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explain how to use key sharing events

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Valentin Deniaud 2018-08-25 17:27:18 +02:00
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specification/modules/end_to_end_encryption.rst
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@ -291,6 +291,17 @@ through his phone for the first time, he may want to have access to the previous
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.