You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
46 lines
1.9 KiB
Markdown
46 lines
1.9 KiB
Markdown
6 years ago
|
# Olm unwedging
|
||
|
|
|
||
|
|
Olm sessions sometimes get out of sync, resulting in undecryptable messages.
|
||
|
|
This proposal documents a method for devices to create a new session to replace
|
||
|
|
the broken session.
|
||
|
|
|
||
|
|
## Proposal
|
||
|
|
|
||
|
|
When a device receives an olm-encrypted message that it cannot decrypt, it
|
||
|
|
should assume that the olm session has become corrupted and create a new olm
|
||
|
|
session to replace it. It should then send a dummy message, using that
|
||
|
|
session, to the other party in order to inform them of the new session. To
|
||
|
|
send a dummy message, clients may send an event with type `m.dummy`, and with
|
||
|
|
empty contents.
|
||
|
|
|
||
|
|
If the corrupted session has already been replaced, the receiving device should
|
||
|
|
do nothing, under the assumption that the message from the corrupted session
|
||
|
|
was sent before the sender was informed of the replacement session, in order to
|
||
|
|
avoid creating too many extra sessions.
|
||
|
|
|
||
|
|
The spec currently says, "If a client has multiple sessions established with
|
||
|
|
another device, it should use the session from which it last received a
|
||
|
|
message." (the last paragraph of the [`m.olm.v1.curve25519-aes-sha2`
|
||
|
|
section](https://matrix.org/docs/spec/client_server/r0.4.0.html#m-olm-v1-curve25519-aes-sha2)).
|
||
|
|
When comparing the time of the last received message for each session, the
|
||
|
|
client should consider only consider messages that were successfully decrypted,
|
||
|
|
and for sessions that have never received a message, it should use the creation
|
||
|
|
time of the session. The spec will be changed to read:
|
||
|
|
|
||
|
|
> If a client has multiple sessions established with another device, it should
|
||
|
|
> use the session from which it last received and successfully decrypted a
|
||
|
|
> message. For these purposes, a session that has not received any messages
|
||
|
|
> should consider its creation time to be the time that it last received a
|
||
|
|
> message.
|
||
|
|
|
||
|
|
## Tradeoffs
|
||
|
|
|
||
|
|
## Potential issues
|
||
|
|
|
||
|
|
## Security considerations
|
||
|
|
|
||
|
|
## Conclusion
|
||
|
|
|
||
|
|
This proposal outlines how wedged olm sessions can be replaced by a new
|
||
|
|
session.
|