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Fix logic error in validation of incoming olm-encrypted messages #2394

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Fix logic error in validation of incoming olm-encrypted messages #2394

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46edc59
Fix logic error in validation of incoming olm-encrypted messages
tusooa Jun 10, 2026
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tusooa Jun 24, 2026
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1 change: 1 addition & 0 deletions changelogs/client_server/newsfragments/2394.clarification
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Correct some errors in the description of the validation process for incoming Olm-encrypted messages.
12 changes: 7 additions & 5 deletions content/client-server-api/modules/end_to_end_encryption.md
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Expand Up @@ -1662,27 +1662,29 @@ of olm sessions maintained per device should be at least 4.
###### Validation of incoming decrypted events

{{% changed-in v="1.15" %}} Existing checks made more explicit, and checks for `sender_device_keys` added.
{{% changed-in v="1.19" %}} Corrections to some errors in the description of the verification checks.

After decrypting an incoming encrypted event, clients MUST apply the
following checks:

1. The `sender` property in the decrypted content must match the
`sender` of the event.
2. The `keys.ed25519` property in the decrypted content must match
the `sender_key` property in the cleartext `m.room.encrypted`
event body.
the Ed25519 identity key of the sending device. This key can be
obtained from either [`/keys/query`](#post_matrixclientv3keysquery)
or the `sender_device_keys` object (see below).
3. The `recipient` property in the decrypted content must match
the user ID of the local user.
4. The `recipient_keys.ed25519` property in the decrypted content
must match the client device's [Ed25519 signing key](#device-keys).
5. Where `sender_device_keys` is present in the decrypted content:
1. `sender_device_keys.user_id` must also match the `sender`
of the event.
2. `sender_device_keys.keys.ed25519:<device_id>` must also match
2. `sender_device_keys.keys.curve25519:<device_id>` must match
the `sender_key` property in the cleartext `m.room.encrypted`
event body.
3. `sender_device_keys.keys.curve25519:<device_id>` must match
the Curve25519 key used to establish the Olm session.
3. `sender_device_keys.keys.ed25519:<device_id>` must be the same
as the `keys.ed25519` property in the decrypted content.
4. The `sender_device_keys` structure must have a valid signature
from the key with ID `ed25519:<device_id>` (i.e., the sending
device's Ed25519 key).
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