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Versions: 00 01 02 03 04                                                
Network Working Group                                         C. Bormann
Internet-Draft                                    Universit├Ąt Bremen TZI
Intended status: Informational                          12 February 2021
Expires: 16 August 2021


                           Notable CBOR Tags
                   draft-bormann-cbor-notable-tags-03

Abstract

   The Concise Binary Object Representation (CBOR, RFC 7049) is a data
   format whose design goals include the possibility of extremely small
   code size, fairly small message size, and extensibility without the
   need for version negotiation.

   In CBOR, one point of extensibility is the definition of CBOR tags.
   RFC 7049 and its revision 7049bis define a basic set of tags as well
   as a registry that can be used to contribute additional tag
   definitions [IANA.cbor-tags].  Since RFC 7049 was published, some 80
   tag definitions have been added to that registry.

   The present document provides a roadmap to a large subset of these
   tag definitions.  Where applicable, it points to a IETF standards or
   standard development document that specifies the tag.  Where no such
   document exists, the intention is to collect specification
   information from the sources of the registrations.  After some more
   development, the present document is intended to be useful as a
   reference document for the IANA registrations of the CBOR tags the
   definitions of which have been collected.

Note to Readers

   This is an individual submission to the CBOR working group of the
   IETF, https://datatracker.ietf.org/wg/cbor/about/
   (https://datatracker.ietf.org/wg/cbor/about/).  Discussion currently
   takes places on the github repository https://github.com/cabo/
   notable-tags (https://github.com/cabo/notable-tags).  If the CBOR WG
   believes this is a useful document, discussion is likely to move to
   the CBOR WG mailing list and a github repository at the CBOR WG
   github organization, https://github.com/cbor-wg (https://github.com/
   cbor-wg).

   The current version is true work in progress; some of the sections
   haven't been filled in yet, and in particular, permission has not
   been obtained from tag definition authors to copy over their text.





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Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 16 August 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  RFC 7049 (CBOR) . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Tags Related to Those Defined in RFC 7049 . . . . . . . .   5
   3.  Security  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  RFC 8152 (COSE) . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  RFC 8392 (CWT)  . . . . . . . . . . . . . . . . . . . . .   6
   4.  CBOR-based Representation Formats . . . . . . . . . . . . . .   6
     4.1.  YANG-CBOR . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Protocols . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  DOTS  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  RAINS . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Datatypes . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Advanced arithmetic . . . . . . . . . . . . . . . . . . .   8
     6.2.  Variants of undefined . . . . . . . . . . . . . . . . . .   8



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     6.3.  Typed and Homogeneous Arrays  . . . . . . . . . . . . . .   9
   7.  Domain-Specific . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Extended Time Formats . . . . . . . . . . . . . . . . . .  11
   8.  Platform-oriented . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Perl  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.2.  JSON  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.3.  Weird text encodings  . . . . . . . . . . . . . . . . . .  13
   9.  Application-specific  . . . . . . . . . . . . . . . . . . . .  13
   10. Implementation aids . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Invalid Tag  . . . . . . . . . . . . . . . . . . . . . .  14
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  15
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     13.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   (TO DO, expand on text from abstract here; move references here and
   neuter them in the abstract as per Section 4.3 of [RFC7322].)

   The selection of the tags presented here is somewhat arbitrary;
   considerations such as how wide the scope and area of application of
   a tag definition is combine with an assessment how "ready to use" the
   tag definition is (i.e., is the tag specification in a state where it
   can be used).

   This document can only be a snapshot of a subset of the current
   registrations.  The most up to date set of registrations is always
   available in the registry at [IANA.cbor-tags].

1.1.  Terminology

   The definitions of [RFC8949] apply.  The term "byte" is used in its
   now customary sense as a synonym for "octet".  Where bit arithmetic
   is explained, this document uses the notation familiar from the
   programming language C (including C++14's 0bnnn binary literals),
   except that the operator "**" stands for exponentiation.

