Network Working Group                                         C. Bormann
Internet-Draft                                    Universität Bremen TZI
Intended status: Standards Track                           30 March                             19 May 2021
Expires: 1 October 20 November 2021

Concise Binary Object Representation (CBOR) Tags for Object Identifiers
                      draft-ietf-cbor-tags-oid-06
                      draft-ietf-cbor-tags-oid-07

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.

   The present document defines CBOR tags for object identifiers (OIDs).
   It is intended as the reference document for the IANA registration of
   the CBOR tags so defined.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 1 October 20 November 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Object Identifiers   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Object Identifiers  . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements on the byte string being tagged  . . . . . .   5
     2.2.  Preferred Serialization Considerations  . . . . . . . . .   6
     2.3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Basic Examples  . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Encoding of the SHA-256 OID . . . . . . . . . . . . . . .   6
     3.2.  Encoding of a MIB Relative OID  . . . . . . . . . . . . .   7
   4.  Tag Factoring with Arrays and Maps  . . . . . . . . . . . . .   8
     4.1.  Preferred Serialization Considerations  . . . . . . . . .   8
     4.2.  Tag Factoring Example: X.500 Distinguished Name . . . . .   8
   5.  CDDL Control Operators  . . . . . . . . . . . . . . . . . . .  10
   6.  CDDL typenames  . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  CBOR Tags . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.2.  CDDL Control Operators  . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  15
     A.1.  Changes from -06 to -07 . . . . . . . .   3
   3.  Basic Examples . . . . . . . . .  15
     A.2.  Changes from -05 to -06 . . . . . . . . . . . . . .   5
   4.  Tag Factoring with Arrays and Maps . . .  15
     A.3.  Changes from -04 to -05 . . . . . . . . . .   7
   5.  CDDL Control Operators . . . . . . .  15
     A.4.  Changes from -03 to -04 . . . . . . . . . . . .   9
   6.  CDDL typenames . . . . .  15
     A.5.  Changes from -02 to -03 . . . . . . . . . . . . . . . . .  15
     A.6.  Changes from -01 to -02 .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . .  15
     A.7.  Changes from -00 to -01 . . . . .  10
   8.  Security Considerations . . . . . . . . . . . .  15
     A.8.  Changes from -07 (bormann) to -00 (ietf)  . . . . . . .  11
   9.  References .  16
     A.9.  Changes from -06 to -07 . . . . . . . . . . . . . . . . .  16
     A.10. Changes from -05 to -06 . . . . . . .  12
     9.1.  Normative References . . . . . . . . . .  16
     A.11. Changes from -04 to -05 . . . . . . . .  12
     9.2.  Informative References . . . . . . . . .  16
     A.12. Changes from -03 to -04 . . . . . . . . . . . .  13
   Appendix A.  Change Log . . . . .  16
     A.13. Changes from -02 to -03 . . . . . . . . . . . . . . . .  13 .  16
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  15  17
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  15  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16  17

1.  Introduction

   The Concise Binary Object Representation (CBOR, [RFC8949]) provides
   for the interchange of structured data without a requirement for a
   pre-agreed schema.  [RFC8949] defines a basic set of data types, as
   well as a tagging mechanism that enables extending the set of data
   types supported via an IANA registry.

   The present document defines CBOR tags for object identifiers (OIDs,
   [X.660]), which many IETF protocols carry.  The ASN.1 Basic Encoding
   Rules (BER, [X.690]) specify binary encodings of both (absolute)
   object identifiers and relative object identifiers.  The contents of
   these encodings (the "value" part of BER's type-length-value
   structure) can be carried in a CBOR byte string.  This document
   defines two CBOR tags that cover the two kinds of ASN.1 object
   identifiers encoded in this way.  The tags can also be applied to
   arrays and maps to efficiently tag all elements of an array or all
   keys of a map.  It is intended as the reference document for the IANA
   registration of the tags so defined.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The terminology of [RFC8949] applies; in particular the term "byte"
   is used in its now customary sense as a synonym for "octet".  The
   term "SDNV" (Self-Delimiting Numeric Value) is used as defined in [RFC6256].
   [RFC6256], with the additional restriction detailed in Section 2.1
   (no leading zeros).

