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add some e2ee clarifications

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Hubert Chathi 2022-10-18 18:02:27 -04:00
parent 1cdfbd3cd8
commit fbbf3b81c5
4 changed files with 29 additions and 9 deletions
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17
content/client-server-api/modules/end_to_end_encryption.md
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@ -987,6 +987,17 @@ If a user's client sees that any other user has changed their master
key, that client must notify the user about the change before allowing
communication between the users to continue.
Since device IDs and cross-signing keys occupy the same namespace, clients must
ensure that they use the correct keys when verifying. While servers must not
allow devices to have the same IDs as cross-signing keys, a malicious server
could construct such a situation, so clients must not rely on the server being
well-behaved and should take precautions against this. For example, clients
should refer to keys using the public keys rather than only by the device
ID. Clients should also fix the keys that are being verified, and ensure that
they do not change in the course of verification. Clients may also display a
warning and refuse to verify a user when it detects that the user has a device
with the same ID as a cross-signing key.
A user's user-signing and self-signing keys are intended to be easily
replaceable if they are compromised by re-issuing a new key signed by
the user's master key and possibly by re-verifying devices or users.
@ -1587,7 +1598,11 @@ that they can decrypt future messages encrypted using this session. An
`m.room_key` events sent by other devices in order to decrypt their
messages.
When a client is updating a Megolm session (room key) in its store, the client MUST ensure:
When a client receives a Megolm session, the client MUST ensure that the
session was received via a channel that ensures authenticity of the messages.
Practically speaking, this means that Megolm sessions must be received via Olm.
When a client is updating a Megolm session in its store, the client MUST ensure:
* that the updated session data comes from a trusted source.
* that the new session key has a lower message index than the existing session key.