graph merge because the same DID document describes both the equivalentId DID and the id property DID.

If a requesting party does not retain the values from the id and equivalentId properties and ensure any subsequent interactions with any of the values they contain are correctly handled as logically equivalent, there might be negative or unexpected issues that arise. Implementers are strongly advised to observe the directives related to this metadata property.

canonicalId

(Feature at Risk) Issue

The canonicalId property is identical to the equivalentId property except: a) it is associated with a single value rather than a set, and b) the DID is defined to be the canonical ID for the DID subject within the scope of the containing DID document.

The value of canonicalId MUST be a string that conforms to the rules in Section § 3.1 DID Syntax. The relationship is a statement that the canonicalId value is logically equivalent to the id property value and that the canonicalId value is defined by the DID Method to be the canonical ID for the DID subject in the scope of the containing DID document. A canonicalId value MUST be produced by, and a form of, the same DID Method as the id property value. (e.g., did:example:abc == did:example:ABC). A conforming DID Method specification MUST guarantee that the canonicalId value is logically equivalent to the id property value.

A requesting party is expected to use the canonicalId value as its primary ID value for the DID subject and treat all other equivalent values as secondary aliases (e.g. update corresponding primary references in their systems to reflect the new canonical ID directive).

Note: Canonical equivalence

canonicalId is the same statement of equivalence as equivalentId except it is constrained to a single value that is defined to be canonical for the DID subject in the scope of the DID document. Like equivalentId, canonicalId represents a full graph merge because the same DID document describes both the canonicalId DID and the id property DID.

If a resolving party does not use the canonicalId value as its primary ID value for the DID subject and treat all other equivalent values as secondary aliases, there might be negative or unexpected issues that arise related to user experience. Implementers are strongly advised to observe the directives related to this metadata property.

7.2 DID URL Dereferencing

The DID URL dereferencing function dereferences a DID URL into a resource with contents depending on the DID URL's components, including the DID method, method-specific identifier, path, query, and fragment. This process depends on DID resolution of the DID contained in the DID URL. DID URL dereferencing might involve multiple steps (e.g., when the DID URL being dereferenced includes a fragment), and the function is defined to return the final resource after all steps are completed. The details of how this process is accomplished are outside the scope of this specification. The following figure depicts the relationship described above.

DIDs resolve to DID documents; DID URLs contains a DID; DID URLs dereferenced to DID document fragments or
external resources. — Figure 4 Overview of DID URL dereferece

All conforming DID resolvers implement the following function which has the following abstract form:

dereference(didUrl, dereferenceOptions) →
   « dereferencingMetadata, contentStream, contentMetadata »

The input variables of the dereference function are as follows:

didUrl: A conformant DID URL as a single string. This is the DID URL to dereference. To dereference a DID fragment, the complete DID URL including the DID fragment MUST be used. This input is REQUIRED.
dereferencingOptions: A metadata structure consisting of input options to the dereference function in addition to the didUrl itself. Properties defined by this specification are in § 7.2.1 DID URL Dereferencing Options. This input is REQUIRED, but the structure MAY be empty.

This function returns multiple values, and no limitations are placed on how these values are returned together. The return values of the dereference include dereferencingMetadata, contentStream, and contentMetadata:

dereferencingMetadata: A metadata structure consisting of values relating to the results of the DID URL dereferencing process. This structure is REQUIRED and in the case of an error in the dereferencing process, this MUST NOT be empty. Properties defined by this specification are in § 7.2.2 DID URL Dereferencing Metadata. If the dereferencing is not successful, this structure MUST contain an error property describing the error.
contentStream: If the dereferencing function was called and successful, this MUST contain a resource corresponding to the DID URL. The contentStream MAY be a resource such as a DID Document that is serializable in one of the conformant representations, a Verification Method, a service, or any other resource format that can be identified via a Media Type and obtained through the resolution process. If the dereferencing is unsuccessful, this value MUST be empty.
contentMetadata: If the dereferencing is successful, this MUST be a metadata structure, but the structure MAY be empty. This structure contains metadata about the contentStream. If the contentStream is a DID document, this MUST be a didDocumentMetadata structure as described in DID Resolution. If the dereferencing is unsuccessful, this output MUST be an empty metadata structure.

Conforming DID URL dereferencing implementations do not alter the signature of these functions in any way. DID URL dereferencing implementations might map the dereference function to a method-specific internal function to perform the actual DID URL dereferencing process. DID URL dereferencing implementations might implement and expose additional functions with different signatures in addition to the dereference function specified here.

7.2.1 DID URL Dereferencing Options

accept: The Media Type that the caller prefers for contentStream. The Media Type MUST be expressed as an ASCII string. The DID URL dereferencing implementation SHOULD use this value to determine the contentType of the representation contained in the returned value if such a representation is supported and available.

7.2.2 DID URL Dereferencing Metadata

contentType

The Media Type of the returned contentStream SHOULD be expressed using this property if dereferencing is successful. The Media Type value MUST be expressed as an ASCII string.

error

The error code from the dereferencing process. This property is REQUIRED when there is an error in the dereferencing process. The value of this property MUST be a single keyword expressed as an ASCII string. The possible property values of this field SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES]. This specification defines the following common error values:

invalidDidUrl: The DID URL supplied to the DID URL dereferencing function does not conform to valid syntax. (See § 3.2 DID URL Syntax.)
notFound: The DID URL dereferencer was unable to find the contentStream resulting from this dereferencing request.

7.3 Metadata Structure

Input and output metadata is often involved during the DID Resolution, DID URL dereferencing, and other DID-related processes. The structure used to communicate this metadata MUST be a map of properties. Each property name MUST be a string. Each property value MUST be a string, map, list, set, boolean, or null. The values within any complex data structures such as maps and lists MUST be one of these data types as well. All metadata property definitions registered in the DID Specification Registries [DID-SPEC-REGISTRIES] MUST define the value type, including any additional formats or restrictions to that value (for example, a string formatted as a date or as a decimal integer). It is RECOMMENDED that property definitions use strings for values. The entire metadata structure MUST be serializable according to the JSON serialization rules in the [INFRA] specification. Implementations MAY serialize the metadata structure to other data formats.

All implementations of functions that use metadata structures as either input or output are able to fully represent all data types described here in a deterministic fashion. As inputs and outputs using metadata structures are defined in terms of data types and not their serialization, the method for representation is internal to the implementation of the function and is out of scope of this specification.

The following example demonstrates a JSON-encoded metadata structure that might be used as DID resolution input metadata.

Example 26: JSON-encoded DID resolution input metadata example

{
  "accept": "application/did+ld+json"
}

This example corresponds to a metadata structure of the following format:

Example 27: DID resolution input metadata example

«[
  "accept" → "application/did+ld+json"
]»

The next example demonstrates a JSON-encoded metadata structure that might be used as DID resolution metadata if a DID was not found.

Example 28: JSON-encoded DID resolution metadata example

{
  "error": "notFound"
}

This example corresponds to a metadata structure of the following format:

Example 29: DID resolution metadata example

«[
  "error" → "notFound"
]»

The next example demonstrates a JSON-encoded metadata structure that might be used as DID document metadata to describe timestamps associated with the DID document.

Example 30: JSON-encoded DID document metadata example

{
  "created": "2019-03-23T06:35:22Z",
  "updated": "2023-08-10T13:40:06Z"
}

This example corresponds to a metadata structure of the following format:

Example 31: DID document metadata example

«[
  "created" → "2019-03-23T06:35:22Z",
  "updated" → "2023-08-10T13:40:06Z"
]»

8. Methods

A DID method defines how implementers can realize the features described by this specification. DID methods are often associated with a particular verifiable data registry. New DID methods are defined in their own specifications to enable interoperability between different implementations of the same DID method.

Conceptually, the relationship between this specification and a DID method specification is similar to the relationship between the IETF generic URI specification [RFC3986] and a specific URI scheme [IANA-URI-SCHEMES], such as the http scheme [RFC7230]. In addition to defining a specific DID scheme, a DID method specification also defines the mechanisms for creating, resolving, updating, and deactivating DIDs and DID documents using a specific type of verifiable data registry. It also documents all implementation considerations related to DIDs as well as Security and Privacy Considerations.

This section specifies the requirements for authoring DID method specifications.

