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
Objectproperties in a recursive process - JSON
Arraydata is also subject to canonicalization, but element order remains untouched
{
"numbers": [333333333.33333329, 1E30, 4.50, 2e-3, 0.000000000000000000000000001],
"string": "\u20ac$\u000F\u000aA'\u0042\u0022\u005c\\\"\/",
"literals": [null, true, false]
}
{"literals":[null,true,false],"numbers":[333333333.3333333,1e+30,4.5,0.002,1e-27],"string":"€$\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
https://cyberphone.github.io/doc/security/browser-json-canonicalization.html
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