Device dehydration v2

[BillCarsonFr]

User story

As a user, if I log out my last device, other users should still be able to send messages to me and I should be able to read them once I come back and log in with some device.

Concept

Initial device dehydration feature has several issues:

• Tricky to implement, as it requires that the device rehydration be done before any other API calls
• User loses the advantage of verifying their other devices via emoji or QR code (passphrase needed anyhow to rehydrate)

It's now replaced with MSC3814.

Tasks

Ground work

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1. Ruma support for MSC3814 vector-im/element-meta#1898
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2. Rust crypto SDK Support for MSC3814 - Dehydrated devices v2 matrix-org/matrix-rust-sdk#2349
3. https://github.com/vector-im/crypto-internal/issues/126
4. MSC updates/Polishing MSC3814: Document new dehydrated device format (probably just a concatenation of the various bits of information needed, similar to existing pickle format) #2602
5. Synapse support part 2 Support MSC3814: Dehydrated Devices Part 2 matrix-org/synapse#16010
6. Fix endpoint improperly declaring support for MSC3814 matrix-org/synapse#16068
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Initial Dehydrated device support

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1. EAR dehydrated device upload (on register)
2. EAR dehydrated device download/rehydrate support after login.
3. IOS SDK Device dehydration v2 matrix-org/matrix-ios-sdk#1807
4. iOS App Device dehydration v2 element-ios#7630
5. WebR full support for dehydrated device v2 #2278
   6 of 7
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6. Dehydrated devices v2 - phase 2 element-web#27336
   A-E2EE T-Enhancement Team: Crypto +3
7. Dehydrated devices: does not detect if another client changed the dehydration key in 4S element-web#28760
   A-E2EE A-E2EE-Dehydration O-Uncommon S-Major T-Defect Team: Crypto +6

Iterating on MSC

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1. Dehydrated Device new format #2601
   1 of 3
   A-E2EE T-Feature T-User Story +3
   
2. Use GET instead of POST for /dehydrated_device/{device_id}/events endpoint
3. signal end of pagination by omitting token
4. Should not send key requests to dehydrated device? https://github.com/element-hq/crypto-internal/issues/178
5. KeySharing, DevicebasedStrategy | Exclude insecure dehydrated devices matrix-org/matrix-rust-sdk#4313
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Dehydrated device settings and management

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1. UX/Settings Dehydrated device Settings #278
2. EIR: Periodically replace the dehydrated device (to adress OTK exhaustion and to_device accumulation)
3. EAR: Periodically replace the dehydrated device (to adress OTK exhaustion and to_device accumulation)
4. Rust SDK: Support the resumption of the rehydration process vector-im/element-meta#1978
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5. Cross-signing Mgmt: reset should rotate the dehydrated device as it would be unsigned (already done in Web)
6. https://github.com/element-hq/crypto-internal/issues/402
7. EX: indicate when a user has a dehydrated device #2635
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EX support

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1. EX full support for dehydrated device v2

Deprecate and remove legacy device dehydration (MSC2697)

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No tasks being tracked yet.

[pmaier1]

Design/UX inputs needed for settings and option to enable disable

As discussed today, we want to make this feature transparent to the user as far as possible. As it requires key backup being enabled, we'd bind the availability of dehydrated devices to the setting to enable/disable key backup.

[emmaburton1]

Work on this can be timesheeted to the project on https://element-io.atlassian.net/browse/PSB-87

[poljar]

So a status update here:
Ruma PR: ruma/ruma#1605
Rust SDK branch: https://github.com/matrix-org/matrix-rust-sdk/tree/poljar/device-dehydration
Synapse branch that can be used for testing: https://github.com/poljar/synapse/tree/poljar/msc3814-v2

@stefanceriu above are the main ingredients that you'll need to get started on this on the iOS side, the Rust SDK branch depends on the Ruma PR, so you only need the later two.

[poljar]

Work on this can be timesheeted to the project on https://element-io.atlassian.net/browse/PSB-87

Where exactly do I find this in the myhours thingy? I can't seem to find a PSB-87 in the task list.

[pmaier1]

Where exactly do I find this in the myhours thingy? I can't seem to find a PSB-87 under the BWI task list.

It should just be the title of this ticket.

[emmaburton1]

@poljar I've added the task to relevant customer retainer project.

[pmaier1]

Considering that device dehydration

• will first be a labs feature and we probably can't ask all the end users to turn it on over and over again (when logging out and logging in again)
• the server-side support will also be an experimental feature at first

can we automatically enable the feature on the client if the server-side setting is enabled? Probably doesn't make sense to have two switches to enable it and this way we could control availability centrally.

[t3chguy]

@pmaier1 we don't tend to have HS-driven labs features due to the potential for data loss or work preventing bugs whilst thinking you are running a stable release of Element

[pmaier1]

then we need a separate switch on the backend to force enabling the labs feature on the client. otherwise this will be unusable.

[t3chguy]

Element web/desktop already support Such via config.json but not via anything HS driven.

[Xyz00777]

hi everyone, what is the state, because in element-hq/element-web#28173 dehydration devices are removed...

[ara4n]

i believe that's the v1 code being removed to make room for the v2 code.