Notable CBOR Tags
draft-bormann-cbor-notable-tags-04
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Carsten Bormann
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2021-08-15
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Network Working Group C. Bormann
Internet-Draft Universität Bremen TZI
Intended status: Informational 15 August 2021
Expires: 16 February 2022
Notable CBOR Tags
draft-bormann-cbor-notable-tags-04
Abstract
The Concise Binary Object Representation (CBOR, RFC 8949) 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 8949's original edition, RFC 7049, defined 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 February 2022.
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 . . . . . . . . . . . . . . . . . . . . . . . 4
2. RFC 7049 (original CBOR specification) . . . . . . . . . . . 4
2.1. Tags Related to Those Defined in RFC 7049 . . . . . . . . 5
2.2. Tags from RFC 7049 not listed in RFC 8949 . . . . . . . . 5
3. Security . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. RFC 8152 (COSE) . . . . . . . . . . . . . . . . . . . . . 6
3.2. RFC 8392 (CWT) . . . . . . . . . . . . . . . . . . . . . 7
4. CBOR-based Representation Formats . . . . . . . . . . . . . . 7
4.1. YANG-CBOR . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. DOTS . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. RAINS . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Datatypes . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Advanced arithmetic . . . . . . . . . . . . . . . . . . . 9
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6.2. Variants of undefined . . . . . . . . . . . . . . . . . . 11
6.3. Typed and Homogeneous Arrays . . . . . . . . . . . . . . 11
7. Domain-Specific . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Extended Time Formats . . . . . . . . . . . . . . . . . . 14
8. Platform-oriented . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Perl . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.2. JSON . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.3. Weird text encodings . . . . . . . . . . . . . . . . . . 17
9. Application-specific . . . . . . . . . . . . . . . . . . . . 17
10. Implementation aids . . . . . . . . . . . . . . . . . . . . . 18
10.1. Invalid Tag . . . . . . . . . . . . . . . . . . . . . . 18
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
12. Security Considerations . . . . . . . . . . . . . . . . . . . 19
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
13.1. Normative References . . . . . . . . . . . . . . . . . . 19
13.2. Informative References . . . . . . . . . . . . . . . . . 20
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 23
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 23
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 "CBOR Tags" [IANA.cbor-tags].
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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 ([C], including C++14's "0bnnn" binary
literals [Cplusplus20]), except that superscript notation (example
for two to the power of 64: 2^64) denotes exponentiation; in the
plain text version of this document, superscript notation is rendered
in paragraph text by C-incompatible surrogate notation as seen in
this example. Ranges expressed using ".." are inclusive of the
limits given. Type names such as "int", "bigint" or "decfrac" are
taken from Appendix D of [RFC8610], the Concise Data Definition
Language (CDDL).
2. RFC 7049 (original CBOR specification)
[RFC7049] defines a number of tags that are listed here for
convenience only.
+============+=============+=======================+============+
| 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 | |
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+------------+-------------+-----------------------+------------+
| 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
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 item.
* 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].
2.2. Tags from RFC 7049 not listed in RFC 8949
Section G.3 of [RFC8949] states:
| Tag 35 is not defined by this document; the registration based on
| the definition in RFC 7049 remains in place.
The reason for this exclusion is that the definition of Tag 35 in
Section 2.4.4.3 of [RFC7049], leaves too much open to ensure
interoperability:
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| Tag 35 is for regular expressions in Perl Compatible Regular
| Expressions (PCRE) / JavaScript syntax [ECMA262].
Not only are two partially incompatible specifications given for the
semantics, JavaScript regular expressions have also developed
significantly within the decade since JavaScript 5.1 (which was
referenced by [RFC7049]), making it less reliable to assume that a
producing application will manage to stay within that 2011 subset.
Nonetheless, the registration is in place, so it is available for
applications that simply want to mark a text string as being a
regular expression roughly of the PCRE/Javascript flavor families.
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]. (The seemingly random tag number was
chosen so that, when represented as an encoded CBOR tag argument, it
contains the Unicode character "雨" (U+96E8) in UTF-8, which
represents rain in a number of languages.)
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.
+============+=============+=======================+===============+
| 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
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CBOR's basic generic data model (Section 2 of [RFC8949]) has a number
system with limited-range integers (major types 0 and 1:
-2^64..2^64-1) and floating point numbers that cover binary16,
binary32, and binary64 (including non-finites) from [IEEE754]. With
the tags defined with [RFC7049], the extended generic data model
(Section 2.1 of [RFC8949]) adds unlimited-range integers (tag numbers
2 and 3, "bigint" in CDDL) as well as floating point values using the
bases 2 (tag number 5, "bigfloat") and 10 (tag number 4, "decfrac").
This pre-defined number system has a number of limitations that are
addressed in three of the tags discussed here:
* Tag number 30 allows the representation of rational numbers as a
ratio of two integers: a numerator (usually written as the top
part of a fraction), and a denominator (the bottom part), where
both integers can be limited-range basic and unlimited-range
integers. The mathematical value of a rational number is the
numerator divided by the denominator. This tag can express all
numbers that the extended generic data model of [RFC7049] can
express, except for non-finites [IEEE754]; it also can express
rational numbers that cannot be expressed with denominators that
are a power of 2 or a power of 10.