2.  RFC 7049 (CBOR)

   [RFC7049] defines a number of tags that are listed here for
   convenience only.





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     +============+=============+=======================+============+
     | Tag number | Tag content | Short Description     | Section of |
     |            |             |                       | RFC 7049   |
     +============+=============+=======================+============+
     | 0          | UTF-8       | Standard date/time    | 2.4.1      |
     |            | string      | string                |            |
     +------------+-------------+-----------------------+------------+
     | 1          | multiple    | Epoch-based date/time | 2.4.1      |
     +------------+-------------+-----------------------+------------+
     | 2          | byte string | Positive bignum       | 2.4.2      |
     +------------+-------------+-----------------------+------------+
     | 3          | byte string | Negative bignum       | 2.4.2      |
     +------------+-------------+-----------------------+------------+
     | 4          | array       | Decimal fraction      | 2.4.3      |
     +------------+-------------+-----------------------+------------+
     | 5          | array       | Bigfloat              | 2.4.3      |
     +------------+-------------+-----------------------+------------+
     | 21         | multiple    | Expected conversion   | 2.4.4.2    |
     |            |             | to base64url encoding |            |
     +------------+-------------+-----------------------+------------+
     | 22         | multiple    | Expected conversion   | 2.4.4.2    |
     |            |             | to base64 encoding    |            |
     +------------+-------------+-----------------------+------------+
     | 23         | multiple    | Expected conversion   | 2.4.4.2    |
     |            |             | to base16 encoding    |            |
     +------------+-------------+-----------------------+------------+
     | 24         | byte string | Encoded CBOR data     | 2.4.4.1    |
     |            |             | item                  |            |
     +------------+-------------+-----------------------+------------+
     | 32         | UTF-8       | URI                   | 2.4.4.3    |
     |            | string      |                       |            |
     +------------+-------------+-----------------------+------------+
     | 33         | UTF-8       | base64url             | 2.4.4.3    |
     |            | string      |                       |            |
     +------------+-------------+-----------------------+------------+
     | 34         | UTF-8       | base64                | 2.4.4.3    |
     |            | string      |                       |            |
     +------------+-------------+-----------------------+------------+
     | 35         | UTF-8       | Regular expression    | 2.4.4.3    |
     |            | string      |                       |            |
     +------------+-------------+-----------------------+------------+
     | 36         | UTF-8       | MIME message          | 2.4.4.3    |
     |            | string      |                       |            |
     +------------+-------------+-----------------------+------------+
     | 55799      | multiple    | Self-describe CBOR    | 2.4.5      |
     +------------+-------------+-----------------------+------------+

                  Table 1: Tag numbers defined in RFC 7049



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2.1.  Tags Related to Those Defined in RFC 7049

   Separately registered tags that are directly related to the tags
   predefined in RFC 7049 include:

   *  Tag 63, registered by this document, is a parallel to tag 24, with
      the single difference that its byte string tag content carries a
      CBOR Sequence [RFC8742] instead of a single CBOR data items.

   *  Tag 257, registered by Peter Occil with a specification in
      http://peteroupc.github.io/CBOR/binarymime.html
      (http://peteroupc.github.io/CBOR/binarymime.html), is a parallel
      to tag 36, except that the tag content is a byte string, which
      therefore can also carry binary MIME messages as per [RFC2045].

3.  Security

   A number of CBOR tags are defined in security specifications that
   make use of CBOR.

3.1.  RFC 8152 (COSE)

   [RFC8152] defines CBOR Object Signing and Encryption (COSE).  A
   revision is in process that splits this specification into the data
   structure definitions [I-D.ietf-cose-rfc8152bis-struct], which will
   define another tag for COSE standalone counter signature, and the
   algorithms employed [I-D.ietf-cose-rfc8152bis-algs].
























