Declaring End-to-end Encryption stable and turning it on by default for private rooms.

[ara4n]

Somehow we seem to be missing a high-level tracking bug for the endgame of E2E. (The starting point was matrix-org/matrix-spec-proposals#501, but that's a spec bug and feels a bit weird to hijack it for this).

In order to declare E2E stable (and by extension Matrix), we need to:

• Cross-sign devices at login to eliminate verification warnings (We could cross-sign devices to aid trust when new ones join a room #2714)
• Optionally incrementally backup encrypted E2E keys to your HS so if you lose all your devices you can restore your history via a recovery key that you own. (Improving megolm key storage (meta) #5675)
• Improve verification UX (comparing per-verification mnemonic passphrases rather than public keys) (Implement E2E key verification process #2142)
• Hook up key sharing to let history be visible from before you joined a room (but after you were invited to it), history visibility allowing. (Let megolm session keys be available to devices added by invited users since the point they are invited #2713) - mainly fixed, other than for edge case where users add devices after being invited to a E2E room
• Have less than 0.0x% unresolved unable-to-decrypt errors reported through telemetry ("Unable to decrypt: The sender's device has not sent us the keys for this message." (The UISI bug) #2996, Telemetry to report incidence of UISIs #6390)
• Fix device lists getting out of sync over federation (E2E device lists can get out of sync over federation when users delete their devices. #6974)
• Support full-text search within E2E rooms (Client-side search for E2E #2548, solved by github.com/matrix-org/seshat)
• Support push and in-app notifications in E2E rooms at least by locally calculating them. We could also support setting metadata on the messages to bing users, especially if we had pseudonymous MXIDs.
• Support NotifPanel in E2E rooms (Notif panel needs to know how to deal with encrypted room #6874)
• Turn it on by default for private rooms. All rooms created with the intent of use as a 1:1 or a private group chat must be E2E (and homeservers would enforce that, as best they can, c.f. Support only E2E or public rooms on my homeserver matrix-org/synapse#3269), although obviously a broken client could still try emitting unencrypted events into such a room). The code exists for this already over at https://github.com/matrix-org/synapse/pull/3426/files.

Ideally:

• Provide some kind of E2E daemon/proxy to stop non-E2E clients/bots/bridges/curl-users being unceremoniously dumped out in the cold. (#6778)
• Improve the UX for managing the trust of the devices which are in a given room (E2E device/key management dashboard to replace UnknownDeviceDialog #4522). In practice if verification is working nicely this might not be so important.
• Optionally hook up key sharing to let history be visible from before you were invited to a room (history visibility allowing) (#2286)
• Get an end-to-end audit of crypto spanning a set of reference implementations - e.g. matrix-{web,ios,android}-sdk + synapse.

[aaronraimist]

#6959 should probably be in here at least under ideally

[dbkr]

I think '* Optionally hook up key sharing to let history be visible from before you were invited to a room' needs to be non-optional, or if not then change the history visibility settings for e2e rooms to line up with what's actually possible, ie. remove 'anyone' and 'Members only (since the point in time of selecting this option)')

[ilmaisin]

It was originally promised that e2e encryption would be enabled by default when it was out of beta. That didn't happen.

But anyway, as I understand, there are basically three things to be done before e2ee can be default: cross-signing, local search and notifications. Are there any on-going efforts to achieve those?

[ara4n]

yes, of course. cross-signing is in the final stages; notifications just got largely fixed on riot/web and already worked on mobile; local search development is kicking off again as of tomorrow. we also want to fix element-hq/element-meta#80 before turning it on by default.