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Network Working Group A. Rundgren
Internet-Draft Independent
Intended status: Informational December 19, 2018
Expires: June 22, 2019
JSON Canonicalization Scheme (JCS)
draft-rundgren-json-canonicalization-scheme-02
Abstract
Cryptographic operations like hashing and signing depend on that the
target data does not change during serialization, transport, or
parsing. By applying the rules defined by JCS (JSON Canonicalization
Scheme), data provided in the JSON [RFC8259] format can be exchanged
"as is", while still being subject to secure cryptographic
operations. JCS achieves this by building on the serialization
formats for JSON primitives as defined by ECMAScript [ES6],
constraining JSON data to the I-JSON [RFC7493] subset, and through a
platform independent property sorting scheme.
The intended audiences of this document are JSON tool vendors, as
well as designers of JSON based cryptographic solutions.
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 https://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 June 22, 2019.
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
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(https://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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Detailed Operation . . . . . . . . . . . . . . . . . . . . . 3
3.1. Creation of JSON Data . . . . . . . . . . . . . . . . . . 3
3.2. Canonicalization of JSON Data . . . . . . . . . . . . . . 4
3.2.1. Whitespace Handling . . . . . . . . . . . . . . . . . 4
3.2.2. Serialization of Primitive Data Types . . . . . . . . 4
3.2.2.1. Serialization of Literals . . . . . . . . . . . . 5
3.2.2.2. Serialization of Strings . . . . . . . . . . . . 5
3.2.2.3. Serialization of Numbers . . . . . . . . . . . . 6
3.2.3. Sorting of Object Properties . . . . . . . . . . . . 6
3.2.4. UTF-8 Generation . . . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informal References . . . . . . . . . . . . . . . . . . . 9
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Appendix A. ES6 Sample Canonicalizer . . . . . . . . . . . . . . 10
Appendix B. Number Serialization Samples . . . . . . . . . . . . 11
Appendix C. Canonicalized JSON as "Wire Format" . . . . . . . . 13
Appendix D. Dealing with Big Numbers . . . . . . . . . . . . . . 14
Appendix E. Implementation Guidelines . . . . . . . . . . . . . 15
Appendix F. Open Source Implementations . . . . . . . . . . . . 16
Appendix G. Other JSON Canonicalization Efforts . . . . . . . . 16
Appendix H. Development Portal . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
Cryptographic operations like hashing and signing depend on that the
target data does not change during serialization, transport, or
parsing. A straightforward way of accomplishing this is converting
the data into a format having a simple and fixed representation like
Base64Url [RFC4648], used in JWS [RFC7515]. Another solution is
creating a canonicalized version of the target data with XML
Signature [XMLDSIG] as a prime example.
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Since the objective was keeping the data "as is", the
canonicalization method was selected. For avoiding "reinventing the
wheel", JCS relies on serialization of JSON primitives compatible
with ECMAScript (aka JavaScript) beginning with version 6 [ES6], from
now on simply referred to as "ES6".
Seasoned XML developers recalling difficulties getting signatures to
validate (usually due to different interpretations of the quite
intricate XML canonicalization rules as well as of the equally
extensive Web Services security standards), may rightfully wonder why
JCS would not suffer from similar issues. The reasons are twofold:
o The absence of a namespace concept and default values, as well as
constraining data to I-JSON eliminate the need for specific
parsing schemes for canonicalized data.
o JCS compatible serialization of JSON primitives is already
supported by most Web browsers and Node.js [NODEJS], while the
full JCS specification is supported by multiple Open Source
implementations (see Appendix F), giving the proposed
canonicalization scheme a head start. Also see Appendix E.
The JCS specification describes how serialization of JSON primitives
compliant with ES6, combined with an elementary property sorting
scheme, can be used for supporting "Crypto Safe" JSON.
JCS is compatible with some existing systems relying on JSON
canonicalization such as JWK Thumbprint [RFC7638] and Keybase
[KEYBASE].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Detailed Operation
This section describes the different issues related to JSON
canonicalization, and how they are addressed by JCS.
