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No, because the second hash is only performed after the first hash has already matched, and so, using the threshold secret sharing crypto, the server has learned the escrowed encryption key for the image. (Well, for its “visual derivative”, at any rate.)
So, Apple retains the ability to decrypt E2EE data? That’s… worse?
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They'd more or less have to be. Well, not necessarily 'police', but NCMEC. I did work in automating abuse detection years back, and the US govt clearly tells you are not to open/confirm suspected, reported, or happened upon cp. There's a lot of other seemingly weird laws and rules around it.
Those laws don’t apply if it’s part of the reporting process. Apple’s stated that they do a manual to decide whether to send a report to NCMEC or not, just like other companies do.
It is of course possible that companies may get some special sign off from LE/NCMEC to do this kind of work - I won't argue with you on that as I truly don't know. I can just tell you my company did not, and was very harshly told how to proceed despite knowing the nature of what we were trying to accomplish. But, we weren't anywhere near Apple big.
I remember chatting with our legal team, who made it explicit that laws didn't to cover carve outs - basically 'seeing' was illegal. But as you can imagine, police didn't come busting down our doors for happening upon it and reporting it. If you have links to law where this is not the case, I'll gladly eat crow. I've never looked myself and relied on what the lawyers had said.
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For better or worse, opaque server-side CSAM models are the norm in the cloud photo hosting world. I imagine that the consequences would be roughly the same as if Google's, Facebook's or Microsoft's "secret classifiers" were leaked.
but in the cloud setting they have the plaintext of what was uploaded. The attack described above is about abusing the lack of information apple has so they will report an innocent user to the authorities.
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I think visual derivative is just a beating-around-the-bush way of saying “thumbnail.”
That's their words that they feel no need to elaborate on. Obviously they actually seem to just be doing the "technically the truth" thing - which shows that someone realized no one would like hearing what it actually is.
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Unless Apple implements this with a backdoor on iCloud, the worst case scenario here is that they receive millions of false positives per day and terminate the program after two weeks. The scalability issue seems to work in our favor because, perhaps, the normal usage will overwhelm the human reviewers Apple prepared and we don't even need to send troll images. And for the entire time, our data remains untouched.
So Apple customers go from paying for a status symbol luxury item to paying for the privilege of participating in this, at best, pointless exercise wherein they rely upon the goodwill and competence of Apple's employees to not get them swatted. The mental gymnastics needed in order to guard one's ego on this issue can't be healthy either.
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I did my best skimming comments the algorithm showed me, including related posts' comments. But man am I bad at reading comprehension. If I miss anything then surely I am willing to be corrected. But so far I don't see comments that show us how to penetrate the four-layer system (local hash check, semantic check by user, on-server hash check, and human reviewer).
Ah ok! Here's the relevant part of the thread for that. https://news.ycombinator.com/item?id=28229832
Can someone explain me what isn neural hash?
NeuralHash is a hashing algorithm made by Apple to create hashes from images. Where other hashing algorithms would look at the pixel values, NeuralHash creates hashes based on the visual features of an image. You can read more about it here: https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni...
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How...exactly did they train that CSAM classifier? Seeing as that training data would be illegal. I'd be most interested in an answer on that one. They are willing to make that training data set a matter of public record on the first trial, yes? Or are we going to say secret evidence is just fine nowadays? Bloody mathwashing.
honestly asking — why is it illegal?
However, the line of thinking was if Apple has a secondary classifier to run against visual derivatives, the intent is it can say "CSAM/Not CSAM". Since the NeuralHash can collide, that means they'd need something to take in the visual derivatives, and match it vs an NN trained on actual CSAM. Not hashes. Actual.
Evidence, as far as I'm aware, is admitted to the public record, and a link needs to exist, and be documented in a publically and auditable way. That to me implies any results of a NN would necessarily require that the initial training set be included for replicability if we were really out to maintain the full integrity of the chain of evidence that is used as justification for locking someone away. That means a snapshot of the actual training source material, which means large CSAM dump snapshots being stored for each case using Apple's classifier as evidence. Even if you handwave the government being blessed to hold onto all that CSAM as fitting comfortably in the law enforcement action exclusions; it's still littering digital storage somewhere with a lotta CSAM. Also Apple would have to update their model over time, which would require retraining, which would require sending that CSAM source material to somewhere other than NCMEC or the FBI (unless both those agencies now rent out ML training infrastructure for you to do your training on leveraging their legal carve out, and I've seen or come across no mention of that.)
Thereby, I feel that logistically speaking, someone is commiting an illegal act somewhere, but no one wants to rock the boat enough to figure it out, because it's more important to catch pedophiles than muck about with blast craters created by legislation.
I need to go read the legislation more carefully, so just take my post as a grunt of frustration at how it seems like everyone just wants an excuse/means to punish pedophiles, but no one seems to be making a fuss over the devil in the details, which should really be the core issue in this type of thing, because it's always the parts nobody reads or bothers articulating that come back to haunt you in the end.
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I didn’t claim it was impossible, just that hash collisions won’t match both. Also, the information needed to create a full match simply is not available.
Are those not the same statement? Unless you're relying on it being computationally infeasible, but I'm not sure we know enough to consider that true at this point. Usually when we make statements on those grounds we do so with substantial proof. I don't think we know enough to do so here. I'm not even sure how feasible it is when you throw DL into the mix.
No.
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I just want to be clear if I understand this... many images can result in the same hash, but the hash can and will be reversible into one image? And that image is a low res porn photo derived from the algorithm's guesswork? So once a hash matches they don't check if there was a collision and the photo is completely unrelated, they just see the CG porn? If that's the case then why even look at the derived image?
No, this is not what's going on at all. The employees never see the original photos in the government CSAM hash database. Apple doesn't even have these photos: it's precisely the kind of content that they don't want to store on their servers. If some conditions are satisfied, the employees gain access to the visual derivatives (low-resolution copies) of your photos, and they judge whether these look like they could p…