2.  Object Identifiers

   The International Object Identifier tree [X.660] is a hierarchically
   managed space of identifiers, each of which is uniquely represented
   as a sequence of unsigned integer values [X.680].  (These integer
   values are called "primary integer values" in X.660 because they can
   be accompanied by (not necessarily unambiguous) secondary
   identifiers.  We ignore the latter and simply use the term "integer
   values" here, occasionally calling out their unsignedness.  We also
   use the term "arc" when the focus is on the edge of the tree labeled
   by such an integer value, as well as in the sense of a "long arc",
   i.e.
   i.e., a (sub)sequence of such integer values.)
   While these sequences can easily be represented in CBOR arrays of
   unsigned integers, a more compact representation can often be
   achieved by adopting the widely used representation of object
   identifiers defined in BER; this representation may also be more
   amenable to processing by other software that makes use of object
   identifiers.

   BER represents the sequence of unsigned integers by concatenating
   self-delimiting [RFC6256] representations of each of the integer
   values in sequence.

   ASN.1 distinguishes absolute object identifiers (ASN.1 Type "OBJECT
   IDENTIFIER"), which begin at a root arc ([X.660] Clause 3.5.21), from
   relative object identifiers (ASN.1 Type "RELATIVE-OID"), which begin
   relative to some object identifier known from context ([X.680] Clause
   3.8.63).  As a special optimization, BER combines the first two
   integers in an absolute object identifier into one numeric identifier
   by making use of the property of the hierarchy that the first arc has
   only three integer values (0, 1, and 2), and the second arcs under 0
   and 1 are limited to the integer values between 0 and 39.  (The root
   arc "joint-iso-itu-t(2)" has no such limitations on its second arc.)
   If X and Y are the first two integer values, the single integer value
   actually encoded is computed as:

      X * 40 + Y

   The inverse transformation (again making use of the known ranges of X
   and Y) is applied when decoding the object identifier.

   Since the semantics of absolute and relative object identifiers
   differ, and it is very common for companies to use self-assigned
   numbers under the arc "1.3.6.1.4.1" (IANA Private Enterprise Number
   OID, [IANA.enterprise-numbers]) that adds 5 fixed bytes to an encoded
   OID value, this specification defines two three tags, collectively called
   the "OID tags" here:

   Tag TBD111: tags a byte string as the [X.690] encoding of an absolute
   object identifier (simply "object identifier" or "OID").

   Tag TBD110: tags a byte string as the [X.690] encoding of a relative
   object identifier (also "relative OID").  Since the encoding of each
   number is the same as for [RFC6256] Self-Delimiting Numeric Values
   (SDNVs), this tag can also be used for tagging a byte string that
   contains a sequence of zero or more SDNVs. SDNVs (or a more application-
   specific tag can be created for such an application).

   Tag TBD112: structurally like TBD110, but understood to be relative
   to "1.3.6.1.4.1" (IANA Private Enterprise Number OID,
   [IANA.enterprise-numbers]).  Hence, the semantics of the result are
   that of an absolute object identifier.

2.1.  Requirements on the byte string being tagged

   To form a valid tag, a byte string tagged by TBD111, TBD110, or
   TBD112 MUST be syntactically valid contents (the value part) for a
   BER representation of an object identifier (Sections 8.19, 8.20, and
   8.20 of [X.690], respectively): A concatenation of zero or more SDNV
   values, where each SDNV value is a sequence of one or more bytes that
   all have their most significant bit set, except for the last byte,
   where it is unset.  Also, the first byte of each SDNV cannot be a
   leading zero in SDNV's base-128 arithmetic, so it cannot take the
   value 0x80 (bullet (c) in Section 8.1.2.4.2 of [X.690]).