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          +============+===============+=======================+
          | Tag number | Tag content   | Short Description     |
          +============+===============+=======================+
          | 16         | COSE_Encrypt0 | COSE Single Recipient |
          |            |               | Encrypted Data Object |
          +------------+---------------+-----------------------+
          | 17         | COSE_Mac0     | COSE Mac w/o          |
          |            |               | Recipients Object     |
          +------------+---------------+-----------------------+
          | 18         | COSE_Sign1    | COSE Single Signer    |
          |            |               | Data Object           |
          +------------+---------------+-----------------------+
          | 96         | COSE_Encrypt  | COSE Encrypted Data   |
          |            |               | Object                |
          +------------+---------------+-----------------------+
          | 97         | COSE_Mac      | COSE MACed Data       |
          |            |               | Object                |
          +------------+---------------+-----------------------+
          | 98         | COSE_Sign     | COSE Signed Data      |
          |            |               | Object                |
          +------------+---------------+-----------------------+

              Table 2: Tag numbers defined in RFC 8152, COSE

3.2.  RFC 8392 (CWT)

   [RFC8392] defines the CBOR Web Token (CWT), making use of COSE to
   define a CBOR variant of the JOSE Web Token (JWT), [RFC7519], a
   standardized security token that has found use in the area of web
   applications, but is not technically limited to those.

       +============+======================+======================+
       | Tag number | Tag content          | Short Description    |
       +============+======================+======================+
       | 61         | CBOR Web Token (CWT) | CBOR Web Token (CWT) |
       +------------+----------------------+----------------------+

         Table 3: Tag number defined for RFC 8392 CBOR Web Token
                                  (CWT)

4.  CBOR-based Representation Formats

   Representation formats can be built on top of CBOR.








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4.1.  YANG-CBOR

   YANG [RFC7950] is a data modeling language originally designed in the
   context of the Network Configuration Protocol (NETCONF) [RFC6241],
   now widely used for modeling management and configuration
   information.  [RFC7950] defines an XML-based representation format,
   and [RFC7951] defines a JSON-based [RFC8259] representation format
   for YANG.

   YANG-CBOR [I-D.ietf-core-yang-cbor] is a representation format for
   YANG data in CBOR.

   +========+======================+=====================+============+
   | Tag    | Tag content          | Short Description   | Section of |
   | number |                      |                     | YANG-CBOR  |
   +========+======================+=====================+============+
   | 43     | byte string          | YANG bits datatype  | 6.7        |
   +--------+----------------------+---------------------+------------+
   | 44     | unsigned integer     | YANG enumeration    | 6.6        |
   |        |                      | datatype            |            |
   +--------+----------------------+---------------------+------------+
   | 45     | unsigned integer or  | YANG identityref    | 6.10       |
   |        | text string          | datatype            |            |
   +--------+----------------------+---------------------+------------+
   | 46     | unsigned integer or  | YANG instance-      | 6.13       |
   |        | text string or array | identifier datatype |            |
   +--------+----------------------+---------------------+------------+
   | 47     | unsigned integer     | YANG Schema Item    | 3.2        |
   |        |                      | iDentifier (sid)    |            |
   +--------+----------------------+---------------------+------------+

                Table 4: Tag number defined for YANG-CBOR

5.  Protocols

   Protocols may want to allocate CBOR tag numbers to identify specific
   protocol elements.

5.1.  DOTS

   DDoS Open Threat Signaling (DOTS) defines tag number 271 for the DOTS
   signal channel object in [RFC8782].









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5.2.  RAINS

   As an example for how experimental protocols can make use of CBOR tag
   definitions, the RAINS (Another Internet Naming Service) Protocol
   Specification defines tag number 15309736 for a RAINS Message
   [I-D.trammell-rains-protocol].

