[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 draft-ietf-cbor-tags-oid

Network Working Group                                         C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Intended status: Standards Track                              S. Leonard
Expires: January 1, 2017                                   Penango, Inc.
                                                           June 30, 2016


          Concise Binary Object Representation (CBOR) Tags for
    ASN.1 Object Identifiers, and Omnibus Corrections and Techniques
                     draft-bormann-cbor-tags-oid-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.

   The present document makes use of this extensibility to define CBOR
   tags <<O>> and <<R>> [values TBD] for ASN.1 object identifiers.  It
   is intended as the reference document for the IANA registration of
   the CBOR tags so defined.  This document also provides other
   corrections and improvements to CBOR.

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 http://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 January 1, 2017.

Copyright Notice

   Copyright (c) 2016 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



Bormann & Leonard        Expires January 1, 2017                [Page 1]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  ASN.1 Object Identifiers  . . . . . . . . . . . . . . . . . .   3
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Diagnostic Notation . . . . . . . . . . . . . . . . . . . . .   7
   6.  Enumerations in CBOR  . . . . . . . . . . . . . . . . . . . .   8
   7.  Tag Factoring and Tag Stacking with OID Arrays and Maps . . .  11
   8.  Applications and Examples of OIDs . . . . . . . . . . . . . .  15
   9.  Binary Internet Messages and MIME Entities  . . . . . . . . .  18
   10. Applications and Examples of Messages and Entities  . . . . .  21
   11. X.690 Series Tags . . . . . . . . . . . . . . . . . . . . . .  21
   12. Regular Expression Clarification  . . . . . . . . . . . . . .  22
   13. Set and Multiset Technique  . . . . . . . . . . . . . . . . .  23
   14. Fruits Basket Example . . . . . . . . . . . . . . . . . . . .  23
   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   16. Security Considerations . . . . . . . . . . . . . . . . . . .  25
   17. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
   Appendix A.  Changes from -02 to -03  . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   The Concise Binary Object Representation (CBOR, [RFC7049]) provides
   for the interchange of structured data without a requirement for a
   pre-agreed schema.  RFC 7049 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.

   Many IETF protocols carry ASN.1 object identifiers, originally
   defined in 1988 [CCITT.X208.1988] and most recently in 2015 [X.680].
   The ASN.1 Basic Encoding Rules (BER, [X.690]) specify the binary
   encodings of both ASN.1 object identifiers and relative object
   identifiers.  The contents of these encodings 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.  It is intended as the
   reference document for the IANA registration of the tags so defined.



Bormann & Leonard        Expires January 1, 2017                [Page 2]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   During development of this Internet-Draft, a couple of deficiencies
   and points of enhancement were noted.  This document updates
   [RFC7049] to handle binary Internet messages natively, and provides
   certain techniques for efficiently encoding sets in CBOR.

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 RFC
   2119 [RFC2119].

   The terminology of RFC 7049 applies; in particular the term "byte" is
   used in its now customary sense as a synonym for "octet".

2.  ASN.1 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 integers ("sub-identifiers") [X.680].
   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 ASN.1 object
   identifiers defined in BER; this representation may also be more
   amenable to processing by other software making use of ASN.1 object
   identifiers.

   BER represents the sequence of unsigned integers by concatenating
   self-delimiting [RFC6256] representations of each of the sub-
   identifiers 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
   integers, the single integer 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 ASN.1 object identifier.



Bormann & Leonard        Expires January 1, 2017                [Page 3]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   Since the semantics of absolute and relative object identifiers
   differ, this specification defines two tags:

   Tag <<O>> (value TBD): tags a byte string as the ASN.1 BER encoding
   of an absolute object identifier (simply "object identifier" or
   "OID").

   Tag <<R>> (value TBD): tags a byte string as the ASN.1 BER encoding
   of a relative object identifier (also "relative OID").

2.1.  Requirements on the byte string being tagged

   A byte string tagged by <<O>> or <<R>> MUST be a syntactically valid
   BER representation of an ASN.1 object identifier.  Specifically:

   o  its first byte, and any byte that follows a byte that has the most
      significant bit unset, MUST NOT be 0x80 (this requirement excludes
      expressing the sub-identifiers with anything but the shortest
      form)

   o  its last byte MUST NOT have the most significant bit set (this
      requirement excludes an incomplete final sub-identifier)

   If either of these invalid conditions are encountered, they MUST be
   treated as decoding errors.  Comparing two OIDs or relative OIDs for
   equality in a byte-for-byte fashion may not be safe before these
   checks succeed on at least one of them (this includes the case where
   one of them is a local constant); a process implementing an exclusion
   list MUST check for decoding errors first.

   [X.680] restricts RELATIVE-OID values to have at least one sub-
   identifier (array element).  This specification permits empty
   relative object identifiers; they may still be excluded by
   application semantics.

   [RFC7049] permits byte strings to be indefinite-length, with chunks
   divided at arbitrary byte boundaries.  This contrasts with text
   strings, where each chunk in an indefinite-length text string is
   required be well-formed UTF-8 on its own: splitting the octets of a
   UTF-8 character encoding between chunks is not allowed.

   By analogy to this principle and to Clauses 8.9.1 and 8.20.1 of
   [X.690], the byte strings carrying the OIDs and relative OIDs are
   also to be treated as indivisible units: They MUST be encoded in
   definite-length form; indefinite-length form is treated as an
   encoding error (and the same considerations as above apply).  (An
   added convenience is that CBOR encodings can be searched through




Bormann & Leonard        Expires January 1, 2017                [Page 4]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   efficiently for specific OIDs or relative OIDs, without initiating
   the decoding process.)

