How do they review the data if your iCloud photos are E2E encrypted?
More details in [1], but briefly:
They hash the images that you're uploading to iCloud. If it matches one of the hashes in the database, then it gets encrypted and transmitted to them. No single data packet can be decrypted, they need 30 (?) matches with that database in order to get a decryption key that then allows them to review the uploaded images. They don't send the actual images to the reviewers, it's altered in some way. At that point the reviewer will have 30 (?) thumbnails (?) to review. If the images look like CSAM, then they'll report it to NCMEC who then report it to law enforcement (NCMEC is not, itself, a law enforcement agency).
The ? are because I don't think they've publicly stated (or I've not read) what the threshold for decryption is or how they modify the images that get sent to the reviewers.
[0] https://www.apple.com/child-safety/
[1] https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni...
Not as closely as some people. That's why I asked the question in the first place. But thanks for answering.
(i.e. They're encrypted in transfer and while stored, but Apple holds the keys: https://qr.ae/pGSHY8, https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/app... [search for 'iCloud'])
> Each file is broken into chunks and encrypted by iCloud using AES128 and a key derived from each chunk’s contents, with the keys using SHA256. The keys and the file’s metadata are stored by Apple in the user’s iCloud account. The encrypted chunks of the file are stored, without any user-identifying information or the keys, using both Apple and third party storage services—such as Amazon Web Services or Google Cloud Platform—but these partners don’t have the keys to decrypt the user’s data stored on their servers.
As far as I can tell, they don't say anything specific about where or how Apple stores the keys and metadata, so it should be assumed that Apple could decrypt your photos if they wanted to.
Which is fine, because I use iCloud and many other cloud services, but you have to acknowledge the fact.
Apple had plans (and, an inside source tells me, an implementation) to do E2E for iCloud Backup, but the FBI asked them not to, so they scrapped it:
https://www.reuters.com/article/us-apple-fbi-icloud-exclusiv...
This undermines the credibility of those who are claiming, without evidence, that this clientside CSAM scanning is a prelude to launching E2E for iCloud data.
This raises the followup question of "why bother scanning the images on-device?", but I can infer two fairly obvious answers. First, the encryption still keeps AWS/Azure/GCP from seeing my photos. Second, and more cynically, they'd have to pay to do computation in the cloud; on-device computation is free to them.
> This undermines the credibility of those who are claiming, without evidence, that this clientside CSAM scanning is a prelude to launching E2E for iCloud data.
I agree; this is consistent with my initial point of confusion. Thanks!
How do you imagine that Google and Microsoft are able to scan the entire contents of your account? They can all read the data on their servers
>This raises the followup question of "why bother scanning the images on-device?
Because running the scan on device and encrypting the results protects users from having their account associated with the inevitable false positives that are going to crop up.
Apple can't decrypt the scan results your device produces until the threshold of 30 matching images is reached.
If someone issues a warrant to Apple for every account that has a single match, they can honestly report that they don't have that information.
Google and Microsoft give you no such protection. Any data held on their server is wide open for misuse by anyone who can issue a warrant.
The fact that the FBI stopped them once before and they've been working to build active solutions to what the FBI tells them their needs are should be evidence alone that E2E is their goal. It seems pretty credible to me.
That's why from some perspectives it is a net privacy win versus Google/Microsoft's similar tools that require them to have decryption backdoor keys on their clouds to process these CSAM requests and other FBI/TLA/et al warrants. Apple is saying they don't have backdoor keys at all on iCloud and if they are forced to do CSAM scanning it has to be on device, without leaving the device to have access to the unencrypted images. Only if you hit the reporting threshold (supposedly 30+ hash violations) would it also encrypt copies to a reporting database on iCloud (and again only if you were uploading those photos to iCloud in the first place).