Internet DRAFT - draft-rundgren-comparable-json
draft-rundgren-comparable-json
Network Working Group A. Rundgren
Internet-Draft Independent
Intended status: Informational February 13, 2019
Expires: August 17, 2019
"Comparable" JSON (JSONCOMP)
draft-rundgren-comparable-json-04
Abstract
This application note describes how JCS [JCS] can be utilized to
support applications needing canonicalization beyond the core JSON
[RFC8259] level, with comparisons as the primary target.
Status of This Memo
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This Internet-Draft will expire on August 17, 2019.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. String Subtype Normalization . . . . . . . . . . . . . . . . 2
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 3
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informal References . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
The purpose of JCS [JCS] is creating "Hashable" representations of
JSON [RFC8259] data intended for cryptographic solutions. JCS
accomplishes this by combining normalization of the native JSON
String and Number primitives with a deterministic property sorting
scheme. That is, JCS provides canonicalization at the core JSON
level. For interoperability reasons JCS also constrains data to the
I-JSON [RFC7493] subset.
However, if you rather would like to compare JSON data from different
sources or runs, JCS would in many cases be inadequate since the JSON
String type is commonly used for holding subtypes like "DateTime" or
"BigInteger" objects.
This application note outlines how JCS in spite of having a limited
canonicalization scope still may be utilized by applications like
above.
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. String Subtype Normalization
Assume you want to compare productions of JSON data where the schema
designer assigned the property "big" for holding a "BigInteger"
subtype and "time" for holding a "DateTime" subtype, while "val" is
supposed to be a JSON Number compliant with JCS. The following
example shows such an object:
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{
"time": "2019-01-28T07:45:10Z",
"big": "055",
"val": 3.5
}
A problem here is that "055" clearly is not a canonical form for a
"BigInteger" while a "DateTime" object like "2019-01-28T07:45:10Z"
might as well be expressed as "2019-01-28T08:45:10.000+01:00" making
comparisons based on JCS canonicalization fail.
To resolve this issue using JCS the following measures MUST be taken:
o The community or standard utilizing a specific JSON schema defines
a strict normalized form for each of the used subtypes.
o Compatible serializers are created for each subtype.
A positive side effect of this arrangement is that it enforces strict
definitions of subtypes which improves interoperability in general as
well.
Defining specific subtypes and their normalized form is out of scope
for this application note. Although the JSON example illustrated a
"BigInteger" in decimal notation, applications transferring huge
integers (like raw RSA keys) typically rather use Base64 [RFC4648]
encoding to conserve space.
Below is an example of a strict serializer expressed in ECMAScript
[ECMASCRIPT] for a "DateTime" subtype:
Date.prototype.toJSON = function() {
let date = this.toISOString();
// In this particular case an ISO/UTC notation was selected
// yyyy-mm-ddThh:mm:ssZ
return date.substring(0, date.indexOf('.')) + 'Z';
};
4. IANA Considerations
This document has no IANA actions.
5. Security Considerations
Systems implementing this application note are subject to the same
security considerations as JCS.
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6. Acknowledgements
This document was created based on feedback (on JCS) from many people
including Mark Nottingham and Jim Schaad.
7. References
7.1. Normative References
[JCS] A. Rundgren, B. Jordan, S. Erdtman, "JSON Canonicalization
Scheme - Work in progress", <https://tools.ietf.org/html/
draft-rundgren-json-canonicalization-scheme-05>.
[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>.
[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>.
7.2. Informal References
[ECMASCRIPT]
Ecma International, "ECMAScript 2015 Language
Specification", <https://www.ecma-international.org/ecma-
262/6.0/index.html>.
[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>.
Author's Address
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Anders Rundgren
Independent
Montpellier
France
Email: anders.rundgren.net@gmail.com
URI: https://www.linkedin.com/in/andersrundgren/
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