MSC4147: Including device keys with Olm-encrypted events #4147

uhoreg · 2024-05-29T20:34:20Z

disclosure: I am on the Spec Core Team and employed by Element. This MSC is written as part of my work in the Crypto team at Element

FCP tickyboxes

proposals/4147-including-device-keys-with-olm-encrypted-events.md

turt2live · 2024-05-29T21:27:38Z

proposals/4147-including-device-keys-with-olm-encrypted-events.md

Implementation requirements:

Client sending this information

Client using this information

Demonstration of the core problem being solved (likely covered by the above tasks)

This has been implemented in the Rust matrix-sdk-crypto crate, both sending and using. Demonstration of the problem being solved: https://youtu.be/b1jJlT2ENT8?feature=shared&t=345

A few links to the implementation.

On the sender side, the field is added here.

On the receiver side, it is deserialized after decryption into a DecryptedOlmV1Event. It is then used in SenderDataFinder whose job it is to construct a SenderData which records our knowledge about the sending device for a given session.

proposals/4147-including-device-keys-with-olm-encrypted-events.md

This patch implements MSC4147[1]. Signed-off-by: Hubert Chathi <hubertc@matrix.org> [1]: matrix-org/matrix-spec-proposals#4147

proposals/4147-including-device-keys-with-olm-encrypted-events.md

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

richvdh · 2024-11-02T18:49:14Z

I think this is ready for FCP, so:

@mscbot fcp merge

mscbot · 2024-11-02T18:49:17Z

clokep · 2024-12-05T15:22:40Z

Thanks for answering all my questions @richvdh -- I think this is OK as an incremental improvement, but sounds like we might need to do a bigger improvement at some point in the future.

mscbot · 2024-12-10T15:22:23Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

andybalaam · 2025-01-10T13:02:36Z

proposals/4147-including-device-keys-with-olm-encrypted-events.md

+
+We propose to solve this by including a copy of the device keys in the
+Olm-encrypted message, along with the cross-signing signatures, so that the
+recipient does not have to try to query the sender's keys.


Is the intention to make sender_device_keys mandatory, and drop to-device messages that do not include it?

That was very much not part of this MSC. It's something we could do in future, but IMHO it would need another MSC, and careful thought, since it would mean cutting off the significant part of the ecosystem which doesn't yet implement this MSC.

Johennes · 2025-03-28T11:57:22Z

Spec PR: matrix-org/matrix-spec#2122

richvdh · 2025-05-13T20:48:05Z

proposals/4147-including-device-keys-with-olm-encrypted-events.md

+If this property is present, the `keys`.`ed25519` property of the plaintext
+payload must be the same as the `sender_device_keys`.`keys`.`ed25519:<DEVICEID>`
+property.  If they differ, the recipient should discard the event.


We don't seem to have specified anything here about sender_device_keys.keys.curve25519:<DEVICEID>, which seems like an oversight: if nothing else, it allows inconsistency within the event which is generally a big red flag in encryption stuff.

The sample implementation of this (matrix-rust-sdk) does check that curve25519:<DEVICEID> matches the olm session used to encrypt the message (https://github.com/matrix-org/matrix-rust-sdk/blob/4d027ec405a20b54c6f9d2e31a20bf2dd1c3854d/crates/matrix-sdk-crypto/src/olm/account.rs#L1539-L1548); I'm inclined to consider it an oversight in the MSC.

cc @uhoreg

I'm taking silence as consent here. matrix-org/matrix-spec#2122 mandates a match.

richvdh · 2025-05-28T17:50:56Z

Spec PR is now merged 🎉

For js-sdk users, this includes the following: - Send stable identifier `sender_device_keys` for MSC4147 (Including device keys with Olm-encrypted events). ([#4964](matrix-org/matrix-rust-sdk#4964)) - Check the `sender_device_keys` field on _all_ incoming Olm-encrypted to-device messages and ignore any to-device messages which include the field but whose data is invalid (as per [MSC4147](matrix-org/matrix-spec-proposals#4147)). ([#4922](matrix-org/matrix-rust-sdk#4922)) - Fix bug which caused room keys to be unnecessarily rotated on every send in the presence of blacklisted/withheld devices in the room. ([#4954](matrix-org/matrix-rust-sdk#4954)) - Fix [matrix-rust-sdk#2729](matrix-org/matrix-rust-sdk#2729) which in rare cases can cause room key oversharing. ([#4975](matrix-org/matrix-rust-sdk#4975))

uhoreg added 2 commits May 29, 2024 15:57

initial version of including device keys with olm-encrypted events

ce31f30

use MSC number

4fa6b3f

uhoreg changed the title ~~MSCxxxx: Including device keys with Olm-encrypted events~~ MSC4147: Including device keys with Olm-encrypted events May 29, 2024

fix typo

62352ca

turt2live added proposal A matrix spec change proposal kind:maintenance MSC which clarifies/updates existing spec needs-implementation This MSC does not have a qualifying implementation for the SCT to review. The MSC cannot enter FCP. labels May 29, 2024

turt2live reviewed May 29, 2024

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turt2live reviewed May 29, 2024