   In other words:

   *  the byte string's first byte, and any byte that follows a byte
      that has the most significant bit unset, MUST NOT be 0x80 (this
      requirement requires expressing the integer values in their
      shortest form, with no leading zeroes)

   *  the byte string's last byte MUST NOT have the most significant bit
      set (this requirement excludes an incomplete final integer value)

   If either of these invalid conditions are encountered, the tag is
   invalid.

   [X.680] restricts RELATIVE-OID values to have at least one arc, i.e.,
   their encoding would have at least one SDNV.  This specification
   permits empty relative object identifiers; they may still be excluded
   by application semantics.

   To facilitate the search for specific object ID values, it is
   RECOMMENDED that definite length encoding (see Section 3.2.3 of
   [RFC8949]) is used for the byte strings used as tag content for these
   tags.

   The valid set of byte strings can also be expressed using regular
   expressions on bytes, using no specific notation but resembling
   [PCRE].  Unlike typical regular expressions that operate on character
   sequences, the following regular expressions take bytes as their
   domain, so they can be applied directly to CBOR byte strings.

   For byte strings with tag TBD111:

      "/^(([\x81-\xFF][\x80-\xFF]*)?[\x00-\x7F])+$/"

   For byte strings with tag TBD110 or TBD112:

      "/^(([\x81-\xFF][\x80-\xFF]*)?[\x00-\x7F])*$/"

   A tag with tagged content that does not conform to does not conform to the applicable
   regular expression is invalid.

2.2.  Preferred Serialization Considerations

   For an absolute OID with a prefix of "1.3.6.1.4.1", representations
   with both the TBD111 and TBD112 tags are applicable, where the
   representation with TBD112 will be five bytes shorter (by leaving out
   the prefix h'2b06010401' from the enclosed byte string).  This
   specification makes that shorter representation the preferred
   serialization (see Sections 3.4 and 4.1 of [RFC8949]).  Note that
   this also implies that the applicable
   regexp Core Deterministic Encoding Requirements
   (Section 4.2.1 of [RFC8949]) require the use of TBD112 tags instead
   of TBD111 wherever that is invalid.

2.2. possible.

2.3.  Discussion

   Staying close to the way object identifiers are encoded in ASN.1 BER
   makes back-and-forth translation easy; otherwise we would choose a
   more efficient encoding.  Object identifiers in IETF protocols are
   serialized in dotted decimal form or BER form, so there is an
   advantage in not inventing a third form.  Also, expectations of the
   cost of encoding object identifiers are based on BER; using a
   different encoding might not be aligned with these expectations.  If
   additional information about an OID is desired, lookup services such
   as the OID Resolution Service (ORS) [X.672] and the OID Repository
   [OID-INFO] are available.

3.  Basic Examples

   This section gives simple examples of an absolute and a relative
   object identifier, represented via tag number TBD111 and TBD110,
   respectively.

   RFC editor: These and other examples assume the allocation of 111 for
   TBD111 and 110 for TBD110 and need to be changed if that isn't the
   actual allocation.  Please remove this paragraph.

3.1.  Encoding of the SHA-256 OID

   ASN.1 Value Notation:  { joint-iso-itu-t(2) country(16) us(840)
      organization(1) gov(101) csor(3) nistalgorithm(4) hashalgs(2)
      sha256(1) }

   Dotted Decimal Notation:  2.16.840.1.101.3.4.2.1

   06                                # UNIVERSAL TAG 6
      09                             # 9 bytes, primitive
         60 86 48 01 65 03 04 02 01  # X.690 Clause 8.19
   #      |   840  1  |  3  4  2  1    show component encoding
   #   2.16         101

                        Figure 1: SHA-256 OID in BER

   D8 6F                             # tag(111)
      49                             # 0b010_01001: mt 2, 9 bytes
         60 86 48 01 65 03 04 02 01  # X.690 Clause 8.19

                       Figure 2: SHA-256 OID in CBOR

3.2.  Encoding of a MIB Relative OID

   Given some OID (e.g., "lowpanMib", assumed to be "1.3.6.1.2.1.226"
   [RFC7388]), to which the following is added:

