draft-miller-json-constrained-representation-00.txt

Network Working Group                                          J. Miller
Internet-Draft
Intended status: Standards Track                          P. Saint-Andre
Expires: July 17, 2018                                  January 13, 2018


                 JSON Constrained Representation (JCOR)
            draft-miller-json-constrained-representation-00

Abstract

   This specification addresses the challenges of using JavaScript
   Object Notation (JSON) with constrained devices by providing a
   standard set of mapping rules to Concise Binary Object Representation
   (CBOR) that preserve all semantic information, such that the original
   JSON string can be identically re-created.  JSON Constrained
   Representation (JCOR) can also be used by devices as a native data
   format, which can then be represented as JSON when necessary for
   diagnostics, compatibility, and ease of integration with higher-level
   systems.

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 July 17, 2018.

Copyright Notice

   Copyright (c) 2018 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
   (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



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   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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  CBOR Encoding . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Structured Types  . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Primitive Types . . . . . . . . . . . . . . . . . . . . .   5
       2.2.1.  Boolean and Null  . . . . . . . . . . . . . . . . . .   5
       2.2.2.  Numbers . . . . . . . . . . . . . . . . . . . . . . .   5
       2.2.3.  Strings . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Reference Sets  . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Canonical Form  . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Formatting-only Whitespace  . . . . . . . . . . . . . . .   7
     4.2.  String Escapes  . . . . . . . . . . . . . . . . . . . . .   9
   5.  Constrained API . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  JSON  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
       6.1.1.  Input . . . . . . . . . . . . . . . . . . . . . . . .  10
       6.1.2.  Optimized JCOR Encoding . . . . . . . . . . . . . . .  11
       6.1.3.  Un-optimized JCOR Encoding  . . . . . . . . . . . . .  13
     6.2.  JSON Web Token  . . . . . . . . . . . . . . . . . . . . .  15
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  CBOR Tags . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.2.  JCOR Reference Sets Registry  . . . . . . . . . . . . . .  17
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  18
     9.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Although JavaScript Object Notation (JSON) [RFC7159] has been widely
   adopted in traditional networking and software environments, its use
   in embedded and constrained environments has been more limited
   because of the minimal storage and network capacities inherent in
   low-cost and low-power devices (see [RFC7228]).

   This specification addresses the challenges of using JSON with
   constrained devices by defining a set of mapping rules to Concise
   Binary Object Representation (CBOR) [RFC7049] that preserve all



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   semantic information, such that the original JSON string can be
   identically re-created.  JSON Constrained Representation (JCOR) can
   be used directly by devices as a native data format, which can be
   represented as JSON when necessary for diagnostics, compatibility,
   and ease of integration with higher-level systems.

   A primary goal of JCOR is to enable all JSON Object Signing and
   Encryption (JOSE) standards ([RFC7515], [RFC7516], [RFC7517],
   [RFC7518], [RFC7519]) to be used unmodified in constrained
   environments.  One result is that OpenID Connect [1] (which utilizes
   JSON Web Tokens [RFC7519]) can more easily be adopted as an identity
   management solution for the Internet of Things.

   JCOR is designed to leverage, not replace, CBOR.  Instead, JCOR
   specifies rules for re-coding JSON structures by mapping them to
   their CBOR parallels whenever possible, and then increasing the
   efficiency through introspection and replacement of well-known
   strings with compact references.

   All transcoding software MUST operate on a UTF-8 JSON string whenever
   complete round-trip compatibility to and from JSON is required,
   including mapping any contained non-structural whitespace (such as
   with JWTs for signature validation).  If a transcoder is only
   operating with an already parsed JSON value (the result of
   "JSON.parse()" in JavaScript for instance), the round-trip can only
   guarantee semantic compatibility of the values as represented in that
   parsed context (only the JavaScript object will always match).

   A significant reduction in space is also provided in JCOR when the
   device and application contexts can make use of built-in or shared
   UTF-8 string references.  These references provide a mapping of
   common JSON string values to an integer that used to replace the
   string in the resulting CBOR during re-coding.  JSON string values
   are also introspected for data that has a more compact CBOR type
   (such as base64url and hexadecimal encoding).