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clokep reviewed May 30, 2024

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indicate what should happen if keys differ

419bed3

richvdh reviewed Jun 12, 2024

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richvdh reviewed Jun 12, 2024

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andybalaam mentioned this pull request Jun 13, 2024

Sender Data: Fetch and store sender data when we receive a new megolm session matrix-org/matrix-rust-sdk#3543

Closed

poljar pushed a commit to matrix-org/matrix-rust-sdk that referenced this pull request Jun 27, 2024

Embed device keys in Olm-encrypted messages (#3517)

d41af39

This patch implements MSC4147[1]. Signed-off-by: Hubert Chathi <hubertc@matrix.org> [1]: matrix-org/matrix-spec-proposals#4147

ara4n reviewed Jun 30, 2024

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andybalaam mentioned this pull request Jul 1, 2024

crypto: Move device_keys to DecryptedOlmV1Event as per MSC4147 matrix-org/matrix-rust-sdk#3633

Merged

BillCarsonFr reviewed Jul 3, 2024

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pmaier1 mentioned this pull request Sep 5, 2024

MSC4161: Crypto terminology for non-technical users #4161

Open

uhoreg mentioned this pull request Oct 17, 2024

Do some work on MSC4147 element-hq/element-meta#2557

Closed

uhoreg and others added 6 commits October 17, 2024 15:06

Apply suggestions from code review

33bb7c2

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

switch to versioned spec links

04acb6b

Clarify the problem being solved

407e1d9

another reason to encrypt device_keys

5bb2093

Document alternative approach properly

0deb58f

minor edits

28d03f5

mscbot added proposed-final-comment-period Currently awaiting signoff of a majority of team members in order to enter the final comment period. disposition-merge labels Nov 2, 2024

mscbot added the final-comment-period This MSC has entered a final comment period in interest to approval, postpone, or delete in 5 days. label Dec 5, 2024

mscbot added finished-final-comment-period and removed disposition-merge final-comment-period This MSC has entered a final comment period in interest to approval, postpone, or delete in 5 days. labels Dec 10, 2024

richvdh merged commit 51ebe01 into matrix-org:main Dec 10, 2024
1 check passed

richvdh added spec-pr-missing Proposal has been implemented and is being used in the wild but hasn't yet been added to the spec and removed finished-final-comment-period labels Dec 10, 2024

andybalaam reviewed Jan 10, 2025

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uhoreg mentioned this pull request Feb 24, 2025

Encrypted history sharing: design "key bundle" format element-hq/element-meta#2688

Closed

Johennes mentioned this pull request Mar 28, 2025

Spec PR - MSC4147: Including device keys with Olm-encrypted events matrix-org/matrix-spec#2122

Merged

3 tasks

turt2live moved this from Requires spec writing to Requires spec PR review in Spec Core Team Backlog Mar 28, 2025

turt2live added spec-pr-in-review A proposal which has been PR'd against the spec and is in review and removed spec-pr-missing Proposal has been implemented and is being used in the wild but hasn't yet been added to the spec labels Mar 28, 2025

richvdh reviewed May 13, 2025

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poljar mentioned this pull request May 28, 2025

Make the sharing and accepting of historic room key bundles more robust matrix-org/matrix-rust-sdk#5118

Merged

richvdh added merged A proposal whose PR has merged into the spec! and removed spec-pr-in-review A proposal which has been PR'd against the spec and is in review labels May 28, 2025

richvdh moved this from Requires spec PR review to Done to some definition in Spec Core Team Backlog May 28, 2025

This was referenced May 30, 2025

Implement Matrix 1.15 changes ruma/ruma#2082

Closed

events: Add support for including devices keys with Olm-encrypted events ruma/ruma#2085

Merged

richvdh mentioned this pull request Jun 21, 2025

Update matrix-sdk-crypto-wasm to 15.0.0 matrix-org/matrix-js-sdk#4882

Merged

Johennes mentioned this pull request Jul 3, 2025

Matrix v1.15 gematik/api-ti-messenger#323

Open

34 tasks

MSC4147: Including device keys with Olm-encrypted events #4147

MSC4147: Including device keys with Olm-encrypted events #4147

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