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Network Working Group                                    P. Hallam-Baker
Internet-Draft                                         Comodo Group Inc.
Intended status: Informational                             March 8, 2016
Expires: September 9, 2016


                                 Title
                      draft-hallambaker-jsonbcd-05

Abstract

   Binary Encodings for JavaScript Object Notation: JSON-B, JSON-C,
   JSON-D

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 9, 2016.

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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.






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1.  Abstract

   Three binary encodings for JavaScript Object Notation (JSON) are
   presented.  JSON-B (Binary) is a strict superset of the JSON encoding
   that permits efficient binary encoding of intrinsic JavaScript data
   types.  JSON-C (Compact) is a strict superset of JSON-B that supports
   compact representation of repeated data strings with short numeric
   codes.  JSON-D (Data) supports additional binary data types for
   integer and floating point representations for use in scientific
   applications where conversion between binary and decimal
   representations would cause a loss of precision.

2.  Definitions

2.1.  Requirements Language

   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 [RFC2119].

3.  Introduction

   JavaScript Object Notation (JSON) is a simple text encoding for the
   JavaScript Data model that has found wide application beyond its
   original field of use.  In particular JSON has rapidly become a
   preferred encoding for Web Services.

   JSON encoding supports just four fundamental data types (integer,
   floating point, string and boolean), arrays and objects which consist
   of a list of tag-value pairs.

   Although the JSON encoding is sufficient for many purposes it is not
   always efficient.  In particular there is no efficient representation
   for blocks of binary data.  Use of base64 encoding increases data
   volume by 33%. This overhead increases exponentially in applications
   where nested binary encodings are required making use of JSON
   encoding unsatisfactory in cryptographic applications where nested
   binary structures are frequently required.

   Another source of inefficiency in JSON encoding is the repeated
   occurrence of object tags.  A JSON encoding containing an array of a
   hundred objects such as {"first":1,"second":2} will contain a hundred
   occurrences of the string "first" (seven bytes) and a hundred
   occurrences of the string "second" (eight bytes).  Using two byte
   code sequences in place of strings allows a saving of 11 bytes per
   object without loss of information, a saving of 50%.





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   A third objection to the use of JSON encoding is that floating point
   numbers can only be represented in decimal form and this necessarily
   involves a loss of precision when converting between binary and
   decimal representations.  While such issues are rarely important in
   network applications they can be critical in scientific applications.
   It is not acceptable for saving and restoring a data set to change
   the result of a calculation.

3.1.  Objectives

   The following were identified as core objectives for a binary JSON
   encoding:

   o

      *  Low overhead encoding and decoding

      *  Easy to convert existing encoders and decoders to add binary
         support

      *  Efficient encoding of binary data

      *  Ability to convert from JSON to binary encoding in a streaming
         mode (i.e. without reading the entire binary data block before
         beginning encoding.

      *  Lossless encoding of JavaScript data types

      *  The ability to support JSON tag compression and extended data
         types are considered desirable but not essential for typical
         network applications.

   Three binary encodings are defined:

   JSON-B (Binary)

   Simply encodes JSON data in binary.  Only the JavaScript data model
   is supported (i.e. atomic types are integers, double or string).
   Integers may be 8, 16, 32 or 64 bits either signed or unsigned.
   Floating points are IEEE 754 binary64 format [IEEE-754].  Supports
   chunked encoding for binary and UTF-8 string types.

   JSON-C (Compact)

   As JSON-B but with support for representing JSON tags in numeric code
   form (16 bit code space).  This is done for both compact encoding and
   to allow simplification of encoders/decoders in constrained




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   environments.  Codes may be defined inline or by reference to a known
   dictionary of codes referenced via a digest value.

   JSON-D (Data)

   As JSON-C but with support for representing additional data types
   without loss of precision.  In particular other IEEE 754 floating
   point formats, both binary and decimal and Intel's 80 bit floating
   point, plus 128 bit integers and bignum integers.

4.  Extended JSON Grammar

   The JSON-B, JSON-C and JSON-D encodings are all based on the JSON
   grammar [RFC4627] using the same syntactic structure but different
   lexical encodings.

   JSON-B0 and JSON-C0 replace the JSON lexical encodings for strings
   and numbers with binary encodings.  JSON-B1 and JSON-C1 allow either
   lexical encoding to be used.  Thus any valid JSON encoding is a valid
   JSON-B1 or JSON-C1 encoding.

   The grammar of JSON-B, JSON-C and JSON-D is a superset of the JSON
   grammar.  The following productions are added to the grammar:

   x-value

   Binary encodings for data values.  As the binary value encodings are
   all self delimiting

   x-member

   An object member where the value is specified as an X-value and thus
   does not require a value-separator.

   b-value

   Binary data encodings defined in JSON-B.

   b-string

   Defined length string encoding defined in JSON-B.

   c-def

   Tag code definition defined in JSON-C.  These may only appear before
   the beginning of an Object or Array and before any preceeding white
   space.




