wholetrans/docs-matrix-spec
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

Merge pull request #1465 from Zil0/key_sharing

Browse source 
Document key sharing events
This commit is contained in:
Hubert Chathi 2018-08-29 23:05:17 -04:00 • committed by GitHub
commit 4230e375fa
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
7 changed files with 186 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

29
specification/modules/end_to_end_encryption.rst
View file

@ -283,6 +283,31 @@ Device verification may reach one of several conclusions. For example:
decrypted by such a device. For the Olm protocol, this is documented at
https://matrix.org/git/olm/about/docs/signing.rst.
Key sharing
-----------
If Bob has an encrypted conversation with Alice on his computer, and then logs in
through his phone for the first time, he may want to have access to the previously
exchanged messages. To address this issue, events exist for requesting and sending
keys from device to device.
When a device is missing keys to decrypt messages, it can request the keys by
sending `m.room_key_request`_ to-device messages to other devices with
``action`` set to ``request``. If a device wishes to share the keys with that
device, it can forward the keys to the first device by sending an encrypted
`m.forwarded_room_key`_ to-device message. The first device should then send an
`m.room_key_request`_ to-device message with ``action`` set to
``cancel_request`` to the other devices that it had originally sent the key
request to; a device that receives a ``cancel_request`` should disregard any
previously-received ``request`` message with the same ``request_id`` and
``requesting_device_id``.
.. NOTE::
Key sharing can be a big attack vector, thus it must be done very carefully.
A reasonable stategy is for a user's client to only send keys requested by the
verified devices of the same user.
Messaging Algorithms
--------------------
@ -470,6 +495,10 @@ Events
{{m_room_key_event}}
{{m_room_key_request_event}}
{{m_forwarded_room_key_event}}
Key management API
~~~~~~~~~~~~~~~~~~