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tl;dr to me seems: Since users can change devices, they'll need to reissue key material, this needs to be supported. WhatsApp reports key changing optionally, but doesn't tell the server that happened. If WhatsApp tries to backdoor a channel and one of the users has key change notification, they'll find out about it, and WhatsApp has no idea whether the warning was shown.
I am not convinced. Why should this option exist at all? Even worse, it is disabled by default. Just enable notifications for everyone and demand verification. If you don't want to verify, just ticking "veryfied" without actual verification is not that bad, it is just a trust-on-first-use principle in action. Actually it is how SSH works and nobody complains about SSH being backdoored.
tl;dr to me seems: Since users can change devices, they'll need to reissue key material, this needs to be supported. WhatsApp reports key changing optionally, but doesn't tell the server that happened. If WhatsApp tries to backdoor a channel and one of the users has key change notification, they'll find out about it, and WhatsApp has no idea whether the warning was shown.
Ofcourse if then one of us checks the signature later and sees it is not correct this would be very harmfull for whatsapp.
But this indeed doesn't sound like a backdoor. It's just the way it works. Which seems good enough.
Even with perfect e2e encryption protocol added, what's preventing WhatsApp developers (FB) from adding in a feature of the app:
if local.user is "TargetUser007" { takeDeviceSnap(); sendDeviceSnapshotToFBOverSameEncryption(); }
Wouldn't this not be ever verifiable unless you ARE that specific user and it's too late?
Can the server change keys twice?
Change once to server keys, ask for the entire history retransmission.
Change again to revert to original receipient keys.
Will the receipient be prompted in that case?
could not this be saved only localy ?
For instance, it could instruct specific clients to encrypt and send each message twice: one for the recipient, and one for the WhatsApp server. As long as this was off for 99.9% of users, it's unlikely that security researchers would ever detect this.
Color me still-unconvinced. This retort does not address the fundamental point made in the Guardian piece: > “[Some] might say that this vulnerability could only be abused to snoop on ‘single’ targeted messages, not entire conversations. This is not true if you consider that the WhatsApp server can just forward messages without sending the ‘message was received by recipient’ notification (or the double tick), which u…