   ASN.1 Value Notation:  { lowpanObjects(1) lowpanStats(1)
      lowpanOutTransmits(29) }

   Dotted Decimal Notation:  .1.1.29

   0D                                # UNIVERSAL TAG 13
      03                             # 3 bytes, primitive
         01 01 1D                    # X.690 Clause 8.20
   #      1  1 29                      show component encoding

              Figure 3: MIB relative object identifier, in BER

   D8 6E                             # tag(110)
      43                             # 0b010_01001: 0b010_00011: mt 2 (bstr), 3 bytes
         01 01 1D                    # X.690 Clause 8.20

             Figure 4: MIB relative object identifier, in CBOR

   This relative OID saves seven bytes compared to the full OID
   encoding.

4.  Tag Factoring with Arrays and Maps

   OID tags can tag byte strings (as discussed above), but also CBOR
   arrays and maps.  The idea in the latter case is that the tag is
   factored out from each individual item in the container; the tag is
   placed on the array or map instead.

   When an OID tag is applied to an array, it means that the respective
   tag is imputed to all elements of the array that are byte strings,
   arrays, or maps.  (There is no effect on other elements, including
   text strings or tags.)  For example, when an array is tagged with
   TBD111, every array element that is a byte string is an OID, and
   every element that is an array or map is in turn treated as discussed
   here.

   When an OID tag is applied to a map, it means that the respective tag
   is imputed to all keys in the map that are byte strings, arrays, or
   maps; again, there is no effect on keys of other major types.  Note
   that there is also no effect on the values in the map.

   As a result of these rules, tag factoring in nested arrays and maps
   is supported.  For example, a 3-dimensional array of OIDs can be
   composed by using a single TBD111 tag containing an array of arrays
   of arrays of byte strings.  All such byte strings are then considered
   OIDs.

4.1.  Preferred Serialization Considerations

   Where tag factoring with tag TBD111 is used, some OIDs enclosed in
   the tag may be encoded in a shorter way by using tag TBD112 instead
   of encoding an unadorned byte string.  This remains the preferred
   serialization (see also Section 2.2).  However, this specification
   does not make the presence or absence of tag factoring a preferred
   serialization; application protocols can define where tag factoring
   is to be used or not (and will need to do so if they have
   deterministic encoding requirements).

4.2.  Tag Factoring Example: X.500 Distinguished Name

   Consider the X.500 distinguished name:

              +==============================+=============+
              | Attribute Types              | Attribute   |
              |                              | Values      |
              +==============================+=============+
              | c (2.5.4.6)                  | US          |
              +------------------------------+-------------+
              | l (2.5.4.7)                  | Los Angeles |
              | s (2.5.4.8)                  | CA          |
              | postalCode (2.5.4.17)        | 90013       |
              +------------------------------+-------------+
              | street (2.5.4.9)             | 532 S Olive |
              |                              | St          |
              +------------------------------+-------------+
              | businessCategory (2.5.4.15)  | Public Park |
              | buildingName                 | Pershing    |
              | (0.9.2342.19200300.100.1.48) | Square      |
              +------------------------------+-------------+

                Table 1: Example X.500 Distinguished Name

   Table 1 has four "relative distinguished names" (RDNs).  The country
   (first) and street (third) RDNs are single-valued.  The second and
   fourth RDNs are multi-valued.

   The equivalent representations in CBOR diagnostic notation (Section 8
   of [RFC8949]) and CBOR are:

   111([{ h'550406': "US" },
        { h'550407': "Los Angeles",
          h'550408': "CA",
          h'550411': "90013" },
        { h'550409': "532 S Olive St" },
        { h'55040f': "Public Park",
          h'0992268993f22c640130': "Pershing Square" }])

