Network Working Group P. Hallam-Baker
Internet-Draft Comodo Group Inc.
Intended status: Informational April 10, 2018
Expires: October 12, 2018
Binary Encodings for JavaScript Object Notation: JSON-B, JSON-C, JSON-D
draft-hallambaker-jsonbcd-10
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.
This document is also available online at
http://prismproof.org/Documents/draft-hallambaker-jsonbcd.html [1] .
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Objectives . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Defined Terms . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Related Specifications . . . . . . . . . . . . . . . . . 4
2.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
3. Extended JSON Grammar . . . . . . . . . . . . . . . . . . . . 5
4. JSON-B . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. JSON-B Examples . . . . . . . . . . . . . . . . . . . . . 13
5. JSON-C . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. JSON-C Examples . . . . . . . . . . . . . . . . . . . . . 16
6. JSON-D (Data) . . . . . . . . . . . . . . . . . . . . . . . . 17
7. JBCD Frames and Records . . . . . . . . . . . . . . . . . . . 19
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Normative References . . . . . . . . . . . . . . . . . . 21
11.2. Informative References . . . . . . . . . . . . . . . . . 21
11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
1. 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
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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%.
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.
1.1. Objectives
The following were identified as core objectives for a binary JSON
encoding:
o Easy to convert existing encoders and decoders to add binary
support
o Efficient encoding of binary data
o Ability to convert from JSON to binary encoding in a streaming
mode (i.e. without reading the entire binary data block before
beginning encoding.
o Lossless encoding of JavaScript data types
o 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) 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 [IEEE754]
. Supports chunked encoding for binary and UTF-8 string types.
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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 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.
Each encoding is a proper superset of JSON, JSON-C is a proper
superset of JSON-B and JSON-D is a proper superset of JSON-C. Thus a
single decoder MAY be used for all three new encodings and for JSON.
Figure 1 shows these relationships graphically:
[[This figure is not viewable in this format. The figure is
available at http://prismproof.org/Documents/draft-hallambaker-
jsonbcd.html [2].]]
Encoding Relationships.
2. Definitions
This section presents the related specifications and standard, the
terms that are used as terms of art within the documents and the
terms used as requirements language.
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].
2.2. Defined Terms
The terms of art used in this document are described in the Mesh
Architecture Guide [draft-hallambaker-mesh-architecture] .
2.3. Related Specifications
The JSON-B, JSON-C and JSON-D encodings are all based on the JSON
grammar [RFC7159] . IEEE 754 Floating Point Standard is used for
encoding floating point numbers [IEEE754] ,
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2.4. Terminology
No new terms of art are defined
3. Extended JSON Grammar
The JSON-B, JSON-C and JSON-D encodings are all based on the JSON
grammar [RFC7159] 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
preceding white space.
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)
Figure 1
Figure 2
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object = *cdef begin-object [
Figure 3
*( member value-separator | x-member )
Figure 4
(member | x-member) ] end-object
Figure 5
Figure 6
member = tag value
Figure 7
x-member = tag x-value
Figure 8
Figure 9
tag = string name-separator | b-string | c-tag
Figure 10
Figure 11
array = *cdef begin-array [ *( value value-separator | x-value )
Figure 12
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(value | x-value) ] end-array
Figure 13
Figure 14
x-value = b-value / d-value
Figure 15
Figure 16
value = false / null / true / object / array / number / string
Figure 17
Figure 18
name-separator = ws %x3A ws ; : colon
Figure 19
value-separator = ws %x2C ws ; , comma
Figure 20
The following lexical values are unchanged:
Figure 21
begin-array = ws %x5B ws ; [ left square bracket
Figure 22
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begin-object = ws %x7B ws ; { left curly bracket
Figure 23
end-array = ws %x5D ws ; ] right square bracket
Figure 24
end-object = ws %x7D ws ; } right curly bracket
Figure 25
Figure 26
ws = *( %x20 %x09 %x0A %x0D )
Figure 27
Figure 28
false = %x66.61.6c.73.65 ; false
Figure 29
null = %x6e.75.6c.6c ; null
Figure 30
true = %x74.72.75.65 ; true
Figure 31
The productions number and string are defined as before:
number = [ minus ] int [ frac ] [ exp ]
Figure 32
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decimal-point = %x2E ; .