8.1 Method Syntax

The requirements for all DID method specifications when defining the method-specific DID Syntax are as follows:

A DID method specification MUST define exactly one method-specific DID scheme that is identified by exactly one method name as specified by the method-name rule in § 3.1 DID Syntax.
The DID method specification MUST specify how to generate the method-specific-id component of a DID.
The DID method specification MUST define sensitivity and normalization of the value of the method-specific-id.
The method-specific-id value MUST be unique within a DID method. The method-specific-id value itself might be globally unique.
Any DID generated by a DID method MUST be globally unique.
To reduce the chances of method-name conflicts, a DID method specification SHOULD be registered in the DID Specification Registries [DID-SPEC-REGISTRIES].
A DID method MAY define multiple method-specific-id formats.
The method-specific-id format MAY include colons. The use of colons MUST comply syntactically with the method-specific-id ABNF rule.
A DID method specification MAY specify ABNF rules for DID paths that are more restrictive than the generic rules in § Path.
A DID method specification MAY specify ABNF rules for DID queries that are more restrictive than the generic rules in this section.
A DID method specification MAY specify ABNF rules for DID fragments that are more restrictive than the generic rules in this section.

Note: Colons in method-specific-id

The meaning of colons in the method-specific-id is entirely method-specific. Colons might be used by DID methods for establishing hierarchically partitioned namespaces, for identifying specific instances or parts of the verifiable data registry, or for other purposes. Implementers are advised to avoid assuming any meanings or behaviors associated with a colon that are generically applicable to all DID methods.

8.2 Method Operations

The requirements for all DID method specifications when defining the method operations are as follows:

A DID method specification MUST define how authorization is performed to execute all operations, including any necessary cryptographic processes.
A DID method specification MUST specify how a DID controller creates a DID and its associated DID document.
A DID method specification MUST specify how a DID resolver uses a DID to resolve a DID document, including how the DID resolver can verify the authenticity of the response.
A DID method specification MUST specify what constitutes an update to a DID document and how a DID controller can update a DID document or state that updates are not possible.
The DID method specification MUST specify how a DID controller can deactivate a DID or state that deactivation is not possible.

The authority of a party that is performing authorization to carry out the operations is specific to a DID method. For example, a DID method might —

make use of the controller property.
use the verification methods listed under authentication.
use other constructs in the DID Document such as the verification method specified via the capabilityInvocation verification relationship.
not use the DID document for this decision at all, and depend on an out-of-band mechanism, instead.

8.3 Security Requirements

The requirements for all DID method specifications when authoring the Security Considerations section are as follows:

A DID method specifications MUST follow all guidelines and normative language provided in RFC3552: Writing Security Considerations Sections for the DID operations defined in the DID method specification.
The Security Considerations section MUST document the following forms of attack for the DID operations defined in the DID method specification: eavesdropping, replay, message insertion, deletion, modification, denial of service, storage or network amplification, and man-in-the-middle. Other known forms of attack SHOULD also be documented.
The Security Considerations section MUST discuss residual risks, such as the risks from compromise in a related protocol, incorrect implementation, or cipher after threat mitigation was deployed.
The Security Considerations section MUST provide integrity protection and update authentication for all operations required by Section § 8.2 Method Operations.
If authentication is involved, particularly user-host authentication, the security characteristics of the authentication method MUST be clearly documented.
The Security Considerations section MUST discuss the policy mechanism by which DIDs are proven to be uniquely assigned.
Method-specific endpoint authentication MUST be discussed. Where DID methods make use of DLTs with varying network topology, sometimes offered as light node or thin client implementations to reduce required computing resources, the security assumptions of the topology available to implementations of the DID method MUST be discussed.
If a protocol incorporates cryptographic protection mechanisms, the DID method specification MUST clearly indicate which portions of the data are protected and by what protections, and it SHOULD give an indication of the sorts of attacks to which the cryptographic protection is susceptible. Some examples are integrity only, confidentiality, and endpoint authentication.
Data which is to be held secret (keying material, random seeds, and so on) SHOULD be clearly labeled.
DID method specifications SHOULD explain and specify the implementation of signatures on DID documents, if applicable.
Where DID methods use peer-to-peer computing resources, such as with all known DLTs, the expected burdens of those resources SHOULD be discussed in relation to denial of service.
DID methods that introduce new authentication service types, as described in § 5.4 Services, SHOULD consider the security requirements of the supported authentication protocol.

8.4 Privacy Requirements

The requirements for all DID method specifications when authoring the Privacy Considerations section are:

The DID method specification's Privacy Considerations section MUST discuss any subsection of Section 5 of [RFC6973] that could apply in a method-specific manner. The subsections to consider are: surveillance, stored data compromise, unsolicited traffic, misattribution, correlation, identification, secondary use, disclosure, and exclusion.

9. Security Considerations

This section is non-normative.

Note: Note to implementers

During the Working Draft stage, this section focuses on security topics that should be important in early implementations. The editors are seeking feedback on threats and threat mitigations that should be reflected in this section or elsewhere in the spec. DIDs are designed to operate under the general Internet threat model used by many IETF standards. We assume uncompromised endpoints, but anticipate that messages could be read or corrupted on the network.

9.1 Choosing DID Resolvers

The DID Method Registry (see [DID-SPEC-REGISTRIES]) contains an informative list of DID method names and their corresponding DID method specifications. Implementors need to bear in mind that there is no central authority to mandate which DID method specification is to be used with any specific DID method name, but can use the DID Method Registry to make an informed decision when choosing which DID resolver implementations to use.

9.2 Binding of Identity

The following sections describe binding identities to DIDs and DID documents.

9.2.1 Proving Control of a DID and DID Document

Issue 583: Proving Control sections are wrong editorial ready for PR

This section is inaccurate and needs revision.

Signatures and verifiable timestamps allow DID documents to be cryptographically verifiable.

By itself, a verified signature on a self-signed DID document does not prove control of a DID. It only proves that the:

DID document was not tampered with since it was timestamped.
DID controller(s) controlled the private key used for the signature at the time the timestamp was created.

Proving control of a DID, that is, the binding between the DID and the DID document that describes it, requires a two step process:

Resolving the DID to a DID document according to its DID method specification.
Verifying that the id property of the resulting DID document matches the DID that was resolved.

It should be noted that this process proves control of a DID and DID document regardless of whether the DID document is signed.

Signatures on DID documents are optional. DID method specifications are expected to explain and specify their implementation if applicable.

9.2.2 Proving Control of a Public Key

Issue 583: Proving Control sections are wrong editorial ready for PR

This section is inaccurate and needs revision.

There are two methods for proving control of the private key corresponding to a public key description in the DID document: static and dynamic.

The static method is to sign the DID document with the private key. This proves control of the private key at a time no later than the DID document was registered. If the DID document is not signed, control of a public key described in the DID document can still be proven dynamically as follows:

Send a challenge message containing a public key description from the DID document and a nonce to an appropriate service endpoint described in the DID document.
Verify the signature of the response message against the public key description.

9.2.3 Real-World Identity

A DID and DID document do not inherently carry any personal data.

It can be useful to express a binding of DID to a person's or company's real world identity, in a way that is provably asserted by a trusted authority such as a government. This can enable interactions that can be considered legally valid under one or more jurisdictions; establishing such bindings has to be carefully balanced against privacy considerations (see § 10. Privacy Considerations).

The process of binding a DID to something in the real world, such as a person or a company, for example using verifiable credentials with the same subject as that DID, is out of scope for this specification. For more information, see the Verifiable Credentials Data Model [VC-DATA-MODEL].

9.3 Authentication Service Endpoints

If a DID document publishes a service intended for authentication or authorization of the DID subject (see Section § 5.4 Services), it is the responsibility of the service endpoint provider, subject, or requesting party to comply with the requirements of the authentication protocols supported at that service endpoint.

9.4 Non-Repudiation

Non-repudiation of DIDs and DID document updates is supported under the assumption that the subject:

Is monitoring for unauthorized updates (see Section § 9.5 Notification of DID Document Changes).
Has had adequate opportunity to revert malicious updates according to the access control mechanism for the DID method (see Section § 5.3.1 Authentication).

Non-repudiation is further supported if timestamps are included (see Section § 7.1.3 DID Document Metadata) and the target DLT system supports timestamps.

9.5 Notification of DID Document Changes

One mitigation against unauthorized changes to a DID document is monitoring and actively notifying the DID subject when there are changes. This is analogous to helping prevent account takeover on conventional username/password accounts by sending password reset notifications to the email addresses on file.

