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<!DOCTYPE html>
<html>
<head>
<title>
Decentralized Identifiers (DIDs) v0.13
</title>
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<body>
<section id='abstract'>
<p>
Decentralized Identifiers (DIDs) are a new type of identifier for
verifiable, decentralized digital identity. These new identifiers
are designed to enable the controller of a DID to prove control over
it and to be implemented independently of any centralized registry,
identity provider, or certificate authority. DIDs are URLs that relate
a <a>DID subject</a> to means for trustable interactions with that subject.
DIDs resolve to DID Documents — simple documents that describe how to
use that specific DID. Each DID Document may express cryptographic
material, verification methods, and/or service endpoints. These provide
a set of mechanisms which enable a <a>DID controller</a> to prove control of the
DID. Service endpoints enable trusted interactions with the <a>DID subject</a>.
</p>
<p>
This document specifies a common data model, format, and operations that
all DIDs support.
</p>
</section>
<section id='sotd'>
<p>
Comments regarding this document are welcome. Please file issues
directly on <a href="https://github.com/w3c-ccg/did-spec/issues/">GitHub</a>, or send them
to <a href="mailto:[email protected]">[email protected]</a> (
<a href="mailto:[email protected]?subject=subscribe">subscribe</a>,
<a href="https://lists.w3.org/Archives/Public/public-credentials/">archives</a>).
</p>
<p>
Portions of the work on this specification have been funded by the
United States Department of Homeland Security's Science and Technology
Directorate under contracts HSHQDC-16-R00012-H-SB2016-1-002 and
HSHQDC-17-C-00019. The content of this specification does not
necessarily reflect the position or the policy of the U.S. Government
and no official endorsement should be inferred.
</p>
<p>
Work on this specification has also been supported by the Rebooting the
Web of Trust community facilitated by Christopher Allen, Shannon
Appelcline, Kiara Robles, Brian Weller, Betty Dhamers, Kaliya Young,
Kim Hamilton Duffy, Manu Sporny, Drummond Reed, Joe Andrieu, and
Heather Vescent.
</p>
</section>
<section class="informative">
<h1>
Introduction
</h1>
<p>
Conventional <a href="https://en.wikipedia.org/wiki/Identity_management">identity
management</a> systems are based on centralized authorities such as
corporate <a href="https://en.wikipedia.org/wiki/Directory_service">directory
services</a>, <a href="https://en.wikipedia.org/wiki/Certificate_authority">certificate
authorities</a>, or <a href="https://en.wikipedia.org/wiki/Domain_name_registry">domain name
registries</a>. From the standpoint of cryptographic trust
verification, each of these centralized authorities serves as its own
<a href="https://en.wikipedia.org/wiki/Trust_anchor">root of
trust</a>. To make identity management work across these systems
requires implementing <a href="https://en.wikipedia.org/wiki/Federated_identity">federated identity
management</a>.
</p>
<p>
The emergence of distributed ledger technology (DLT), sometimes
referred to as blockchain technology, provides the opportunity for
fully <a>decentralized identity management</a>. In a decentralized
identity system, entities (in the sense of discrete identifiable units
such as — but not limited to — people, organizations, and
things) are free to use any shared root of trust.
Globally distributed ledgers, decentralized P2P networks, or other systems
with similar capabilities, provide the means for managing a root of
trust without introducing a centralized authority or a single point of
failure. In combination, DLTs and decentralized identity systems
enable any entity to create and manage their own identifiers on any
number of distributed, independent roots of trust.
</p>
<p>
Entities are identified by decentralized identifiers (DIDs), and
may authenticate via proofs (e.g., digital signatures,
privacy-preserving biometric protocols, etc.). DIDs point to DID
Documents. A DID Document contains a set of service endpoints for
interacting with the entity the DID identifies (aka the <a>DID subject</a>).
Following the dictums of
<a href="https://en.wikipedia.org/wiki/Privacy_by_design">Privacy by
Design</a>, any entity may have as many DIDs as necessary (and
corresponding DID Documents and service endpoints), to respect the
entity’s desired separation of identities, personas, and contexts.