Figure 33
digit1-9 = %x31-39 ; 1-9
Figure 34
e = %x65 / %x45 ; e E
Figure 35
exp = e [ minus / plus ] 1*DIGIT
Figure 36
frac = decimal-point 1*DIGIT
Figure 37
int = zero / ( digit1-9 *DIGIT )
Figure 38
minus = %x2D ; -
Figure 39
plus = %x2B ; +
Figure 40
zero = %x30 ; 0
Figure 41
Figure 42
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string = quotation-mark *char quotation-mark
Figure 43
char = unescaped /
Figure 44
escape ( %x22 / %x5C / %x2F / %x62 / %x66 /
Figure 45
%x6E / %x72 / %x74 / %x75 4HEXDIG )
Figure 46
Figure 47
escape = %x5C ; \
Figure 48
quotation-mark = %x22 ; "
Figure 49
unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
Figure 50
4. JSON-B
The JSON-B encoding defines the b-value and b-string productions:
b-value = b-atom | b-string | b-data | b-integer |
Figure 51
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b-float
Figure 52
Figure 53
b-string = *( string-chunk ) string-term
Figure 54
b-data = *( data-chunk ) data-last
Figure 55
Figure 56
b-integer = p-int8 | p-int16 | p-int32 | p-int64 | p-bignum16 |
Figure 57
n-int8 | n-int16 | n-int32 | n-int64 | n-bignum16
Figure 58
Figure 59
b-float = binary64
Figure 60
The lexical encodings of the productions are defined in the following
tables 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:
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+--------------+-----+-------+--------+-----------------------------+
| Production | Tag | Fixed | Length | Data Description |
+--------------+-----+-------+--------+-----------------------------+
| string-term | x80 | - | 1 | Terminal String 8 bit |
| | | | | length |
| string-term | x81 | - | 2 | Terminal String 16 bit |
| | | | | length |
| string-term | x82 | - | 4 | Terminal String 32 bit |
| | | | | length |
| string-term | x83 | - | 8 | Terminal String 64 bit |
| | | | | length |
| string-chunk | x84 | - | 1 | Terminal String 8 bit |
| | | | | length |
| string-chunk | x85 | - | 2 | Terminal String 16 bit |
| | | | | length |
| string-chunk | x86 | - | 4 | Terminal String 32 bit |
| | | | | length |
| string-chunk | x87 | - | 8 | Terminal String 64 bit |
| | | | | length |
| data-term | x88 | - | 1 | Terminal String 8 bit |
| | | | | length |
| data-term | x89 | - | 2 | Terminal String 16 bit |
| | | | | length |
| data-term | x8A | - | 4 | Terminal String 32 bit |
| | | | | length |
| data-term | x8B | - | 8 | Terminal String 64 bit |
| | | | | length |
| data-term | X8C | - | 1 | Terminal String 8 bit |
| | | | | length |
| data-term | x8D | - | 2 | Terminal String 16 bit |
| | | | | length |
| data-term | x8E | - | 4 | Terminal String 32 bit |
| | | | | length |
| data-term | x8F | - | 8 | Terminal String 64 bit |
| | | | | length |
+--------------+-----+-------+--------+-----------------------------+
Table 1
Table 1: Codes for String and Data items
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+------------+-----+-------+--------+-------------------------------+
| Production | Tag | Fixed | Length | Data Description |
+------------+-----+-------+--------+-------------------------------+
| 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 |
| p-bignum16 | Xa7 | - | 2 | Positive Bignum |
| 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 | xAF | - | 2 | Negative Bignum |
| binary64 | x92 | 8 | - | IEEE 754 Floating Point |
| | | | | Binary 64 bit |
| b-value | xB0 | - | - | True |
| b-value | xB1 | - | - | False |
| b-value | xB2 | - | - | Null |
+------------+-----+-------+--------+-------------------------------+
Table 2
Table 2: Codes for Integers, 64 Bit Floating Point, Boolean and Null
items.