For example, the rational number 1/3 is encoded:
d8 1e ---- Tag 30
82 ---- Array length 2
01 ---- 1
03 ---- 3
Many programming languages have built-in support for rational
numbers or support for them is included in their standard
libraries; tag number 30 is a way for these platforms to
interchange these rational numbers in CBOR.
* Tag numbers 4 and 5 are limited in the range of the (base 10 or
base 2) exponents by the limited-range integers in the basic
generic data model. Tag numbers 264 and 265 are exactly
equivalent to 4 and 5, respectively, but also allow unlimited-
range integers as exponents. While applications for floating
point numbers with exponents outside the CBOR basic integer range
are limited, tags 264 and 265 allow unlimited roundtripping with
other formats that allow very large or very small exponents, such
as those JSON [RFC8259] can provide if the limitations of I-JSON
[RFC7493] do not apply.
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The tag numbers 268..270 extend these tags further by providing a way
to express non-finites within a tag with this number. This does not
increase the expressiveness of the data model (the non-finites can
already be expressed using major type 7 floating point numbers), but
does allow both finite and non-finite values to carry the same tag.
In most applications, a choice that includes some of the three tags
30, 264, 265 for finite values and major type 7 floating point values
for non-finites (as well as possibly other parts of the CBOR number
system) will be the preferred solution.
This document suggests using the CDDL typenames defined in Figure 1
for the three most useful tag numbers in this section.
rational = #6.30([numerator: integer, denominator: integer .ne 0])
rational_of<N,D> = #6.30([numerator: N, denominator: D])
; the value 1/3 can be notated as rational_of<1, 3>
extended_decfrac = #6.264([e10: integer, m: integer])
extended_bigfloat = #6.265([e2: integer, m: integer])
Figure 1: CDDL for extended arithmetic tags
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.)
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 |
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+------+-------------+---------------------------------------------+
| 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 |
+------+-------------+---------------------------------------------+
| 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* | |
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+------+-------------+---------------------------------------------+
| 41 | array | Homogeneous Array |
+------+-------------+---------------------------------------------+
Table 6: Tag numbers defined for Arrays
7. Domain-Specific
(TO DO: Obtain permission to copy the definitions here; explain how
tags 52 and 54 essentially obsolete 260/261.)
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+======+=======+=================+=================================+========+
|Tag |Tag |Short Description|Reference |Author |
|number|content| | | |
+======+=======+=================+=================================+========+
|37 |byte |Binary UUID |https://github.com/lucas- |Lucas |
| |string |(Section 4.1.2 of|clemente/cbor-specs/blob/master/ |Clemente|
| | |[RFC4122]) |uuid.md | |
+------+-------+-----------------+---------------------------------+--------+
|38 |array |Language-tagged |http://peteroupc.github.io/CBOR/ |Peter |
| | |string |langtags.html |Occil |
+------+-------+-----------------+---------------------------------+--------+
|257 |byte |Binary MIME |http://peteroupc.github.io/CBOR/ |Peter |
| |string |message |binarymime.html |Occil |
+------+-------+-----------------+---------------------------------+--------+
|260 |byte |Network Address |http://www.employees.org/~ravir/ |Ravi |
| |string |(IPv4 or IPv6 or |cbor-network.txt |Raju |
| | |MAC Address) | | |
+------+-------+-----------------+---------------------------------+--------+
|261 |map |Network Address |https://github.com/toravir/CBOR- |Ravi |
| | |Prefix (IPv4 or |Tag-Specs/blob/master/ |Raju |
| | |IPv6 Address + |networkPrefix.md | |
| | |Mask Length) | | |
+------+-------+-----------------+---------------------------------+--------+
|263 |byte |Hexadecimal |https://github.com/toravir/CBOR- |Ravi |
| |string |string |Tag-Specs/blob/master/ |Raju |
| | | |hexString.md | |
+------+-------+-----------------+---------------------------------+--------+
|266 |text |Internationalized|https://peteroupc.github.io/CBOR/|Peter |
| |string |resource |iri.html |Occil |
| | |identifier (IRI) | | |
+------+-------+-----------------+---------------------------------+--------+
|267 |text |Internationalized|https://peteroupc.github.io/CBOR/|Peter |
| |string |resource |iri.html |Occil |
| | |identifier | | |
| | |reference (IRI | | |
| | |reference) | | |
+------+-------+-----------------+---------------------------------+--------+
Table 7
7.1. Extended Time Formats
Additional tag definitions have been provided for date and time
values.
