.. Copyright 2019 The Matrix.org Foundation C.I.C.
..
.. Licensed under the Apache License, Version 2.0 (the "License");
.. you may not use this file except in compliance with the License.
.. You may obtain a copy of the License at
..
..     http://www.apache.org/licenses/LICENSE-2.0
..
.. Unless required by applicable law or agreed to in writing, software
.. distributed under the License is distributed on an "AS IS" BASIS,
.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
.. See the License for the specific language governing permissions and
.. limitations under the License.

Room Version 5
==============

This room version builds on `version 4 <v4.html>`_ while enforcing signing
key validity periods for events.

.. contents:: Table of Contents
.. sectnum::


Client considerations
---------------------

There are no specific requirements for clients in this room version. Clients should
be aware of event ID changes in `room version 4 <v4.html>`_, however.


Server implementation components
--------------------------------

.. WARNING::
   The information contained in this section is strictly for server implementors.
   Applications which use the Client-Server API are generally unaffected by the
   intricacies contained here. The section above regarding client considerations
   is the resource that Client-Server API use cases should reference.


Room version 5 uses the same algorithms defined in `room version 4 <v4.html>`_, ensuring
that signing key validity is respected.

Signing key validity period
~~~~~~~~~~~~~~~~~~~~~~~~~~~

When validating event signatures, servers MUST enforce the ``valid_until_ts`` property
from a key request is at least as large as the ``origin_server_ts`` for the event being
validated. Servers missing a copy of the signing key MUST try to obtain one via the
`GET /_matrix/key/v2/server <../server_server/%SERVER_RELEASE_LABEL%.html#get-matrix-key-v2-server-keyid>`_
or `POST /_matrix/key/v2/query <../server_server/%SERVER_RELEASE_LABEL%.html#post-matrix-key-v2-query>`_
APIs. When using the ``/query`` endpoint, servers MUST set the ``minimum_valid_until_ts``
property to prompt the notary server to attempt to refresh the key if appropriate.

Servers MUST use the lesser of ``valid_until_ts`` and 7 days into the future when
determining if a key is valid. This is to avoid a situation where an attacker
publishes a key which is valid for a significant amount of time without a way for
the homeserver owner to revoke it.