In the case of a DID, there is no intermediary registrar or account provider to generate such notifications. However, if the verifiable data registry on which the DID is registered directly supports change notifications, a subscription service can be offered to DID controllers. Notifications could be sent directly to the relevant service endpoints listed in an existing DID.

If a DID controller chooses to rely on a third-party monitoring service (other than the verifiable data registry itself), this introduces another vector of attack.

9.6 Key and Signature Expiration

In a decentralized identifier architecture, there are no centralized authorities to enforce key or signature expiration policies. Therefore DID resolvers and requesting parties need to validate that keys were not expired at the time they were used. Because some use cases have legitimate reasons why already-expired keys can be extended, make sure key expiration does not prevent any further use of the key. Implementations of a resolver ought to be compatible with such extension behavior.

9.7 Verification Method Rotation

Verification method rotation is a proactive security measure.

Verification method rotation applies only to the current or latest version of a DID Document.

When a verification method has been active for a long time, or used for many operations, a controller might wish to perform a rotation.

It is considered a best practice to perform verification method rotation on a regular basis.

Proofs or signatures that rely on verification methods that are not present in the latest version of a DID Document are not impacted by rotation, and might require additional information to mitigate compromise.

Section § 8.2 Method Operations specifies the DID operations to be supported by a DID method specification, including update which is expected to be used to perform a verification method rotation.

A controller performs a rotation when they add a new verification method that is meant to replace an existing verification method after some time.

Not all DID Methods support verification method rotation.

Rotation is a key management process that enables the private cryptographic material associated with an existing verification method to be deactivated or destroyed once a new verification method has been added to the DID Document. Going forward, any new proofs that a controller would have generated using the old cryptographic material can now instead be generated using the new material and can be verified using the new verification method.

Rotation is a useful mechanism for protecting against verification method compromise, since frequent rotation of a verification method by the controller reduces the value of a single compromised verification method to an attacker. Performing revocation immediately after rotation is useful for verification methods that a controller designates for short-lived verifications, such as those involved in encrypting messages and authentication.

Note

Higher security environments tend to employ more frequent verification method rotation.

Note

Frequent rotation of a verification method might be frustrating for parties that are forced to continuously renew or refresh associated credentials.

9.8 Verification Method Revocation

Verification method revocation is a reactive security measure.

Verification method revocation applies only to the current or latest version of a DID Document.

If a verification method is no longer exclusively accessible to the controller or parties trusted to act on behalf of the controller, it is expected to be revoked immediately to reduce the risk of masquerading, theft, and fraud.

It is considered a best practice to support key revocation.

A controller is expected to immediately revoke any verification method that is believed to be compromised.

Revocation is expected to be understood as a controller expressing that proofs or signatures associated with a revoked verification method might have been created by an attacker. Verifiers, however, might still choose to accept or reject such proofs or signatures at their own discretion.

Note

As described in § 5.2.1 Verification Material, absence of a verification method is the only form of revocation that applies to all DID Methods.

§ 8.2 Method Operations specifies the DID operations to be supported by a DID method specification, including update and deactivate which might be used to remove verification method from a DID Document.

Not all DID Methods support verification method revocation.

Even if a verification method is present in a DID Document, additional information, such as a public key revocation certificate, or an external allow or deny list, might be used to determine whether a verification method has been revoked.

Note

Compromise of the secrets associated with a verification method allows the attacker to use them according to the verification relationship expressed by controller in the DID Document, for example, for authentication. The attacker's use of the secrets might be indistinguishable from the legitimate controller's use starting from the time the verification method was registered, to the time it was revoked.

Note

The day-to-day operation of any software relying on a compromised verification method, such as an individual's operating system, antivirus, or endpoint protection software, might be impacted when the verification method is publicly revoked.

Note

Although verifiers might choose not to accept proofs or signatures from a revoked verification method, knowing whether a verification was made with a revoked verification method is trickier than it might seem. Some DID methods provide the ability to look back at the state of a DID at a point in time, or at a particular version of the DID document. When such a feature is combined with a reliable way to determine the time or DID version that existed when a cryptographically verifiable statement was made, then revocation does not undo that statement. This can be the basis for using DIDs to make binding commitments (e.g., to sign a mortgage).

If these conditions are met, revocation is not retroactive; it only nullifies future use of the method.

However, in order for such semantics to be safe, the second condition — an ability to know what the state of the DID document was at the time the assertion was made — is expected to apply. Without that guarantee, someone could discover a revoked key and use it to make cryptographically verifiable statements with a simulated date in the past.

Some DID methods only allow the retrieval of the current state of a DID. When this is true, or when the state of a DID at the time of cryptographically verifiable statement cannot be reliably determined, then the only safe interpretation of revocation is to make it apply both forward and backward in time. DID ecosystems that take this approach essentially provide cryptographically verifiable statements as ephemeral tokens that can be invalidated at any time by the DID controller.

Note

Trustless systems are those where all trust is derived from cryptographically provable assertions, and more specifically, where no metadata outside of the cryptographic system is factored into the determination of trust in the system. To verify a signature of proof for a verification method which has been revoked in a trustless system, a DID method needs to support either or both of the versionId or versionTime, as well as both the updated and nextUpdate, DID document metadata properties. A verifier can validate a signature or proof of a revoked key if and only if all of the following are true:

The proof or signature includes the versionId or versionTime of the DID document that was used at the point the signature or proof was created.
The verifier can determine the point in time at which the signature or proof was made, e.g., it was anchored on a blockchain.
For the resolved DID document metadata, the updated timestamp is before, and the nextUpdate timestamp is after, the point in time at which the signature or proof was made.

9.9 DID Recovery

Recovery is a reactive security measure, whereby a controller is able to regain the ability to perform DID operations.

Recovery is advised when a controller or services trusted to act on their behalf no longer have the exclusive ability to perform DID operations as described in § 8.2 Method Operations.

It is considered a best practice to never reuse a verification method or key material associated with recovery for any other purposes.

Recovery is commonly performed in conjunction with verification method rotation and verification method revocation.

There are no common recovery mechanisms that apply to all DID Methods.

DID method specifications might choose to enable support for a quorum of trusted parties to faciliate recovery. Some of the facilities to do so are suggested in Section § 5.1.2 DID Controller.

Not all DID method specifications will recognize control from DIDs registered using other DID methods and they might restrict third-party control to DIDs that use the same method.

Access control and recovery in a DID method specification can also include a time lock feature to protect against key compromise by maintaining a second track of control for recovery.

Note

Performing recovery proactively on an infrequent but regular basis, can help to ensure that control has not been lost.

9.10 The Role of Human-Friendly Identifiers

DIDs achieve global uniqueness without the need for a central registration authority. This comes at the cost of human memorability. The algorithms capable of generating globally unique identifiers produce random strings of characters that have no human meaning (see also Zooko's Triangle).

There are use cases where it is desirable to discover a DID when starting from a human-friendly identifier. For example, a natural language name, a domain name, or a conventional address for a DID controller, such as a mobile telephone number, email address, social media username, or blog URL. However, the problem of mapping human-friendly identifiers to DIDs (and doing so in a way that can be verified and trusted) is outside the scope of this specification.

Solutions to this problem should be defined in separate specifications that reference this specification. It is strongly recommended that such specifications carefully consider the:

Numerous security attacks based on deceiving users about the true human-friendly identifier for a target entity.
Privacy consequences of using human-friendly identifiers that are inherently correlatable, especially if they are globally unique.

Note

A draft specification for discovering a DID from domain names and email addresses using DNS lookups is available at [DNS-DID].

9.11 DIDs as Enhanced URNs

If desired by a DID controller, a DID is capable of acting as an enhanced Uniform Resource Name (URN) as defined by [RFC8141], i.e., "a persistent, location-independent resource identifier". DIDs used in this way provide a cryptographically secure, location-independent identifier for a digital resource, while also providing metadata that enables retrieval. Because of the indirection between the DID document and the DID itself, the DID controller can adjust the actual location of the resource — or even provide the resource directly — without adjusting the DID. DIDs of this type can definitively verify that the resource retrieved is, in fact, the resource identified.

A DID controller who intends to use a DID for this purpose is advised to follow the security considerations in [RFC8141]. In particular:

The DID controller is expected to choose a DID method that supports the controller's requirements for persistence. The Decentralized Characteristics Rubric [DID-RUBRIC] is one tool available to help implementers decide upon the most suitable DID method.
The DID controller is expected to publish its operational policies so relying parties can determine the degree to which they can rely on the persistence of a DID controlled by that DID controller. In the absence of such policies, relying parties are not expected to make any assumption about whether a DID is a persistent identifier for the same DID subject.

