Introduction

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

CBOR 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 representations">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 conforming producer">representation, a conforming producer MUST specify a media type of application/did+cbor to downstream applications such as described in .

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

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

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 # "Ed25519VerificationKey2020"
      6A                             # text(10)
         636F6E74726F6C6C6572        # "controller"
      78 1E                          # text(30)
         6469643A6578616D706C653A313233343536373839616263646566676869 # "did:example:123456789abcdefghi"
      6F                             # text(15)
         7075626C69634B6579426173653538 # "publicKeyMultibase"
      78 2C                          # text(44)
         483343324156764C4D7636676D4D4E616D337556416A5A70666B634A437744776E5A6E367A3377586D715056 # "zH3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"

CBOR 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 representations">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 conforming consumer">DID document. A conforming consumer for a CBOR DID document">representation that is consuming a DID document with a root element that is not a CBOR map (major type 5) MUST report an error.

IANA Considerations

This section will be submitted to the Internet Engineering Steering Group (IESG) for review, approval, and registration with IANA when this specification becomes a W3C Proposed Recommendation.

application/did+cbor

Type name:

application

Subtype name:

did+cbor

Required parameters:

None

Optional parameters:

None

Encoding considerations:

See RFC 8949, section 4.2.1.

Security considerations:

See RFC 8949, section 10 [[RFC8949]].

Interoperability considerations:

Not Applicable

Published specification:

http://www.w3.org/TR/did-core/

Applications that use this media type:

Any application that requires an identifier that is decentralized, persistent, cryptographically verifiable, and resolvable. Applications typically consist of cryptographic identity systems, decentralized networks of devices, and websites that issue or verify W3C Verifiable Credentials.

Additional information:

Magic number(s):: Not Applicable
File extension(s):: .didcbor
Macintosh file type code(s):: TEXT

Person & email address to contact for further information:

Ivan Herman <ivan@w3.org>

Intended usage:

Common

Restrictions on usage:

None

Author(s):

Drummond Reed, Manu Sporny, Markus Sabadello, Dave Longley, Christopher Allen

Change controller:

W3C

Fragment identifiers used with application/did+cbor are treated according to the rules defined in .

Terminology

Introduction

CBOR Production

CBOR Consumption

IANA Considerations

application/did+cbor