A sufficiently advanced catfishing attack could probably take advantage of this to get someone raided and have all their electronics confiscated.
Just send someone a zip of photos and let them extract it...
But OK, say someone sends you a sunset that fools the hasher. Then what? Of course one match won’t do anything, so you’d need to download however many matching sunsets. Then what? The Apple reviewer would see they’re sunsets and you’d challenge the flag saying they’re sunsets. And if somehow NCMEC got involved, they’d see they’re just sunsets. And if law enforcement got involved, they’d see they’re just sunsets.
These proofs of concept might seem interesting from a ML pov, but all they do is just highlight why Apple put so many layers of checking into this.
We all want privacy but it seems odd to try to DoS this, with high risk for yourself and very little to gain.
Might be useful when the system turns into mass political surveillance tho.
A real attack would be to take legal porn images and make them collide with illegal images, so when a human goes to review the scaled down derivative images, those images very well look like they could be CSAM. Since there are many of them, they'd get sent to law enforcement. Then law enforcement would raid the victim's home and take all of their electronic devices in order to determine if they can be charged with a crime or not.
And that's assuming someone develops a hash collision which doesn't substantially mangle the photograph like the example offered on Github.
Specifically, only images categorised as "A1" are being included in the hash set on iOS. The category definitions are:
A = prepubescent minor
B = pubescent minor
1 = sex act
2 = "lascivious exhibition"
Do we know that for sure?
Apple has changed their mind enough times in the last week and a half that I'm convinced they're in full on defensive "wing it and say whatever will get people off our backs!" mode.
You can't read the threat modeling PDF and conclude that it was run through the normal Apple document review process. It reads nothing like a standard Apple document - it reads like a bunch of sleep deprived people were told to whip it up and publish it.
But by fog of war I was thinking more like the victim already has some sleazy (though marginally legal) stuff on their computer, or a search led to a find of pot in their house, or they lied to try and get out of the rap, or perhaps the FBI offered them a deal and they took it because they saw no way out, or perhaps they were simply an unlikable individual who the jury took a dislike to.
Basically that things are not always clear cut, and they come out of the wrong side of things, in a situation created by Apple's surveillance.
Surveillance is surveillance. It's a bit more obnoxious that a CPU which I paid money for is being used to compute the hashes instead of some CPU in a server farm somewhere (which I indirectly paid for) but the outcome is the same. The risk of being SWAT-ed is the same.
If it was anything like the image used to demonstrate this technique on Github, it's unlikely that anyone would describe that sunset as "beautiful". They'd be more likely to describe it as "bugger, this JPEG file is corrupted."
It was quite literally less than 24h from "Oh, hey, I can collide this grey blob with a dog!" to "Hey, this thing that looks like cat hashes to the same thing as this dog!"
You really think this is going to end at this proof of concept stage?
Regardless, this whole thing is moot because there are two classifiers, only one of which has been made public. Before any matches can make it to human review, photos in decrypted vouchers have to pass the CSAM match against a second classifier that Apple keeps to itself.