9.12 Immutability

Many cybersecurity abuses hinge on exploiting gaps between reality and the assumptions of rational, good-faith actors. Immutability of DID documents can provide some security benefits. Individual DID methods ought to consider constraints that would eliminate behaviors or semantics they do not need. The more locked down a DID method is, while providing the same set of features, the less it can be manipulated by malicious actors.

As an example, consider that a single edit to a DID document can change anything except the root id property of the document. But is it actually desirable for a service to change its type after it is defined? Or for a key to change its value? Or would it be better to require a new id when certain fundamental properties of an object change? Malicious takeovers of a website often aim for an outcome where the site keeps its identifier (the host name), but is subtly changed underneath. If certain properties of the site were required by the specification to be immutable (for example, the ASN associated with its IP address), such attacks might be much harder and more expensive to carry out, and anomaly detection would be easier.

For DID methods tied to a global source of truth, a direct, just-in-time lookup of the latest version of a DID document is always possible. However, it seems likely that layers of cache might eventually sit between a DID resolver and that source of truth. If they do, believing the attributes of an object in the DID document to have a given state when they are actually subtly different might invite exploits. This is particularly true if some lookups are of a full DID document, and others are of partial data where the larger context is assumed.

9.13 Encrypted Data in DID Documents

Encryption algorithms have been known to fail due to advances in cryptography and computing power. Implementers are advised to assume that any encrypted data placed in a DID document might eventually be made available in clear text to the same audience to which the encrypted data is available. This is particularly pertinent if the DID document is public.

Encrypting all or parts of DID documents is not an appropriate means to protect data in the long term. Similarly, placing encrypted data in DID documents is not an appropriate means to include personal data.

Given the caveats above, if encrypted data is included in a DID document, implementers are advised to not encrypt with the public keys of entities that do not wish to be correlated with the DID.

9.14 Equivalence Properties

The three equivalence properties—alsoKnownAs, equivalentId, and canonicalId—are subject to special security considerations related to attacks against DIDs that are asserted to be equivalent.

The equivalentId and canonicalId properties that constrain equivalence assertions to variants of a single DID produced by the same DID method (e.g., did:foo:123 ≡ did:foo:hash(123)) can be trusted to the extent the requesting party trusts the DID method (and a conforming producer) itself.

The alsoKnownAs property that permits an equivalence assertion to URIs that are not governed by the same DID method (or may not be DIDs at all) cannot be trusted without performing verification steps outside of the governing DID method. See additional guidence in § 5.1.3 Also Known As.

As with any other sensitive properties in the DID document (e.g., public key references), parties relying on any equivalence statement in a DID document should guard against the values of these properties being substituted by an attacker after the proper verification has been performed. Any write access to a DID document stored in memory or disk after verification has been performed is an attack vector that will circumvent verification unless the DID document is re-verified.

9.15 Content Integrity Protection

DID documents which include external JSON-LD contexts (see § 6.3 JSON-LD) or any other links to external machine-readable content are vulnerable to tampering.

DID document consumers can cache local static copies of JSON-LD contexts and/or verify the integrity of external contexts against the cryptographic hash for the context as registered in the DID Specification Registries (see the registration process for more detail) [DID-SPEC-REGISTRIES].

9.16 Persistence

DIDs are designed to be persistent such that a controller need not rely upon a single trusted third party or administrator to maintain their identifiers. No administrator can take control away from the controller, nor can an administrator prevent their identifiers' use for any particular purpose such as authentication, authorization, and attestation. No third party can act on behalf of a controller to remove or render inoperable an individual's (or an organization's) identifier without the controller's consent.

However, it is important to note that in all DID Methods that enable cryptographic proof-of-control, the means of proving control can always be transferred to another party by transferring the cryptographic secrets. Therefore, it is vital that systems relying on the persistence of an identifier over time regularly check to ensure that the identifier is, in fact, still under the control of the intended party.

Unfortunately, it is impossible to determine from the cryptography alone whether or not the private key material associated with a given proof mechanism has been compromised. It might well be that the expected controller still has access to the private keys — and as such can execute a proof-of-control as part of a verification process — while at the same time, a bad actor also has access to (or a copy of) those same keys.

As such, cryptographic proof-of-control is expected to only be used as one factor in evaluating the level of identity assurance for a given service. DID-based authentication provides much greater assurance than a username and password, thanks to the ability to determine control over a secret without transmitting that secret between systems. However, it is not infallible. Services that perform sensitive, high value, or life-critical operations should use additional factors as appropriate.

In addition to potential ambiguity from use by different controllers, it is impossible to guarantee, in general, that a given DID is being used in reference to the same subject at any given point in time. It is technically possible for the controller to reuse a DID for different subjects and, more subtly, for the precise definition of the Subject to either change over time or be misunderstood.

For example, consider a DID used for a sole proprietership, receiving various credentials used for financial transactions. To the controller, that identifier referred to the business. As the business grows, it eventually gets incorporated as an LLC. The controller continues using that same DID, because to them the DID refers to the business. However, to the state, the tax authority, and the local municipality, the DID no longer refers to the same entity. Whether or not the subtle shift in meaning matters to a credit provider or supplier is necessarily up to them to decide. In many cases, as long as the bills get paid and collections can be enforced, the shift is immaterial.

Because of these potential ambiguities, DIDs should be considered valid contextually rather than absolutely. Their persistence does not imply that they refer to the exact same Subject, nor that they are under the control of the same controller. Instead, one needs to understand the context in which the DID was created, how it is used, and consider the likely shifts in their meaning, and adopt procedures and policies to address both potential and inevitable semantic drift.

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9.17 Level of Assurance

Additional information about the security context of authentication events is often required for compliance reasons, especially in regulated areas such as the financial and public sectors. Examples include but are not limited to protection of secret keys, the identity proofing process, and the form-factor of the authenticator. For example, Payment services (PSD 2) and eIDAS introduce such requirements to the security context. Level of Assurance (LoA) frameworks are classified and defined by, for example, eIDAS, NIST 800-63-3 and ISO/IEC 29115:2013, including their requirements for the security context, and making recommendations on how to achieve them. This might include strong user authentication and FIDO2/WebAuthn can be potential implementations. A LoA represents the level of confidence that an entity is in fact that entity. Some regulated use cases require the implementation of a certain LoA. Since verification relationships such as assertionMethod and authentication might be used in some of these use cases, information about the applied security context might need to be expressed and provided to a verifier. Whether and how to encode this information in the DID document data model is out of scope for this specification, but it should be noted that the DID document data model can be extended if necessary (see Extensibility section). Section Privacy Considerations remains applicable for such extensions.

10. Privacy Considerations

This section is non-normative.

It is critically important to apply the principles of Privacy by Design [PRIVACY-BY-DESIGN] to all aspects of the decentralized identifier architecture, because DIDs and DID documents are, by design, administered directly by the DID controller(s). There is no registrar, hosting company, or other intermediate service provider to recommend or apply additional privacy safeguards. The authors of this specification have applied all seven Privacy by Design principles throughout its development. Privacy in this specification is preventative not remedial, and privacy is an embedded default.

10.1 Keep Personal Data Private

If a DID method specification is written for a public verifiable data registry where all DIDs and DID documents are publicly available, it is critical that DID documents contain no personal data.

Personal data can instead be placed behind service endpoints under control of the DID subject or DID controller. Due diligence should be taken around the use of URLs in service endpoints to prevent leakage of personal data or correlation within a URL of a service endpoint. For example, a URL that contains a username is dangerous to include in a DID Document because the username is likely to be human-meaningful in a way that can reveal information that the DID subject did not consent to sharing. With this privacy architecture, personal data can be exchanged on a private, peer-to-peer basis using communications channels identified and secured by public key descriptions in DID documents. This also enables DID subjects and requesting parties to implement the GDPR right to be forgotten, because no personal data is written to an immutable distributed ledger.

10.2 DID Correlation Risks and Pseudonymous DIDs

Like any type of globally unique identifier, DIDs might be used for correlation. DID controllers can mitigate this privacy risk by using pairwise unique DIDs, that is, sharing a different private DID for every relationship. In effect, each DID acts as a pseudonym. A pseudonymous DID need only be shared with more than one party when the DID subject explicitly authorizes correlation between those parties. If pseudonymous DIDs are the default, then the only need for a public DID (a DID published openly or shared with a large number of parties) is when the DID subject explicitly desires public identification.