   The use of this specification can ensure that a UTF-8 JSON string
   before and after re-coding will be byte-for-byte identical across
   implementations, whereas the CBOR encoding is not designed to have
   this property and MAY vary based on implementation choices and
   reference sets available.  There are basic API rules defined for
   constrained software such that directly accessing the CBOR data
   values will always provide a uniform view to an application across
   variations in the underlying CBOR representation.







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1.1.  Terminology

   Many terms used in this document are defined in the specifications
   for JSON [RFC7159] and CBOR [RFC7049].  This specification defines
   the following additional terms:

   o  Constrained JSON Tag

      *  The CBOR tag registered in this specification to indicate an
         array that contains JSON data encoded as CBOR according to this
         specification.

   o  Reference

      *  A pointer within JCOR data that refers to a well-known UTF-8
         string by using a CBOR byte string of length one, where the
         byte value is the lookup identifier for the Reference.

   o  Reference Set

      *  A CBOR array of UTF-8 strings that are used to replace any
         Reference within any JCOR data, where the Reference identifier
         is the array offset to the replacement string and the first
         position in the array identifies the Reference Set.

   o  Canonical Hints

      *  A CBOR array of integers that indicate positional offsets for
         JSON string escape sequences or structural formatting
         whitespace strings (, "\n", "\r", and "\t") such that when any
         CBOR encoded data is stringified into JSON it can also
         optionally be corrected to exactly match the original JSON
         string.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  CBOR Encoding

   JCOR encodes JSON data types to CBOR data types as described in the
   following sections.

2.1.  Structured Types

   JSON defines two structured types: arrays and objects.  These are
   serialized to CBOR major type 4 (array) and type 5 (map),




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   respectively.  Ordering of key/value pairs in JSON objects and CBOR
   maps MUST be preserved.

2.2.  Primitive Types

2.2.1.  Boolean and Null

   The JSON literal names "false", "true", and "null" are serialized to
   the CBOR major type 7 simple values 20, 21, and 22 respectively.

2.2.2.  Numbers

   A JCOR encoder attempts to encode a JSON number as a CBOR unsigned
   integer (type 0), negative integer (type 1), or float (type 7) and
   then test for compatibility by round-tripping the CBOR data item back
   to a JSON number.  If the resulting JSON number is not equivalent to
   the input number, the encoder MUST instead encode it as a CBOR
   Bigfloat (tag 5).

   The JSON exponent value (if any) is encoded as a CBOR exponent (tag
   4).  If the contained "e" symbol is upper case in JSON, the "Upper
   Case Modifier" tag defined below MUST be included.

2.2.3.  Strings

   A JSON string is normally encoded as an un-escaped CBOR UTF-8 string
   (type 3), i.e., as a series of UTF-8 [RFC3629] characters (e.g., the
   word "one" is encoded as "6F6E65") without any backspace escaping for
   control or unicode characters.

2.2.3.1.  Base64 / Base16 Encoded

   A JCOR encoder MUST round-trip test all JSON strings for possible
   encodings (base64url, base64, and hexadecimal) by attempting to
   decode and re-encode them.  If identical byte strings result, the
   decoded value is tagged in CBOR with the encoding format (tags 21,
   22, and 23).  For hexadecimal, the "Upper Case Modifier" tag defined
   below MUST be included if the hexadecimal letters A-F are upper case
   in the original JSON string.

   A JCOR encoder MUST perform introspection on the resulting decoded
   byte string to determine if it begins with a JSON structure byte of
   '{' or '['.  The encoder SHOULD then round-trip test the string as a
   possible JSON object or array so that it can encode the string more
   efficiently into a CBOR data item instead of a byte string (this
   pattern is common in the JOSE specification).





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3.  Reference Sets

   The Constrained JSON Tag is followed by an array whose second item
   identifies the Reference Set used in the data.  This is either a
   Reference Set identifier or an array that defines an inline Reference
   Set.

   A Reference Set identifier is a unique integer that maps to a
   Reference Set known to applications using the set.  Public, well-
   known reference sets can be registered as described in the IANA
   Considerations section of this document.

   The Reference Set definition is encoded as a JCOR array, where the
   first value is the Reference Set identifier followed by all of the
   UTF-8 string keys.  A key's position in the array is the byte value
   with which it is replaced.