3.  Examples

   In the following examples, we are using tag number 6 for <<O>> and
   tag number 7 for <<R>>.  See Section 15.2.

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 (also XML Value 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

   C6                                # 0b110_00110: mt 6, tag 6
      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 UUID OID

   UUID
   8b0d1a20-dcc5-11d9-bda9-0002a5d5c51b

   ASN.1 Value Notation
   { joint-iso-itu-t(2) uuid(25)
   geomicaGPAS(184830721219540099336690027854602552603) }

   Dotted Decimal Notation (also XML Value Notation)
   2.25.184830721219540099336690027854602552603









Bormann & Leonard        Expires January 1, 2017                [Page 5]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   06                                # UNIVERSAL TAG 6
      14                             # 20 bytes, primitive
         69 82 96 8D 8D 88 9B CC A8 C7 B3 BD D4 C0 80 AA AE D7 8A 1B
   #      |                  184830721219540099336690027854602552603
   #   2.25

              Figure 3: UUID in an object identifier, in BER

   C6                                # 0b110_00110: mt 6, tag 6
      54                             # 0b010_10100: mt 2, 20 bytes
         69 82 96 8D 8D 88 9B CC A8 C7 B3 BD D4 C0 80 AA AE D7 8A 1B

              Figure 4: UUID in an object identifier, in CBOR

3.3.  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 (not suitable for diagnostic notation)
   { lowpanObjects(1) lowpanStats(1) lowpanOutTransmits(29) }

   Dotted Decimal Notation (diagnostic notation; see Section 5)
   .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 5: MIB relative object identifier, in BER

   C7                                # 0b110_00110: mt 6, tag 7
      43                             # 0b010_01001: mt 2 (bstr), 3 bytes
         01 01 1D                    # X.690 Clause 8.20

             Figure 6: MIB relative object identifier, in CBOR

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

4.  Discussion

   Staying close to the way ASN.1 object identifiers are encoded in
   ASN.1 BER makes back-and-forth translation easy.  As of today, ASN.1
   object identifiers are either used 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 ASN.1 object identifiers are



Bormann & Leonard        Expires January 1, 2017                [Page 6]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   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.

   This specification allocates two numbers out of the single-byte tag
   space.  This use of code point space is justified by the wide use of
   object identifiers in data interchange.  For most common OIDs in use
   (namely those whose contents encode to less than 24 bytes), the CBOR
   encoding will match the efficiency of [X.690].  (This preliminary
   conclusion is likely to generate some discussion, see Section 15.2.)

5.  Diagnostic Notation

   Implementers will likely want to see OIDs and relative OIDs in their
   "natural forms" (as sequences of decimal unsigned integers) for
   diagnostic purposes.  Accordingly, this section defines additional
   syntactic elements that can be used in conjunction with the
   diagnostic notation described in Section 6 of [RFC7049].

   An object identifier may be written in ASN.1 value notation (with
   enclosing braces and secondary identifiers, ObjectIdentifierValue of
   Clause 32.3 of [X.680]), or in dotted decimal notation with at least
   three arcs.  Both examples are shown in Section 3.  The surrounding
   tag notation is not to be used, because the tag is implied.  The
   ASN.1 value notation for OIDs does not overlap with JSON object
   notation for CBOR maps, because at least two arcs are required for a
   valid OID.

   A relative object identifier may be written in dotted decimal
   notation or in ASN.1 value notation, in both cases prefixed with a
   dot as shown in Section 3.3.  The surrounding tag notation is not to
   be used, because the tag is implied.

   The notation in this section may be employed in addition to the basic
   notation, which would be a tagged binary string.

       +------------------------------+--------------+------------+
       | RFC 7049 diagnostic notation | 6(h'2b0601') | 7(h'0601') |
       +------------------------------+--------------+------------+
       | Dotted decimal notation      | 1.3.6.1      | .6.1       |
       | ASN.1 value notation         | {1 3 6 1}    | .{6 1}     |
       +------------------------------+--------------+------------+

            Table 1: Examples for extended diagnostic notation






Bormann & Leonard        Expires January 1, 2017                [Page 7]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


6.  Enumerations in CBOR

   This section provides a roadmap to using enumerated items in CBOR,
   including design considerations for choosing between OIDs, integers,
   and UTF-8 strings.

   CBOR does not have an ENUMERATED type like ASN.1 to identify named
   values in a protocol element with three or more states (Clause 20 and
   Clause G.2.3 of [X.680]).  ASN.1 ENUMERATED turns out to be
   superfluous because ASN.1 INTEGER values can get named (and have
   historically been used for finite, multistate variables, such as
   version numbers), while ASN.1 ENUMERATED types can be defined to be
   extensible with the ellipsis lexical item.  Practically, the named
   integers are not serialized in the binary encodings anyway; they
   merely serve as a semantic hints for designers and debuggers.

   CBOR expects that protocol designers will use one of the basic major
   types for multistate variables, assigning semantics to particular
   values using higher-level schemas.  The obvious choices for the basic
   types are integers (particularly unsigned integers) and UTF-8
   strings.  However, these major types are not without drawbacks.

   Integers are compact for small values, but have a flat namespace so
   there are mis-assignment and collision risks that can only be
   mitigated with protocol-specific registries.  Arrays of integers are
   possible, but arrays require more processing logic for equality
   comparisons, and the JSON conversion is not intuitive when the
   enumerated value serves as a key in a map.

