Canonical JSON

  This page is monitored by the OLPC team.

A "canonical JSON" format is provided in order to provide meaningful and repeatable hashes of JSON-encoded data. Canonical JSON is parsable with any full JSON parser, but security-conscious applications will want to verify that input is in canonical form before authenticating any hash or signature on that input.

The grammar for canonical JSON closely matches the grammar presented at json.org:

object:
    {}
    { members } 
 members:
   pair
   pair , members
pair:
   string : value
array:
   []
   [ elements ]
elements:
   value
   value , elements
value:
   string
   number
   object
   array
   true
   false
   null
string:
   ""
   " chars "
chars:
   char
   char chars
char:
   any-7-bit-ASCII-character-except-"-or-\-and-control-characters
   \u four-hex-digits-in-lowercase
number:
   int
int:
   digit
   digit1-9 digits
   - digit1-9
   - digit1-9 digits
digits:
   digit
   digit digits

Whitespace is not permitted between tokens. Leading and trailing whitespace is likewise disallowed. The members production in object must consist of keys in lexicographically sorted order. Contents of strings must be in a UTF-16 encoding of unicode Normalization Form D (UAX #15) with no byte-order mark (since each character-or-escape-sequence encodes a full 16-bit codepoint). Control characters are defined as unicode codepoint 127 (decimal) and those with unicode codepoints less than 32. The "backslash u" escape form must not be used for any unicode character with code point greater than 31 (decimal) or less than 127 (decimal), except for codepoint 34 (decimal) and codepoint 92 (decimal), which are, respectively, the quotation and backslash character.

Notes

• Floating point numbers are not allowed in canonical JSON. Neither are leading zeros or "minus 0" for integers.
• All map keys must be quoted, and must appear in sorted order.
• All whitespace is eliminated.
• Trailing commas in members and elements are not allowed.
• Only one 'escape' sequence is defined for strings, and its use is mandatory for certain characters.