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That's a claim by Apple. Due to the opaque process this is completely unverifiable. As well this statement relies on the fact that no malicious actor out there

by chopin 5y ago

That's a claim by Apple. Due to the opaque process this is completely unverifiable. As well this statement relies on the fact that no malicious actor out there is trying to thwart the system. The hashes used are deliberately chosen to easily produce collisions otherwise the system won't work. This almost certainly will be abused.

robertoandred 5y ago
“This almost certainly will be abused.” is a claim by you and completely unverifiable. Apple has published white papers explaining how their hashing, matching, and cryptography work. How do you see someone thwarting that process specifically?
- drampelt 5y ago
  Apple's claims on how it will work are also completely unverifiable. What's stopping a government from providing Apple with hashes of any other sort of content they dislike?
  - robertoandred 5y ago
    And then Apple reviews the account and sees that what was flagged was not CSAM. And again, the hashes aren’t of arbitrary subject matter, they’re of specific images. Using that to police subject matter would be ludicrous.
    - drampelt 5y ago
      How would Apple know what the content was that was flagged if all they are provided with is a list of hashes? I completely agree it's ludicrous, but there are plenty of countries that want that exact functionality.
      - robertoandred 5y ago
        The matched image’s decrypted security voucher includes a “visual derivative.” I’m sure in other words they can do some level of human comparison to verify that it is or is not a valid match.
      - gordon_gee123 5y ago
        If they have the hash/derivative they dont need to look on device or even decrypt, theyll know that data with this hash is on device, and presumably 100s of other matching hashes from the same device
- JohnFen 5y ago
  Easy -- by having the authorities expand what is being searched for.
snowwrestler 5y ago
The concept of checking images against a hash list is not unique to Apple or even new. https://en.m.wikipedia.org/wiki/PhotoDNA https://en.m.wikipedia.org/wiki/PhotoDNA What Apple announced is a way to do it on the client device instead of the server. That has some security implications, but they’re more specific than just “hashes might collide.”
- heavyset_go 5y ago
  They're not just checking against a hash list, they're using perceptual hashing, which is inexact and unlike cryptographic hashing or checksumming. Then, they use a fuzzy metric like hamming distance to determine if one image is a derivative of an illegal image. The problem is that the space for false positives is huge when you use perceptual hashing, and it gets even larger when you start looking for derivative images, which they have to do otherwise criminals would just crop or shift color channels in order to bypass filters.

by chopin 5y ago

robertoandred 5y ago

“This almost certainly will be abused.” is a claim by you and completely unverifiable. Apple has published white papers explaining how their hashing, matching, and cryptography work. How do you see someone thwarting that process specifically?

drampelt 5y ago
Apple's claims on how it will work are also completely unverifiable. What's stopping a government from providing Apple with hashes of any other sort of content they dislike?
- robertoandred 5y ago
  And then Apple reviews the account and sees that what was flagged was not CSAM. And again, the hashes aren’t of arbitrary subject matter, they’re of specific images. Using that to police subject matter would be ludicrous.
  - drampelt 5y ago
    How would Apple know what the content was that was flagged if all they are provided with is a list of hashes? I completely agree it's ludicrous, but there are plenty of countries that want that exact functionality.
    - robertoandred 5y ago
      The matched image’s decrypted security voucher includes a “visual derivative.” I’m sure in other words they can do some level of human comparison to verify that it is or is not a valid match.
    - gordon_gee123 5y ago
      If they have the hash/derivative they dont need to look on device or even decrypt, theyll know that data with this hash is on device, and presumably 100s of other matching hashes from the same device
JohnFen 5y ago
Easy -- by having the authorities expand what is being searched for.

snowwrestler 5y ago

The concept of checking images against a hash list is not unique to Apple or even new. https://en.m.wikipedia.org/wiki/PhotoDNA https://en.m.wikipedia.org/wiki/PhotoDNA What Apple announced is a way to do it on the client device instead of the server. That has some security implications, but they’re more specific than just “hashes might collide.”

heavyset_go 5y ago
They're not just checking against a hash list, they're using perceptual hashing, which is inexact and unlike cryptographic hashing or checksumming. Then, they use a fuzzy metric like hamming distance to determine if one image is a derivative of an illegal image. The problem is that the space for false positives is huge when you use perceptual hashing, and it gets even larger when you start looking for derivative images, which they have to do otherwise criminals would just crop or shift color channels in order to bypass filters.