   UTF-8 strings are less compact when the strings are supposed to
   resemble their semantics, and there are normalization issues if the
   strings contain characters beyond the ASCII range.  UTF-8 strings
   also comprise a flat namespace like integers unless the higher-level
   schema employs delimiters (which makes the string even larger).  This
   section provides a novel alternative in OIDs.

6.1.  Factors Favoring OID Enumerations

   A protocol designer might choose OIDs or relative OIDs for an
   enumerated item in view of the following observations:

   1.  OIDs and relative OIDs are quite compact: a single-arc relative
       OID encoded according to this specification occupies just two
       bytes for primary integer values 0-127 (excluding the semantic
       tag <<R>>), and three bytes for primary integer values 128-16383.
       (In contrast, an unsigned integer requires one byte for 0-23, two
       bytes for 24-255, and three bytes for 256-65535.)




Bormann & Leonard        Expires January 1, 2017                [Page 8]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   2.  OIDs and relative OIDs (with base) are persistent and globally
       unambiguous.

   3.  OIDs and relative OIDs have built-in semantics for designers and
       debuggers.  Specifically, the advent of universal OID
       repositories such as [OID-INFO] makes it easy for a designer or
       debugger to pull up useful information about the object of
       interest (Clause 3.5.10 of [X.660]).  This useful information
       (for humans) does not have to bleed into the encoded
       representation (for machines).

   4.  OIDs and relative OIDs are always compared for exact equality: no
       need to deal with case folding, case sensitivity, or other
       normalization issues.  ("Overlong" encodings are PROHIBITED;
       therefore overlong encodings MUST be treated as coding errors.)

   5.  OIDs and relative OIDs have a built-in hierarchy, so if
       implementers want to extend an enumeration without assigning new
       values "horizontally", they have the option of assigning new
       values "vertically", possibly with more or less stringent
       assignment rules.

   6.  Because OIDs and relative OIDs (with base) are part of the so-
       called International Object Identifier tree [X.660], any other
       protocol specification can reuse the enumeration if the designers
       find it useful.

   7.  OIDs and relative OIDs have natural JSON representations in the
       dotted decimal notations prescribed in Section 5.  OIDs and
       relative OIDs can be distinguished from each other by the
       presence or absence of the leading dot ".".  As the resulting
       JSON string is entirely numeric in the ASCII range, case and
       normalization are irrelevant to the comparison.  (An object
       identifier also has a semantic string representation in the form
       of an OID-IRI [X.680], for those who really want that type of
       thing.)

   8.  OIDs and relative OIDs are human language-neutral.  A protocol
       designer working in US-English might name an enumerated value
       "sig" for "signature", but "sig" could also stand for
       "significand", "signal", or "special interest group".  In Swedish
       and Norwegian, "sig" is a pronoun that means "himself, herself,
       itself, one, them", etc.--an entirely different meaning.








Bormann & Leonard        Expires January 1, 2017                [Page 9]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


6.2.  Factors Favoring Integer Enumerations

   A protocol designer might choose integers for an enumerated item in
   view of the following observations:

   1.  The CBOR encoding of unsigned integers 0-23 is the most compact,
       occupying exactly one byte (excluding any semantic tags).

   2.  A protocol designer may wish to prohibit extensibility as a
       matter of course.  Integers comprise a single flat namespace:
       there is no hierarchy.

   3.  If greater range is desired while sticking to one byte, a
       protocol designer may double the range of possible values by
       allowing negative integers -24 - -1.  However, enumerating values
       using negative integers may have unintended side-effects, because
       some programming environments (e.g., C/C++) make implementation-
       defined assumptions about the number of bits needed for an
       enumerated type.

6.3.  Factors Favoring UTF-8 String Enumerations

   A protocol designer might choose UTF-8 strings for an enumerated item
   in view of the following observations:

   1.  A specification can practically limit the content of UTF-8
       strings to the ASCII range (or narrower), mitigating some
       normalization problems.

   2.  UTF-8 strings are easier to read on-the-wire for humans.

   3.  UTF-8 strings can contain arbitrary textual identifiers, which
       can be hierarchical, e.g., URIs.

6.4.  OID Enumeration Example

   An enumerated item indicates the revision level of a data format.
   Revision levels are issued by year, such as 2011, 2012, etc.
   However, in the year 2013, two revisions were issued: the first one
   and an important update in June that needs to be distinguished.  The
   revision levels are assigned to some OID arc:

   "{2 25 6464646464 revs(4)}"

   In this arc, the following sub-arcs are assigned:






Bormann & Leonard        Expires January 1, 2017               [Page 10]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


                          +--------------------+
                          | Sub-Arc            |
                          +--------------------+
                          | {v2011(1)}         |
                          | {v2012(2)}         |
                          | {v2013(3)}         |
                          | {v2013(3) june(6)} |
                          | {v2014(4)}         |
                          | {v2015(5)}         |
                          +--------------------+

                         Table 2: Example Sub-Arcs

   In CBOR, the enumeration is encoded as a relative OID.  The schema
   specifies the base OID arc, which is omitted:

   c7         # tag(7)
      41 03   # .3

   c7         # tag(7)
      42 0306 # .3.6

                    Figure 7: Enumerated Items in CBOR

   .3
   .{v2013(3) june(6)}

          Figure 8: Enumerated Items in CBOR Diagnostic Notation

   ".3"
   ".3.6"

            Figure 9: Enumerated Items in JSON (possibility 1)

   "v2013"
   "v2013/june"

            Figure 10: Enumerated Items in JSON (possibility 2)

7.  Tag Factoring and Tag Stacking with OID Arrays and Maps

   A common use of OIDs in ASN.1 is to identify the kind of data in an
   open type (Clause 3.8.57 of [X.680]), using information object
   classes [X.681].  CBOR is schema-neutral, and (although not fully
   discussed in [RFC7049]) semantic tagging was originally intended to
   identify items in a global, context-free way (i.e., where a
   specification would not repurpose a tag with different semantics than




Bormann & Leonard        Expires January 1, 2017               [Page 11]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   its IANA registration).  Therefore, using OIDs to identify contextual
   data in a similar fashion to [X.681] is RECOMMENDED.