6.  Datatypes

6.1.  Advanced arithmetic

   A number of tags have been registered for arithmetic representations
   beyond those built into CBOR and defined by tags in [RFC7049].  These
   are all documented under "http://peteroupc.github.io/CBOR/"; the last
   pathname component is given in Table 5.

   (TO DO: Obtain permission to copy the definitions here.)

   +============+=============+=======================+===============+
   | Tag number | Tag content | Short Description     | Reference     |
   +============+=============+=======================+===============+
   | 30         | array       | Rational number       | rational.html |
   +------------+-------------+-----------------------+---------------+
   | 264        | array       | Decimal fraction with | bigfrac.html  |
   |            |             | arbitrary exponent    |               |
   +------------+-------------+-----------------------+---------------+
   | 265        | array       | Bigfloat with         | bigfrac.html  |
   |            |             | arbitrary exponent    |               |
   +------------+-------------+-----------------------+---------------+
   | 268        | array       | Extended decimal      | extended.html |
   |            |             | fraction              |               |
   +------------+-------------+-----------------------+---------------+
   | 269        | array       | Extended bigfloat     | extended.html |
   +------------+-------------+-----------------------+---------------+
   | 270        | array       | Extended rational     | extended.html |
   |            |             | number                |               |
   +------------+-------------+-----------------------+---------------+

                  Table 5: Tags for advanced arithmetic

6.2.  Variants of undefined

   "https://github.com/svaarala/cbor-specs/blob/master/cbor-absent-
   tag.rst" defines tag 31 to be applied to the CBOR value Undefined
   (0xf7), slightly modifying its semantics to stand for an absent value
   in a CBOR Array.

   (TO DO: Obtain permission to copy the definitions here.)



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6.3.  Typed and Homogeneous Arrays

   [RFC8746] defines tags for various kinds of arrays.  A summary is
   reproduced in Table 6.

   +======+=============+=============================================+
   | Tag  | Data Item   | Semantics                                   |
   +======+=============+=============================================+
   | 64   | byte string | uint8 Typed Array                           |
   +------+-------------+---------------------------------------------+
   | 65   | byte string | uint16, big endian, Typed Array             |
   +------+-------------+---------------------------------------------+
   | 66   | byte string | uint32, big endian, Typed Array             |
   +------+-------------+---------------------------------------------+
   | 67   | byte string | uint64, big endian, Typed Array             |
   +------+-------------+---------------------------------------------+
   | 68   | byte string | uint8 Typed Array, clamped arithmetic       |
   +------+-------------+---------------------------------------------+
   | 69   | byte string | uint16, little endian, Typed Array          |
   +------+-------------+---------------------------------------------+
   | 70   | byte string | uint32, little endian, Typed Array          |
   +------+-------------+---------------------------------------------+
   | 71   | byte string | uint64, little endian, Typed Array          |
   +------+-------------+---------------------------------------------+
   | 72   | byte string | sint8 Typed Array                           |
   +------+-------------+---------------------------------------------+
   | 73   | byte string | sint16, big endian, Typed Array             |
   +------+-------------+---------------------------------------------+
   | 74   | byte string | sint32, big endian, Typed Array             |
   +------+-------------+---------------------------------------------+
   | 75   | byte string | sint64, big endian, Typed Array             |
   +------+-------------+---------------------------------------------+
   | 76   | byte string | (reserved)                                  |
   +------+-------------+---------------------------------------------+
   | 77   | byte string | sint16, little endian, Typed Array          |
   +------+-------------+---------------------------------------------+
   | 78   | byte string | sint32, little endian, Typed Array          |
   +------+-------------+---------------------------------------------+
   | 79   | byte string | sint64, little endian, Typed Array          |
   +------+-------------+---------------------------------------------+
   | 80   | byte string | IEEE 754 binary16, big endian, Typed Array  |
   +------+-------------+---------------------------------------------+
   | 81   | byte string | IEEE 754 binary32, big endian, Typed Array  |
   +------+-------------+---------------------------------------------+
   | 82   | byte string | IEEE 754 binary64, big endian, Typed Array  |
   +------+-------------+---------------------------------------------+
   | 83   | byte string | IEEE 754 binary128, big endian, Typed Array |
   +------+-------------+---------------------------------------------+



