Fwiw, that “encryption” never used your own key or password. Facebook held the key, Google held the encrypted blob, and I doubt the extra warrant to get data from both companies was a huge hurdle.

Definitely was not E2EE before.

That's correct. And yet ... back then, Google couldn't read your messages; Facebook couldn't read your backup; And hackers or law enforcement would need to both get a copy of the blob from Google and the key from Facebook - not insurmountable, but requiring a lot more work and more likely to raise suspicion.

Whereas ... after that change, Google can read your messages, hackers/law-enforcement only need to talk to Google, and yet -- you yourself can't get that backup without impersonating the WhatsApp app to Google Drive; The local backup is still encrypted with a key that only Facebook knows (and would give you, but only if you impersonate the WhatsApp app when talking to Facebook).

I've looked for the logic and failed. Only reasons I can find is that FB wants to let Google index your messages behind your back (unlikely) or some plausibly deniable legal backdoor.

If you read Texas's antitrust lawsuit against Google, you will see that FB and Google signed an exclusive agreement, where Google gets access to WhatsApp messages stored on Drive in exchange for [redacted].

https://www.theverge.com/2020/12/17/22180258/google-whatsapp...

Ah so that's how it worked? I heard that concept once and thought it was a really interesting way to ensure a user wouldn't lose their backup while preventing the company from accessing it.

It's not solely law enforcement. It's a commercial deal.

https://www.theverge.com/2020/12/17/22180258/google-whatsapp...

Deduplication could be a thing

Incredibly unlikely. The backup is AFAIK an SQLite file that contains the text messages (and indexes, etc). The bigger files - images, videos and voice messages - are not included in that backup, and are backed up independently to Google Photos (and always have been).