JSON Canonicalization

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 [ES], constraining JSON data to the I-JSON [RFC7493] subset, and through a platform independent property sorting scheme.

Public RFC: https://tools.ietf.org/html/rfc8785

The JSON Canonicalization Scheme concept in a nutshell:

• Serialization of primitive JSON data types using methods compatible with ECMAScript's JSON.stringify()
• Lexicographic sorting of JSON Object properties in a recursive process
• JSON Array data is also subject to canonicalization, but element order remains untouched

Original Work

This code was originally created by Anders Rundgren aka cyberphone and can be found here: https://github.com/cyberphone/json-canonicalization. This fork and work is done with Anders' permission and is an attempt to clean up the Golang version.

Sample Input

{
  "numbers": [333333333.33333329, 1E30, 4.50, 2e-3, 0.000000000000000000000000001],
  "string": "\u20ac$\u000F\u000aA'\u0042\u0022\u005c\\\"\/",
  "literals": [null, true, false]
}

Expected Output

{"literals":[null,true,false],"numbers":[333333333.3333333,1e+30,4.5,0.002,1e-27],"string":"€$\u000f\nA'B\"\\\\\"/"}

Note: for platform interoperable canonicalization, the output must be converted to UTF-8 as well, 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

Combining JCS and JWS (RFC7515)

JWS-JCS

On-line Browser JCS Test

https://cyberphone.github.io/doc/security/browser-json-canonicalization.html

ECMAScript Proposal: JSON.canonify()

JSON.canonify()

Other Canonicalization Efforts

https://tools.ietf.org/html/draft-staykov-hu-json-canonical-form-00

http://wiki.laptop.org/go/Canonical_JSON

https://gibson042.github.io/canonicaljson-spec/

https://gist.github.com/mikesamuel/20710f94a53e440691f04bf79bc3d756