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.
4.1. JSON-B Examples
The following examples show examples of using JSON-B encoding:
A0 2A 42 (as 8 bit integer)
Figure 61
A1 00 2A 42 (as 16 bit integer)
Figure 62
A2 00 00 00 2A 42 (as 32 bit integer)
Figure 63
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A3 00 00 00 00 00 00 00 2A 42 (as 64 bit integer)
Figure 64
A5 00 01 42 42 (as Bignum)
Figure 65
Figure 66
80 05 48 65 6c 6c 6f "Hello" (single chunk)
Figure 67
81 00 05 48 65 6c 6c 6f "Hello" (single chunk)
Figure 68
84 05 48 65 6c 6c 6f 80 00 "Hello" (as two chunks)
Figure 69
Figure 70
92 3f f0 00 00 00 00 00 00 1.0
Figure 71
92 40 24 00 00 00 00 00 00 10.0
Figure 72
92 40 09 21 fb 54 44 2e ea 3.14159265359
Figure 73
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92 bf f0 00 00 00 00 00 00 -1.0
Figure 74
Figure 75
B0 true
Figure 76
B1 false
Figure 77
B2 null
Figure 78
5. 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 and definition |
| c-tag | xC9 | 2 | - | 16 bit tag code and |
| | | | | definition |
| c-tag | xCA | 4 | - | 32 bit tag code and |
| | | | | 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 |
+------------+-----+-------+--------+-------------------------------+
Table 3
Table 3: Codes Used for Compression
All integer values are encoded in Network Byte Order (most
significant byte first).
5.1. JSON-C Examples
The following examples show examples of using JSON-C encoding:
C8 20 80 05 48 65 6c 6c 6f "Hello" 20 = "Hello"
Figure 79
C4 21 80 05 48 65 6c 6c 6f 21 = "Hello"
Figure 80
C0 20 "Hello"
Figure 81
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C1 00 20 "Hello"
Figure 82
Figure 83
D0 00 00 01 00 20 Insert dictionary at code 256
Figure 84
e3 b0 c4 42 98 fc 1c 14
Figure 85
9a fb f4 c8 99 6f b9 24
Figure 86
27 ae 41 e4 64 9b 93 4c
Figure 87
a4 95 99 1b 78 52 b8 55 UDF (C4 21 80 05 48 65 6c 6c 6f)
Figure 88
6. 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 [IEEE754] and the Intel extended
precision 80 bit floating point representation [INTEL] .
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.
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d-value = d-integer | d-float
Figure 89
Figure 90
d-float = binary16 | binary32 | binary128 | binary80 |
Figure 91
decimal32 | decimal64 | decimal 128
Figure 92
The codes for these values are as follows:
+------------+-----+-------+--------+-------------------------------+
| Production | Tag | Fixed | Length | Data Description |
+------------+-----+-------+--------+-------------------------------+
| p-int128 | xA4 | 16 | - | Positive 128 bit Integer |
| n-int128 | xAC | 16 | - | Negative 128 bit Integer |
| binary16 | x90 | 2 | - | IEEE 754 Floating Point |
| | | | | Binary 16 bit |
| binary32 | x91 | 4 | - | IEEE 754 Floating Point |
| | | | | Binary 32 bit |
| binary128 | x94 | 16 | - | IEEE 754 Floating Point |
| | | | | Binary 64 bit |
| Intel80 | x95 | 10 | - | Intel extended Floating Point |
| | | | | 80 bit |
| decimal32 | x96 | 4 | - | IEEE 754 Floating Point |
| | | | | Decimal 32 |
| Decimal64 | x97 | 8 | - | IEEE 754 Floating Point |
| | | | | Decimal 64 |
| Decimal128 | x98 | 16 | - | IEEE 754 Floating Point |
| | | | | Decimal 128 |
+------------+-----+-------+--------+-------------------------------+
Table 4
Table 4: Additional Codes for Scientific Data
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7. JBCD Frames and Records
Tag codes in the range xF0-XFF are reserved for specifying markers
for frames and records. These tags are not used to encode JSON data,
they are only used to encapsulate opaque binary data blobs as a unit.