</p>
<p>
DID methods are the mechanism by which a DID and its associated DID
Document are created, read, updated, and deactivated on a specific
distributed ledger or network. DID methods are defined using separate
DID method specifications.
</p>
<p>
This design eliminates dependence on centralized registries for
identifiers as well as centralized certificate authorities for key
management — the standard pattern in hierarchical
<a href="https://en.wikipedia.org/wiki/Public_key_infrastructure">PKI
(public key infrastructure</a>). In cases where the <a>DID Registry</a>
is a distributed ledger, each entity may serve as its own root authority
— an architecture referred to as
<a href="https://github.com/WebOfTrustInfo/rebooting-the-web-of-trust/blob/master/final-documents/dpki.pdf">DPKI
(decentralized PKI)</a>.
</p>
<p>
Note that DID methods may also be developed for identifiers
registered in federated or centralized identity management systems.
For their part, all types of identifier systems may add support for
DIDs. This creates an interoperability bridge between the worlds of
centralized, federated, and decentralized identifiers.
</p>
<p>
The first purpose of this specification is to define the generic
DID scheme and a generic set of operations on DID Documents that can be
implemented for any <a>DID Registry</a>. The second
purpose of this specification is to
define the conformance requirements for a DID method
specification — a separate specification that defines a specific DID
scheme and specific set of DID Document operations for a specific
<a>DID Registry</a>.
</p>
<p class="note">
Conceptually, the relationship of this specification and a DID
method specification is similar to the relationship of the IETF
generic URI specification ([[RFC3986]]) and a specific URI scheme
([[IANA-URI-SCHEMES]] (such as the http: and https: schemes
specified in [[RFC7230]]). It is also similar to the relationship
of the IETF generic URN specification ([[RFC8141]]) and a specific URN
namespace definition (such as the UUID URN namespace defined in
[[RFC4122]]). The difference is that a DID Method specification, in
addition to defining a specific DID scheme, also specifies the
methods for resolving and deactivating DIDs and writing DID Documents on the
appropriate <a>DID Registry</a>.
</p>
<p>
The hierarchical design of a generic DID specification with specific DID method
specifications introduces some of the same concepts as the URI specification:
</p>
<ul>
<li>
DIDs from different DID methods may not be interoperable, just as URIs from
different URI schemes may not be interoperable.
</li>
<li>
Entities may need multiple DIDs to support different relationships, as the other
party may only support certain DID methods, just as some browsers may only
support certain URI schemes.
</li>
<li>
Entities may need multiple DIDs to support the different cryptographic schemes
of different DID methods, as not all parties will support the same cryptographic
schemes, just as not all browsers support the same URI schemes.
</li>
<li>
Managing multiple DIDs, and tracking which DID belongs to which relationship,
under which cryptographic scheme, introduces similar logistical challenges as
managing multiple web addresses and tracking which address belongs to which
website, or tracking which email address belongs to which relationship.
</li>
</ul>
<p>
For a list of DID Methods and their corresponding specifications,
see the DID Method Registry [[DID-METHOD-REGISTRY]].
</p>
<section class="informative">
<h2>
A Simple Example
</h2>
<p>
A DID is a simple text string that consists of three parts: 1) the URL scheme
identifier (<code>did</code>), 2) the identifier for the
DID Method, and 3) the DID Method-specific identifier.
</p>
<pre class="example nohighlight" title="A simple example of a Decentralized Identifier (DID)">
did:example:123456789abcdefghi
</pre>
<p>
The DID above resolves to a DID Document. A DID Document contains information
associated with the DID such as ways to cryptographically authenticate the
entity in control of the DID, as well as services that can be used to
interact with the entity.
</p>
<pre class="example nohighlight" title="Minimal self-managed DID Document">
{
"@context": "https://www.w3.org/2019/did/v1",
"id": "did:example:123456789abcdefghi",
"authentication": [{
<span class="comment">// used to authenticate as did:...fghi</span>
"id": "did:example:123456789abcdefghi#keys-1",
"type": "RsaVerificationKey2018",
"controller": "did:example:123456789abcdefghi",
"publicKeyPem": "-----BEGIN PUBLIC KEY...END PUBLIC KEY-----\r\n"
}],
"service": [{
<span class="comment">// used to retrieve Verifiable Credentials associated with the DID</span>
"id":"did:example:123456789abcdefghi#vcs",
"type": "VerifiableCredentialService",
"serviceEndpoint": "https://example.com/vc/"
}]
}
</pre>
</section>
<section class="informative">
<h2>
Design Goals
</h2>
<p>
Decentralized Identifiers are a component of larger systems, such as
the Verifiable Credentials ecosystem [[?VC-DATA-MODEL]], which have driven
the design goals for this specification. This section summarizes the
primary design goals for this specification.