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+======+===========+===================+==========================+
| Tag | Data Item | Semantics | Reference |
+======+===========+===================+==========================+
| 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.ietf-cbor-time-tag] |
+------+-----------+-------------------+--------------------------+
| 1002 | map | duration | [I-D.ietf-cbor-time-tag] |
+------+-----------+-------------------+--------------------------+
| 1003 | map | period | [I-D.ietf-cbor-time-tag] |
+------+-----------+-------------------+--------------------------+
Table 8: 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 2 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 2: 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.
8. Platform-oriented
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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 9.
(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 9: Tag numbers that aid the Perl platform
8.2. JSON
(TO DO: Obtain permission to copy the definitions here.)
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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 10: Tag numbers for UTF-8 variants
9. Application-specific
(TO DO: Obtain permission to copy the definitions here.)
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+======+========+=====================+===================================================+========+
|Tag |Tag |Short Description |Reference |Author |
|number|content | | | |
+======+========+=====================+===================================================+========+
|39 |multiple|Identifier |[https://github.com/lucas-clemente/cbor- |Lucas |
| | | |specs/blob/master/id.md |Clemente|
+------+--------+---------------------+---------------------------------------------------+--------+
|42 |byte |IPLD content |[https://github.com/ipld/cid-cbor/ |Volker |
| |string |identifier | |Mische |
+------+--------+---------------------+---------------------------------------------------+--------+
|103 |array |Geographic |[https://github.com/allthingstalk/cbor/blob/master/|Danilo |
| | |Coordinates |CBOR-Tag103-Geographic-Coordinates.md |Vidovic |
+------+--------+---------------------+---------------------------------------------------+--------+
|104 |multiple|Geographic Coordinate|[I-D.clarke-cbor-crs] | |
| | |Reference System WKT | | |
| | |or EPSG number | | |
+------+--------+---------------------+---------------------------------------------------+--------+
|120 |multiple|Internet of Things |[https://github.com/allthingstalk/cbor/blob/master/|Danilo |
| | |Data Point |CBOR-Tag120-Internet-of-Things-Data-Points.md |Vidovic |
+------+--------+---------------------+---------------------------------------------------+--------+
|258 |array |Mathematical finite |[https://github.com/input-output-hk/cbor-sets- |Alfredo |
| | |set |spec/blob/master/CBOR_SETS.md |Di |
| | | | |Napoli |
+------+--------+---------------------+---------------------------------------------------+--------+
|259 |map |Map datatype with |[https://github.com/shanewholloway/js-cbor- |Shane |
| | |key-value operations |codec/blob/master/docs/CBOR-259-spec--explicit- |Holloway|
| | |(e.g. ".get |maps.md | |
| | |()/.set()/.delete()")| | |
+------+--------+---------------------+---------------------------------------------------+--------+
Table 11
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.
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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 "CBOR Tags" [IANA.cbor-tags], IANA has allocated the
first to third tag in Table 12 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.
+======================+========+==============+====================+
| 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 12: 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
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[I-D.ietf-core-yang-cbor]
Veillette, M., Petrov, I., Pelov, A., and C. Bormann,
"CBOR Encoding of Data Modeled with YANG", Work in
Progress, Internet-Draft, draft-ietf-core-yang-cbor-16, 24
June 2021, <https://www.ietf.org/archive/id/draft-ietf-
core-yang-cbor-16.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>.
[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
[C] International Organization for Standardization,
"Information technology - Programming languages - C", ISO/
IEC 9899:2018, June 2018,
<https://www.iso.org/standard/74528.html>.
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[Cplusplus20]
International Organization for Standardization,
"Programming languages - C++", ISO/IEC ISO/IEC JTC1 SC22
WG21 N 4860, March 2020,
<https://isocpp.org/files/papers/N4860.pdf>.
[I-D.clarke-cbor-crs]
Clarke, T. R., "Concise Binary Object Representation
(CBOR) Tag for Coordinate Reference System (CRS)
Specification", Work in Progress, Internet-Draft, draft-
clarke-cbor-crs-02, 17 March 2020,
<https://www.ietf.org/archive/id/draft-clarke-cbor-crs-
02.txt>.
[I-D.ietf-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-ietf-
cbor-time-tag-00, 19 May 2021,
<https://www.ietf.org/archive/id/draft-ietf-cbor-time-tag-
00.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,
<https://www.ietf.org/archive/id/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-15, 1 February 2021,
<https://www.ietf.org/archive/id/draft-ietf-cose-
rfc8152bis-struct-15.txt>.
[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, <https://www.ietf.org/archive/id/draft-
trammell-rains-protocol-05.txt>.
[IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE
Std 754-2019, DOI 10.1109/IEEESTD.2019.8766229,
<https://ieeexplore.ieee.org/document/8766229>.
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[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>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
[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>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>.
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[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
(Many, TBD)
Contributors
Peter Occil
Email: poccil14 at gmail dot com
Peter Occil registered tags 30, 264, 265, 268-270 (Section 6.1), 38,
257, 266 and 267 (Section 7), and contributed much of the text about
these tags in this document.
Jane Doe
To do
Further contributors will be listed here as text is added.
Plase stay tuned.
Author's Address
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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