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   | 84   | byte string | IEEE 754 binary16, little endian, Typed     |
   |      |             | Array                                       |
   +------+-------------+---------------------------------------------+
   | 85   | byte string | IEEE 754 binary32, little endian, Typed     |
   |      |             | Array                                       |
   +------+-------------+---------------------------------------------+
   | 86   | byte string | IEEE 754 binary64, little endian, Typed     |
   |      |             | Array                                       |
   +------+-------------+---------------------------------------------+
   | 87   | byte string | IEEE 754 binary128, little endian, Typed    |
   |      |             | Array                                       |
   +------+-------------+---------------------------------------------+
   | 40   | array of    | Multi-dimensional Array, row-major order    |
   |      | two arrays* |                                             |
   +------+-------------+---------------------------------------------+
   | 1040 | array of    | Multi-dimensional Array, column-major order |
   |      | two arrays* |                                             |
   +------+-------------+---------------------------------------------+
   | 41   | array       | Homogeneous Array                           |
   +------+-------------+---------------------------------------------+

                 Table 6: Tag numbers defined for Arrays

7.  Domain-Specific

   (TO DO: Obtain permission to copy the definitions here; create proper
   table.)

37                            byte string   Binary UUID ([RFC4122] section    [https://github.com/lucas-clemente/cbor-specs/blob/master/uuid.md][Lucas_Clemente]
                                            4.1.2)
38                            array         Language-tagged string            [http://peteroupc.github.io/CBOR/langtags.html][Peter_Occil]
257                           byte string   Binary MIME message               [http://peteroupc.github.io/CBOR/binarymime.html][Peter_Occil]


260                           byte string   Network Address (IPv4 or IPv6 or  [http://www.employees.org/~ravir/cbor-network.txt][Ravi_Raju]
                                            MAC Address)
                              map           Network Address Prefix (IPv4 or
261                           (IPAddress +  IPv6 Address + Mask Length)       [https://github.com/toravir/CBOR-Tag-Specs/blob/master/networkPrefix.md][Ravi_Raju]
                              Mask Length)

263                           byte string   Hexadecimal string                [https://github.com/toravir/CBOR-Tag-Specs/blob/master/hexString.md][Ravi_Raju]

266                           text string   Internationalized resource        [https://peteroupc.github.io/CBOR/iri.html][Peter_Occil]
                                            identifier (IRI)
                                            Internationalized resource
267                           text string   identifier reference (IRI         [https://peteroupc.github.io/CBOR/iri.html][Peter_Occil]
                                            reference)




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7.1.  Extended Time Formats

   Additional tag definitions have been provided for date and time
   values.

   +======+=========+===================+=============================+
   |  Tag | Data    | Semantics         | Reference                   |
   |      | Item    |                   |                             |
   +======+=========+===================+=============================+
   |  100 | integer | date in number of | [RFC8943]                   |
   |      |         | days since epoch  |                             |
   +------+---------+-------------------+-----------------------------+
   | 1004 | text    | RFC 3339 full-    | [RFC8943]                   |
   |      | string  | date string       |                             |
   +------+---------+-------------------+-----------------------------+
   | 1001 | map     | extended time     | [I-D.bormann-cbor-time-tag] |
   +------+---------+-------------------+-----------------------------+
   | 1002 | map     | duration          | [I-D.bormann-cbor-time-tag] |
   +------+---------+-------------------+-----------------------------+
   | 1003 | map     | period            | [I-D.bormann-cbor-time-tag] |
   +------+---------+-------------------+-----------------------------+

                  Table 7: Tag numbers for date and time

   Note that tags 100 and 1004 are for calendar dates that are not
   anchored to a specific time zone; they are meant to specify calendar
   dates as perceived by humans, e.g. for use in personal identification
   documents.  Converting such a calendar date into a specific point in
   time needs the addition of a time-of-day (for which a CBOR tag is
   outstanding) and timezone information (also outstanding).
   Alternatively, a calendar date plus timezone information can be
   converted into a time period (range of time values given by the
   starting and the ending time); note that these time periods are not
   always exactly 24 h (86400 s) long.

