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Comparing hashes reminds me of this announcement from a few years ago that Google had produced a SHA1 collision: https://security.googleblog.com/2017/02/announc

Comparing hashes reminds me of this announcement from a few years ago that Google had produced a SHA1 collision: https://security.googleblog.com/2017/02/announcing-first-sha1-collision.html https://security.googleblog.com/2017/02/announcing-first-sha... Can you imagine the chaos of a successful collision matching some explicit material being sent as a prank or targeted attack?

benlivengood 5y ago
No chaos. The photos would be reported, reviewers would say "that's weird" since the false positive was obviously harmless and the industry would eventually switch to a different hash method while ignoring the false positives generated by the collision. If there were a flood of false positive images being produced the agencies would work faster to come up with a new solution, not perform mass arrests.
- farmerstan 5y ago
  Right. Kind of like how copyright violations on YouTube are double checked and the humans say “that’s weird” and deny the request. Or maybe they will just report everything and let the law work everything out. If they’re innocent they have nothing to worry about, right?
  - mastazi 5y ago
    I don't understand how most people are still willing to "trust the system" when it's evident that this type of mechanism keeps failing time and time again. And in the example you gave we are talking about Google, not some early-stage understaffed startup.
- aczerepinski 5y ago
  I thought the images were encrypted after the hashing was done locally. Reviewers can still view them?
  - Hackbraten 5y ago
    Any local match causes a “safety voucher” to be uploaded along with the encrypted image. The voucher contains a (fragment of a) decryption key. If that fragment is combined with enough of its buddies from other vouchers, Apple gets to decrypt the image.
    - simondotau 5y ago
      More precisely, once they have sufficient vouchers, Apple gets to decrypt the contents of the safety vouchers, which contains a low resolution, grayscale copy of the original image. Safety vouchers don't give Apple access to your photo library.

benlivengood 5y ago

No chaos. The photos would be reported, reviewers would say "that's weird" since the false positive was obviously harmless and the industry would eventually switch to a different hash method while ignoring the false positives generated by the collision. If there were a flood of false positive images being produced the agencies would work faster to come up with a new solution, not perform mass arrests.

farmerstan 5y ago
Right. Kind of like how copyright violations on YouTube are double checked and the humans say “that’s weird” and deny the request. Or maybe they will just report everything and let the law work everything out. If they’re innocent they have nothing to worry about, right?
- mastazi 5y ago
  I don't understand how most people are still willing to "trust the system" when it's evident that this type of mechanism keeps failing time and time again. And in the example you gave we are talking about Google, not some early-stage understaffed startup.
aczerepinski 5y ago
I thought the images were encrypted after the hashing was done locally. Reviewers can still view them?
- Hackbraten 5y ago
  Any local match causes a “safety voucher” to be uploaded along with the encrypted image. The voucher contains a (fragment of a) decryption key. If that fragment is combined with enough of its buddies from other vouchers, Apple gets to decrypt the image.
  - simondotau 5y ago
    More precisely, once they have sufficient vouchers, Apple gets to decrypt the contents of the safety vouchers, which contains a low resolution, grayscale copy of the original image. Safety vouchers don't give Apple access to your photo library.