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Comment by colinbartlett | Hacker News Reader

The shocking thing for me is that Apple is using Amazon S3 to store iCloud photos. Apparently this is not news[1], but it's news to me. What are all those huge green data centers for if not for mountains of iCloud content?

1. http://readwrite.com/2014/08/26/apple-icloud-amazon-web-serv...

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What's the deal with iCloud Photos and privacy anyway? I've heard talk of "encrypted at rest" but what does this mean in practice? If someone gets root on Apple's servers, can they see my photos, or only if I'm logged in, or what?

It means that unencrypted data is never written to disk. In the case of S3 it means that if someone gains access to your S3 buckets the data is encrypted.

Of course if you have root-level access to Apple's servers that read S3 you could find the decryption key, though that might not be an easy task.

Not necessarily. The encryption key could be stored in your iCloud keychain, or derived from your login credentials and/or an account-specific identifier stored on your devices. That would prevent anyone from decrypting your data even with root on their servers unless they managed to capture the decryption key out of memory.

Right. In principle, it's possible. Apple maintains it can't read your iMessages, for example. And are there any operations that happen on your photos that have to happen in the cloud? Thumbnail generation/optimisation can happen during upload.

However, since iCloud Photos has a web interface, I imagine they're not doing this.

It is mostly a protection in cases where an attacker gains physical access to a system (or dumpster dives hard drives). If they are holding on the the encryption key for you then they can obviously decrypt them. I wouldn't consider it safe for anything important.

I've also seen iMessage talk to services hosted on Azure at various points.

They pretty much use everything. Apple was also an early investor in Akamai, and I believe Akamai is still used to transfer iOS and OS X updates.

Factoring keys?

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