   [RFC8943] does not suggest CDDL [RFC8610] type names for the two
   tags.  We suggest copying the definitions in Figure 1 into
   application-specific CDDL as needed.

caldate = #6.100(int) ; calendar date as a number of days from 1970-01-01
tcaldate = #6.1004(tstr) ; calendar date as an RFC 3339 full-date string

           Figure 1: CDDL for calendar date tags (RFC8943)

   Tag 1001 extends tag 1 by additional information (such as picosecond
   resolution) and allows the use of Decimal and Bigfloat numbers for
   the time.




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8.  Platform-oriented

8.1.  Perl

   (These are actually not as Perl-specific as the title of this section
   suggests.  See also the penultimate paragraph of Section 3.4 of
   [RFC8949].)

   These are all documented under "http://cbor.schmorp.de/"; the last
   pathname component is given in Table 8.

   (TO DO: Obtain permission to copy the definitions here.)

      +=======+==========+========================+================+
      |   Tag | Data     | Semantics              | Reference      |
      |       | Item     |                        |                |
      +=======+==========+========================+================+
      |   256 | multiple | mark value as having   | stringref      |
      |       |          | string references      |                |
      +-------+----------+------------------------+----------------+
      |    25 | unsigned | reference the nth      | stringref      |
      |       | integer  | previously seen string |                |
      +-------+----------+------------------------+----------------+
      |    26 | array    | Serialised Perl object | perl-object    |
      |       |          | with classname and     |                |
      |       |          | constructor arguments  |                |
      +-------+----------+------------------------+----------------+
      |    27 | array    | Serialised language-   | generic-object |
      |       |          | independent object     |                |
      |       |          | with type name and     |                |
      |       |          | constructor arguments  |                |
      +-------+----------+------------------------+----------------+
      |    28 | multiple | mark value as          | value-sharing  |
      |       |          | (potentially) shared   |                |
      +-------+----------+------------------------+----------------+
      |    29 | unsigned | reference nth marked   | value-sharing  |
      |       | integer  | value                  |                |
      +-------+----------+------------------------+----------------+
      | 22098 | multiple | hint that indicates an | indirection    |
      |       |          | additional level of    |                |
      |       |          | indirection            |                |
      +-------+----------+------------------------+----------------+

             Table 8: Tag numbers that aid the Perl platform







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8.2.  JSON

   (TO DO: Obtain permission to copy the definitions here.)

   Tag number 262 has been registered to identify byte strings that
   carry embedded JSON text ("https://github.com/toravir/CBOR-Tag-
   Specs/blob/master/embeddedJSON.md").

   Tag number 275 can be used to identify maps that contain keys that
   are all of type Text String, as they would occur in JSON
   ("https://github.com/ecorm/cbor-tag-text-key-map").

8.3.  Weird text encodings

   (TO DO: Obtain permission to copy the definitions here.)

   Some variants of UTF-8 are in use in specific areas of application.
   Tags have been registered to be able to carry around strings in these
   variants in case they are not also valid UTF-8 and can therefore not
   be represented as a CBOR text string ("https://github.com/svaarala/
   cbor-specs/blob/master/cbor-nonutf8-string-tags.rst").