</p>
<table class="simple">
<thead>
<tr>
<th>
Goal
</th>
<th>
Description
</th>
</tr>
</thead>
<tbody>
<tr>
<td>
Decentralization
</td>
<td>
Eliminate the requirement for
centralized authorities or single points of failure in
identifier management, including the registration of globally
unique identifiers, public verification keys, service
endpoints, and other metadata.
</td>
</tr>
<tr>
<td>
Control
</td>
<td>
Give entities, both human and
non-human, the power to directly control their digital
identifiers without the need to rely on external authorities.
</td>
</tr>
<tr>
<td>
Privacy
</td>
<td>
Enable entities to control the privacy
of their information, including minimal, selective, and
progressive disclosure of attributes or other data.
</td>
</tr>
<tr>
<td>
Security
</td>
<td>
Enable sufficient security for relying
parties to depend on DID Documents for their required level of
assurance.
</td>
</tr>
<tr>
<td>
Proof-based
</td>
<td>
Enable the <a>DID subject</a> to provide
cryptographic proof when interacting with other entities.
</td>
</tr>
<tr>
<td>
Discoverability
</td>
<td>
Make it possible for entities to
discover DIDs for other entities to learn more about or
interact with those entities.
</td>
</tr>
<tr>
<td>
Interoperability
</td>
<td>
Use interoperable standards so DID
infrastructure can make use of existing tools and software
libraries designed for interoperability.
</td>
</tr>
<tr>
<td>
Portability
</td>
<td>
Be system and network-independent and
enable entities to use their digital identifiers with any
system that supports DIDs and DID Methods.
</td>
</tr>
<tr>
<td>
Simplicity
</td>
<td>
Favor a reduced set of simple features in order to make the technology
easier to understand, implement, and deploy.
</td>
</tr>
<tr>
<td>
Extensibility
</td>
<td>
When possible, enable extensibility
provided it does not greatly hinder interoperability,
portability, or simplicity.
</td>
</tr>
</tbody>
</table>
</section>
<section>
<h3>Interoperability</h3>
<p>Interoperability of implementations for DIDs and DID Documents will be tested by evaluating an implementation's ability to create and parse DIDs and DID Documents that conform to the specification. Interoperability for DID methods will be determined by evaluating each DID method's specification to determine, at a minimum, </p>
<ol>
<li> the DID method name is unique and not used by an existing, incompatible DID method, </li>
<li> the required operations are supported,</li>
<li> operations requiring descriptions are described,</li>
<li> the specification is specific, detailed, and complete enough for independent implementation, and</li>
<li> the specification contains sections describing security and privacy considerations.</li>
</ol>
<p>Interoperability for producers and consumers of DIDs and DID Documents is provided by ensuring the DIDs and DID Documents conform. Interoperability for method specifications is provided by the details in each method specification. It is understood that, just like 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 must be interoperable for that method.</p>
</section>
</section>
</section>
<section class="informative">
<h1>
Terminology
</h1>
<div data-include="terms.html" data-oninclude="restrictReferences">
</div>
</section>
<section class="informative">
<h1>
Data Model
</h1>
<p>
This section outlines the Decentralized Identifier data model concepts,
in particular how keys, services, and the <a>DID Subject</a> are related to the
<a>DID Document</a>.
</p>
<p>
For information about how the data model can be extended, see
<a href="#extensibility"></a>.
</p>
<section>
<h2>
Document
</h2>
<p>
A DID resolves to a <a>DID Document</a>. This is the concrete serialization of
the data model, according to a particular syntax (see
<a href="#did-document-syntax"></a>). The <a>DID Document</a> contains attributes
or claims about the <a href="#did-subject"></a>, and the DID itself is
contained in the <code>id</code> property.