   Any Reference Set can include another Reference Set by encoding the
   second set's identifer in the JCOR array that defines the first
   Reference Set.  Any byte strings in the definition array are then
   replaced with the key from the references contained in the second
   Reference Set.

   JSON UTF-8 strings representing keys or values are first checked
   against all active references (if any) for possible replacement.  A
   replacement is always a CBOR byte string (type 2) of length 1, where
   the single byte represents the index value of the key in the
   references array from 1-255.  Value 0 and byte lengths greater than 1
   are reserved for future use.

   When a JCOR decoder generates JSON values from CBOR and it encounters
   a CBOR byte string (type 2), single byte value MUST match the array
   offset of the active references to be used as the replacement for
   that byte string.

   The following is the encoded form of a Reference Set as defined by
   the JSON array of "[1,"map","value","array","one","two","three","bool
   ","neg","simple","ints"]":













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                  D4                       # tag(20)
                     81                    # array(1)
                        8B                 # array(11)
                           01              # unsigned(1)
                           63              # text(3)
                              6D6170       # "map"
                           65              # text(5)
                              76616C7565   # "value"
                           65              # text(5)
                              6172726179   # "array"
                           63              # text(3)
                              6F6E65       # "one"
                           63              # text(3)
                              74776F       # "two"
                           65              # text(5)
                              7468726565   # "three"
                           64              # text(4)
                              626F6F6C     # "bool"
                           63              # text(3)
                              6E6567       # "neg"
                           66              # text(6)
                              73696D706C65 # "simple"
                           64              # text(4)
                              696E7473     # "ints"

4.  Canonical Form

   This specification directly supports use-cases such as JSON Web
   Tokens ([RFC7518]) where the canonical form of UTF-8 JSON strings
   always needs to be available for validation.  This is accomplished by
   optionally including any additional information to reproduce the
   exact UTF-8 string as an array of Canonical Hints included with the
   Constrained JSON Tag.

   These hints are not typically necessary as most machine-generated
   JSON does not include any extra insignificant bytes by default, even
   when included they do not need to be processed unless the original
   canonical form is requested.  When required, these additional hints
   also take a highly constrained form and are independently additive to
   the contained CBOR data values such that those values remain uniform
   to any constrained application.

4.1.  Formatting-only Whitespace

   When a Constrained JSON tag is present and the first item in the
   tagged array is a CBOR structure (map or array), a third optional
   item in the tagged array is a set of canonical whitespace hints for




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   any non-structural whitespace characters contained in the original
   UTF-8 representation of the JSON object or array.

   o  Whitespace hints are contained in an array of integers that
      indicate offsets of the locations of whitespace characters in an
      original JSON string, and lookup values identifying which
      whitespace characters were there.

   o  Each offset integer is relative to the position of the previous
      offset such that all integers are of small values.

   o  A negative integer offset indicates a single ASCII space character
      (0x20) at the offset of the positive value of that integer.

   o  An unsigned integer offset is followed by another integer, where
      unsigned values (0-23) indicate a whitespace string in the pre-
      defined lookup table, and negative values specify the number of
      space characters (0x20) to repeat.

   o  When re-inserting whitespace characters to a JSON string, the
      array MUST be applied sequentially so that each new offset matches
      the original JSON string position.

   The following 24 whitespace character hexadecimal sequences are used
   as the shared reference lookup table by row (0-23) when processing
   whitespace hints.  This table is constructed to minimize the number
   of references commonly required while also allowing any possible
   whitespace character sequences to be identified.























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                      0a
                      0a2020
                      0a20202020
                      0a202020202020
                      0a2020202020202020
                      0a20202020202020202020
                      0a202020202020202020202020
                      0a2020202020202020202020202020
                      09
                      0a09
                      0a0909
                      0a090909
                      0a09090909
                      0a0909090909
                      0a090909090909
                      0a09090909090909
                      0a0909090909090909
                      0d
                      0d0a
                      0d0a2020
                      0d0a20202020
                      0d0a09
                      0d0a0909
                      0d0a090909

4.2.  String Escapes

   JSON string values MAY contain escaped characters (as defined in
   Section 7 of [RFC7159]) that become un-escaped in the process of re-
   coding them into a CBOR UTF-8 string.  When the canonical form is
   being preserved and any escaped characters are detected in the
   process of converting them from JSON to CBOR, those string values
   MUST be individually tagged as Constrained JSON where the first
   element in the tagged array is the CBOR UTF-8 string value and the
   second value is an array of positional integers similar to the
   whitespace hints.