10.3 DID Document Correlation Risks

The anti-correlation protections of pseudonymous DIDs are easily defeated if the data in the corresponding DID documents can be correlated. For example, using same public key descriptions or bespoke service endpoints in multiple DID documents can provide as much correlation information as using the same DID. Therefore the DID document for a pseudonymous DID also needs to use pairwise unique public keys. It might seem natural to also use pairwise unique service endpoints in the DID document for a pseudonymous DID. However, unique endpoints allow all traffic between two DIDs to be isolated perfectly into unique buckets, where timing correlation and similar analysis is easy. Therefore, a better strategy for endpoint privacy might be to share an endpoint among thousands or millions of DIDs controlled by many different subjects. See also § 10.5 Herd Privacy.

10.4 Assigning a type to the DID subject

It is dangerous to add properties to the DID document that can be used to indicate, explicitly or through inference, what type or nature of thing the DID subject is, particularly if the DID subject is a person.

Not only do such properties potentially result in personal data (see § 10.1 Keep Personal Data Private) or correlatable data (see § 10.2 DID Correlation Risks and Pseudonymous DIDs and § 10.3 DID Document Correlation Risks) being present in the DID document, but they can be used for grouping particular DIDs in such a way that they are included in or excluded from certain operations or functionalities.

Including type information in a DID Document can result in personal privacy harms even for DID Subjects that are non-person entities, such as IoT devices. The aggregation of such information around a DID Controller could serve as a form of digital fingerprint and this is best avoided.

To minimize these risks, all properties in a DID document ought to be for expressing cryptographic material, endpoints, or verification methods related to using the DID.

10.5 Herd Privacy

When a DID subject is indistinguishable from others in the herd, privacy is available. When the act of engaging privately with another party is by itself a recognizable flag, privacy is greatly diminished.

DIDs and DID methods need to work to improve herd privacy, particularly for those who legitimately need it most. Choose technologies and human interfaces that default to preserving anonymity and pseudonymity. To reduce digital fingerprints, share common settings across requesting party implementations, keep negotiated options to a minimum on wire protocols, use encrypted transport layers, and pad messages to standard lengths.

10.6 Service Privacy

The ability for a controller to optionally state at least one service endpoint in the DID document increases their control and agency. Each additional endpoint in the DID document adds privacy risk either due to correlation (e.g., across endpoint descriptions) or because the services are not protected by an authorization mechanism, or both.

DID documents are often public and will be stored and indexed efficiently by their very standards-based nature. This risk is worse if DID documents are published to immutable Verifiable Data Registries. Access to a history of the DID documents referenced by a DID represents a form of traffic analysis made more efficient through the use of standards.

The degree of additional privacy risk caused by using multiple service endpoints in one DID document can be difficult to estimate. Privacy harms are typically unintended consequences. DIDs can identify documents, services, schemas, and other things that may be associated with individual people, households, clubs, and employers — and correlation of their service endpoints could become a powerful surveillance and inference tool. An example of this is that including multiple common country-level top level domain such as https://example.co.uk could be used to infer the approximate location of the DID Subject with a greater degree of probability.

The variety of possible endpoints makes it particularly challenging to maintain herd privacy, in which no information about the DID subject is leaked.

First, because service endpoints may be specified as URIs, they could unintentionally leak personal information because of the architecture of the service. For example, a service endpoint of http://example.com/MyFirstName is leaking the term MyFirstName to everyone who can access the DID Document. When linking to legacy systems, this is an unavoidable risk and care should be taken in such cases. We encourage new, DID-aware endpoints to use nothing more than the DID itself for any identification necessary, e.g., http://example.com/did%3Aexample%3Aabc123. Since that did:example:abc123 is already exposed in the DID Document, it leaks no additional information.

Second, because a DID document can list multiple service endpoints, it is possible to irreversibly associate services that are not associated in any other context. This correlation on its own may lead to de-anonymization, revealing information about the DID subject even if the URIs used did not.

Third, because some types of DID subjects may be more or less likely to list specific endpoints, e.g., a DID for an automobile may include a pointer to a public title record at the Department of Motor Vehicles, while a DID for an individual would not. As such, the listing of a given service could, by itself, leak information that can be used to infer something about the subject.

It is the goal of herd privacy to ensure that the nature of specific subjects is obscured by the population of the whole. To maximize herd privacy, implementers need to rely on one — and only one — service endpoint, with that endpoint providing a proxy or mediator service that the controller is willing to depend on to protect such associations and that blinds requests to the ultimate service.

Torward this end, consider any of the following:

Negotiator Endpoint — Service for negotiating mutually agreeable communications channels, preferably using private set intersection. The output of negotiation is a communication channel and whatever credentials may be needed to access it.
Tor Endpoint (Tor Onion Router) — Provide a privacy-respecting address for reaching service endpoints. Any service that can be provided online can be provided through TOR for additional privacy.
Mediator Endpoint — Mediators provide a generic endpoint, for multiple parties, receive encrypted messages on behalf of those parties, and forward them to the intended recipient. This avoids the need to have a specific endpoint per subject, which could create a correlation risk. Also called a proxy.
Confidential Storage — Proprietary or confidential personal information may need to be kept off-registry to provide additional privacy and/or security guarantees, especially for those methods where DID documents are published on a public ledger. Pointing to external resource services provides a means for authorization checks and deletion.
Polymorphic Proxy — A proxy endpoint that can act as any number of services, depending on how it is called. For example, the same URL could be used for both negotiator and mediator functions, depending on a mechanism for re-routing.

These service endpoint types continue to be an area of innovation.

11. Examples

This section is non-normative.

11.1 DID Documents

This section is non-normative.

See Verification Method Types [DID-SPEC-REGISTRIES] for optional extensions and other verification method types.

Note

These examples are for information purposes only, it is considered a best practice to avoid using the same verification method for multiple purposes.

Example 32: DID Document with 1 verification method type

  {
    "@context": "https://www.w3.org/ns/did/v1",
    "id": "did:example:123",
    "authentication": [
      {
        "id": "did:example:123#z6MkecaLyHuYWkayBDLw5ihndj3T1m6zKTGqau3A51G7RBf3",
        "type": "Ed25519VerificationKey2018", // external (property value)
        "controller": "did:example:123",
        "publicKeyBase58": "AKJP3f7BD6W4iWEQ9jwndVTCBq8ua2Utt8EEjJ6Vxsf"
      }
    ],
    "capabilityInvocation": [
      {
        "id": "did:example:123#z6MkhdmzFu659ZJ4XKj31vtEDmjvsi5yDZG5L7Caz63oP39k",
        "type": "Ed25519VerificationKey2018", // external (property value)
        "controller": "did:example:123",
        "publicKeyBase58": "4BWwfeqdp1obQptLLMvPNgBw48p7og1ie6Hf9p5nTpNN"
      }
    ],
    "capabilityDelegation": [
      {
        "id": "did:example:123#z6Mkw94ByR26zMSkNdCUi6FNRsWnc2DFEeDXyBGJ5KTzSWyi",
        "type": "Ed25519VerificationKey2018", // external (property value)
        "controller": "did:example:123",
        "publicKeyBase58": "Hgo9PAmfeoxHG8Mn2XHXamxnnSwPpkyBHAMNF3VyXJCL"
      }
    ],
    "assertionMethod": [
      {
        "id": "did:example:123#z6MkiukuAuQAE8ozxvmahnQGzApvtW7KT5XXKfojjwbdEomY",
        "type": "Ed25519VerificationKey2018", // external (property value)
        "controller": "did:example:123",
        "publicKeyBase58": "5TVraf9itbKXrRvt2DSS95Gw4vqU3CHAdetoufdcKazA"
      }
    ]
}