7.1.  Tag Factoring

   <<O>> and <<R>> can tag CBOR arrays and maps.  The idea is that the
   tag is factored out from each individual byte string; the tag is
   placed in front of the array or map instead.  The tags <<O>> and
   <<R>> are left-distributive.

   When the <<O>> or <<R>> tag is applied to an array, it means that the
   respective tag is imputed to all items in the array.  For example,
   when the array is tagged with <<O>>, every array item that is a
   binary string is an OID.

   When the <<O>> or <<R>> tag is applied to a map, it means that the
   respective tag is imputed to all keys in the map.  The values in the
   map are not considered specially tagged.

   Array and map stacking is permitted.  For example, a 3-dimensional
   array of OIDs can be composed by using a single <<O>> tag, followed
   by an array of arrays of arrays of binary strings.  All such binary
   strings are considered OIDs.

7.2.  Switching OID and Relative OID

   If an individual item in a <<O>> or <<R>> tagged array, or an
   individual key in a <<O>> or <<R>> tagged map, is tagged with the
   opposite tag (<<R>> or <<O>>) of the array or map itself, that tag
   cancels and replaces the outer tag for that item.  Like tags MUST NOT
   be used on such individual items; such tagging is a coding error.
   For example, if <<R>> is the outer tag on an array and <<O>> is the
   inner tag on a binary string, semantically the inner item is treated
   as a regular OID, not as a relative OID.

   The purpose is to create more compact and flexible identifier spaces,
   especially when object identifiers are used as enumerated items.
   Examples:

   <<R>> outside, <<O>> inside: An implementation that strives for a
   compact representation, does not have to emit base OID arcs
   repeatedly for each item.  At the same time, if a private
   organization or standards body separate from the specification needs
   to identify something that the specification maintainers disagree
   with, the separate body does not need to request registration of an
   identifier under a controlled arc (i.e., the base arc of the relative
   OIDs).




Bormann & Leonard        Expires January 1, 2017               [Page 12]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   <<O>> outside, <<R>> inside: A collection of OIDs is supposed to be
   open to all-comers, but a certain set of OIDs issued under a
   particular arc is foreseeable for the majority of implementations.
   For example, an OID protocol slot may identify cryptographic
   algorithms: anyone can write (and has written) an algorithm with an
   arbitrary OID.  However, the protocol slot designer may wish to
   privilege certain algorithms (and therefore OIDs) that are well-known
   in that field of use.

7.3.  Tag Stacking

   CBOR permits tag stacking (tagging a tagged item), although this
   technique has not been used much yet.  This specification anticipates
   that OIDs and relative OIDs will be associated with values with
   uniform semantics.  This section provides specific semantics when
   tags are "stacked", that is, a CBOR item starts with tag <<O>> or
   <<R>>, followed by one or more arbitrary tags ("subsequent tags"),
   followed by a map or array.

7.3.1.  Map

   The overall gist is that the first tag applies to the keys in a map;
   the subsequent tags apply to the values in a map.

   When <<O>> or <<R>> is the first tag in a stack of tags, followed by
   a map:

   o  The <<O>> or <<R>> tag indicates that the keys of the map are byte
      string OIDs, byte string relative OIDs, or tag-factored arrays or
      maps of the same.

   o  The subsequent tags uniformly apply to all of the values.

   For example, if tag 32 (URL) is the subsequent tag, then all values
   in the map are treated semantically as if tag 32 is applied to them
   individually.  See Figure 11.

   It is possible that individual values can be tagged.  Semantically,
   these tags cumulate with the outer subsequent tags; inner value tags
   do not cancel or replace the outer tags.

7.3.2.  Array

   The overall gist is that the first tag applies to the ordered "keys"
   in the array (even-numbered items, assuming that the index starts at
   0); the subsequent tags apply to the ordered "values" in the array
   (odd-numbered items).  This tagging technique creates an ordered




Bormann & Leonard        Expires January 1, 2017               [Page 13]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   associative array.  [[NB: Some call this the FORTRAN approach. need
   to cite]]

   When <<O>> or <<R>> is the first tag in a stack of tags, followed by
   an array:

   o  The <<O>> or <<R>> tag indicates that alternating items, starting
      with the first item, are byte string OIDs, byte string relative
      OIDs, or tag-factored arrays or maps of the same.

   o  The subsequent tags uniformly apply to the alternating items,
      starting with the second item.

   o  The array MUST have an even number of items; an array that has an
      odd number of items is a coding error.

   To create an ordered associative array wherein the values (even
   elements) are arbitrarily tagged, stack tag 55799, self-describe CBOR
   (Section 2.4.5 of [RFC7049]), after the <<O>> or <<R>> tag.  Tag
   55799 imparts no special semantics, so it is an effective
   placeholder.  (This sequence is mainly provided for completeness: it
   is a more compact alternative to an array of duple-arrays that each
   contain an OID or relative OID, and an arbitrary value.)

7.4.  Diagnostic Notation for OID Arrays and Maps

   There are no syntactic changes to diagnostic notation beyond
   Section 5.  Using <<O>> or <<R>> with arrays and maps, however, leads
   to some sublime results.