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   c-tag

   Tag code value defined in JSON-C.

   d-value

   Additional binary data encodings defined in JSON-D for use in
   scientific data applications.

   The JSON grammar is modified to permit the use of x-value productions
   in place of ( value value-separator ) :

   JSON-text = (object / array)

   object = *cdef begin-object [
            *( member value-separator | x-member )
            (member | x-member) ] end-object

   member = tag value
   x-member = tag x-value

   tag = string name-separator | b-string | c-tag

   array = *cdef begin-array [  *( value value-separator | x-value )
   (value | x-value) ] end-array

   x-value = b-value / d-value

   value = false / null / true / object / array / number / string

   name-separator  = ws %x3A ws  ; : colon
   value-separator = ws %x2C ws  ; , comma

   The following lexical values are unchanged:
   begin-array     = ws %x5B ws  ; [ left square bracket
   begin-object    = ws %x7B ws  ; { left curly bracket
   end-array       = ws %x5D ws  ; ] right square bracket
   end-object      = ws %x7D ws  ; } right curly bracket

   ws = *( %x20 %x09 %x0A  %x0D )

   false = %x66.61.6c.73.65   ; false
   null  = %x6e.75.6c.6c      ; null
   true  = %x74.72.75.65      ; true

   The productions number and string are defined as before:





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   number = [ minus ] int [ frac ] [ exp ]
   decimal-point = %x2E       ; .
   digit1-9 = %x31-39         ; 1-9
   e = %x65 / %x45            ; e E
   exp = e [ minus / plus ] 1*DIGIT
   frac = decimal-point 1*DIGIT
   int = zero / ( digit1-9 *DIGIT )
   minus = %x2D               ; -
   plus = %x2B                ; +
   zero = %x30                ; 0

   string = quotation-mark *char quotation-mark
   char = unescaped /
   escape ( %x22 / %x5C / %x2F / %x62 / %x66 /
   %x6E / %x72 / %x74 /  %x75 4HEXDIG )

   escape = %x5C              ; \
   quotation-mark = %x22      ; "
   unescaped = %x20-21 / %x23-5B / %x5D-10FFFF

5.  JSON-B

   The JSON-B encoding defines the b-value and b-string productions:

   b-value = b-atom | b-string | b-data | b-integer |
   b-float

   b-string = *( string-chunk ) string-term
   b-data = *( data-chunk ) data-last

   b-integer = p-int8 | p-int16 | p-int32 | p-int64 | p-bignum16 |
   n-int8 | n-int16 | n-int32 | n-int64 | n-bignum16

   b-float = binary64

   The lexical encodings of the productions are defined in the following
   table where the column 'tag' specifies the byte code that begins the
   production, 'Fixed' specifies the number of data bytes that follow
   and 'Length' specifies the number of bytes used to define the length
   of a variable length field following the data bytes:

   +--------------+-----+-------+--------+-----------------------------+
   | Production   | Tag | Fixed | Length | Data Description            |
   +--------------+-----+-------+--------+-----------------------------+
   | string-term  | x80 | -     | 1      | Terminal String 8 bit       |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | string-term  | x81 | -     | 2      | Terminal String 16 bit      |



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   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | string-term  | x82 | -     | 4      | Terminal String 32 bit      |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | string-term  | x83 | -     | 8      | Terminal String 64 bit      |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | string-chunk | x84 | -     | 1      | Non-Terminal String 8 bit   |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | string-chunk | x85 | -     | 2      | Non-Terminal String 16 bit  |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | string-chunk | x86 | -     | 4      | Non-Terminal String 32 bit  |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | string-chunk | x87 | -     | 8      | Non-Terminal String 64 bit  |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | data-term    | x88 | -     | 1      | Terminal Data 8 bit length  |
   |              |     |       |        |                             |
   | data-term    | x89 | -     | 2      | Terminal Data 16 bit length |
   |              |     |       |        |                             |
   | data-term    | x8A | -     | 4      | Terminal Data 32 bit length |
   |              |     |       |        |                             |
   | data-term    | x8B | -     | 8      | Terminal Data 64 bit length |
   |              |     |       |        |                             |
   | data-chunk   | x8C | -     | 1      | Non-Terminal Data 8 bit     |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | data-chunk   | x8D | -     | 2      | Non-Terminal Data 16 bit    |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | data-chunk   | x8E | -     | 4      | Non-Terminal Data 32 bit    |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | data-chunk   | x8F | -     | 8      | Non-Terminal String 64 bit  |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | p-int8       | xA0 | 1     | -      | Positive 8 bit Integer      |
   |              |     |       |        |                             |
   | p-int16      | xA1 | 2     | -      | Positive 16 bit Integer     |
   |              |     |       |        |                             |
   | p-int32      | xA2 | 4     | -      | Positive 32 bit Integer     |
   |              |     |       |        |                             |
   | p-int64      | xA3 | 8     | -      | Positive 64 bit Integer     |
   |              |     |       |        |                             |