Example 33: DID Document with many different verification methods

{
  "@context": "https://www.w3.org/ns/did/v1",
  "id": "did:example:123",
  "verificationMethod": [
    {
      "id": "did:example:123#ZC2jXTO6t4R501bfCXv3RxarZyUbdP2w_psLwMuY6ec",
      "type": "Ed25519VerificationKey2018", // external (property value)
      "controller": "did:example:123",
      "publicKeyBase58": "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
    },
    {
      "id": "did:example:123#zQ3shP2mWsZYWgvgM11nenXRTx9L1yiJKmkf9dfX7NaMKb1pX",
      "type": "EcdsaSecp256k1VerificationKey2019", // external (property value)
      "controller": "did:example:123",
      "publicKeyBase58": "d5cW2R53NHTTkv7EQSYR8YxaKx7MVCcchjmK5EgCNXxo",
    },
    {
      "id": "did:example:123#_Qq0UL2Fq651Q0Fjd6TvnYE-faHiOpRlPVQcY_-tA4A",
      "type": "JsonWebKey2020", // external (property value)
      "controller": "did:example:123",
      "publicKeyJwk": {
        "kty": "OKP", // external (property name)
        "crv": "Ed25519", // external (property name)
        "x": "VCpo2LMLhn6iWku8MKvSLg2ZAoC-nlOyPVQaO3FxVeQ" // external (property name)
      }
    },
    {
      "id": "did:example:123#z6LSnjagzhe8Df6gZmroW3wjDd7XQLwAuYfwa4ZeTBCGFoYc",
      "type": "JsonWebKey2020", // external (property value)
      "controller": "did:example:123",
      "publicKeyJwk": {
        "kty": "OKP", // external (property name)
        "crv": "X25519", // external (property name)
        "x": "pE_mG098rdQjY3MKK2D5SUQ6ZOEW3a6Z6T7Z4SgnzCE" // external (property name)
      },
    }
    {
      "id": "did:example:123#4SZ-StXrp5Yd4_4rxHVTCYTHyt4zyPfN1fIuYsm6k3A",
      "type": "JsonWebKey2020", // external (property value)
      "controller": "did:example:123",
      "publicKeyJwk": {
        "kty": "EC", // external (property name)
        "crv": "secp256k1", // external (property name)
        "x": "Z4Y3NNOxv0J6tCgqOBFnHnaZhJF6LdulT7z8A-2D5_8", // external (property name)
        "y": "i5a2NtJoUKXkLm6q8nOEu9WOkso1Ag6FTUT6k_LMnGk" // external (property name)
      }
    },
    {
      "id": "did:example:123#n4cQ-I_WkHMcwXBJa7IHkYu8CMfdNcZKnKsOrnHLpFs",
      "type": "JsonWebKey2020", // external (property value)
      "controller": "did:example:123",
      "publicKeyJwk": {
        "kty": "RSA", // external (property name)
        "e": "AQAB", // external (property name)
        "n": "omwsC1AqEk6whvxyOltCFWheSQvv1MExu5RLCMT4jVk9khJKv8JeMXWe3bWHatjPskdf2dlaGkW5QjtOnUKL742mvr4tCldKS3ULIaT1hJInMHHxj2gcubO6eEegACQ4QSu9LO0H-LM_L3DsRABB7Qja8HecpyuspW1Tu_DbqxcSnwendamwL52V17eKhlO4uXwv2HFlxufFHM0KmCJujIKyAxjD_m3q__IiHUVHD1tDIEvLPhG9Azsn3j95d-saIgZzPLhQFiKluGvsjrSkYU5pXVWIsV-B2jtLeeLC14XcYxWDUJ0qVopxkBvdlERcNtgF4dvW4X00EHj4vCljFw" // external (property name)
      }
    },
    {
      "id": "did:example:123#_TKzHv2jFIyvdTGF1Dsgwngfdg3SH6TpDv0Ta1aOEkw",
      "type": "JsonWebKey2020", // external (property value)
      "controller": "did:example:123",
      "publicKeyJwk": {
        "kty": "EC", // external (property name)
        "crv": "P-256", // external (property name)
        "x": "38M1FDts7Oea7urmseiugGW7tWc3mLpJh6rKe7xINZ8", // external (property name)
        "y": "nDQW6XZ7b_u2Sy9slofYLlG03sOEoug3I0aAPQ0exs4" // external (property name)
      }
    },
    {
      "id": "did:example:123#8wgRfY3sWmzoeAL-78-oALNvNj67ZlQxd1ss_NX1hZY",
      "type": "JsonWebKey2020", // external (property value)
      "controller": "did:example:123",
      "publicKeyJwk": {
        "kty": "EC", // external (property name)
        "crv": "P-384", // external (property name)
        "x": "GnLl6mDti7a2VUIZP5w6pcRX8q5nvEIgB3Q_5RI2p9F_QVsaAlDN7IG68Jn0dS_F", // external (property name)
        "y": "jq4QoAHKiIzezDp88s_cxSPXtuXYFliuCGndgU4Qp8l91xzD1spCmFIzQgVjqvcP" // external (property name)
      }
    },
    {
      "id": "did:example:123#NjQ6Y_ZMj6IUK_XkgCDwtKHlNTUTVjEYOWZtxhp1n-E",
      "type": "JsonWebKey2020", // external (property value)
      "controller": "did:example:123",
      "publicKeyJwk": {
        "kty": "EC", // external (property name)
        "crv": "P-521", // external (property name)
        "x": "AVlZG23LyXYwlbjbGPMxZbHmJpDSu-IvpuKigEN2pzgWtSo--Rwd-n78nrWnZzeDc187Ln3qHlw5LRGrX4qgLQ-y", // external (property name)
        "y": "ANIbFeRdPHf1WYMCUjcPz-ZhecZFybOqLIJjVOlLETH7uPlyG0gEoMWnIZXhQVypPy_HtUiUzdnSEPAylYhHBTX2" // external (property name)
      }
    }
  ]
}

11.2 Proving

This section is non-normative.

Note

These examples are for information purposes only. See W3C Verifiable Credentials Data Model for additional examples.

Example 34: Verifiable Credential linked to a verification method of type Ed25519VerificationKey2018

{  // external (all terms in this example)
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://w3id.org/citizenship/v1"
  ],
  "type": [
    "VerifiableCredential",
    "PermanentResidentCard"
  ],
  "credentialSubject": {
    "id": "did:example:123",
    "type": [
      "PermanentResident",
      "Person"
    ],
    "givenName": "JOHN",
    "familyName": "SMITH",
    "gender": "Male",
    "image": "data:image/png;base64,iVBORw0KGgo...kJggg==",
    "residentSince": "2015-01-01",
    "lprCategory": "C09",
    "lprNumber": "000-000-204",
    "commuterClassification": "C1",
    "birthCountry": "Bahamas",
    "birthDate": "1958-08-17"
  },
  "issuer": "did:example:456",
  "issuanceDate": "2020-04-22T10:37:22Z",
  "identifier": "83627465",
  "name": "Permanent Resident Card",
  "description": "Government of Example Permanent Resident Card.",
  "proof": {
    "type": "Ed25519Signature2018",
    "created": "2020-04-22T10:37:22Z",
    "proofPurpose": "assertionMethod",
    "verificationMethod": "did:example:456#key-1",
    "jws": "eyJjcml0IjpbImI2NCJdLCJiNjQiOmZhbHNlLCJhbGciOiJFZERTQSJ9..BhWew0x-txcroGjgdtK-yBCqoetg9DD9SgV4245TmXJi-PmqFzux6Cwaph0r-mbqzlE17yLebjfqbRT275U1AA"
  }
}

Example 35: Verifiable Credential linked to a verification method of type JsonWebKey2020

{  // external (all terms in this example)
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://www.w3.org/2018/credentials/examples/v1"
  ],
  "id": "http://example.gov/credentials/3732",
  "type": ["VerifiableCredential", "UniversityDegreeCredential"],
  "issuer": { "id": "did:example:123" },
  "issuanceDate": "2020-03-10T04:24:12.164Z",
  "credentialSubject": {
    "id": "did:example:456",
    "degree": {
      "type": "BachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  },
  "proof": {
    "type": "JsonWebSignature2020",
    "created": "2020-02-15T17:13:18Z",
    "verificationMethod": "did:example:123#_Qq0UL2Fq651Q0Fjd6TvnYE-faHiOpRlPVQcY_-tA4A",
    "proofPurpose": "assertionMethod",
    "jws": "eyJiNjQiOmZhbHNlLCJjcml0IjpbImI2NCJdLCJhbGciOiJFZERTQSJ9..Y0KqovWCPAeeFhkJxfQ22pbVl43Z7UI-X-1JX32CA9MkFHkmNprcNj9Da4Q4QOl0cY3obF8cdDRdnKr0IwNrAw"
  }
}

