Encryption keys not shared in one of my DMs

Steps to reproduce

1. Open a DM
2. Send a message

Outcome

What did you expect?

The message can be decrypted by the recipient.

What happened instead?

Here’s the DM from the recipient (@Half-Shot)'s side:

The messages that were successfully decrypted were sent from Element Web, the ones which keys seem to be withheld were sent from Element Android.

This room (!CxwbkNeawVzFvdXwza:half-shot.uk) is the only one impacted that I’ve seen (I’ve been able to send encrypted messages in other rooms which Half-Shot has been able to see), but this issue happens consistently with every message that I send to this room with Element Android.

Your phone model

Fairphone 3

Operating system version

Android 11

Application version and app store

Element version 1.5.2 [40105022] (G-b11679) - Matrix SDK version 1.5.2 (f6411d67) - Olm version 3.2.12 - From Play Store with beta channel joined

Homeserver

abolivier.bzh

Will you send logs?

Yes

Are you willing to provide a PR?

No

[robertmx]

I had the same problem and could fix that by deleting all “dead” sessions. I suspect (might be totally wrong here) that session A1 (my side) sent encrypted messages to session B2, that was stale / not accessible. Thus session B1 (the intended recipient) could not decrypt these messages because it could not get the required keys from session B2. Anyway it is rather unfortunate for a decrypted DM to suddenly stop working. It did not recover for three weeks.

NB: I had another session A2 open, that could still communicate without problems with peer session B1. That was rather confusing. The nontechnical user owning session B1 was not particularly impressed 😕.

[richvdh]

@Half-Shot’s device sent room-key-requests to @babolivier’s, but it’s currently unclear to me if they were answered.

They weren’t, because Element Android no longer responds to room-key-requests from other users.

Unfortunately I don’t think we can do much more here, since we don’t have the logs from when the room key should have been sent in the first place.