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   | p-bignum16   | xA5 | -     | 2      | Positive Bignum 16 bit      |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | n-int8       | xA8 | 1     | -      | Negative 8 bit Integer      |
   |              |     |       |        |                             |
   | n-int16      | xA9 | 2     | -      | Negative 16 bit Integer     |
   |              |     |       |        |                             |
   | n-int32      | xAA | 4     | -      | Negative 32 bit Integer     |
   |              |     |       |        |                             |
   | n-int64      | xAB | 8     | -      | Negative 64 bit Integer     |
   |              |     |       |        |                             |
   | n-bignum16   | xAD | -     | 2      | Negative Bignum 16 bit      |
   |              |     |       |        | length                      |
   |              |     |       |        |                             |
   | binary64     | x92 | 8     | -      | IEEE 754 Floating Point     |
   |              |     |       |        | binary64                    |
   |              |     |       |        |                             |
   | b-value      | xB0 | -     | -      | True                        |
   |              |     |       |        |                             |
   | b-value      | xB1 | -     | -      | False                       |
   |              |     |       |        |                             |
   | b-value      | xB2 | -     | -      | Null                        |
   +--------------+-----+-------+--------+-----------------------------+

   A data type commonly used in networking that is not defined in this
   scheme is a datetime representation.  To define such a data type, a
   string containing a date-time value in Internet type format is
   typically used.

5.1.  JSON-B Examples

   The following examples show examples of using JSON-B encoding:



















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   A0 2A                            42 (as 8 bit integer)
   A1 00 2A                         42 (as 16 bit integer)
   A2 00 00 00 2A                   42 (as 32 bit integer)
   A3 00 00 00 00 00 00 00 2A       42 (as 64 bit integer)
   A5 00 01 42                      42 (as Bignum)

   80 05 48 65 6c 6c 6f             "Hello" (single chunk)
   81 00 05 48 65 6c 6c 6f          "Hello" (single chunk)
   84 05 48 65 6c 6c 6f 80 00       "Hello" (as two chunks)

   92 3f f0 00 00 00 00 00 00       1.0
   92 40 24 00 00 00 00 00 00       10.0
   92 40 09 21 fb 54 44 2e ea       3.14159265359
   92 bf f0 00 00 00 00 00 00       -1.0

   B0                               true
   B1                               false
   B2                               null

6.  JSON-C

   JSON-C (Compressed) permits numeric code values to be substituted for
   strings and binary data.  Tag codes MAY be 8, 16 or 32 bits long
   encoded in network byte order.

   Tag codes MUST be defined before they are referenced.  A Tag code MAY
   be defined before the corresponding data or string value is used or
   at the same time that it is used.

   A dictionary is a list of tag code definitions.  An encoding MAY
   incorporate definitions from a dictionary using the dict-hash
   production.  The dict hash production specifies a (positive) offset
   value to be added to the entries in the dictionary followed by the
   UDF fingerprint [draft-hallambaker-udf] of the dictionary to be used.

















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   +------------+-----+-------+--------+-------------------------------+
   | Production | Tag | Fixed | Length | Data Description              |
   +------------+-----+-------+--------+-------------------------------+
   | c-tag      | xC0 | 1     | -      | 8 bit tag code                |
   |            |     |       |        |                               |
   | c-tag      | xC1 | 2     | -      | 16 bit tag code               |
   |            |     |       |        |                               |
   | c-tag      | xC2 | 4     | -      | 32 bit tag code               |
   |            |     |       |        |                               |
   | c-def      | xC4 | 1     | -      | 8 bit tag definition          |
   |            |     |       |        |                               |
   | c-def      | xC5 | 2     | -      | 16 bit tag definition         |
   |            |     |       |        |                               |
   | c-def      | xC6 | 4     | -      | 32 bit tag definition         |
   |            |     |       |        |                               |
   | c-tag      | xC8 | 1     | -      | 8 bit tag code & definition   |
   |            |     |       |        |                               |
   | c-tag      | xC9 | 2     | -      | 16 bit tag code & definition  |
   |            |     |       |        |                               |
   | c-tag      | xCA | 4     | -      | 32 bit tag code & definition  |
   |            |     |       |        |                               |
   | c-def      | xCC | 1     | -      | 8 bit tag dictionary          |
   |            |     |       |        | definition                    |
   |            |     |       |        |                               |
   | c-def      | xCD | 2     | -      | 16 bit tag dictionary         |
   |            |     |       |        | definition                    |
   |            |     |       |        |                               |
   | c-def      | xCE | 4     | -      | 32 bit tag dictionary         |
   |            |     |       |        | definition                    |
   |            |     |       |        |                               |
   | dict-hash  | xD0 | 4     | 1      | UDF fingerprint of dictionary |
   +------------+-----+-------+--------+-------------------------------+

   All integer values are encoded in Network Byte Order (most
   significant byte first).