   When an array or map is tagged, that item is embraced with the usual
   tag format: "<<O>>(<item>)" or "<<R>>(<item>)".  This syntax
   indicates the presence of the tag on the outer item.  Inner items in
   the array or keys in the map are noted in Section 5 form, but are not
   individually tagged on-the-wire when the tag is the same as the outer
   tag, because like-tagging is a coding error.

   An array or map that involves a stack of tags is notated the usual
   way.  For example, the CBOR diagnostic notation of a map of OIDs to
   URIs is:

   6(32({0.9.2342.7776.1: "http://example.com/",
         0.9.2342.7776.2: "ftp://ftp.example.com/pub/"}))

       Figure 11: Map of OIDs to URIs, in CBOR Diagnostic Diagnostic
                                 Notation





Bormann & Leonard        Expires January 1, 2017               [Page 14]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


8.  Applications and Examples of OIDs

8.1.  GPU Farm

   Consider a 3-dimensional OID array, indicating certain operations to
   perform on a matrix of values in a GPU farm.  Default operations are
   under the OID arc 0.9.2342.7777 (such as .1, .2, .124, etc.); the arc
   0.9.2342.7777 itself represents the identity operation.  Certain
   cryptographic operations like SHA-256 hashing
   (2.16.840.1.101.3.4.2.1) are also permitted.  The resulting notation
   would be:

   7([[[.1,   .2,   .3],
       [.1,   .2,   .3],
       [.1,   .2,   .3]],
      [[.124, .125, .126],
       [.95,  .96,  .97 ],
       [.11,  .12,  .13 ]],
      [[h'',  .6,   .4.2],
       [.6,   h'',  .4.2],
       [.6,   2.16.840.1.101.3.4.2.1, h'']]])

    Figure 12: GPU Farm Matrix Operations, in CBOR Diagnostic Notation




























Bormann & Leonard        Expires January 1, 2017               [Page 15]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   c7                                   # tag(7)
      83                                # array(3)
         83                             # array(3)
            83                          # array(3)
               41 01                    # .1 (2)
               41 02                    # .2 (2)
               41 03                    # .3 (2)
            83                          # array(3)
               41 01                    # .1 (2)
               41 02                    # .2 (2)
               41 03                    # .3 (2)
            83                          # array(3)
               41 01                    # .1 (2)
               41 02                    # .2 (2)
               41 03                    # .3 (2)
         83                             # array(3)
            83                          # array(3)
               41 7c                    # .124 (2)
               41 7d                    # .125 (2)
               41 7e                    # .126 (2)
            83                          # array(3)
               41 5f                    # .95 (2)
               41 60                    # .96 (2)
               41 61                    # .97 (2)
            83                          # array(3)
               41 0b                    # .11 (2)
               41 0c                    # .12 (2)
               41 0d                    # .13 (2)
         83                             # array(3)
            83                          # array(3)
               40                       # (empty) (1)
               41 06                    # .6 (2)
               42 0402                  # .4.2 (3)
            83                          # array(3)
               41 06                    # .6 (2)
               40                       # (empty) (1)
               42 0402                  # .4.2 (3)
            83                          # array(3)
               41 06                    # .6 (2)
               c6 49 608648016503040201 # 2.16.840.1.101.3.4.2.1 (10)
               40                       # (empty) (1)

         Figure 13: GPU Farm Matrix Operations, in CBOR (76 bytes)








Bormann & Leonard        Expires January 1, 2017               [Page 16]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


8.2.  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 (0.9.2342.19200300.100.1.48)    | Pershing Square    |
   +----------------------------------------------+--------------------+

                 Table 3: Example X.500 Distinguished Name

   Table 3 has four RDNs.  The country and street RDNs are single-
   valued.  The second and fourth RDNs are multi-valued.

   The equivalent representations in CBOR diagnostic notation and CBOR
   are:

   6([{ 2.5.4.6: "US" },
      { 2.5.4.7: "Los Angeles", 2.5.4.8: "CA", 2.5.4.17: "90013" },
      { 2.5.4.9: "532 S Olive St" },
      { 2.5.4.15: "Public Park",
        0.9.2342.19200300.100.1.48: "Pershing Square" }])

        Figure 14: Distinguished Name, in CBOR Diagnostic Notation

   6([{ 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 15: Distinguished Name, in CBOR Diagnostic Notation (RFC 7049
                                   only)








Bormann & Leonard        Expires January 1, 2017               [Page 17]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   c6                                         # tag(6)
      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 16: Distinguished Name, in CBOR (108 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.)

   For reference, the [RFC4514] LDAP string encoding of such data would
   be:

   buildingName=Pershing Square+businessCategory=Public Park,
   street=532 S Olive St,l=Los Angeles+postalCode=90013+st=CA,c=US

    Figure 17: Distinguished Name, in LDAP String Encoding (121 bytes)

9.  Binary Internet Messages and MIME Entities

   Section 2.4.4.3 of [RFC7049] assigns tag 36 to "MIME messages
   (including all headers)" [RFC2045], and prescribes UTF-8 strings,
   without further elaboration.  Actually MIME encircles several




Bormann & Leonard        Expires January 1, 2017               [Page 18]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   different formats, and is not limited to UTF-8 strings.  This section
   updates tag 36.

9.1.  CBOR Byte String and Binary MIME

   Tag 36 is to be used with byte strings.  When the tagged item is a
   byte string, any octet can be used in the content.  Arbitrary octets
   are supported by [RFC2045] and can be supported in protocols such as
   SMTP using BINARYMIME [RFC3030].