   When the position is an unsigned integer it indicates the UTF-8
   character at that position is to be escaped with the "\uXXXX" form
   with lower-case hexadecimal characters.  When it is a negative
   integer it indicates that it is to be escaped with the "\X" form and
   MUST be in the set of JSON escaped control characters.

   When the original escaping in the "\uXXXX" form was with upper case
   hexadecimal characters the entire array MUST be tagged with Upper
   Case Modifier.  In the unlikely case that the original escaping
   contained mixed-case hexadecimal, then the positional integer will
   instead itself be an array of length two with the position being the



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   first element and a 4-byte UTF-8 string of the mixed-case hexadecimal
   value being the second element.

5.  Constrained API

   In order to ease the use of JCOR in constrained environments, an
   implementation SHOULD make data values available both as native CBOR
   types and as JSON strings; this enables a constrained application to
   choose either format regardless of how the data is represented in
   CBOR.

   For example, when the original JSON string value is encoded as a CBOR
   base64url tag plus byte string, a constrained application accessing
   the value as a string MUST receive the base64url encoded value and
   not the decoded byte value.  If the constrained application instead
   accesses the value as a byte array it MUST get the decoded value if
   available.

   The representation of the value in CBOR SHOULD NOT alter behavior of
   the application, a string value encoded as tag plus byte array SHOULD
   NOT be used as an indication that it is a binary value and only the
   application can make this determination based on external context.

6.  Examples

6.1.  JSON

6.1.1.  Input

   Consider the following JSON as input to a JCOR encoder.





















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                           {
                             "map": "value",
                             "array": [
                               "one",
                               "two",
                               "three",
                               42
                             ],
                             "bool": true,
                             "neg": -42,
                             "simple": [
                               false,
                               null,
                               ""
                             ],
                             "ints": [
                               0,
                               1,
                               23,
                               24,
                               255,
                               256,
                               65535,
                               65536,
                               4294967295,
                               4294967296,
                               281474976710656,
                               -281474976710656
                             ]
                           }

6.1.2.  Optimized JCOR Encoding

   An optimized encoding would remove whitespace and use a Reference
   Set. Here the references would be:

   "[1,"map","value","array","one","two","three","bool","neg","simple","
   ints"]"

   The resulting JCOR encoding is 90 bytes compared to 318 bytes for the
   JSON input.










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        D4                              # tag(20)
           82                           # array(2)
              A6                        # map(6)
                 41                     # bytes(1)
                    01                  # "\x01"
                 41                     # bytes(1)
                    02                  # "\x02"
                 41                     # bytes(1)
                    03                  # "\x03"
                 84                     # array(4)
                    41                  # bytes(1)
                       04               # "\x04"
                    41                  # bytes(1)
                       05               # "\x05"
                    41                  # bytes(1)
                       06               # "\x06"
                    18 2A               # unsigned(42)
                 41                     # bytes(1)
                    07                  # "\a"
                 F5                     # primitive(21)
                 41                     # bytes(1)
                    08                  # "\b"
                 38 29                  # negative(41)
                 41                     # bytes(1)
                    09                  # "\t"
                 83                     # array(3)
                    F4                  # primitive(20)
                    F6                  # primitive(22)
                    60                  # text(0)
                                        # ""
                 41                     # bytes(1)
                    0A                  # "\n"
                 8C                     # array(12)
                    00                  # unsigned(0)
                    01                  # unsigned(1)
                    17                  # unsigned(23)
                    18 18               # unsigned(24)
                    19 00FF             # unsigned(255)
                    19 0100             # unsigned(256)
                    19 FFFF             # unsigned(65535)
                    1A 00010000         # unsigned(65536)
                    1B 00000000FFFFFFFF # unsigned(4294967295)
                    1B 0000000100000000 # unsigned(4294967296)
                    1B 0001000000000000 # unsigned(281474976710656)
                    3B 0000FFFFFFFFFFFF # negative(281474976710655)
              01                        # unsigned(1)





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6.1.3.  Un-optimized JCOR Encoding

   An un-optimized encoding would not use a Reference Set and would
   preserve whitespace.  The un-optimized encoding would reduce the data
   from the 318 bytes (JSON) to 187 bytes (JCOR).