6.1.  JSON-C Examples

   The following examples show examples of using JSON-C encoding:












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   C8 20 80 05 48 65 6c 6c 6f       "Hello"    20 = "Hello"
   C4 21 80 05 48 65 6c 6c 6f                  21 = "Hello"
   C0 20                            "Hello"
   C1 00 20                         "Hello"

   D0 00 00 01 00 20             Insert dictionary at code 256
   e3 b0 c4 42 98 fc 1c 14
   9a fb f4 c8 99 6f b9 24
   27 ae 41 e4 64 9b 93 4c
   a4 95 99 1b 78 52 b8 55       UDF (C4 21 80 05 48 65 6c 6c 6f)

7.  JSON-D (Data)

   JSON-B and JSON-C only support the two numeric types defined in the
   JavaScript data model: Integers and 64 bit floating point values.
   JSON-D (Data) defines binary encodings for additional data types that
   are commonly used in scientific applications.  These comprise
   positive and negative 128 bit integers, six additional floating point
   representations defined by IEEE 754 [RFC2119] and the Intel extended
   precision 80 bit floating point representation.

   Should the need arise, even bigger bignums could be defined with the
   length specified as a 32 bit value permitting bignums of up to 2^35
   bits to be represented.

   d-value = d-integer | d-float

   d-float = binary16 | binary32 | binary128 | binary80 |
   decimal32 | decimal64 | decimal 128

8.




















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   +------------+-----+-------+--------+-------------------------------+
   | Production | Tag | Fixed | Length | Data Description              |
   +------------+-----+-------+--------+-------------------------------+
   | p-int128   | xA4 | 16    | -      | Positive 128 bit Integer      |
   |            |     |       |        |                               |
   | n-in7128   | xAC | 16    | -      | Negative 128 bit Integer      |
   |            |     |       |        |                               |
   | binary16   | x90 | 2     | -      | IEEE 754 Floating Point       |
   |            |     |       |        | binary16                      |
   |            |     |       |        |                               |
   | binary32   | x91 | 4     | -      | IEEE 754 Floating Point       |
   |            |     |       |        | binary32                      |
   |            |     |       |        |                               |
   | binary128  | x94 | 16    | -      | IEEE 754 Floating Point       |
   |            |     |       |        | binary128                     |
   |            |     |       |        |                               |
   | intel80    | x95 | 10    | -      | Intel 80 bit extended binary  |
   |            |     |       |        | Floating Point                |
   |            |     |       |        |                               |
   | decimal32  | x96 | 4     | -      | IEEE 754 Floating Point       |
   |            |     |       |        | decimal32                     |
   |            |     |       |        |                               |
   | decimal64  | x97 | 8     | -      | IEEE 754 Floating Point       |
   |            |     |       |        | decimal64                     |
   |            |     |       |        |                               |
   | decimal128 | x98 | 18    | -      | IEEE 754 Floating Point       |
   |            |     |       |        | decimal128                    |
   +------------+-----+-------+--------+-------------------------------+

9.

10.  Acknowledgements

   This work was assisted by conversations with Nico Williams and other
   participants on the applications area mailing list.

11.  Security Considerations

   A correctly implemented data encoding mechanism should not introduce
   new security vulnerabilities.  However, experience demonstrates that
   some data encoding approaches are more prone to introduce
   vulnerabilities when incorrectly implemented than others.

   In particular, whenever variable length data formats are used, the
   possibility of a buffer overrun vulnerability is introduced.  While
   best practice suggests that a coding language with native mechanisms
   for bounds checking is the best protection against such errors, such
   approaches are not always followed.  While such vulnerabilities are



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   most commonly seen in the design of decoders, it is possible for the
   same vulnerabilities to be exploited in encoders.

   A common source of such errors is the case where nested length
   encodings are used.  For example, a decoder relies on an outermost
   length encoding that specifies a length on 50 bytes to allocate
   memory for the entire result and then attempts to copy a string with
   a declared length of 1000 bytes within the sequence.

   The extensions to the JSON encoding described in this document are
   designed to avoid such errors.  Length encodings are only used to
   define the length of x-value constructions which are always terminal
   and cannot have nested data entries.

12.  IANA Considerations

   [TBS list out all the code points that require an IANA registration]

13.  Normative References

   [IEEE-754]
              "[Reference Not Found!]".

   [draft-hallambaker-udf]
              "[Reference Not Found!]".

Author's Address

   Phillip Hallam-Baker
   Comodo Group Inc.

   Email: philliph@comodo.com



















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