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Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

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Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#281

Post by sgent »

Alupis wrote: post #184
simondotau wrote: post #182

Earlier quoted context omitted.

I agree CSAM isn't likely to be pervasive in the photo libraries on iOS devices. Android does not do on-device scanning, but Google does scan photos after they are uploaded to their cloud photo service. It's not on-device scanning, but the effect is functionally identical: photos that are being uploaded to the cloud are being scanned for CSAM. The only real distinction is who owns the CPU which computes the hash. I d…

> Android doesn't do on-device scanning, but Google does scan photos after they are uploaded to their cloud photo service. So did Apple, and pretty much all cloud hosting providers. This, on device, scanning is what's new, and very out of character for Apple. > If Apple's lobbyists can show that iPhones are already searching for CSAM, arguments for such laws get weaker. I'm not aware of any big anti-CSAM push being m…

Apple did not scan uploaded images. Apple has never scanned iPhone images. Last year Apple reported 245 cases to missing and exploited children, and Facebook reported 50M, Google ~4M, Microsoft reported, and Apple was below the line.

https://www.nytimes.com/2020/02/07/us/online-child-sexual-ab...

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#282

Post by t-writescode »

ThinBold wrote: post #156

Despite that Apple scanning our images is a horrible privacy practice, I don't get why 𝚜̶𝚘̶ ̶𝚖̶𝚊̶𝚗̶𝚢̶ some people think this is an ineffective idea. Surely you can easily fabricate innocent images whose NeuralHash matches the database. But in what way are you going to send them to victims and convince them to save them to their photo library? The moment you send it via WhatsApp FB will stop you because (they th…

Some people sync iMessages. That might even be the default.

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#283

Post by MrMoenty »

blintz wrote: post #272
63 wrote: post #100

Earlier quoted context omitted.

I'm fairly sure they do, actually. It was in one of the articles earlier today that Apple has a distinct, secret algorithm they perform on suspected CSAM server side after it gets flagged by the client side neural hash. Then only after 30 such images from a single user are identified as CSAM by both algorithms will they be sent to a human reviewer who will confirm their contents. Then, finally, law enforcement will b…

But relying on an algorithm staying secret is security-by-obscurity 101. You can rely on a cryptographic key staying secret; you can't rely on the design of an algorithm staying secret (I do agree there's a little blurring of these lines with large, trained models, but the gist remains - you can't just hope that nobody sees the structure/weights of your second hash function).

Given that training the same network (with the same structure) will result in different weights and different hashes with high probability, I would argue that the weights actually have all the important properties of a secret key. You would just need to treat them as one operationally, i.e., make sure as few people as possible have access, and use truly random instead of pseudorandom numbers during training.

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#284

Post by K5EiS »

animanoir wrote: post #77

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...

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#285

Post by sethgecko »

salawat wrote: post #228
fay59 wrote: post #123

Earlier quoted context omitted.

Before they make it to human review, photos in decrypted vouchers have to pass the CSAM match against a second classifier that Apple keeps to itself. Presumably, if it doesn’t match the same asset, it won’t be passed along. This is explained towards the end of the threat model document that Apple posted to its website. https://www.apple.com/child-safety/pdf/Security_Threat_Model...

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.

They didn't train a classifier, just a hashing function.

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#286

Post by corgihamlet »

yoz-y wrote: post #246

To me the most interesting findings from this fiasco were: 1. People actually do use generally publicly available services to store and distribute CP (as suggested by the amount of reports done by Facebook) 2. A lot of people evidently use iCloud Photo Library to store images of things other than pictures they took themselves. This is not really surprising, I've learned that the answer of "does anybody ever?" questio…

My iCloud Photo Library is full of pictures saved from the Web and screenshots.

That is just the way it works on iOS and it is really annoying to have random cute dog pictures saved from Reddit crop up in "Your Furry Friends"-Compilations.

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#287

Post by signal11 »

yoz-y wrote: post #246

To me the most interesting findings from this fiasco were: 1. People actually do use generally publicly available services to store and distribute CP (as suggested by the amount of reports done by Facebook) 2. A lot of people evidently use iCloud Photo Library to store images of things other than pictures they took themselves. This is not really surprising, I've learned that the answer of "does anybody ever?" questio…

> 2. A lot of people evidently use iCloud Photo Library to store images of things other than pictures they took themselves

Not in the context of CSAM, but this is iOS’s “appliance” user interface coming back to bite it. The iOS photos app doesn’t appear to have a way to show the user only the photos they took.

Apps like Twitter, browsers, chat apps, screenshots all get to save their photos in the photo library. I believe iOS 15 has a way to filter photos by originating app, but for most users currently, it’s hard not to use iCloud Photo Library for photos I didn’t take myself.

Interestingly, users save chat history including images, from apps like iMessage and WhatsApp, on iCloud too. I’m not sure what happens to e2e encryption for backed up data.

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#289

Post by sethgecko »

simondotau wrote: post #137
copperx wrote: post #75

Earlier quoted context omitted.

None needed. You could just send a photo to the target through WhatsApp, and the photo would be automatically synced with iCloud.

Wouldn't the photo be scanned for CSAM by WhatsApp first?

Whatsapp messages are e2e encrypted so no.

Re: Show HN: Neural-hash-collider – Find target hash collisions for NeuralHash

#290

Post by mikeyla85 »

londons_explore wrote: post #278
blintz wrote: post #272

Earlier quoted context omitted.

But relying on an algorithm staying secret is security-by-obscurity 101. You can rely on a cryptographic key staying secret; you can't rely on the design of an algorithm staying secret (I do agree there's a little blurring of these lines with large, trained models, but the gist remains - you can't just hope that nobody sees the structure/weights of your second hash function).

Security by obscurity has protected a lot of things successfully...

In this context, security by obscurity is literally what protects private keys.
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