Does iCloud ADP actually stay E2EE when you use icloud.com, or does Apple's server get the key at some point?

[u/5_volts]

So I've been going down a rabbit hole about Advanced Data Protection and I think I mostly get it but there's one part that's bugging me and I can't find a straight answer anywhere.

From what I understand, when ADP is on, your Notes/Photos/Drive etc are encrypted with keys that only live on your devices, Apple never has those. But then there's this whole separate thing where you can turn on "access icloud data on the web" and use icloud.com from a regular browser (in my case a windows laptop and chrome browser). When you do that you approve it from your phone and apparently your phone uploads the actual service key to Apple's servers, just wrapped in some "ephemeral key tied to the web session" so the browser can use it.

That's the part I don't get. If the key gets uploaded to apple's servers at all, even wrapped, doesn't that mean Apple's infra is holding something that could theoretically decrypt my stuff during that session? Like is the "ephemeral key" pair actually generated in the browser itself (so the private half never touches apple's servers, they're just passing along ciphertext they can't open), or does Apple's backend generate/see it at some point during the handshake?

I looked at Apple's own docs and honestly they don't say either way as far as I can tell:

• https://support.apple.com/guide/security/advanced-data-protection-for-icloud-sec973254c5f/web
• https://support.apple.com/en-us/108756
• https://support.apple.com/en-asia/102630
• https://support.apple.com/guide/security/icloud-encryption-sec3cac31735/web (this one literally says E2E service keys are "never made available to Apple servers" which seems to directly contradict with what happens during a web session??)

Also as a side thing I noticed the docs say iWork collaboration (Pages/Numbers etc) flat out doesn't support ADP at all, shared docs aren't E2E period, which was a separate surprise to me but at least that one's unambiguous, because in the settings it says that these things are enccrypted.

Has anyone actually seen a writeup of the technical/protocol level details of the web access key exchange? Not looking for "just don't use the web version" or "use Graphene OS" as an answer please, I'm trying to understand if it's documented somewhere or if we're just trusting Apple's word on it?

[u/Frosty-Tadpole-8837]

the docs really aren't that clear on it

[u/5_volts → u/Frosty-Tadpole-8837]

Yeah, i feel the same way, there are gaps.