         Figure 5: Distinguished Name, in CBOR Diagnostic Notation

   d8 6f                                      # tag(111)
      84                                      # array(4)
         a1                                   # map(1)
            43 550406                         # 2.5.4.6 (4)
            62                                # text(2)
               5553                           # "US"
         a3                                   # map(3)
            43 550407                         # 2.5.4.7 (4)
            6b                                # text(11)
               4c6f7320416e67656c6573         # "Los Angeles"
            43 550408                         # 2.5.4.8 (4)
            62                                # text(2)
               4341                           # "CA"
            43 550411                         # 2.5.4.17 (4)
            65                                # text(5)
               3930303133                     # "90013"
         a1                                   # map(1)
            43 550409                         # 2.5.4.9 (4)
            6e                                # text(14)
               3533322053204f6c697665205374   # "532 S Olive St"
         a2                                   # map(2)
            43 55040f                         # 2.5.4.15 (4)
            6b                                # text(11)
               5075626c6963205061726b         # "Public Park"
            4a 0992268993f22c640130    # 0.9.2342.19200300.100.1.48 (11)
            6f                                # text(15)
               5065727368696e6720537175617265 # "Pershing Square"

             Figure 6: Distinguished Name, in CBOR (109 bytes)

   (This example encoding assumes that all attribute values are UTF-8
   strings, or can be represented as UTF-8 strings with no loss of
   information.)

5.  CDDL Control Operators

   CDDL

   Concise Data Definition Language (CDDL [RFC8610]) specifications may
   want to specify the use of SDNVs or SDNV sequences (as defined for
   the tag content for TBD110).  This document introduces two new
   control operators that can be applied to a target value that is a
   byte string:

   *  ".sdnv", with a control type that contains unsigned integers.  The
      byte string is specified to be encoded as an [RFC6256] SDNV (BER
      encoding) for the matching values of the control type.

   *  ".sdnvseq", with a control type that contains arrays of unsigned
      integers.  The byte string is specified to be encoded as a
      sequence of [RFC6256] SDNVs (BER encoding) that decodes to an
      array of unsigned integers matching the control type.

   *  ".oid", like ".sdnvseq", except that the X*40+Y translation for
      absolute OIDs is included (see Figure 8).

   Figure 7 shows an example for the use of ".sdnvseq" for a part of a
   structure using OIDs that could be used in Figure 6; Figure 8 shows
   the same with the ".oid" operator.

   country-rdn = {country-oid => country-value}
   country-oid = bytes .sdnvseq [85, 4, 6]
   country-value = text .size 2

                          Figure 7: Using .sdnvseq

   country-rdn = {country-oid => country-value}
   country-oid = bytes .oid [2, 5, 4, 6]
   country-value = text .size 2

                            Figure 8: Using .oid

   Note that the control type need not be a literal; e.g., "bytes .oid
   [2, 5, 4, *uint]" matches all OIDs inside OID arc 2.5.4,
   "attributeType".

6.  CDDL typenames

   For the use with CDDL [RFC8610], CDDL, the typenames defined in Figure 9 are
   recommended:

   oid = #6.111(bstr)
   roid = #6.110(bstr)
   pen = #6.112(bstr)

                  Figure 9: Recommended typenames for CDDL

7.  IANA Considerations

7.1.  CBOR Tags

   IANA is requested to assign in the 1+1 byte space (24..255) of the
   CBOR tags registry [IANA.cbor-tags] the CBOR tags in Table 2, with
   the present document as the specification reference.

         +========+================+============================+

   +========+================+============================+============+
   | Tag    | Data Item      |                  Semantics |
         +========+================+============================+ Reference  |
   +========+================+============================+============+
   | TBD111 | byte string or    |     object identifier (BER | [this      |
   |        | or array or map    |                  encoding) |
         +--------+----------------+----------------------------+ document,  |
   |        | map            |                            | Section 2] |
   +--------+----------------+----------------------------+------------+
   | TBD110 | byte string or    | relative object identifier | [this      |
   |        | or array or map    |            (BER encoding); | document,  |
   |        | map            |    SDNV [RFC6256] sequence |
         +--------+----------------+----------------------------+ Section 2] |
   +--------+----------------+----------------------------+------------+
   | TBD112 | byte string or    |     object identifier (BER | [this      |
   |        | or array or map    |     encoding), relative to | document,  |
   |        | map            |                1.3.6.1.4.1 |
         +--------+----------------+----------------------------+ Section 2] |
   +--------+----------------+----------------------------+------------+

                        Table 2: Values for New Tags

7.2.  CDDL Control Operators

   IANA is requested to assign in the CDDL Control Operators registry
   [IANA.cddl] the CDDL Control Operators in Table 3, with the present
   document as the specification reference.