3.1. Creation of JSON Data
In order to canonicalize JSON data, an internal representation of the
JSON data is needed. This can be achieved by:
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o Parsing externally supplied JSON data.
o Programmatic creation of JSON data.
Irrespective of method used, the JSON data MUST be compatible both
with ES6 and I-JSON [RFC7493], which implies the following:
o There MUST NOT be any duplicate property names within an "Object".
o Data of the type "String" MUST be expressible as Unicode [UNICODE]
strings. Also see Section 3.2.2.2.
o Data of the type "Number" MUST be expressible as IEEE-754
[IEEE754] double precision values. Also see Section 3.2.2.3.
3.2. Canonicalization of JSON Data
The following sub sections describe the steps required for creating a
canonicalized version of internal JSON data elaborated on in the
previous section.
Appendix A shows sample code for an ES6 based canonicalizer, matching
the JCS specification.
3.2.1. Whitespace Handling
Whitespace between JSON elements MUST NOT be emitted.
3.2.2. Serialization of Primitive Data Types
Assume that you parse a JSON object like the following:
{
"numbers": [333333333.33333329, 1E30, 4.50,
2e-3, 0.000000000000000000000000001],
"string": "\u20ac$\u000F\u000aA'\u0042\u0022\u005c\\\"\/",
"literals": [null, true, false]
}
If you subsequently serialize the object created by the operation
above using an serializer compliant with ES6's "JSON.stringify()",
the result would (with a line wrap added for display purposes only),
be rather divergent with respect to representation of data:
{"numbers":[333333333.3333333,1e+30,4.5,0.002,1e-27],"string":
"\u20ac$\u000f\nA'B\"\\\\\"/","literals":[null,true,false]}
Note: \u20ac denotes the Euro character, which not
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being ASCII, is currently not displayable in RFCs.
The reason for the difference between the parsed data and its
serialized counterpart, is due to a wide tolerance on input data (as
defined by JSON [RFC8259]), while output data (as defined by ES6),
has a fixed representation. As can be seen by the example, numbers
are subject to rounding as well.
The following sub sections describe serialization of primitive JSON
data types according to JCS. This part is identical to that of ES6.
3.2.2.1. Serialization of Literals
The JSON literals "null", "true", and "false" present no challenge
since they already have a fixed definition in JSON [RFC8259].
3.2.2.2. Serialization of Strings
For JSON data of the type "String" (which includes "Object" property
names as well), each character MUST be serialized as described below
(also matching section 24.3.2.2 of ES6):
o If the Unicode value falls within the traditional ASCII control
character range (U+0000 through U+001F), it MUST be serialized
using lowercase hexadecimal Unicode notation (\uhhhh) unless it is
in the set of predefined JSON control characters U+0008, U+0009,
U+000A, U+000C or U+000D which MUST be serialized as \b, \t, \n,
\f and \r respectively.
o If the Unicode value is outside of the ASCII control character
range, it MUST be serialized "as is" unless it is equivalent to
U+005C (\) or U+0022 (") which MUST be serialized as \\ and \"
respectively.
Finally, the serialized string value MUST be enclosed in double
quotes (").
Note: some JSON systems permit the use of invalid Unicode data like
"lone surrogates" (e.g. U+DEAD), which also is dealt with in a
platform specific way. Since this leads to interoperability issues
including broken signatures, such usages MUST be avoided.
Note: although the Unicode standard offers a possibility combining
certain characters into one, referred to as "Unicode Normalization"
(https://www.unicode.org/reports/tr15/ [1]), such functionality MUST
be delegated to the application layer which already is the case for
most other uses of JSON.
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3.2.2.3. Serialization of Numbers
JSON data of the type "Number" MUST be serialized according to
section 7.1.12.1 of ES6; for maximum interoperability preferably
including the "Note 2" enhancement as well. The latter is
implemented by for example Google's V8 [V8].
Due to the relative complexity of this part, it is not included in
this specification.