Example 36: Verifiable Credential linked to a bls12381 verification method

{  // external (all terms in this example)
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://w3id.org/security/bbs/v1",
    {
      "name": "https://schema.org/name",
      "birthDate": "https://schema.org/birthDate"
    }
  ],
  "id": "urn:uuid:c499e122-3ba9-4e95-8d4d-c0ebfcf8c51a",
  "type": ["VerifiableCredential"],
  "issuanceDate": "2021-02-07T16:02:08.571Z",
  "issuer": {
    "id": "did:example:123"
  },
  "credentialSubject": {
    "id": "did:example:456",
    "name": "John Smith",
    "birthDate": "2021-02-07"
  },
  "proof": {
    "type": "BbsBlsSignature2020",
    "created": "2021-02-07T16:02:10Z",
    "proofPurpose": "assertionMethod",
    "proofValue": "o7zD2eNTp657YzkJLub+IO4Zqy/R3Lv/AWmtSA/kUlEAOa73BNyP1vOeoow35jkABolx4kYMKkp/ZsFDweuKwe/p9vxv9wrMJ9GpiOZjHcpjelDRRJLBiccg9Yv7608mHgH0N1Qrj14PZ2saUlfhpQ==",
    "verificationMethod": "did:example:123#bls12381-g2-key"
  }
}

Example 37: Verifiable Credential selective disclosure zero knowledge proof linked to a bls12381 verification method

{  // external (all terms in this example)
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://w3id.org/security/bbs/v1",
    {
      "name": "https://schema.org/name",
      "birthDate": "https://schema.org/birthDate"
    }
  ],
  "id": "urn:uuid:c499e122-3ba9-4e95-8d4d-c0ebfcf8c51a",
  "type": "VerifiableCredential",
  "issuanceDate": "2021-02-07T16:02:08.571Z",
  "issuer": {
    "id": "did:example:123"
  },
  "credentialSubject": {
    "id": "did:example:456",
    "birthDate": "2021-02-07"
  },
  "proof": {
    "type": "BbsBlsSignatureProof2020",
    "created": "2021-02-07T16:02:10Z",
    "nonce": "OqZHsV/aunS34BhLaSoxiHWK+SUaG4iozM3V+1jO06zRRNcDWID+I0uwtPJJ767Yo8Q=",
    "proofPurpose": "assertionMethod",
    "proofValue": "AAsH34lcKsqaqPaLQWcnLMe3mDM+K7fZM0t4Iesfj7BhD//HBtuWCmZE946BqW7OHYU106MP8mLntutqB8FyGwS7AOyK+5/7iW6JwLNVCvh4Nt3IaF3AN47fqVs2VikD9DiCsaFAUU6ISj5pbad8O+6jiT9Yw6ug8t8vJn3XHvMUhCPnDZJeBEdKD1qo4Z0LOq3L8QAAAHSEgtC9BoZL2MLjz4QuPxpwbhTTRC08MIUjdJnP4JUtz6163Lsl3rpadGu2d3Te7loAAAACZBD4YWOgV0xpPoYZ5vywNA5/NTeDHDbX36gvoV5RDJtY1SLU2LN/IDPZGrfhEiASbD1/QXqj8dod6FbjBs9m/LchBcy7z4yDBv/8DnBzDJ9dEaM4bDjpwmqtgJqha2kwtlyNog67xG9tNjnp5rrbIgAAAANMVanwWmlkg5I/f1M2QJ5GRvQiBL4lyL5sttxwIOalbTZP8VqWtFJI54xMNjTiK71aFWWN8SlNEwfVIX34HO5zBIb6fvc+Or21ubYllT9eXv1epl2o2CojuieCZyxE8/Q=",
    "verificationMethod": "did:example:123#bls12381-g2-key"
  }
}

Example 38: Verifiable Credential as Decoded JWT

{ // external (all terms in this example)
  "protected": {
    "kid": "did:example:123#_Qq0UL2Fq651Q0Fjd6TvnYE-faHiOpRlPVQcY_-tA4A",
    "alg": "EdDSA"
  },
  "payload": {
    "iss": "did:example:123",
    "sub": "did:example:456",
    "vc": {
      "@context": [
        "https://www.w3.org/2018/credentials/v1",
        "https://www.w3.org/2018/credentials/examples/v1"
      ],
      "id": "http://example.gov/credentials/3732",
      "type": [
        "VerifiableCredential",
        "UniversityDegreeCredential"
      ],
      "issuer": {
        "id": "did:example:123"
      },
      "issuanceDate": "2020-03-10T04:24:12.164Z",
      "credentialSubject": {
        "id": "did:example:456",
        "degree": {
          "type": "BachelorDegree",
          "name": "Bachelor of Science and Arts"
        }
      }
    },
    "jti": "http://example.gov/credentials/3732",
    "nbf": 1583814252
  },
  "signature": "qSv6dpZJGFybtcifLwGf4ujzlEu-fam_M7HPxinCbVhz9iIJCg70UMeQbPa1ex6BmQ2tnSS7F11FHnMB2bJRAw"
}

11.3 Encrypting

This section is non-normative.

Note

These examples are for information purposes only, it is considered a best practice to avoid dislosing unnecessary information in JWE headers.

Example 39: JWE linked to a verification method via kid

{ // external (all terms in this example)
  "ciphertext": "3SHQQJajNH6q0fyAHmw...",
  "iv": "QldSPLVnFf2-VXcNLza6mbylYwphW57Q",
  "protected": "eyJlbmMiOiJYQzIwUCJ9",
  "recipients": [
    {
      "encrypted_key": "BMJ19zK12YHftJ4sr6Pz1rX1HtYni_L9DZvO1cEZfRWDN2vXeOYlwA",
      "header": {
        "alg": "ECDH-ES+A256KW",
        "apu": "Tx9qG69ZfodhRos-8qfhTPc6ZFnNUcgNDVdHqX1UR3s",
        "apv": "ZGlkOmVsZW06cm9wc3RlbjpFa...",
        "epk": {
          "crv": "X25519",
          "kty": "OKP",
          "x": "Tx9qG69ZfodhRos-8qfhTPc6ZFnNUcgNDVdHqX1UR3s"
        },
        "kid": "did:example:123#zC1Rnuvw9rVa6E5TKF4uQVRuQuaCpVgB81Um2u17Fu7UK"
      }
    }
  ],
  "tag": "xbfwwDkzOAJfSVem0jr1bA"
}

C. Frequently Asked Questions about DID Identification

C.1 What types of resources can a DID identify?

Since a DID is a specific type of URI (Uniform Resource Identifier), the answer to this question is provided by section 1.1 of the URI specification [RFC3986]:

This specification does not limit the scope of what might be a resource; rather, the term "resource" is used in a general sense for whatever might be identified by a URI. Familiar examples include an electronic document, an image, a source of information with a consistent purpose (e.g., "today's weather report for Los Angeles"), a service (e.g., an HTTP-to-SMS gateway), and a collection of other resources. A resource is not necessarily accessible via the Internet; e.g., human beings, corporations, and bound books in a library can also be resources. Likewise, abstract concepts can be resources, such as the operators and operands of a mathematical equation, the types of a relationship (e.g., "parent" or "employee"), or numeric values (e.g., zero, one, and infinity).

In other words, it does not matter whether a resource is "on" or "off" the Internet—if it can be identified, it can be assigned a URI, and therefore it can be assigned a DID.

C.2 How do you know what a DID identifies?

For any DID, the DID controller determines the DID subject. It is not expected to be possible to determine the DID subject from looking at the DID itself. The reason is that, in order to satisfy several core properties of a DID as an identifier—especially decentralization and cryptographic verifiability—DIDs are generally only meaningful to machines, not humans. To illustrate, compare the following two URIs:

https://www.w3.org/2019/did-wg/WorkMode/getting-started

did:example:8uQhQMGzWxR8vw5P3UWH1j

The first is the URL of the Getting Started page of the W3C DID Working Group. This is a human-meaningful identifier (at least to someone who understands the English language). In this sense, the reader can be said to "know" what the URL identifies without having to dereference it (provided the reader trusts the publisher of the URL).

The second URI—the example DID—is meaningless to humans no matter what language you speak. What it identifies is anyone’s guess in the absence of further information describing the DID subject. So further information about the DID subject is only discoverable by resolving the DID to the DID document, obtaining a verifiable credential about the DID, or via some other description of the DID.

C.3 Does the DID identify the DID document?

No. To be very precise, the DID identifies the DID subject and resolves to the DID document (by following the protocol specified by the DID method). The DID document is not a separate resource from the DID subject and does not have a URI separate from the DID. Rather the DID document is an artifact of DID resolution controlled by the DID controller for the purpose of describing the DID subject.