   A conforming implementation that purports to process tag 36-tagged
   items, MUST accept byte strings as well as UTF-8 strings.  Byte
   strings, rather than UTF-8 strings, SHOULD be considered the default.
   (While binary Content-Transfer-Encoding is not particularly common as
   of this writing, 8-bit encoding is, and it is foreseeable that many
   8-bit encoded messages will still have charsets other than UTF-8.)

9.2.  Internet Messages, MIME Messages, and MIME Entities

   Definitions: "MIME message" is not explicitly defined in [RFC2045],
   but a careful read suggests that a MIME message is: "either a
   (complete or "top-level") RFC 822 message being transferred on a
   network, or a message encapsulated in a body of type "message/rfc822"
   or "message/partial"," that also contains MIME header fields, namely,
   MIME-Version field, which MUST be present (Section 4 of [RFC2045].
   Other MIME header fields such as Content-Type and Content-Transfer-
   Encoding are assumed to be their [RFC2045] default values, if not
   present in the data.

   When the contents have a From field (a type of "originator address
   field") and a Date field (the lone "origination date field")
   (Section 3.6 of [RFC5322]), the item is concluded to have a Content-
   Type of message/rfc822 or message/global, as appropriate, except as
   otherwise specified in this section.

   (TBD: Do we need a separate tag for a MIME entity?)  (Alternate
   proposal: When the tagged data does not include a MIME-Version field
   or other fields required by RFC822 (5322) (e.g., no From field), it
   is presumed to be a MIME entity, rather than a MIME message.
   Therefore, it has no top-level content-type: instead it is simply a
   "MIME entity", consisting of one element, whose Content-Type is the
   content of the Content-Type header field, if present, or the
   [RFC2045] default of "text/plain; charset=us-ascii", if absent.
   Content-Transfer-Encoding SHALL be assumed to be 8bit when the CBOR
   item is a UTF-8 string, and SHALL be assumed to be binary when the
   CBOR item is a byte string.  (Or should all be considered CTE:
   binary?)  And, when the tagged data has RFC822 required fields but no




Bormann & Leonard        Expires January 1, 2017               [Page 19]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   MIME-Version, shall we assume it's a MIME entity, or shall we assume
   it's an Internet message that does not conform to MIME?)

   Content that has no headers whatsoever is valid, and implementations
   that process tag 36 MUST permit this case: in such a case, the data
   starts with CRLF CRLF, followed by the body.  In such a case, the
   content is assumed to be a MIME entity of Content-Type "text/plain;
   charset=us-ascii", and not an RFC822 (RFC5322) Internet message.
   (TBD: Confirm.)

9.3.  Netnews, HTTP, and SIP Messages

   Other message types that are MIME-related are message/news, message/
   http, and message/sip.

   [RFC5537] specifies that message/news is deprecated (marked as
   obsolete) and that message/rfc822 SHOULD be used in its place;
   presumably this also extends to message/global over time.  Netnews
   Article Format [RFC5536] is a strict subset of Internet Message
   Format; it can be detected by the presence of the six mandatory
   header fields: Date, From, Message-ID, Newsgroups, Path, and Subject.
   (Newsgroups and Path fields are specific to Netnews.)

   message/http [RFC7230] is the media type for HTTP requests and
   responses.  It can be detected by analyzing the first line of the
   body, which is an HTTP Start Line (Section 3.1 of [RFC7230]): it does
   not conform to the syntax of an Internet Message Format header field.
   The optional parameter "msgtype" can be inferred from the Start Line.
   Implementers need to be aware that the default character encoding for
   message/http is ISO-8859-1, not UTF-8.  Therefore, implementations
   SHOULD NOT encode HTTP messages with CBOR UTF-8 strings.

   Similarly, message/sip [RFC3261] is the media type of SIP request and
   response messages.  It can be detected by analyzing the first line of
   the body, which is a SIP start-line (Section 7.1 of [RFC3261]): it
   does not conform to the syntax of an Internet Message Format header
   field.  The optional parameter can be inferred from the start-line.

9.4.  Other Messages

   The CBOR binary or UTF-8 string MAY contain other types of messages.
   An implementation MAY send such a message as a MIME entity with the
   Content-Type field appropriately set, or alternatively, MAY send the
   message at the top-level directly.  However, if a purported message
   type is ambiguous with a message/rfc822 (or message/global) message,
   a receiver SHALL treat the message as message/rfc822 (or message/
   global).  If a purported message type is ambiguous with a MIME entity




Bormann & Leonard        Expires January 1, 2017               [Page 20]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   (and unambiguously not message/rfc822 or message/global), a receiver
   SHALL treat the message as a MIME entity.

10.  Applications and Examples of Messages and Entities

   Tag 36 is the RECOMMENDED way to convey data with MIME-related
   metadata, including messages (which may or may not actually be MIME-
   enabled) and MIME entities.

   Example 1: A legacy RFC822 message is encoded as a UTF-8 string or
   byte string with tag 36.  The contents have From, To, Date, and
   Subject header fields, two CRLFs, and a single line "Hello World!",
   terminated with a CRLF.

   Example 2a: A [RFC5280] certificate is encoded as a byte string with
   tag 36.  The contents are comprised of "Content-Type: application/
   pkix-cert", two CRLFs, and the DER encoding of the certificate.  (The
   "Content-Transfer-Encoding: binary" header is not necessary.)

   Example 2b: A [RFC5280] certificate is encoded as a UTF-8 string or
   byte string with tag 36.  The contents are comprised of "Content-
   Type: application/pkix-cert", a CRLF, "Content-Transfer-Encoding:
   base64", two CRLFs, and the base64 encoding of the DER encoding of
   the certificate, conforming to Section 6.8 of [RFC2045].  In
   particular, base64 lines are limted to 76 characters, separated by
   CRLF, and the final line is supposed to end with CRLF.  Needless to
   say, this is not nearly as efficient as Example 2a.