          +============+=============+=========================+
          | Tag Number | Data Item   | Semantics               |
          +============+=============+=========================+
          |        272 | byte string | Non-UTF-8 CESU-8 string |
          +------------+-------------+-------------------------+
          |        273 | byte string | Non-UTF-8 WTF-8 string  |
          +------------+-------------+-------------------------+
          |        274 | byte string | Non-UTF-8 MUTF-8 string |
          +------------+-------------+-------------------------+

                 Table 9: Tag numbers for UTF-8 variants

9.  Application-specific

   (TO DO: Obtain permission to copy the definitions here; create proper
   table.)













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39                            multiple      Identifier                        [https://github.com/lucas-clemente/cbor-specs/blob/master/id.md][Lucas_Clemente]
42                            byte string   IPLD content identifier           [https://github.com/ipld/cid-cbor/][Volker_Mische]

103                           array         Geographic Coordinates            [https://github.com/allthingstalk/cbor/blob/master/CBOR-Tag103-Geographic-Coordinates.md][Danilo_Vidovic]
104                           multiple      Geographic Coordinate Reference   [draft-clarke-cbor-crs]
                                            System WKT or EPSG number

120                           multiple      Internet of Things Data Point     [https://github.com/allthingstalk/cbor/blob/master/CBOR-Tag120-Internet-of-Things-Data-Points.md][Danilo_Vidovic]



258                           array         Mathematical finite set           [https://github.com/input-output-hk/cbor-sets-spec/blob/master/CBOR_SETS.md][Alfredo_Di_Napoli]
                                            Map datatype with key-value
259                           map           operations (e.g.                  [https://github.com/shanewholloway/js-cbor-codec/blob/master/docs/CBOR-259-spec--explicit-maps.md][Shane_Holloway]
                                            `.get()/.set()/.delete()`)

10.  Implementation aids

10.1.  Invalid Tag

   The present document registers tag numbers 65535, 4294967295, and
   18446744073709551615 (16-bit 0xffff, 32-bit 0xffffffff, and 64-bit
   0xffffffffffffffff) as Invalid Tags, tags that are always invalid,
   independent of the tag content provided.  The purpose of these tag
   number registrations is to enable the tag numbers to be reserved for
   internal use by implementations to note the absence of a tag on a
   data item where a tag could also be expected with that data item as
   tag content.

   The Invalid Tags are not intended to ever occur in interchanged CBOR
   data items.  Generic CBOR decoder implementations are encouraged to
   raise an error if an Invalid Tag occurs in a CBOR data item even if
   there is no validity checking implemented otherwise.

11.  IANA Considerations

   In the registry [IANA.cbor-tags], IANA has allocated the first to
   third tag in Table 10 from the FCFS space, with the present document
   as the specification reference.  IANA has allocated the fourth tag
   from the Specification Required space, with the present document as
   the specification reference.










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   +======================+========+==============+====================+
   |                  Tag | Data   | Semantics    | Reference          |
   |                      | Item   |              |                    |
   +======================+========+==============+====================+
   |                65535 | (none  | always       | draft-bormann-     |
   |                      | valid) | invalid      | cbor-notable-tags, |
   |                      |        |              | Section 10.1       |
   +----------------------+--------+--------------+--------------------+
   |           4294967295 | (none  | always       | draft-bormann-     |
   |                      | valid) | invalid      | cbor-notable-tags, |
   |                      |        |              | Section 10.1       |
   +----------------------+--------+--------------+--------------------+
   | 18446744073709551615 | (none  | always       | draft-bormann-     |
   |                      | valid) | invalid      | cbor-notable-tags, |
   |                      |        |              | Section 10.1       |
   +----------------------+--------+--------------+--------------------+
   |                   63 | byte   | Encoded      | draft-bormann-     |
   |                      | string | CBOR         | cbor-notable-tags, |
   |                      |        | Sequence     | Section 2.1        |
   |                      |        | [RFC8742]    |                    |
   +----------------------+--------+--------------+--------------------+

                         Table 10: Values for Tags

12.  Security Considerations

   The security considerations of [RFC8949] apply; the tags discussed
   here may also have specific security considerations that are
   mentioned in their specific sections above.