This distinction is illustrated by the graph model shown below.

Diagram showing a graph model for how DID controllers assign DIDs to identify
DID subjects and resolve to DID documents that describe the DID subjects. — Figure 6 A DID is an identifier assigned by a DID controller to identify a DID subject and resolve to a DID document that describes the DID subject. The DID document is an artifact of DID resolution and not a separate resource distinct from the DID subject.

C.4 What does the DID document say about the DID subject?

Each property in a DID document is a statement by the DID controller that refers to:

The string of characters defining identifiers for the DID subject (e.g., the id and alsoKnownAs properties)
How to interact with the DID subject (e.g., the verificationMethod and service properties).
How to interpret the specific representation of the DID document (e.g., the @context property for a JSON-LD representation).

There is only one required property in a DID document—the id property—so that is the only statement guaranteed to be in a DID document. That statement is illustrated by the solid red arrow in figure 2 asserting that the DID identifies the DID subject.

C.5 How can you discover more information about the DID subject?

There are two basic options for discovery of more information about the DID subject. The first option is to request more information from a service endpoint if one or more are present in the DID document. An example would be to query a service endpoint that supports verifiable credentials for one or more claims (attributes) describing the DID subject.

A second option is to use the alsoKnownAs property if it is present in the DID document. The DID controller can use it to provide a list of other URIs (including other DIDs) that identify the same DID subject. Resolving or dereferencing these URIs might yield other descriptions or representations of the DID subject as illustrated in the figure below.

Diagram showing a graph model that adds to figure 2 by showing an
alsoKnownAs property with an arc to another node representing a
different resource that dereferences to another description of the
DID subject. — Figure 7 A DID document can use the alsoKnownAs property to assert another URI (including another DID) that identifies the same DID subject

This mechanism is how DID identification can fulfill guidance from the W3C in Cool URIs for the Semantic Web:

Given only a URI, machines and people should be able to retrieve a description about the resource identified by the URI from the Web. Such a look-up mechanism is important to establish shared understanding of what a URI identifies. Machines should get RDF data and humans should get a readable representation, such as HTML.

Note that it is not required that a DID document use an RDF-based representation; see § 6. Representations.

C.6 Can the DID document serve as a representation of the DID subject?

If the DID subject is a digital resource that can be retrieved from the Internet, then yes, the DID document can serve as a representation of the DID subject. For example, a data schema that needs a persistent, cryptographically verifiable identifier could be assigned a DID, and its DID document could be used as a standard way to retrieve a representation of that schema.

Alternately, a DID can be used to identify a digital resource that can be returned directly from a verifiable data registry if that functionality is supported by the applicable DID method.

C.7 Can existing web resources also be assigned DIDs?

Yes, if the controller of a web page or any other web resource wants to assign it a persistent, cryptographically verifiable identifier, the controller can give it a DID. For example, the author of a blog hosted by a blog hosting company (under that hosting company’s own URL) could create a DID for the blog. In the DID document, the author can include an alsoKnownAs property pointing to the current URL of the blog:


          "alsoKnownAs": ["https://myblog.blogging-host.example/home"]

If the author subsequently moves the blog to a different hosting company (or to the author’s own domain), the author can update the DID document to point to the new URL for the blog:


          "alsoKnownAs": ["https://myblog.example/"]

The DID effectively adds a layer of indirection for the blog URL. This layer of indirection is under the control of the author instead of under the control of an external administrative authority such as the blog hosting company. This is how a DID can effectively function as an enhanced URN (Uniform Resource Name)—a persistent identifier for an information resource whose network location might change over time.

C.8 What is the relationship between DID controllers and DID subjects?

To avoid confusion, it is helpful to classify DID subjects into two disjoint sets based on their relationship to the DID controller.

C.8.1 Set #1: The DID subject is the DID controller

The first case, shown in figure 4, is the common scenario where the DID subject is also the DID controller. This is the case when an individual or organization creates a DID to self-identify.

Diagram showing the same graph model as figure 2 except with an
equivalence arc from the DID subject to the DID controller. — Figure 8 The DID subject is the same entity as the DID controller

From a graph model perspective, even though the nodes identified as the DID controller and DID subject in figure 4 are distinct, there is a logical arc connecting them to express a semantic equivalence relationship. (In RDF/OWL, this is expressed using the owl:sameAs predicate.)

C.8.2 Set #2: The DID subject is not the DID controller

The second case is when the DID subject is a separate entity from the DID controller. This is the case when, for example, a parent creates and maintains control of a DID for a child; a corporation creates and maintains control of a DID for a subsidiary; or a manufacturer creates and maintains control of a DID for a product, an IoT device, or a digital file.

From a graph model perspective, the only difference from Set 1 that there is no equivalence arc relationship between the DID subject and DID controller nodes.

C.9 Can a DID document have multiple DID Controllers?

Yes. A DID document might have more than one DID controller. In this situation there are two basic options available for how control can be shared.

C.9.1 Option #1: Independent Control

In the first option, shown in the figure below, each of the DID controllers might act on its own, i.e., each one has full power to update the DID document independently. From a graph model perspective, in this configuration:

Each additional DID controller is another distinct graph node (which might be identified by its own DID).
The same arcs ("controls" and "controller") exist between each DID controller and the DID document.

Diagram showing three DID controllers each with an independent
control relationship with the DID document — Figure 9 Multiple independent DID controllers that can each act independently

C.9.2 Option #2: Group Control

In the second option, the DID controllers are expected to act together in some fashion, such as when using a cryptographic algorithm that requires multiple digital signatures ("multi-sig") or a threshold number of digital signatures ("m-of-n"). From a functional standpoint, this option is similar to a single DID controller because, although each of the DID controllers in the DID controller group has its own graph node, the actual control collapses into a single logical graph node representing the DID controller group as shown in this figure:

Diagram showing how three DID controllers act together as a single
DID controller group to control a DID document — Figure 10 Multiple DID controllers who are expected to act together as a DID controller group

This configuration will often apply when the DID subject is an organization, corporation, government agency, community, or other group that is not controlled by a single individual.

Decentralized Identifiers (DIDs) v1.0

Core architecture, data model, and representations

W3C Working Draft 26 February 2021

Abstract

Status of This Document

1. Introduction

1.1 A Simple Example

1.2 Design Goals

1.3 Architecture Overview

1.4 Conformance

2. Terminology

3. Identifier

3.1 DID Syntax

3.2 DID URL Syntax

Path

Query

Fragment

3.2.1 DID Parameters

3.2.2 Relative DID URLs

4. Data Model

4.1 Extensibility

5. Core Properties

DID Document properties

Verification Method properties

Service properties

5.1 Identifiers

5.1.1 DID Subject

5.1.2 DID Controller

5.1.3 Also Known As

5.2 Verification Methods

5.2.1 Verification Material

5.2.2 Referring to Verification Methods

5.3 Verification Relationships

5.3.1 Authentication

5.3.2 Assertion

5.3.3 Key Agreement

5.3.4 Capability Invocation

5.3.5 Capability Delegation

5.4 Services

6. Representations

6.1 Production and Consumption

6.2 JSON

6.2.1 Production

6.2.2 Consumption

6.3 JSON-LD

6.3.1 Production

6.3.2 Consumption

6.4 CBOR

6.4.1 Production

6.4.2 Consumption

7. Resolution

7.1 DID Resolution

7.1.1 DID Resolution Options

7.1.2 DID Resolution Metadata

7.1.3 DID Document Metadata

7.2 DID URL Dereferencing

7.2.1 DID URL Dereferencing Options

7.2.2 DID URL Dereferencing Metadata

7.3 Metadata Structure

8. Methods

8.1 Method Syntax

8.2 Method Operations

8.3 Security Requirements

8.4 Privacy Requirements

9. Security Considerations

9.1 Choosing DID Resolvers

9.2 Binding of Identity

9.2.1 Proving Control of a DID and DID Document

9.2.2 Proving Control of a Public Key

9.2.3 Real-World Identity

9.3 Authentication Service Endpoints

9.4 Non-Repudiation

9.5 Notification of DID Document Changes

9.6 Key and Signature Expiration

9.7 Verification Method Rotation

9.8 Verification Method Revocation

9.9 DID Recovery

9.10 The Role of Human-Friendly Identifiers

9.11 DIDs as Enhanced URNs

9.12 Immutability