</p>
<p>
The properties that can be present in a <a>DID Document</a> are detailed
further in <a href="#did-documents"></a>.
</p>
<p>
The properties present in a <a>DID Document</a> can be updated according to
the applicable <a href="#did-methods"></a>.
</p>
</section>
<section>
<h2>
Keys
</h2>
<p>
One or more <a href="#public-keys"></a> can be included in a <a>DID
Document</a> using, for example, the <code>publicKey</code> or <code>authentication</code>
properties depending on what they are to be used for. Each public key
has an identifier (<code>id</code>) of its own, a <code>type</code>,
and a <code>controller</code>, as well as other properties which
depend on what type of key it is.
</p>
</section>
<section>
<h2>
Services
</h2>
<p>
A <a>DID Document</a> can contain pointers to services using the <code>
service</code> property. Services can be anything the <a>DID Subject</a>
wishes to advertise, for example other ways to interact with
the <a>DID Subject</a>. Each service has its own <code>id</code> and
<code>type</code>, as well as a <code>serviceEndpoint</code> with a
URI or further properties describing the service.
</p>
<p>
For more information see <a href="#service-endpoints"></a>.
</p>
</section>
</section>
<section>
<h1>
Decentralized Identifiers (DIDs)
</h1>
<p>
The concept of a globally unique <a>decentralized identifier</a> is not
new; <a href="https://en.wikipedia.org/wiki/Universally_unique_identifier">Universally
Unique Identifiers</a> (UUIDs) were first developed in the 1980s and
later became a standard feature of the Open Software Foundation’s
<a href="https://en.wikipedia.org/wiki/Distributed_Computing_Environment">Distributed
Computing Environment</a>. UUIDs achieve global uniqueness without a
centralized registry service by using an algorithm that generates
128-bit values with sufficient entropy that the chance of collision are
infinitesimally small. UUIDs are formally specified in [[RFC4122]] as a
specific type of Unified Resource Name (URN).
</p>
<p>
A DID is similar to a UUID except: (a) like a URL, it can be resolved
or dereferenced to a standard resource describing the subject (a <a>DID
Document</a> — see Section <a href="#did-documents"></a>), and (b) unlike
a URL, the DID Document typically contains cryptographic material that
enables authentication of the <a>DID subject</a>.
</p>
<section>
<h2>
Generic DID Syntax
</h2>
<p>
The generic <a>DID scheme</a> is a URI scheme conformant with
[[RFC3986]]. The DID scheme specializes only the scheme and
authority components of a DID URI — the <code>path-abempty</code>,
<code>query</code>, and <code>fragment</code> components are
identical to the ABNF rules defined
in [[RFC3986]].
</p>
<p class="note">
The term <a>DID</a> refers only to the URI
conforming to the <code>did</code> rule in the ABNF below. A
DID always identifies the <a>DID subject</a>. The term <a>DID URL</a>,
defined by the <code>did-url</code> rule,
refers to a URL that begins with a DID followed by one or more
additional components. A DID URL always identifies the resource to
be located.
</p>
<p>
The following is the ABNF definition using the syntax in [[RFC5234]]
which defines <code>ALPHA</code> and <code>DIGIT</code>. All other
rule names not defined in this ABNF are defined in [[RFC3986]].
</p>
<pre class="nohighlight">
did = "did:" method-name ":" method-specific-id
method-name = 1*method-char
method-char = %x61-7A / DIGIT
method-specific-id = *idchar *( ":" *idchar )
idchar = ALPHA / DIGIT / "." / "-" / "_"
did-url = did *( ";" param ) path-abempty [ "?" query ]
[ "#" fragment ]
param = param-name [ "=" param-value ]
param-name = 1*param-char
param-value = *param-char
param-char = ALPHA / DIGIT / "." / "-" / "_" / ":" /
pct-encoded
</pre>
<p class="issue" data-number="198">
The grammar currently allows an empty <code>method-specific-id</code>,
e.g., <code>did:example:</code> would be a valid DID that could identify
the DID method itself.