11.  X.690 Series Tags

   [[NB: Carsten probably won't like this.  Plan on removing this
   section.  It is mainly provided to contrast with Section 10.]]

   It is foreseeable that CBOR applications will need to send and
   receive ASN.1 data, for example, for legacy or security applications.
   While a native representation in CBOR is preferred, preserving the
   data in an ASN.1 encoding may be necessary, for example, to preserve
   cryptographic verification.  A tag <<X>> is allocated for this
   purpose.

   When the tagged item is a byte string, the byte string contents are
   encoded according to [X.690], i.e., BER, CER, or DER.  CBOR
   implementations are not required to validate conformance of the
   contained data to [X.690].

   When the tagged item is an array with 3 items:





Bormann & Leonard        Expires January 1, 2017               [Page 21]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   1.  The first item SHALL be an OID (with tag <<O>> omitted; it SHALL
       NOT be a relative OID), indicating the ASN.1 module containing
       the type of the PDU.  [[NB: this is a good example of a non-
       trivial structure in which an element is well-defined to be an
       OID, which has a tag.  Is the CBOR philosophy to tag the item, or
       omit the tag on the item, when the item's semantics are already
       fixed by the outer tag?  Similar situations can apply to tag 32
       (URI), etc.]]

   2.  The second item SHALL be a UTF-8 string indicating the ASN.1
       value's _type reference name_ (Clause 3.8.88 of [X.680])
       conforming to the "typereference" production (Clause 12.2 of
       [X.680]).

   3.  The third item SHALL be a byte string, whose contents are encoded
       per the prior paragraph.

   (TBD: Use of tagged UTF-8 string is reserved for ASN.1 textual
   formats such as XER and ASN.1 value notation?  Probably not
   necessary.  Just omit.)

   Implementation note: DER-encoded items are always definite-length, so
   there is very little reason to use CBOR byte string indefinite
   encoding when encoding such DER-encoded items.

   Example: A [RFC5280] certificate can be encoded:

   1.  as a byte string with tag <<X>>, or

   2.  as an array with tag <<X>>, with three elements:

       (1)  a byte string "h'2B 06 01 05 05 07 00 12'", which is the BER
            encoding of 1.3.6.1.5.5.7.0.18,

       (2)  a UTF-8 string "Certificate", and

       (3)  a byte string containing the DER encoding of the
            certificate.

12.  Regular Expression Clarification

   (TODO: better specify conformance to actual regular expression
   standards with tag 35.  PCRE and JavaScript/ECMAScript regular
   expressions are very different; [RFC7049] is not specific enough
   about this.)






Bormann & Leonard        Expires January 1, 2017               [Page 22]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


13.  Set and Multiset Technique

   CBOR has no native type for a set, which is an arbitrary unordered
   collection of items.  The following technique is RECOMMENDED to
   express set and multiset semantics concisely in native CBOR data.

   In computer science, a _set_ is a collection of distinct items; there
   is no ordering to the items.  Thus, implementations can optimize set
   storage in many ways that are not available with ordered elements in
   arrays.  Sets can be stored in hashtables, bit fields, trees, or
   other abstract data types.

   In computer science, a _multiset_ allows multiple instances of a
   set's elements.  Put another way, each distinct item has a
   cardinality property indicating the number of these items in the
   multiset.

   To store items in a set or multiset, it is RECOMMENDED to store the
   CBOR items as keys in a map; the values SHALL all be positive
   integers (major type 0, value/additional information greater than or
   equal to 1).  In the special case of a set, the values SHALL be the
   integer 1.  This technique has no special tag associated with it.  As
   with arrays that schemas classify as "records" (i.e., arrays with
   positionally defined elements), schemas are likewise free to classify
   maps as sets in particular instances.

14.  Fruits Basket Example

   Consider a basket of fruits.  The basket can contain any number of
   fruits; each fruit of the same species is considered identical.  This
   basket has two apples, four bananas, six pears, and one pineapple:

   {"\u{1F34E}": 2, "\u{1F34C}": 4,
    "\u{1F350}": 6, "\u{1F34D}": 1}

           Figure 18: Fruits Basket in CBOR Diagnostic Notation















Bormann & Leonard        Expires January 1, 2017               [Page 23]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   A4                       # map(4)
      64                    # text(4)
         f09f8d8e           # "\u{1F34E}"
      02                    # unsigned(2)
      64                    # text(4)
         f09f8d8c           # "\u{1F34C}"
      04                    # unsigned(4)
      64                    # text(4)
         f09f8d90           # "\u{1F350}"
      06                    # unsigned(6)
      64                    # text(4)
         f09f8d8d           # "\u{1F34D}"
      01                    # unsigned(1)

                Figure 19: Fruits Basket in CBOR (33 bytes)

   [[TODO: Consider a Merkle Tree example: set of sets of sets of sets
   of things. ???]]

15.  IANA Considerations

   (This section to be edited by the RFC editor.)

15.1.  CBOR Tags

   IANA is requested to assign the CBOR tags in Table 4, with the
   present document as the specification reference.

   +----------+-------------+------------------------------------------+
   | Tag      | Data Item   |                                Semantics |
   +----------+-------------+------------------------------------------+
   | 6<<TBD>> | byte string |    ASN.1 object identifier (absolute, in |
   |          |             |                            BER encoding) |
   | 7<<TBD>> | byte string |    ASN.1 object identifier (relative, in |
   |          |             |                            BER encoding) |
   +----------+-------------+------------------------------------------+

                         Table 4: Values for Tags

15.2.  Discussion

   (This subsection to be removed by the RFC editor.)