Note: ES6 builds on the IEEE-754 [IEEE754] double precision standard
for storing "Number" data. Appendix B holds a set of IEEE-754 sample
values and their corresponding JSON serialization.
Occasionally applications need higher precision or longer integers
than offered by the current implementation of JSON "Number" in ES6.
Appendix D outlines how this can be achieved in a portable and
extensible way.
3.2.3. Sorting of Object Properties
Although the previous step indeed normalized the representation of
primitive JSON data types, the result would not qualify as canonical
since JSON "Object" properties are not in lexicographic
(alphabetical) order.
Applied to the sample in Section 3.2.2, a properly canonicalized
version should (with a line wrap added for display purposes only),
read as:
{"literals":[null,true,false],"numbers":[333333333.3333333,
1e+30,4.5,0.002,1e-27],"string":"\u20ac$\u000f\nA'B\"\\\\\"/"}
Note: \u20ac denotes the Euro character, which not
being ASCII, is currently not displayable in RFCs.
The rules for lexicographic sorting of JSON "Object" properties
according to JCS are as follows:
o JSON "Object" properties MUST be sorted in a recursive manner
which means that a found JSON child "Object" type MUST be subject
to sorting as well.
o JSON "Array" data MUST also be scanned for presence of sortable
JSON "Object" elements, but array element order MUST NOT be
changed.
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When a JSON "Object" is about to have its properties sorted, the
following measures MUST be adhered to:
o The sorting process is applied to the internal representation of
property strings. That is, their state before serialization.
o Property strings to be sorted depend on that such strings are
formatted as arrays of UTF-16 [UNICODE] code units. The sorting
is based on pure value comparisons, where code units are treated
as unsigned integers, independent of locale settings.
o Property strings either have different values at some index that
is a valid index for both strings, or their lengths are different,
or both. If they have different values at one or more index
positions, let k be the smallest such index; then the string whose
value at position k has the smaller value, as determined by using
the < operator, lexicographically precedes the other string. If
there is no index position at which they differ, then the shorter
string lexicographically precedes the longer string.
The rationale for basing the sort algorithm on UTF-16 code units is
that it maps directly to the string type in ECMAScript, Java and
.NET. Systems using another internal representation of string data
will need to convert JSON property strings into arrays of UTF-16 code
units before sorting.
Note: for the purpose obtaining a deterministic property order,
sorting on UTF-8 or UTF-32 encoded data would also work, but the
result would differ (and thus be incompatible with this
specification).
3.2.4. UTF-8 Generation
Finally, in order to create a platform independent representation,
the resulting JSON string data MUST be encoded in UTF-8.
Applied to the sample in Section 3.2.3 this should yield the
following bytes here shown in hexadecimal notation:
7b 22 6c 69 74 65 72 61 6c 73 22 3a 5b 6e 75 6c 6c 2c 74 72
75 65 2c 66 61 6c 73 65 5d 2c 22 6e 75 6d 62 65 72 73 22 3a
5b 33 33 33 33 33 33 33 33 33 2e 33 33 33 33 33 33 33 2c 31
65 2b 33 30 2c 34 2e 35 2c 30 2e 30 30 32 2c 31 65 2d 32 37
5d 2c 22 73 74 72 69 6e 67 22 3a 22 e2 82 ac 24 5c 75 30 30
30 66 5c 6e 41 27 42 5c 22 5c 5c 5c 5c 5c 22 2f 22 7d
This data is intended to be usable as input to cryptographic methods
as well as for value comparisons of JSON objects.
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For other uses see Appendix C.
4. IANA Considerations
This document has no IANA actions.
5. Security Considerations
It is vital performing "sanity" checks on input data to avoid
overflowing buffers and similar things that could affect the
integrity of the system. By doing that an incorrectly implemented
JCS algorithm or improperly canonicalized data should not introduce a
security problem, but rather make the associated application
(preferably gracefully) fail due to a broken signature, hash or
comparison.
