5 ms·

How do they review the data if your iCloud photos are E2E encrypted?

by philwelch 5y ago

jduckles 5y ago
They're only encrypted when on iCloud, not when on your device. The hashes are computed on your device.
- philwelch 5y ago
  So how do they capture the unencrypted images from my device for "review"?
  - WorldMaker 5y ago
    That's why the CSAM scanner is on your device. It computes the hashes in place on then unencrypted images before uploading encrypted copies to iCloud. 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).
    - philwelch 5y ago
      So, again, how do they review those images? Does Apple have the key to the reporting database?
      - WorldMaker 5y ago
        Yes, that would be why it sends copies, encrypted with a different key to the users' own storage keys.
        philwelch 5y ago
        So in other words, the only thing stopping Apple from viewing my iCloud photos is an if statement.
        kemayo 5y ago
        That would also be true for any use of iCloud Photos, no? If you don't trust this, then you also can't trust them to be storing them encrypted on their servers.
Jtsummers 5y ago
I'm guessing you haven't been following the issue. 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/ https://www.apple.com/child-safety/ [1] https://www.apple.com/child-safety/pdf/CSAM_Detection_Technical_Summary.pdf https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni...
- philwelch 5y ago
  > I'm guessing you haven't been following the issue. Not as closely as some people. That's why I asked the question in the first place. But thanks for answering.
tillinghast 5y ago
Let the reader understand. (i.e. They're encrypted in transfer and while stored, but Apple holds the keys: https://qr.ae/pGSHY8 https://qr.ae/pGSHY8, https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/apple-platform-security-guide.pdf https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/app... [search for 'iCloud'])
- danudey 5y ago
  For the lazy: > 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.
  - thrashh 5y ago
    End-to-end encryption prevents a third party from reading your content, but if you are getting your encryption software from the same people that are storing your encrypted data, the only thing stopping them from reading your data is corporate policy. Which is fine, because I use iCloud and many other cloud services, but you have to acknowledge the fact.
sneak 5y ago
iCloud photos are not E2E encrypted. Apple has announced no plans whatsoever to make them such. Apple, their sysadmins, and the government can see every photo you have in iCloud. 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-exclusive/exclusive-apple-dropped-plan-for-encrypting-backups-after-fbi-complained-sources-idUSKBN1ZK1CT 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.
- philwelch 5y ago
  Okay, so basically they are just sort of pinky-swearing that your iCloud photos are encrypted on iCloud, but not in any way that prevents Apple or the government from decrypting them anyway. 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!
  - GeekyBear 5y ago
    > Okay, so basically they are just sort of pinky-swearing that your iCloud photos are encrypted on iCloud, but not in any way that prevents Apple or the government from decrypting them anyway. 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.

How do they review the data if your iCloud photos are E2E encrypted?

jduckles 5y ago

They're only encrypted when on iCloud, not when on your device. The hashes are computed on your device.

philwelch 5y ago
So how do they capture the unencrypted images from my device for "review"?
- WorldMaker 5y ago
  That's why the CSAM scanner is on your device. It computes the hashes in place on then unencrypted images before uploading encrypted copies to iCloud. 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).
  - philwelch 5y ago
    So, again, how do they review those images? Does Apple have the key to the reporting database?
    - WorldMaker 5y ago
      Yes, that would be why it sends copies, encrypted with a different key to the users' own storage keys.
      - philwelch 5y ago
        So in other words, the only thing stopping Apple from viewing my iCloud photos is an if statement.
        kemayo 5y ago
        That would also be true for any use of iCloud Photos, no? If you don't trust this, then you also can't trust them to be storing them encrypted on their servers.

Jtsummers 5y ago

I'm guessing you haven't been following the issue. 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/ https://www.apple.com/child-safety/ [1] https://www.apple.com/child-safety/pdf/CSAM_Detection_Technical_Summary.pdf https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni...

philwelch 5y ago
> I'm guessing you haven't been following the issue. Not as closely as some people. That's why I asked the question in the first place. But thanks for answering.

tillinghast 5y ago

Let the reader understand. (i.e. They're encrypted in transfer and while stored, but Apple holds the keys: https://qr.ae/pGSHY8 https://qr.ae/pGSHY8, https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/apple-platform-security-guide.pdf https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/app... [search for 'iCloud'])

danudey 5y ago
For the lazy: > 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.
- thrashh 5y ago
  End-to-end encryption prevents a third party from reading your content, but if you are getting your encryption software from the same people that are storing your encrypted data, the only thing stopping them from reading your data is corporate policy. Which is fine, because I use iCloud and many other cloud services, but you have to acknowledge the fact.

sneak 5y ago

iCloud photos are not E2E encrypted. Apple has announced no plans whatsoever to make them such. Apple, their sysadmins, and the government can see every photo you have in iCloud. 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-exclusive/exclusive-apple-dropped-plan-for-encrypting-backups-after-fbi-complained-sources-idUSKBN1ZK1CT 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.

philwelch 5y ago
Okay, so basically they are just sort of pinky-swearing that your iCloud photos are encrypted on iCloud, but not in any way that prevents Apple or the government from decrypting them anyway. 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!
- GeekyBear 5y ago
  > Okay, so basically they are just sort of pinky-swearing that your iCloud photos are encrypted on iCloud, but not in any way that prevents Apple or the government from decrypting them anyway. 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.