A JBCD record consists of consist of the tag, a length and the data
item. The length indication provided by the record format allows
efficient traversal of a sequence of records in the forward direction
only.
A JBCD Frames consists of consist of the tag, a length and the data
item followed by the tag-length sequence repeated with the bytes
written in the reverse order. The first length indication allows
efficient traversal of a sequence of records in the forward direction
and the second allows efficient traversal in the reverse direction.
[[This figure is not viewable in this format. The figure is
available at http://prismproof.org/Documents/draft-hallambaker-
jsonbcd.html [3].]]
JBCD Records and Frames
The JBCD-Frame tags currently defined are:
+------------+---------+-------+--------+-----------------------+
| Production | Tag | Fixed | Length | Data Description |
+------------+---------+-------+--------+-----------------------+
| uframe | xF0 | - | 1 | Record, 8 bit length |
| uframe | xF1 | - | 2 | Record, 16 bit length |
| uframe | xF2 | - | 4 | Record, 32 bit length |
| uframe | xF3 | - | 8 | Record, 64 bit length |
| bframe | xF4 | - | 1 | Frame, 8 bit length |
| bframe | xF5 | - | 2 | Frame, 16 bit length |
| bframe | xF6 | - | 4 | Frame, 32 bit length |
| bframe | xF7 | - | 8 | Frame, 64 bit length |
| | xF8-xFF | - | - | Reserved |
+------------+---------+-------+--------+-----------------------+
Table 5
The author does not expect additional framing tags to be added but
codes F8-FF are reserved in case this is desired.
It may prove convenient to represent message digest values as large
integers rather than binary strings. While very few platforms or
programming languages support mathematical operations on fixed size
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integers larger than 64, this is not a major concern since message
digests are rarely used for any purpose other than comparison for
equality.
+------------+-----+-------+--------+--------------------------+
| Production | Tag | Fixed | Length | Data Description |
+------------+-----+-------+--------+--------------------------+
| p-int128 | Xa4 | 16 | - | Positive 128 bit Integer |
| p-int256 | Xa5 | 32 | - | Positive 256 bit Integer |
| p-int512 | Xa6 | 64 | - | Positive 512 bit Integer |
+------------+-----+-------+--------+--------------------------+
Table 6
8. Acknowledgements
This work was assisted by conversations with Nico Williams and other
participants on the applications area mailing list.
9. 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
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.
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10. IANA Considerations
[TBS list out all the code points that require an IANA registration]
11. References
11.1. Normative References
[draft-hallambaker-udf]
Hallam-Baker, P., "Uniform Data Fingerprint (UDF)", draft-
hallambaker-udf-08 (work in progress), October 2017.
[IEEE754] IEEE Computer Society, "IEEE Standard for Floating-Point
Arithmetic", IEEE 754-2008,
DOI 10.1109/IEEESTD.2008.4610935, August 2008.
[INTEL] Intel Corp., "Unknown".
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014.
11.2. Informative References
[draft-hallambaker-mesh-architecture]
Hallam-Baker, P., "Mathematical Mesh: Architecture",
draft-hallambaker-mesh-architecture-04 (work in progress),
September 2017.
11.3. URIs
[1] http://prismproof.org/Documents/draft-hallambaker-jsonbcd.html
[2] http://prismproof.org/Documents/draft-hallambaker-jsonbcd.html
[3] http://prismproof.org/Documents/draft-hallambaker-jsonbcd.html
Author's Address
Phillip Hallam-Baker
Comodo Group Inc.
Email: philliph@comodo.com
Hallam-Baker Expires October 12, 2018 [Page 21]