alt Hacker NewsIt's not entirely accurate to say "any party other than the sender and the intended receiver," since the messaging app running on the user's device can read the messages. Something like "any third party (other than the app vendor)" would be more accurate. Without actually analyze app behavior, it comes down to trusting that the vendor doesn't do anything nefarious.
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I think the draft covers this well: https://www.ietf.org/archive/id/draft-knodel-e2ee-definition...
As far as I remember, Google does the final signing of the APK, which is eventually the signature verified by the OS to verify if an update is valid or not.
So Google can, if ordered or willing to help, create a new release track (e.g. experimental-do-not-deleted) and add specific e-mails to that track with the "improved" version.
Nobody would be able to see that in real world, and you know what, if WhatsApp themselves are ordered, they can also create their own "test" track, it's just less covert but it would technically be working.
In all cases, Google and Apple have to respect US laws, and the laws of earning money too.
If you do not cooperative with intelligence / police services of your country, only bad things can happen.
One could imagine a design where even the app vendor is untrusted... You would send an encrypted chunk direct to the GPU, which would then decrypt and render the message text in some secure environment onto the screen.
Neither the OS nor the application would know the contents of your message beyond "it's 500x700 pixels".
Similar things are done for DRM video, and widevine level 1 or 2 haven't seen many breaches despite running on a wide array of hardware open to physical attack.