6. Acknowledgements
Building on ES6 "Number" normalization was originally proposed by
James Manger. This ultimately led to the adoption of the entire ES6
serialization scheme for JSON primitives.
Other people who have contributed with valuable input to this
specification include John-Mark Gurney, Mike Jones, Mike Miller, Mike
Samuel, Michal Wadas, Richard Gibson, Robert Tupelo-Schneck and Scott
Ananian.
7. References
7.1. Normative References
[ES6] Ecma International, "ECMAScript 2015 Language
Specification", <https://www.ecma-international.org/ecma-
262/6.0/index.html>.
[IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic",
August 2008, <http://grouper.ieee.org/groups/754/>.
[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>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
10.0.0",
<https://www.unicode.org/versions/Unicode10.0.0/>.
7.2. Informal References
[KEYBASE] "Keybase",
<https://keybase.io/docs/api/1.0/canonical_packings#json>.
[NODEJS] "Node.js", <https://nodejs.org>.
[OPENAPI] "The OpenAPI Initiative", <https://www.openapis.org/>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[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>.
[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK)
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
2015, <https://www.rfc-editor.org/info/rfc7638>.
[V8] Google LLC, "Chrome V8 Open Source JavaScript Engine",
<https://developers.google.com/v8/>.
[XMLDSIG] W3C, "XML Signature Syntax and Processing Version 1.1",
<https://www.w3.org/TR/xmldsig-core1/>.
7.3. URIs
[1] https://www.unicode.org/reports/tr15/
[2] https://www.npmjs.com/package/canonicalize
[3] https://github.com/erdtman/java-json-canonicalization
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[4] https://github.com/cyberphone/json-canonicalization/tree/master/
dotnet
[5] https://github.com/cyberphone/json-canonicalization/tree/master/
python3
[6] https://tools.ietf.org/html/draft-staykov-hu-json-canonical-
form-00
[7] https://gibson042.github.io/canonicaljson-spec/
[8] http://wiki.laptop.org/go/Canonical_JSON
[9] https://github.com/cyberphone/json-canonicalization
Appendix A. ES6 Sample Canonicalizer
Below is a functionally complete example of a JCS compliant
canonicalizer for usage with ES6 based systems.
Note: the primary purpose of this code is highlighting the
canonicalization algorithm. Using the full power of ES6 would reduce
the code size considerably but would also be more difficult to follow
by non-experts.
var canonicalize = function(object) {
var buffer = '';
serialize(object);
return buffer;
function serialize(object) {
if (object === null || typeof object !== 'object') {
/////////////////////////////////////////////////
// Primitive data type - Use ES6/JSON //
/////////////////////////////////////////////////
buffer += JSON.stringify(object);
} else if (Array.isArray(object)) {
/////////////////////////////////////////////////
// Array - Maintain element order //
/////////////////////////////////////////////////
buffer += '[';
let next = false;
object.forEach((element) => {
if (next) {
buffer += ',';
}
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next = true;
/////////////////////////////////////////
// Array element - Recursive expansion //
/////////////////////////////////////////
serialize(element);
});
buffer += ']';
} else {
/////////////////////////////////////////////////
// Object - Sort properties before serializing //
/////////////////////////////////////////////////
buffer += '{';
let next = false;
Object.keys(object).sort().forEach((property) => {
if (next) {
buffer += ',';
}
next = true;
///////////////////////////////////////////////
// Property names are strings - Use ES6/JSON //
///////////////////////////////////////////////
buffer += JSON.stringify(property);
buffer += ':';
//////////////////////////////////////////
// Property value - Recursive expansion //
//////////////////////////////////////////
serialize(object[property]);
});
buffer += '}';
}
}
};
Appendix B. Number Serialization Samples
The following table holds a set of ES6 "Number" serialization
samples, including some edge cases. The column "IEEE-754" refers to
the internal ES6 representation of the "Number" data type which is
based on the IEEE-754 [IEEE754] standard using 64-bit (double
precision) values, here expressed in hexadecimal.
