IIRC, Apple will only scans if iCloud photo is enabled:
https://www.apple.com/child-safety/pdf/Expanded_Protections_...
> This feature only impacts users who have chosen to use iCloud Photos to store their photos.
https://www.apple.com/child-safety/pdf/Expanded_Protections_...
> This feature only impacts users who have chosen to use iCloud Photos to store their photos.
The only reason to scan clientside for a cloud service is to scan files that are not uploaded, or are end to end encrypted.
Apple already maintains an e2e backdoor (in the form of non e2e iCloud Backup) for the FBI and US intelligence agencies. It is extremely unlikely that they will e2e encrypt iCloud Photos.
I suppose had they not gone down this road, the headlines would have been "Apple makes it easier to share child porn online".
I doubt they'd bother doing e2e for iCloud Photos if they're intentionally not doing it for iCloud Backup.
Citation? I don't believe this is correct, or at least it's an incomplete assertion.
Assuming they do get with the iCloud backup, these keys would be inside the device's Keychain file which is encrypted at rest by the Secure Enclave. Thus even with access to a full, unencrypted backup of your iPhone, the keychain itself cannot be decrypted by Apple
(It can't be decrypted by you either, if it's restored to different hardware. This is why iCloud Keychain exists. And that is end-to-end encrypted.)