mirror of
https://github.com/element-hq/synapse.git
synced 2024-11-28 15:08:49 +03:00
haven't i already moved you to matrix-doc twice? :/
This commit is contained in:
Matthew Hodgson
parent
216d5f6b52
commit
b6c48a694b
1 changed files with 0 additions and 151 deletions
|
|
@ -1,151 +0,0 @@
|
||||||
Signing JSON
|
|
||||||
============
|
|
||||||
|
|
||||||
JSON is signed by encoding the JSON object without ``signatures`` or ``unsigned``
|
|
||||||
keys using a canonical encoding. The JSON bytes are then signed using the
|
|
||||||
signature algorithm and the signature encoded using base64 with the padding
|
|
||||||
stripped. The resulting base64 signature is added to an object under the
|
|
||||||
*signing key identifier* which is added to the ``signatures`` object under the
|
|
||||||
name of the server signing it which is added back to the original JSON object
|
|
||||||
along with the ``unsigned`` object.
|
|
||||||
|
|
||||||
The *signing key identifier* is the concatenation of the *signing algorithm*
|
|
||||||
and a *key version*. The *signing algorithm* identifies the algorithm used to
|
|
||||||
sign the JSON. The currently support value for *signing algorithm* is
|
|
||||||
``ed25519`` as implemented by NACL (http://nacl.cr.yp.to/). The *key version*
|
|
||||||
is used to distinguish between different signing keys used by the same entity.
|
|
||||||
|
|
||||||
The ``unsigned`` object and the ``signatures`` object are not covered by the
|
|
||||||
signature. Therefore intermediate servers can add unsigneddata such as time stamps
|
|
||||||
and additional signatures.
|
|
||||||
|
|
||||||
|
|
||||||
::
|
|
||||||
|
|
||||||
{
|
|
||||||
"name": "example.org",
|
|
||||||
"signing_keys": {
|
|
||||||
"ed25519:1": "XSl0kuyvrXNj6A+7/tkrB9sxSbRi08Of5uRhxOqZtEQ"
|
|
||||||
},
|
|
||||||
"unsigned": {
|
|
||||||
"retrieved_ts_ms": 922834800000
|
|
||||||
},
|
|
||||||
"signatures": {
|
|
||||||
"example.org": {
|
|
||||||
"ed25519:1": "s76RUgajp8w172am0zQb/iPTHsRnb4SkrzGoeCOSFfcBY2V/1c8QfrmdXHpvnc2jK5BD1WiJIxiMW95fMjK7Bw"
|
|
||||||
}
|
|
||||||
}
|
|
||||||
}
|
|
||||||
|
|
||||||
::
|
|
||||||
|
|
||||||
def sign_json(json_object, signing_key, signing_name):
|
|
||||||
signatures = json_object.pop("signatures", {})
|
|
||||||
unsigned = json_object.pop("unsigned", None)
|
|
||||||
|
|
||||||
signed = signing_key.sign(encode_canonical_json(json_object))
|
|
||||||
signature_base64 = encode_base64(signed.signature)
|
|
||||||
|
|
||||||
key_id = "%s:%s" % (signing_key.alg, signing_key.version)
|
|
||||||
signatures.setdefault(sigature_name, {})[key_id] = signature_base64
|
|
||||||
|
|
||||||
json_object["signatures"] = signatures
|
|
||||||
if unsigned is not None:
|
|
||||||
json_object["unsigned"] = unsigned
|
|
||||||
|
|
||||||
return json_object
|
|
||||||
|
|
||||||
Checking for a Signature
|
|
||||||
------------------------
|
|
||||||
|
|
||||||
To check if an entity has signed a JSON object a server does the following
|
|
||||||
|
|
||||||
1. Checks if the ``signatures`` object contains an entry with the name of the
|
|
||||||
entity. If the entry is missing then the check fails.
|
|
||||||
2. Removes any *signing key identifiers* from the entry with algorithms it
|
|
||||||
doesn't understand. If there are no *signing key identifiers* left then the
|
|
||||||
check fails.
|
|
||||||
3. Looks up *verification keys* for the remaining *signing key identifiers*
|
|
||||||
either from a local cache or by consulting a trusted key server. If it
|
|
||||||
cannot find a *verification key* then the check fails.
|
|
||||||
4. Decodes the base64 encoded signature bytes. If base64 decoding fails then
|
|
||||||
the check fails.