</p>
</section>
<section>
<h2>
Method-Specific Syntax
</h2>
<p>
A DID method specification MUST further restrict the generic DID
syntax by defining its own <code>method-name</code> and its own
<code>method-specific-id</code> syntax. See Section <a href="#did-methods"></a>.
</p>
</section>
<section>
<h2>
Generic DID Parameter Names
</h2>
<p>
DID URL syntax supports a simple, generalized format for parameters based on the
matrix parameter syntax ([[MATRIX-URIS]]).
The ABNF above does not specify any parameter names (the <code>param-name</code>
rule).
</p>
<p>
Some generic DID parameter names (e.g., for service selection) are completely
independent of any specific DID method and MUST always function the same way
for all DIDs.
Others (e.g., for versioning) MAY be supported by
certain DID methods, but MUST operate uniformly across those DID methods that
do support them.
</p>
<p>
Parameter names that are completely method-specific are covered in
<a href="#method-specific-did-parameter-names"></a>.
</p>
<p>
The following table defines a set of generic DID parameter names:
</p>
<table class="simple">
<thead>
<tr>
<th>Generic DID Parameter Name</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<code>hl</code>
</td>
<td>
A resource hash of the DID Document to add integrity
protection, as specified in [[HASHLINK]].
</td>
</tr>
<tr>
<td>
<code>service</code>
</td>
<td>
Identifies a service from the DID Document by service id.
</td>
</tr>
<tr>
<td>
<code>version-id</code>
</td>
<td>
Identifies a specific version of a DID Document to be resolved (the version ID
could be sequential, or a UUID, or method-specific). Note: This parameter may
not be supported by all DID methods.
</td>
</tr>
<tr>
<td>
<code>version-time</code>
</td>
<td>
Identifies a certain version timestamp of a DID Document to be resolved (i.e.,
the DID Document that was valid for a DID at a certain time). Note: This
parameter may not be supported by all DID methods.
</td>
</tr>
</tbody>
</table>
<p>
The exact processing rules for these parameters are specified in [[DID-RESOLUTION]].
</p>
<p class="note">
Note that there may be additional parameters or options that are not part
of the DID URL but instead passed to a DID resolver "out of band", i.e.,
using a resolution protocol or some other mechanism. Such options could
for example control caching or the desired format of a resolution result.
This is similar to HTTP, where caching or result format are expressed as
HTTP headers rather than as part of an HTTP URL. The important distinction
is that DID parameters that are part of the DID URL specify what resource
is being identified, whereas DID resolver options that are not part of the
DID URL control how that resource is dereferenced.
</p>
</section>
<section>
<h2>
Method-Specific DID Parameter Names
</h2>
<p>
A DID method specification MAY specify additional method-specific parameter
names. A method-specific parameter name MUST be prefixed by the method name
as defined by the <code>method-name</code> rule.
</p>
<p>
For example, if the method <code>did:foo:</code> defines the parameter bar,
the parameter name must be <code>foo:bar</code>. An example DID URL using
this method and this method-specific parameter would be:
</p>
<p>
<code>did:foo:21tDAKCERh95uGgKbJNHYp;foo:bar=high</code>
</p>
<p class="issue" data-number="199">
Consider using kebab-case style instead of colon separator,
e.g., <code>foo-bar</code> instead of <code>foo:bar</code>.
</p>
<p>
A method-specific parameter name defined by one DID method MAY
be used by other DID methods. For example:
</p>
<p>
<code>did:example:21tDAKCERh95uGgKbJNHYp;foo:bar=low</code>
</p>
<p>
Method-specific parameter names MAY be combined with generic parameter
names in any order.
</p>
<p>
<code>did:example:21tDAKCERh95uGgKbJNHYp;service=agent;foo:bar=high</code>
</p>
<p>
Both DID method namespaces and method-specific parameter
namespaces MAY include colons, so they may be partitioned hierarchically
as defined by a DID method specification. Here is an example DID URL that
illustrates both:
</p>
<p>
<code>did:foo:baz:21tDAKCERh95uGgKbJNHYp;foo:baz:hex=b612</code>
</p>
</section>
<p class="issue" data-number="200">
Review what exactly we want to say about method-specific parameters
defined by one method but used in a DID URL with a different method.