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|===================================================================|
| IEEE-754 | JSON Representation | Comment |
|===================================================================|
| 0000000000000000 | 0 | Zero |
|-------------------------------------------------------------------|
| 8000000000000000 | 0 | Minus zero |
|-------------------------------------------------------------------|
| 0000000000000001 | 5e-324 | Smallest pos number |
|-------------------------------------------------------------------|
| 8000000000000001 | -5e-324 | Smallest neg number |
|-------------------------------------------------------------------|
| 7fefffffffffffff | 1.7976931348623157e+308 | Largest pos number |
|-------------------------------------------------------------------|
| ffefffffffffffff | -1.7976931348623157e+308 | Largest neg number |
|-------------------------------------------------------------------|
| 4340000000000000 | 9007199254740992 | Largest pos integer |
|-------------------------------------------------------------------|
| c340000000000000 | -9007199254740992 | Largest neg integer |
|-------------------------------------------------------------------|
| 7fffffffffffffff | | Error (NaN) |
|-------------------------------------------------------------------|
| 7ff0000000000000 | | Error (Infinity) |
|-------------------------------------------------------------------|
| 44b52d02c7e14af5 | 9.999999999999997e+22 | |
|-------------------------------------------------------------------|
| 44b52d02c7e14af6 | 1e+23 | |
|-------------------------------------------------------------------|
| 44b52d02c7e14af7 | 1.0000000000000001e+23 | |
|-------------------------------------------------------------------|
| 444b1ae4d6e2ef4e | 999999999999999700000 | |
|-------------------------------------------------------------------|
| 444b1ae4d6e2ef4f | 999999999999999900000 | |
|-------------------------------------------------------------------|
| 444b1ae4d6e2ef50 | 1e+21 | |
|-------------------------------------------------------------------|
| 444b1ae4d6e2ef51 | 1.0000000000000001e+21 | |
|-------------------------------------------------------------------|
| 41b3de4355555553 | 333333333.3333332 | |
|-------------------------------------------------------------------|
| 41b3de4355555554 | 333333333.33333325 | |
|-------------------------------------------------------------------|
| 41b3de4355555555 | 333333333.3333333 | |
|-------------------------------------------------------------------|
| 41b3de4355555556 | 333333333.3333334 | |
|-------------------------------------------------------------------|
| 41b3de4355555557 | 333333333.33333343 | |
|-------------------------------------------------------------------|
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Note: for maximum compliance with ECMAScript's JSON object, values
that are to be interpreted as true integers, SHOULD be in the range
-9007199254740991 to 9007199254740991.
Note: although a set of specific integers like 2**68
(4430000000000000 in IEEE-754 format) could be regarded as having
extended precision, the JCS/ES6 number serialization algorithm does
not take this in consideration.
Appendix C. Canonicalized JSON as "Wire Format"
Since the result from the canonicalization process (see
Section 3.2.4), is fully valid JSON, it can also be used as
"Wire Format". However, this is just an option since cryptographic
schemes based on JCS, in most cases would not depend on that
externally supplied JSON data already is canonicalized.
In fact, the ES6 standard way of serializing objects using
"JSON.stringify()" produces a more "logical" format, where properties
are kept in the order they were created or received. The example
below shows an address record which could benefit from ES6 standard
serialization:
{
"name": "John Doe",
"address": "2000 Sunset Boulevard",
"city": "Los Angeles",
"zip": "90001",
"state": "CA"
}
Using canonicalization the properties above would be output in the
order "address", "city", "name", "state" and "zip", which adds
fuzziness to the data from a human (developer or technical support),
perspective.
That is, for many applications, canonicalization would only be used
internally for creating a "hashable" representation of the data
needed for cryptographic operations.
Note: if message size is not a concern, you may even send
"Pretty Printed" JSON data on the wire (since whitespace always is
ignored by the canonicalization process).
