Failed to decrypt Olm message with InvalidMAC(MacError)

[richvdh]

Steps to reproduce

n/a

Outcome

See https://github.com/matrix-org/element-ios-rageshakes/issues/23065; in particular https://rageshakes.element.io/api/listing/2023-02-07/145153-6DJDEHFV/console.2.log.gz at 10:41:28.270:

2023-02-07 10:41:28.270 Element[22034:7611900] [MXCryptoSDK]  WARN receive_sync_changes:receive_to_device_event{sender="@Amandine:matrix.org" event_type="m.room.encrypted" message_id="36b8c441-8739-42f6-85a1-fd80f55d5bcb"}: matrix_sdk_crypto::olm::account: Failed to create a new Olm session from a pre-key message: InboundCreation(Decryption(InvalidMAC(MacError))) sender_key="curve25519:yCzeJlVPpPrg6prkD4l4UezGxye3aXJE9Rd40wzNNhg" session_keys=SessionKeys { identity_key: "yCzeJlVPpPrg6prkD4l4UezGxye3aXJE9Rd40wzNNhg", base_key: "QjzU4LLyreQNMBTczt4bI1+wRzexKfqdrzYoGxEwf04", one_time_key: "gw9P5us0F4J3Zs2s0TUfel4zC1qOSgpeK0U3zQuBfxc" }

An InvalidMac should only happen if there was a MITM, so this suggests one end or the other has gotten its maths wrong.

For the record, the sender side is https://github.com/matrix-org/element-web-rageshakes/issues/19977:

2023-02-07T10:29:34.727Z I encryptMessage: Olm Session ID LZEEkkqCVeOb9ar7lwSaZNtZR0Ym2MD2VaCsktXOJkg to OG9C4AjzK563NZ0Wzm3H4uZ1ySqWNpQv8PSdJlU3ZiI: sender chain index: 2 receiver chain indices: skipped message keys:
2023-02-07T10:29:34.727Z I Saving Olm session LZEEkkqCVeOb9ar7lwSaZNtZR0Ym2MD2VaCsktXOJkg with device OG9C4AjzK563NZ0Wzm3H4uZ1ySqWNpQv8PSdJlU3ZiI: sender chain index: 3 receiver chain indices: skipped message keys:

It's interesting to note the chain index here, suggesting that this is in fact the third attempt to send on this Olm session. I wonder if that is related. We do not have logs going back any further.

Your phone model

iPhone 11 Pro

Operating system version

iOS 16.2

Application version

1.10.0

Homeserver

No response

Will you send logs?

Yes

[BillCarsonFr]

Closing as cannot reproduce

[richvdh]

Likely this was matrix-org/matrix-rust-sdk#3110