4 ms·

If you're in close physical contact with a person (like at a job) you just wait for them to put their phone down while unlocked, and do all this.

FabHK 5y ago
Then, with all due respect, the attacker could just download actual CSAM. > If your adversary is the Mossad, YOU’RE GONNA DIE AND THERE’S NOTHING THAT YOU CAN DO ABOUT IT. The Mossad is not intimidated by the fact that you employ https:// https://. If the Mossad wants your data, they’re going to use a drone to replace your cellphone with a piece of uranium that’s shaped like a cellphone, and when you die of tumors filled with tumors, they’re going to hold a press conference and say “It wasn’t us” as they wear t-shirts that say “IT WAS DEFINITELY US,” and then they’re going to buy all of your stuff at your estate sale so that they can directly look at the photos of your vacation instead of reading your insipid emails about them. https://www.usenix.org/system/files/1401_08-12_mickens.pdf https://www.usenix.org/system/files/1401_08-12_mickens.pdf
- incrudible 5y ago
  Also, this XKCD: https://xkcd.com/538/ https://xkcd.com/538/ People are getting nerd-sniped about hash collisions. It's completely irrelevant. The real-world vector is that an attacker sends CSAM through one of the channels that will trigger a scan. Through iMessage, this should be possible in an unsolicited fashion (correct me if I'm wrong). Otherwise, it's possible through a hacked device. Of course there's plausible deniability here, but like with swatting, it's not a situation you want to be in.
  - aardvarkr 5y ago
    Love the relevant xkcd! And to reply to your point, simply sending unsolicited CSAM via iMessage doesn’t trigger anything. That message has to be saved to your phone then uploaded to iCloud. Someone else above said repeat this process 20-30 times so I presume it can’t be a single incident of CSAM. Seems really really hard to trigger this thing by accident or maliciously
    - ziml77 5y ago
      People are saying that, by default, WhatsApp will save images directly to your camera roll without any interaction. That would be an easy way to trigger the CSAM detection remotely. There are many people who use WhatsApp so it's a reasonable concern.
      - incrudible 5y ago
        Can you send images to people that are not on your friend list?
  - deelowe 5y ago
    FWIW, this sort of argument may not trigger a change in policy, but a technical failure in the hashing algorithm might.
  - UseStrict 5y ago
    Plausible deniability or not, it could have real impact if Apple decides to implement the policy of locking your account after tripping the threshold, which you then have to wait or fight to get unlocked. Or now you have police records against you for an investigation that lead nowhere. It's not a zero impact game if I can spam a bunch of grey blobs to people and potentially have a chain of human failures that leads police knock down your door.
  - cyanite 5y ago
    > Through iMessage, this should be possible in an unsolicited fashion Sure, but those don’t go into your photo library, so it won’t trigger any scanning. Presumably people wouldn’t actively save CSAM into their library.
- spicybright 5y ago
  Have you not worked a minimum wage job in the US? It's incredibly easy to gain phone access to semi-trusting people. If you don't like someone (which happens very often in this line of work) you could potentially screw someone over with this.
- superjan 5y ago
  Great article!
- mrits 5y ago
  "Then, with all due respect, the attacker could just download actual CSAM." If you didn't have Apple scanning your drive trying to find a new way for you to go to prison then it wouldn't be a problem.
  - cyanite 5y ago
    It’s misleading to say that they scan your “drive”. They scan pictures as they are uploaded to iCloud Photo Library. Also, most other major cloud photo providers scan images server side, leading to the same effect (but with them accessing more data).
  - FabHK 5y ago
    Yes. But this whole discussion is about potential problems/exploits with hash collisions (see title).

FabHK 5y ago

Then, with all due respect, the attacker could just download actual CSAM. > If your adversary is the Mossad, YOU’RE GONNA DIE AND THERE’S NOTHING THAT YOU CAN DO ABOUT IT. The Mossad is not intimidated by the fact that you employ https:// https://. If the Mossad wants your data, they’re going to use a drone to replace your cellphone with a piece of uranium that’s shaped like a cellphone, and when you die of tumors filled with tumors, they’re going to hold a press conference and say “It wasn’t us” as they wear t-shirts that say “IT WAS DEFINITELY US,” and then they’re going to buy all of your stuff at your estate sale so that they can directly look at the photos of your vacation instead of reading your insipid emails about them. https://www.usenix.org/system/files/1401_08-12_mickens.pdf https://www.usenix.org/system/files/1401_08-12_mickens.pdf

incrudible 5y ago
Also, this XKCD: https://xkcd.com/538/ https://xkcd.com/538/ People are getting nerd-sniped about hash collisions. It's completely irrelevant. The real-world vector is that an attacker sends CSAM through one of the channels that will trigger a scan. Through iMessage, this should be possible in an unsolicited fashion (correct me if I'm wrong). Otherwise, it's possible through a hacked device. Of course there's plausible deniability here, but like with swatting, it's not a situation you want to be in.
- aardvarkr 5y ago
  Love the relevant xkcd! And to reply to your point, simply sending unsolicited CSAM via iMessage doesn’t trigger anything. That message has to be saved to your phone then uploaded to iCloud. Someone else above said repeat this process 20-30 times so I presume it can’t be a single incident of CSAM. Seems really really hard to trigger this thing by accident or maliciously
  - ziml77 5y ago
    People are saying that, by default, WhatsApp will save images directly to your camera roll without any interaction. That would be an easy way to trigger the CSAM detection remotely. There are many people who use WhatsApp so it's a reasonable concern.
    - incrudible 5y ago
      Can you send images to people that are not on your friend list?
- deelowe 5y ago
  FWIW, this sort of argument may not trigger a change in policy, but a technical failure in the hashing algorithm might.
- UseStrict 5y ago
  Plausible deniability or not, it could have real impact if Apple decides to implement the policy of locking your account after tripping the threshold, which you then have to wait or fight to get unlocked. Or now you have police records against you for an investigation that lead nowhere. It's not a zero impact game if I can spam a bunch of grey blobs to people and potentially have a chain of human failures that leads police knock down your door.
- cyanite 5y ago
  > Through iMessage, this should be possible in an unsolicited fashion Sure, but those don’t go into your photo library, so it won’t trigger any scanning. Presumably people wouldn’t actively save CSAM into their library.
spicybright 5y ago
Have you not worked a minimum wage job in the US? It's incredibly easy to gain phone access to semi-trusting people. If you don't like someone (which happens very often in this line of work) you could potentially screw someone over with this.
superjan 5y ago
Great article!
mrits 5y ago
"Then, with all due respect, the attacker could just download actual CSAM." If you didn't have Apple scanning your drive trying to find a new way for you to go to prison then it wouldn't be a problem.
- cyanite 5y ago
  It’s misleading to say that they scan your “drive”. They scan pictures as they are uploaded to iCloud Photo Library. Also, most other major cloud photo providers scan images server side, leading to the same effect (but with them accessing more data).
- FabHK 5y ago
  Yes. But this whole discussion is about potential problems/exploits with hash collisions (see title).