   The space for single-byte tags in CBOR (0..23) is severely limited.
   It is not clear that the benefits of encoding OIDs/relative OIDs with
   one less byte per instance outweigh the consumption of two values in
   this code point space.




Bormann & Leonard        Expires January 1, 2017               [Page 24]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   Procedurally, this space is also reserved for standards action.

   An alternative would be to go for the specification required space,
   e.g. tag number 40 for <<O>> and tag number 41 for <<R>>.  As an
   example this would change Figure 2 into:

   d8 28                            # tag(40)
      49                            # bytes(9)
         60 86 48 01 65 03 04 02 01 #

     Figure 20: SHA-256 OID in cbor (using specification required tag)

15.3.  Pre-Existing Tags

   (TODO: complete.)  IANA is requested to modify the registrations for
   the following CBOR tags:

   Tag 36.

15.4.  New Tags

   (TODO: complete.)

16.  Security Considerations

   The security considerations of RFC 7049 apply.

   The encodings in Clauses 8.19 and 8.20 of [X.690] are extremely
   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 integers of the sub-
   identifiers need to be handled as unlimited-range integers (cf.
   Figure 4).





Bormann & Leonard        Expires January 1, 2017               [Page 25]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


16.1.  Conversions Between BER and Dotted Decimal Notation

   [PKILCAKE] uncovers exploit vectors for the illegal values above, as
   well as for cases in which conversion to or from the dotted decimal
   notation goes awry.  Neither [X.660] nor [X.680] place an upper bound
   on the range of unsigned integer values for an arc; the integers are
   arbitrarily valued.  An implementation SHOULD NOT attempt to convert
   each component using a fixed-size accumulator, as an attacker will
   certainly be able to cause the accumulator to overflow.  Compact and
   efficient techniques for such conversions, such as the double dabble
   algorithm [DOUBLEDABBLE] are well-known in the art; their application
   to this field is left as an exercise to the reader.

17.  References

17.1.  Normative References

   [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,
              <http://www.rfc-editor.org/info/rfc2045>.

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

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI
              10.17487/RFC5322, October 2008,
              <http://www.rfc-editor.org/info/rfc5322>.

   [RFC5536]  Murchison, K., Ed., Lindsey, C., and D. Kohn, "Netnews
              Article Format", RFC 5536, DOI 10.17487/RFC5536, November
              2009, <http://www.rfc-editor.org/info/rfc5536>.

   [RFC5537]  Allbery, R., Ed. and C. Lindsey, "Netnews Architecture and
              Protocols", RFC 5537, DOI 10.17487/RFC5537, November 2009,
              <http://www.rfc-editor.org/info/rfc5537>.

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



Bormann & Leonard        Expires January 1, 2017               [Page 26]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing", RFC
              7230, DOI 10.17487/RFC7230, June 2014,
              <http://www.rfc-editor.org/info/rfc7230>.

   [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.

   [X.680]    International Telecommunications Union, "Information
              technology -- Abstract Syntax Notation One (ASN.1):
              Specification of basic notation", ITU-T Recommendation
              X.680, August 2015.

   [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.

17.2.  Informative References

   [CCITT.X208.1988]
              International Telephone and Telegraph Consultative
              Committee, "Specification of Abstract Syntax Notation One
              (ASN.1)", CCITT Recommendation X.208, November 1988.

   [DOUBLEDABBLE]
              Gao, S., Al-Khalili, D., and N. Chabini, "An improved BCD
              adder using 6-LUT FPGAs", IEEE 10th International New
              Circuits and Systems Conference (NEWCAS 2012), pp. 13-16,
              DOI: 10.1109/NEWCAS.2012.6328944, June 2012.

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

   [PKILCAKE]
              Kaminsky, D., Patterson, M., and L. Sassaman, "PKI Layer
              Cake: New Collision Attacks Against the Global X.509
              Infrastructure", FC 2010, Lecture Notes in Computer
              Science 6052 289-303, DOI: 10.1007/978-3-642-14577-3_22,
              January 2010, <http://dl.acm.org/citation.cfm?id=2163593>.






Bormann & Leonard        Expires January 1, 2017               [Page 27]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


   [RFC3030]  Vaudreuil, G., "SMTP Service Extensions for Transmission
              of Large and Binary MIME Messages", RFC 3030, DOI
              10.17487/RFC3030, December 2000,
              <http://www.rfc-editor.org/info/rfc3030>.

   [RFC4514]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
              (LDAP): String Representation of Distinguished Names", RFC
              4514, DOI 10.17487/RFC4514, June 2006,
              <http://www.rfc-editor.org/info/rfc4514>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

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

   [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,
              <http://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.

   [X.681]    International Telecommunications Union, "Information
              technology -- Abstract Syntax Notation One (ASN.1):
              Information object specification", ITU-T Recommendation
              X.681, August 2015.

Appendix A.  Changes from -02 to -03

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

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

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

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




Bormann & Leonard        Expires January 1, 2017               [Page 28]


Internet-Draft          CBOR Tags for ASN.1 OIDs               June 2016


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

   o  Added technique for representing sets and multisets.

   o  Added references and fixed typos.

Authors' Addresses

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

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


   Sean Leonard
   Penango, Inc.
   5900 Wilshire Boulevard
   21st Floor
   Los Angeles, CA  90036
   USA

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























Bormann & Leonard        Expires January 1, 2017               [Page 29]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/