                 +==========+============================+
                 | Name     | Reference                  |
                 +==========+============================+
                 | .sdnv    | [this document, Section 5] |
                 +----------+----------------------------+
                 | .sdnvseq | [this document, Section 5] |
                 +----------+----------------------------+
                 | .oid     | [this document, Section 5] |
                 +----------+----------------------------+

                        Table 3: New CDDL Operators

8.  Security Considerations

   The security considerations of [RFC8949] apply.

   The encodings in Clauses 8.19 and 8.20 of [X.690] are quite compact
   and unambiguous, but MUST be followed precisely to avoid security
   pitfalls.  In particular, the requirements set out in Section 2.1 of
   this document need to be followed; otherwise, an attacker may be able
   to subvert a checking process by submitting alternative
   representations that are later taken as the original (or even
   something else entirely) by another decoder supposed to be protected
   by the checking process.

   OIDs and relative OIDs can always be treated as opaque byte strings.
   Actually understanding the structure that was used for generating
   them is not necessary, and, except for checking the structure
   requirements, it is strongly NOT RECOMMENDED to perform any
   processing of this kind (e.g., converting into dotted notation and
   back) unless absolutely necessary.  If the OIDs are translated into
   other representations, the usual security considerations for non-
   trivial representation conversions apply; the integer values are
   unlimited in range.

   An attacker might trick an application into using a byte string
   inside a tag-factored data item, where the byte string is not
   actually intended to fall under one of the tags defined here.  This
   may cause the application to emit data with semantics different from
   what was intended.  Applications therefore need to be restrictive
   with respect to what data items they apply tag factoring to.

9.  References

9.1.  Normative References

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

   [IANA.cddl]
              IANA, "Concise Data Definition Language (CDDL)",
              <http://www.iana.org/assignments/cddl>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6256]  Eddy, W. and E. Davies, "Using Self-Delimiting Numeric
              Values in Protocols", RFC 6256, DOI 10.17487/RFC6256, May
              2011, <https://www.rfc-editor.org/info/rfc6256>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

   [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>.

   [X.660]    International Telecommunications Union, "Information
              technology — Procedures for the operation of object
              identifier registration authorities: General procedures
              and top arcs of the international object identifier tree",
              ITU-T Recommendation X.660, July 2011,
              <https://www.itu.int/rec/T-REC-X.660>.

   [X.680]    International Telecommunications Union, "Information
              technology — Abstract Syntax Notation One (ASN.1):
              Specification of basic notation", ITU-T Recommendation
              X.680, August 2015, <https://www.itu.int/rec/T-REC-X.680>.

   [X.690]    International Telecommunications Union, "Information
              technology — ASN.1 encoding rules: Specification of Basic
              Encoding Rules (BER), Canonical Encoding Rules (CER) and
              Distinguished Encoding Rules (DER)", ITU-T Recommendation
              X.690, August 2015, <https://www.itu.int/rec/T-REC-X.690>.

9.2.  Informative References

   [IANA.enterprise-numbers]
              IANA, "enterprise-numbers", "Enterprise Numbers",
              <http://www.iana.org/assignments/enterprise-numbers>.

   [OID-INFO] Orange SA, "OID Repository", 2016,
              <http://www.oid-info.com/>.

   [PCRE]     Ho, A., "PCRE - Perl Compatible Regular Expressions",
              2018, <http://www.pcre.org/>.