Also discuss hierarchical method namespaces in DID parameter names.
</p>
<section>
<h2>
Path
</h2>
<p>
A generic <a>DID path</a> is identical to a URI path and MUST
conform to the <code>path-abempty</code> ABNF rule in [[RFC3986]]. A
DID path SHOULD be used to address resources available via a DID
service endpoint. See Section <a href="#service-endpoints"></a>.
</p>
<p>
A specific DID scheme MAY specify ABNF rules for DID paths that are
more restrictive than the generic rules in this section.
</p>
<pre class="example nohighlight">
did:example:123456/path
</pre>
</section>
<section>
<h2>
Query
</h2>
<p>
A generic <a>DID query</a> is identical to a URI query and MUST
conform to the <code>query</code> ABNF rule in [[RFC3986]]. A
DID query SHOULD be used to address resources available via a DID
service endpoint. See Section <a href="#service-endpoints"></a>.
</p>
<p>
A specific DID scheme MAY specify ABNF rules for DID queries that are
more restrictive than the generic rules in this section.
</p>
<pre class="example nohighlight">
did:example:123456?query=true
</pre>
</section>
<section>
<h2>
Fragment
</h2>
<p>
A generic <a>DID fragment</a> is identical to a URI
fragment and MUST conform to the <code>fragment</code> ABNF rule in
[[RFC3986]]. Implementers are strongly discouraged from using a DID fragment
for anything other than a method-independent
reference into the DID Document to identify a component of a DID Document
(e.g. a unique key description or service endpoint). To resolve this reference,
the complete DID URL including the DID fragment MUST be used as input to the
DID URL dereferencing algorithm (see [[DID-RESOLUTION]]) for the target
component in the DID Document object.
</p>
<p>
A specific DID scheme MAY specify ABNF rules for DID fragments that
are more restrictive than the generic rules in this section.
</p>
<p>
It is desirable that we enable tree-based processing of DIDs that include
DID fragments (which resolve directly within the DID Document) to locate
metadata contained directly in the DID Document or the service resource
given by the target URL without needing to rely on graph-based processing.
</p>
<p>
Implementations SHOULD NOT prevent the use of JSON pointers ([[RFC6901]]).
</p>
<pre class="example nohighlight">
did:example:123456#oidc
</pre>
</section>
<section>
<h2>
Normalization
</h2>
<p>
For the broadest interoperability, DID normalization should be as
simple and universal as possible. Therefore:
</p>
<ol start="1">
<li>
The did: scheme name MUST be lowercase.
</li>
<li>
The method name MUST be lowercase.
</li>
<li>
Case sensitivity and normalization of the value of the
<code>method-specific-id</code> rule in Section <a href="#generic-did-syntax">
</a> MUST be defined by the governing DID method specification.
</li>
</ol>
</section>
<section>
<h2>
Persistence
</h2>
<p>
A DID is expected to be persistent and immutable, i.e., bound exclusively
and permanently to its one and only subject. Even after a DID has been
deactivated, it is intended that it never be repurposed.
</p>
<p>
Ideally a DID would be a completely
abstract decentralized identifier (like a UUID) that could be bound
to multiple underlying <a>DID Registries</a> over time,
thus maintaining its persistence independent of any particular system.
However registering the same identifier on multiple
<a>DID Registries</a> introduces extremely hard entityship and
<a href="https://en.wikipedia.org/wiki/List_of_DNS_record_types%23SOA">start-of-authority</a>
(SOA) problems. It also greatly increases implementation complexity
for developers.
</p>
<p>
To avoid these issues, it is RECOMMENDED that <a>DID method</a>
specifications only produce DIDs and <a>DID methods</a> bound to strong,
stable <a>DID Registries</a> capable of making the highest level of
commitment to persistence of the DID and DID method over time.
</p>
<p class="note">
Although not included in this version, future versions of this
specification may support a DID Document equivID property to
establish verifiable equivalence relations between DIDs
representing the same subject on multiple <a>DID
Registries</a>. Such equivalence relations can produce the practical
equivalent of a single persistent abstract DID. See Future Work
(Section <a href="#future-work"></a>).
</p>
</section>
</section>
<section>
<h1>
DID Documents
</h1>