        D4                              # tag(20)
           83                           # array(3)
              A6                        # map(6)
                 63                     # text(3)
                    6D6170              # "map"
                 65                     # text(5)
                    76616C7565          # "value"
                 65                     # text(5)
                    6172726179          # "array"
                 84                     # array(4)
                    63                  # text(3)
                       6F6E65           # "one"
                    63                  # text(3)
                       74776F           # "two"
                    65                  # text(5)
                       7468726565       # "three"
                    18 2A               # unsigned(42)
                 64                     # text(4)
                    626F6F6C            # "bool"
                 F5                     # primitive(21)
                 63                     # text(3)
                    6E6567              # "neg"
                 38 29                  # negative(41)
                 66                     # text(6)
                    73696D706C65        # "simple"
                 83                     # array(3)
                    F4                  # primitive(20)
                    F6                  # primitive(22)
                    60                  # text(0)
                                        # ""
                 64                     # text(4)
                    696E7473            # "ints"
                 8C                     # array(12)
                    00                  # unsigned(0)
                    01                  # unsigned(1)
                    17                  # unsigned(23)
                    18 18               # unsigned(24)
                    19 00FF             # unsigned(255)
                    19 0100             # unsigned(256)
                    19 FFFF             # unsigned(65535)
                    1A 00010000         # unsigned(65536)
                    1B 00000000FFFFFFFF # unsigned(4294967295)



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                    1B 0000000100000000 # unsigned(4294967296)
                    1B 0001000000000000 # unsigned(281474976710656)
                    3B 0000FFFFFFFFFFFF # negative(281474976710655)
              00                        # unsigned(0)
              98 40                     # array(64)
                 01                     # unsigned(1)
                 01                     # unsigned(1)
                 26                     # negative(6)
                 08                     # unsigned(8)
                 01                     # unsigned(1)
                 28                     # negative(8)
                 01                     # unsigned(1)
                 02                     # unsigned(2)
                 06                     # unsigned(6)
                 02                     # unsigned(2)
                 06                     # unsigned(6)
                 02                     # unsigned(2)
                 08                     # unsigned(8)
                 02                     # unsigned(2)
                 02                     # unsigned(2)
                 01                     # unsigned(1)
                 02                     # unsigned(2)
                 01                     # unsigned(1)
                 27                     # negative(7)
                 05                     # unsigned(5)
                 01                     # unsigned(1)
                 26                     # negative(6)
                 04                     # unsigned(4)
                 01                     # unsigned(1)
                 29                     # negative(9)
                 01                     # unsigned(1)
                 02                     # unsigned(2)
                 06                     # unsigned(6)
                 02                     # unsigned(2)
                 05                     # unsigned(5)
                 02                     # unsigned(2)
                 02                     # unsigned(2)
                 01                     # unsigned(1)
                 02                     # unsigned(2)
                 01                     # unsigned(1)
                 27                     # negative(7)
                 01                     # unsigned(1)
                 02                     # unsigned(2)
                 02                     # unsigned(2)
                 02                     # unsigned(2)
                 02                     # unsigned(2)
                 02                     # unsigned(2)
                 03                     # unsigned(3)



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                 02                     # unsigned(2)
                 03                     # unsigned(3)
                 02                     # unsigned(2)
                 04                     # unsigned(4)
                 02                     # unsigned(2)
                 04                     # unsigned(4)
                 02                     # unsigned(2)
                 06                     # unsigned(6)
                 02                     # unsigned(2)
                 06                     # unsigned(6)
                 02                     # unsigned(2)
                 0B                     # unsigned(11)
                 02                     # unsigned(2)
                 0B                     # unsigned(11)
                 02                     # unsigned(2)
                 10                     # unsigned(16)
                 02                     # unsigned(2)
                 10                     # unsigned(16)
                 01                     # unsigned(1)
                 01                     # unsigned(1)
                 00                     # unsigned(0)

