060 - Advanced Data Protection

Apple can't see inside your hidden photo album. They still know you have those photos, when you took them, and how often you look at them. None of that is a leak or a hack. It sits in Apple's own documentation, and the reason comes down to storage costs.

To store photos for a billion people, Apple has to avoid keeping ten million copies of the same meme. That means comparing photos, which is a problem when the photos are encrypted and Apple has no way to look at them. The solution has been part of iCloud since launch, it has a name, and it quietly makes one specific thing possible: checking whether you have a particular photo without ever decrypting it.

In this video: what Advanced Data Protection actually does when you switch it on, why deduplication needs a fingerprint of every photo you own, what else stays readable in your Photos library, and when any of it actually matters.

Two things I'm careful about. Apple has never confirmed that checksums get compared across different accounts, so I explain why I think they do and what would change my mind. And the same mechanism applies to iCloud Drive, where filenames get hashed too. That's a much softer target, because filenames carry almost no entropy.

Sources Apple, iCloud data security overview https://support.apple.com/en-us/102651

Apple Platform Security, Advanced Data Protection for iCloud https://support.apple.com/guide/security/advanced-data-protection-for-icloud-sec973254c5f/web