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Appendix D. Dealing with Big Numbers
There are two major issues associated with the JSON "Number" type,
here illustrated by the following sample object:
{
"giantNumber": 1.4e+9999,
"payMeThis": 26000.33,
"int64Max": 9223372036854775807
}
Although the sample above conforms to JSON (according to [RFC8259]),
there are some practical hurdles to consider:
o Standard JSON parsers rarely process "giantNumber" in a meaningful
way. 64-bit integers like "int64Max" normally pass through
parsers, but in systems like ES6, at the expense of lost
precision.
o Another issue is that parsers typically would use different
schemes for handling "giantNumber" and "int64Max". In addition,
monetary data like "payMeThis" would presumably not rely on a
floating point system due to rounding issues with respect to
decimal arithmetic.
The (to the author NB), only known way handling this kind of
"overloading" of the "Number" type (at least in an extensible
manner), is through mapping mechanisms, instructing parsers what
to do with different properties based on their name. However,
this greatly limits the value of using the "Number" type outside
of its original somewhat constrained, JavaScript context.
For usage with JCS (and in fact for any usage of JSON by multiple
parties potentially using independently developed software), numbers
that do not have a natural place in the current JSON ecosystem MUST
be wrapped using the JSON "String" type. This is close to a de-facto
standard for open systems.
Aided by a mapping system; be it programmatic like
var obj = JSON.parse('{"giantNumber": "1.4e+9999"}');
var biggie = new BigNumber(obj.giantNumber);
or declarative schemes like OpenAPI [OPENAPI], there are no real
limits, not even when using ES6.
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Appendix E. Implementation Guidelines
The optimal solution is integrating support for JCS directly in JSON
serializers (parsers need no changes). That is, canonicalization
would just be an additional "mode" for a JSON serializer. However,
this is currently not the case. Fortunately JCS support can be
performed through externally supplied canonicalizer software,
enabling signature creation schemes like the following:
1. Create the data to be signed.
2. Serialize the data using existing JSON tools.
3. Let the external canonicalizer process the serialized data and
return canonicalized result data.
4. Sign the canonicalized data.
5. Add the resulting signature value to the original JSON data
through a designated signature property.
6. Serialize the completed (now signed) JSON object using existing
JSON tools.
A compatible signature verification scheme would then be as follows:
1. Parse the signed JSON data using existing JSON tools.
2. Read and save the signature value from the designated signature
property.
3. Remove the signature property from the parsed JSON object.
4. Serialize the remaining JSON data using existing JSON tools.
5. Let the external canonicalizer process the serialized data and
return canonicalized result data.
6. Verify that the canonicalized data matches the saved signature
value using the algorithm and key used for creating the
signature.
A canonicalizer like above is effectively only a "filter",
potentially usable with a multitude of quite different cryptographic
schemes.
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Using a JSON serializer with integrated JCS support, the
serialization performed before the canonicalization step could be
eliminated for both processes.
Appendix F. Open Source Implementations
The following Open Source implementations have been verified to be
compatible with JCS:
o JavaScript: https://www.npmjs.com/package/canonicalize [2]
o Java: https://github.com/erdtman/java-json-canonicalization [3]
o .NET/C#: https://github.com/cyberphone/json-
canonicalization/tree/master/dotnet [4]
o Python: https://github.com/cyberphone/json-
canonicalization/tree/master/python3 [5]
Appendix G. Other JSON Canonicalization Efforts
There are (and have been) other efforts creating "Canonical JSON".
Below is a list of URLs to some of them:
o https://tools.ietf.org/html/draft-staykov-hu-json-canonical-
form-00 [6]
o https://gibson042.github.io/canonicaljson-spec/ [7]
o http://wiki.laptop.org/go/Canonical_JSON [8]
Appendix H. Development Portal
The JSC specification is currently developed at
https://github.com/cyberphone/json-canonicalization [9].
The portal also provides software for on-line testing as well as test
data for implementers.
Author's Address
Anders Rundgren
Independent
Montpellier
France
Email: anders.rundgren.net@gmail.com
URI: https://www.linkedin.com/in/andersrundgren/
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