13.  References

13.1.  Normative References

   [I-D.ietf-core-yang-cbor]
              Veillette, M., Petrov, I., and A. Pelov, "CBOR Encoding of
              Data Modeled with YANG", Work in Progress, Internet-Draft,
              draft-ietf-core-yang-cbor-15, 25 January 2021,
              <http://www.ietf.org/internet-drafts/draft-ietf-core-yang-
              cbor-15.txt>.

   [IANA.cbor-tags]
              IANA, "Concise Binary Object Representation (CBOR) Tags",
              <http://www.iana.org/assignments/cbor-tags>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.



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   [RFC8392]  Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <https://www.rfc-editor.org/info/rfc8392>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

   [RFC8746]  Bormann, C., Ed., "Concise Binary Object Representation
              (CBOR) Tags for Typed Arrays", RFC 8746,
              DOI 10.17487/RFC8746, February 2020,
              <https://www.rfc-editor.org/info/rfc8746>.

   [RFC8782]  Reddy.K, T., Ed., Boucadair, M., Ed., Patil, P.,
              Mortensen, A., and N. Teague, "Distributed Denial-of-
              Service Open Threat Signaling (DOTS) Signal Channel
              Specification", RFC 8782, DOI 10.17487/RFC8782, May 2020,
              <https://www.rfc-editor.org/info/rfc8782>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/info/rfc8949>.

13.2.  Informative References

   [I-D.bormann-cbor-time-tag]
              Bormann, C., Gamari, B., and H. Birkholz, "Concise Binary
              Object Representation (CBOR) Tags for Time, Duration, and
              Period", Work in Progress, Internet-Draft, draft-bormann-
              cbor-time-tag-03, 9 March 2020, <http://www.ietf.org/
              internet-drafts/draft-bormann-cbor-time-tag-03.txt>.

   [I-D.ietf-cose-rfc8152bis-algs]
              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Initial Algorithms", Work in Progress, Internet-Draft,
              draft-ietf-cose-rfc8152bis-algs-12, 24 September 2020,
              <http://www.ietf.org/internet-drafts/draft-ietf-cose-
              rfc8152bis-algs-12.txt>.

   [I-D.ietf-cose-rfc8152bis-struct]
              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", Work in Progress, Internet-Draft,
              draft-ietf-cose-rfc8152bis-struct-14, 24 September 2020,
              <http://www.ietf.org/internet-drafts/draft-ietf-cose-
              rfc8152bis-struct-14.txt>.



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   [I-D.trammell-rains-protocol]
              Trammell, B. and C. Fehlmann, "RAINS (Another Internet
              Naming Service) Protocol Specification", Work in Progress,
              Internet-Draft, draft-trammell-rains-protocol-05, 29
              January 2019, <http://www.ietf.org/internet-drafts/draft-
              trammell-rains-protocol-05.txt>.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
              <https://www.rfc-editor.org/info/rfc2045>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/info/rfc4122>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7322]  Flanagan, H. and S. Ginoza, "RFC Style Guide", RFC 7322,
              DOI 10.17487/RFC7322, September 2014,
              <https://www.rfc-editor.org/info/rfc7322>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.





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   [RFC8742]  Bormann, C., "Concise Binary Object Representation (CBOR)
              Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
              <https://www.rfc-editor.org/info/rfc8742>.

   [RFC8943]  Jones, M., Nadalin, A., and J. Richter, "Concise Binary
              Object Representation (CBOR) Tags for Date", RFC 8943,
              DOI 10.17487/RFC8943, November 2020,
              <https://www.rfc-editor.org/info/rfc8943>.

Acknowledgements

Contributors

   Peter Occil

   Email: poccil14 at gmail dot com


   Many More
   To do


Author's Address

   Carsten Bormann
   Universit├Ąt Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.org



















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