   [RFC7388]  Schoenwaelder, J., Sehgal, A., Tsou, T., and C. Zhou,
              "Definition of Managed Objects for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 7388,
              DOI 10.17487/RFC7388, October 2014,
              <https://www.rfc-editor.org/info/rfc7388>.

   [X.672]    International Telecommunications Union, "Information
              technology — Open systems interconnection — Object
              identifier resolution system", ITU-T Recommendation X.672,
              August 2010, <https://www.itu.int/rec/T-REC-X.672>.

Appendix A.  Change Log

   This section is to be removed before publishing as an RFC.

A.1.  Changes from -06 to -07

   *  Various editorial changes prompted by IESG feedback; clarify the
      usage of "SDNV" in this document (no leading zeros).

   *  Add security consideration about tag-factoring.

   *  Make TBD112, where applicable, the preferred serialization (and
      thus the required deterministic encoding) over TBD111.

A.2.  Changes from -05 to -06

   Add references to specific section numbers of [X.690] to better
   explain validity of enclosed byte string.

A.2.

A.3.  Changes from -04 to -05

   *  Update acknowledgements, contributor list, and author list

A.3.

A.4.  Changes from -03 to -04

   Process WGLC and shepherd comments:

   *  Update references (RFC 8949, URIs for ITU-T)

   *  Define arc for this document, reference SDN definition

   *  Restructure, small editorial clarifications

A.4.

A.5.  Changes from -02 to -03

   *  Add tag TBD112 for PEN-relative OIDs

   *  Add suggested CDDL typenames; reference RFC8610

A.5.

A.6.  Changes from -01 to -02

   Minor editorial changes, remove some remnants, ready for WGLC.

A.6.

A.7.  Changes from -00 to -01

   Clean up OID tag factoring.

A.7.

A.8.  Changes from -07 (bormann) to -00 (ietf)

   Resubmitted as WG draft after adoption.

A.8.

A.9.  Changes from -06 to -07

   Reduce the draft back to its basic mandate: Describe CBOR tags for
   what is colloquially know as ASN.1 Object IDs.

A.9.

A.10.  Changes from -05 to -06

   Refreshed the draft to the current date ("keep-alive").

A.10.

A.11.  Changes from -04 to -05

   Discussed UUID usage in CBOR, and incorporated fixes proposed by
   Olivier Dubuisson, including fixes regarding OID nomenclature.

A.11.

A.12.  Changes from -03 to -04

   Changes occurred based on limited feedback, mainly centered around
   the abstract and introduction, rather than substantive technical
   changes.  These changes include:

   *  Changed the title so that it is about tags and techniques.

   *  Rewrote the abstract to describe the content more accurately, and
      to point out that no changes to the wire protocol are being
      proposed.

   *  Removed "ASN.1" from "object identifiers", as OIDs are independent
      of ASN.1.

   *  Rewrote the introduction to be more about the present text.

   *  Proposed a concise OID arc.

   *  Provided binary regular expression forms for OID validation.

   *  Updated IANA registration tables.

A.12.

A.13.  Changes from -02 to -03

   Many significant changes occurred in this version.  These changes
   include:

   *  Expanded the draft scope to be a comprehensive CBOR update.

   *  Added OID-related sections: OID Enumerations, OID Maps and Arrays,
      and Applications and Examples of OIDs.

   *  Added Tag 36 update (binary MIME, better definitions).

   *  Added stub/experimental sections for X.690 Series Tags (tag <<X>>)
      and Regular Expressions (tag 35).

   *  Added technique for representing sets and multisets.

   *  Added references and fixed typos.

Acknowledgments

   Sean Leonard started the work on this document in 2014 with an
   elaborate proposal.  Jim Schaad provided a significant review of this
   document.  Rob Wilton's IESG review prompted us to provide preferred
   serialization considerations.

Contributors

   Sean Leonard
   Penango, Inc.
   5900 Wilshire Boulevard
   21st Floor
   Los Angeles, CA,  90036
   United States of America

   Email: dev+ietf@seantek.com
   URI:   http://www.penango.com/

Author's Address

   Carsten Bormann
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany

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