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Why can't they just scan iCloud uploads on-server then? Why does anything need to be done on-device?

xanaxagoras 5y ago
The theory is they were going to use this tech to finally enable E2EE iCloud Photos and reactionary privacy absolutist psychopaths who didn't understand how it works -- such as myself -- made a big ruckus and spoiled everything. Also at the point that the image hash matches, Apple thinks it is CSAM (and it probably is). Doing it locally lets them avoid storing it, which they definitely do not want to do.
JimDabell 5y ago
This scheme is obviously designed to work when Apple has no direct access to the photos. Because of this, there is a lot of speculation that Apple plans on making iCloud photos encrypted. This scheme would continue to work in that situation, whereas the on-server approach would fail. However that’s just speculation, Apple haven’t announced anything.
- modeless 5y ago
  That speculation is pretty out there considering that there have been no barriers to them doing true end-to-end encryption of iMessage backups, but they have chosen not to for many years despite marketing iMessage as "end-to-end" encrypted. Reportedly at the direct request of the FBI. 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...
Spooky23 5y ago
They almost certainly do. Every major provider does, and even some enterprises. The whole point of the CSAM stuff was that it would allow for end to end encryption while not turning Apple’s ecosystem into preferred tool of child pornographers. Apple poorly communicated the feature, then the EFF put out a deliberately misguided written hitpiece that conflated parental controls with CSAM, and started an online freak out. The “privacy activists” won, and your data is sitting on Apple servers with Apple’s managed encryption keys outside of your control today.
- sebzim4500 5y ago
  I think that's a pretty bad summary of the concerns that were raised. Sure they are scanning your files on icloud, but there is a 100% reliable way to prevent that: just don't upload them. In their proposal they would scan your files on device, which is fundamentally different. Initially they would not run the scanning when icloud upload was disabled but how long would that last for?
  - ziml77 5y ago
    No. The proposal was to generate the perceptual hash on device at the time of uploading to iCloud. It would not be doing any scanning on-device. The comparison to the CSAM database would still happen on Apple's servers.
    - matthewdgreen 5y ago
      The device would download an encrypted database. It would compute a hash on the device. It would compute a value (“voucher”) from this hash and the database and upload that value to iCloud, which could decrypt it iff there were a sufficient number of matches. The voucher is independent of the plaintext file uploaded to iCloud: hence you could upload only the voucher and not the file and the system would still alert. Phrases like “it would not be doing any scanning on-device” don’t have any precise meaning. Scanning is a series of operations including hashing and cryptographic calculations plus a voucher upload and decryption. All of the former operations are happening on the device, only the latter happens on the server. So in fact a significant fraction of the scanning is indeed happening on your device. And this two-computer design isn’t being used to preserve your privacy: it’s designed this way solely to prevent you (the device owner) from knowing whether your files match the database. Without that requirement, the system would be much simpler: it would download a hash database and simply send a notification to iCloud whenever (a sufficient number of) local files hash to values matching the database.

The theory is they were going to use this tech to finally enable E2EE iCloud Photos and reactionary privacy absolutist psychopaths who didn't understand how it works -- such as myself -- made a big ruckus and spoiled everything. Also at the point that the image hash matches, Apple thinks it is CSAM (and it probably is). Doing it locally lets them avoid storing it, which they definitely do not want to do.

JimDabell 5y ago

This scheme is obviously designed to work when Apple has no direct access to the photos. Because of this, there is a lot of speculation that Apple plans on making iCloud photos encrypted. This scheme would continue to work in that situation, whereas the on-server approach would fail. However that’s just speculation, Apple haven’t announced anything.

modeless 5y ago
That speculation is pretty out there considering that there have been no barriers to them doing true end-to-end encryption of iMessage backups, but they have chosen not to for many years despite marketing iMessage as "end-to-end" encrypted. Reportedly at the direct request of the FBI. 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...

Spooky23 5y ago

They almost certainly do. Every major provider does, and even some enterprises. The whole point of the CSAM stuff was that it would allow for end to end encryption while not turning Apple’s ecosystem into preferred tool of child pornographers. Apple poorly communicated the feature, then the EFF put out a deliberately misguided written hitpiece that conflated parental controls with CSAM, and started an online freak out. The “privacy activists” won, and your data is sitting on Apple servers with Apple’s managed encryption keys outside of your control today.

sebzim4500 5y ago
I think that's a pretty bad summary of the concerns that were raised. Sure they are scanning your files on icloud, but there is a 100% reliable way to prevent that: just don't upload them. In their proposal they would scan your files on device, which is fundamentally different. Initially they would not run the scanning when icloud upload was disabled but how long would that last for?
- ziml77 5y ago
  No. The proposal was to generate the perceptual hash on device at the time of uploading to iCloud. It would not be doing any scanning on-device. The comparison to the CSAM database would still happen on Apple's servers.
  - matthewdgreen 5y ago
    The device would download an encrypted database. It would compute a hash on the device. It would compute a value (“voucher”) from this hash and the database and upload that value to iCloud, which could decrypt it iff there were a sufficient number of matches. The voucher is independent of the plaintext file uploaded to iCloud: hence you could upload only the voucher and not the file and the system would still alert. Phrases like “it would not be doing any scanning on-device” don’t have any precise meaning. Scanning is a series of operations including hashing and cryptographic calculations plus a voucher upload and decryption. All of the former operations are happening on the device, only the latter happens on the server. So in fact a significant fraction of the scanning is indeed happening on your device. And this two-computer design isn’t being used to preserve your privacy: it’s designed this way solely to prevent you (the device owner) from knowing whether your files match the database. Without that requirement, the system would be much simpler: it would download a hash database and simply send a notification to iCloud whenever (a sufficient number of) local files hash to values matching the database.