|
|
||||||
5. Checks the signature bytes using the *verification key*. If this fails then
|
|
||||||
the check fails. Otherwise the check succeeds.
|
|
||||||
|
|
||||||
Canonical JSON
|
|
||||||
--------------
|
|
||||||
|
|
||||||
The canonical JSON encoding for a value is the shortest UTF-8 JSON encoding
|
|
||||||
with dictionary keys lexicographically sorted by unicode codepoint. Numbers in
|
|
||||||
the JSON value must be integers in the range [-(2**53)+1, (2**53)-1].
|
|
||||||
|
|
||||||
::
|
|
||||||
|
|
||||||
import json
|
|
||||||
|
|
||||||
def canonical_json(value):
|
|
||||||
return json.dumps(
|
|
||||||
value,
|
|
||||||
ensure_ascii=False,
|
|
||||||
separators=(',',':'),
|
|
||||||
sort_keys=True,
|
|
||||||
).encode("UTF-8")
|
|
||||||
|
|
||||||
Grammar
|
|
||||||
+++++++
|
|
||||||
|
|
||||||
Adapted from the grammar in http://tools.ietf.org/html/rfc7159 removing
|
|
||||||
insignificant whitespace, fractions, exponents and redundant character escapes
|
|
||||||
|
|
||||||
::
|
|
||||||
|
|
||||||
value = false / null / true / object / array / number / string
|
|
||||||
false = %x66.61.6c.73.65
|
|
||||||
null = %x6e.75.6c.6c
|
|
||||||
true = %x74.72.75.65
|
|
||||||
object = %x7B [ member *( %x2C member ) ] %7D
|
|
||||||
member = string %x3A value
|
|
||||||
array = %x5B [ value *( %x2C value ) ] %5B
|
|
||||||
number = [ %x2D ] int
|
|
||||||
int = %x30 / ( %x31-39 *digit )
|
|
||||||
digit = %x30-39
|
|
||||||
string = %x22 *char %x22
|
|
||||||
char = unescaped / %x5C escaped
|
|
||||||
unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
|
|
||||||
escaped = %x22 ; " quotation mark U+0022
|
|
||||||
/ %x5C ; \ reverse solidus U+005C
|
|
||||||
/ %x62 ; b backspace U+0008
|
|
||||||
/ %x66 ; f form feed U+000C
|
|
||||||
/ %x6E ; n line feed U+000A
|
|
||||||
/ %x72 ; r carriage return U+000D
|
|
||||||
/ %x74 ; t tab U+0009
|
|
||||||
/ %x75.30.30.30 (%x30-37 / %x62 / %x65-66) ; u000X
|
|
||||||
/ %x75.30.30.31 (%x30-39 / %x61-66) ; u001X
|
|
||||||
|
|
||||||
Signing Events
|
|
||||||
==============
|
|
||||||
|
|
||||||
Signing events is a more complicated process since servers can choose to redact
|
|
||||||
non-essential event contents. Before signing the event it is encoded as
|
|
||||||
Canonical JSON and hashed using SHA-256. The resulting hash is then stored
|
|
||||||
in the event JSON in a ``hash`` object under a ``sha256`` key. Then all
|
|
||||||
non-essential keys are stripped from the event object, and the resulting object
|
|
||||||
which included the ``hash`` key is signed using the JSON signing algorithm.
|
|
||||||
|
|
||||||
Servers can then transmit the entire event or the event with the non-essential
|
|
||||||
keys removed. Receiving servers can then check the entire event if it is
|
|
||||||
present by computing the SHA-256 of the event excluding the ``hash`` object, or
|
|
||||||
by using the ``hash`` object included in the event if keys have been redacted.
|
|
||||||
|
|
||||||
New hash functions can be introduced by adding additional keys to the ``hash``
|
|
||||||
object. Since the ``hash`` object cannot be redacted a server shouldn't allow
|
|
||||||
too many hashes to be listed, otherwise a server might embed illict data within
|
|
||||||
the ``hash`` object. For similar reasons a server shouldn't allow hash values
|
|
||||||
that are too long.
|
|
||||||
|
|
||||||
[[TODO(markjh): We might want to specify a maximum number of keys for the
|
|
||||||
``hash`` and we might want to specify the maximum output size of a hash]]
|
|
||||||
|
|
||||||
[[TODO(markjh) We might want to allow the server to omit the output of well
|
|
||||||
known hash functions like SHA-256 when none of the keys have been redacted]]
|
|
||||||
Loading…
Reference in a new issue