6.2.  JSON Web Token

   Consider the following JSON Web Token [RFC7519], which natively is
   149 bytes (line endings are not significant):

              eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiO
              iIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWR
              taW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZ
              geFONFh7HgQ

   In a JSON encoding, the JWT would be 191 bytes (line endings are not
   significant):

                 {"protected":
                 "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9",
                 "payload":"eyJzdWIiOiIxMjM0NTY3ODkwIiwib
                 mFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9",
                 "signature":
                 "TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh
                 7HgQ"}

   Using a Reference Set of "[1,"payload","signature","protected","alg",
   "HS256","sub","name","admin"]", the JCOR encoding would be 80 bytes.






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        D4                                      # tag(20)
           82                                   # array(2)
              A3                                # map(3)
                 41                             # bytes(1)
                    03                          # "\x03"
                 D5                             # tag(21)
                    A2                          # map(2)
                       41                       # bytes(1)
                          04                    # "\x04"
                       41                       # bytes(1)
                          05                    # "\x05"
                       41                       # bytes(1)
                          06                    # "\x06"
                       41                       # bytes(1)
                          07                    # "\a"
                 41                             # bytes(1)
                    01                          # "\x01"
                 D5                             # tag(21)
                    A3                          # map(3)
                       41                       # bytes(1)
                          08                    # "\b"
                       D7                       # tag(23)
                          45                    # bytes(5)
                             1234567890         # "\x124Vx\x90"
                       41                       # bytes(1)
                          09                    # "\t"
                       68                       # text(8)
                          4A6F686E20446F65      # "John Doe"
                       41                       # bytes(1)
                          0A                    # "\n"
                       F5                       # primitive(21)
                 41                             # bytes(1)
                    02                          # "\x02"
                 D5                             # tag(21)
                    58 20                       # bytes(32)
                       4C9540F793AB33B13670169BDF444C1EB1C37047F18
                       E861981E14E34587B1E04 # "L\x95@\xF7\x93\xAB3
                       \xB16p\x16\x9B\xDFDL\x1E\xB1\xC3pG\xF1\x8E
                       \x86\x19\x81\xE1N4X{\x1E\x04"
              01                                # unsigned(1)

7.  IANA Considerations

7.1.  CBOR Tags

   The IANA is requested to assign the following tags from the "CBOR
   Tags" registry defined in RFC 7049 [RFC7049]:




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   o  Assign the tag "Constrained JSON" in the 1 to 23 value range (one
      byte in length when encoded).

   o  Assign the tag "Upper Case Modifier" in the 24 to 255 value range
      (two bytes in length when encoded).

   The tags to be assigned are described below.

      Tag             20 (Constrained JSON)
      Data Item       array
      Semantics       The first value in the array is a constrained
                      JSON data item encoded using JCOR, optionally
                      followed by an integer or array identifying any
                      embedded references, and then an optional array
                      of canonical hints (if any).
      Reference       http://quartzjer.github.io/JCOR
      Contact         Jeremie Miller <jeremie.miller@gmail.com>

      Tag             31 (Upper Case Modifier)
      Data Item       multiple
      Semantics       Indicates that the data item following contains
                      values where the upper case is semantically
                      important when interpreted in a UTF-8 string
                      context.
      Reference       http://quartzjer.github.io/JCOR
      Contact         Jeremie Miller <jeremie.miller@gmail.com>

7.2.  JCOR Reference Sets Registry

   A future version of this document will request creation of a registry
   for JCOR Reference Sets and provide initial registrations for the
   existing JOSE JWE, JWS, and JWA RFCs.

8.  Security Considerations

   TODO

9.  References

9.1.  Normative References

   [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>.






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   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

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

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015, <https://www.rfc-
              editor.org/info/rfc7517>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015, <https://www.rfc-
              editor.org/info/rfc7518>.

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

9.2.  Informative References

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014, <https://www.rfc-
              editor.org/info/rfc7228>.

9.3.  URIs

   [1] http://openid.net/connect/

Appendix A.  Acknowledgements

   Thanks to Carsten Bormann and David Waite for their comments.





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Authors' Addresses

   Jeremie Miller

   Email: jeremie@jabber.org


   Peter Saint-Andre

   Email: stpeter@jabber.org









































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