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Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

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Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#51

Post by GistNoesis »

amelius wrote: post #49
jonathanmayer wrote: post #23

(Context: I teach computer security at Princeton and have a paper at this week's Usenix Security Symposium describing and analyzing a protocol that is similar to Apple's: https://www.usenix.org/conference/usenixsecurity21/presentat... .) The proposed attack on Apple's protocol doesn't work. The user's device adds randomness when generating an outer encryption key for the voucher. Even if an adversary obtains both the…

There may be another attack. Given some CP image, an attacker could perhaps morph it into an innocent looking image while maintaining the hash. Then spread this image on the web, and incriminate everybody.

Yes perceptual hashes are not cryptographically secure so you can probably generate collisions easily, (i.e. a natural looking image which has a attacker-specified hash).

Here is a proof of concept I just created on how to proceed : https://news.ycombinator.com/item?id=28105849

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#52

Post by [deleted] »

casefields wrote: post #50
Teever wrote: post #11

Earlier quoted context omitted.

What terrible reasoning. 'Child pornography' is already too long to say repeatedly in a sentence so it is often shortened to "child porn." CSAM has far too many syllables so it too is shortened to two syllables in the form of the spoken acronym "CSAM" and so we're back to square one. With that said this is a fascinating display someone pressing the reverse button on the euphemism treadmill. I don't think I've ever se…

You ever notice when cops bust a prostitution ring they never call it that? It's been renamed human trafficking. Law enforcement is all in on the marketing game. Using scarier words will get the public to trade liberty for security every time.

[deleted]

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#53

Post by selsta »

joe_the_user wrote: post #26

Regardless of whether this attack works or not, you'd assume this scheme produces a wider attack surface against pictures in iCloud and against iCloud users. One attack I could imagine is a hacker uploading child porn to a hacked device to trigger immediate enforcement against a user (and sure, maybe there are more controls involved but would you carry around a very well-protected, well-designed hand grenade in your…

How is this iCloud specific? You could do the same with Google Photos or OneDrive.

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#54

Post by cube00 »

amelius wrote: post #49
jonathanmayer wrote: post #23

(Context: I teach computer security at Princeton and have a paper at this week's Usenix Security Symposium describing and analyzing a protocol that is similar to Apple's: https://www.usenix.org/conference/usenixsecurity21/presentat... .) The proposed attack on Apple's protocol doesn't work. The user's device adds randomness when generating an outer encryption key for the voucher. Even if an adversary obtains both the…

There may be another attack. Given some CP image, an attacker could perhaps morph it into an innocent looking image while maintaining the hash. Then spread this image on the web, and incriminate everybody.

It'd be interesting to see how the way common images are reused (for example in memes by only adding text) would be enough to change that hash. If it wasn't enough it could spread very quickly.

Of course I'd dare not research or tinker with it lest I'll be added to a list somewhere such is the chilling effect.

I guess in that case they'd delete that single hash from the database because they'd still have an endless (sadly) supply of other bad image hashes to use instead.

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#55

Post by macintux »

amelius wrote: post #49
jonathanmayer wrote: post #23

(Context: I teach computer security at Princeton and have a paper at this week's Usenix Security Symposium describing and analyzing a protocol that is similar to Apple's: https://www.usenix.org/conference/usenixsecurity21/presentat... .) The proposed attack on Apple's protocol doesn't work. The user's device adds randomness when generating an outer encryption key for the voucher. Even if an adversary obtains both the…

There may be another attack. Given some CP image, an attacker could perhaps morph it into an innocent looking image while maintaining the hash. Then spread this image on the web, and incriminate everybody.

> Then spread this image on the web, and incriminate everybody.

You'd still have to generate several images and persuade people to download multiple of them into their photo roll. And as I understand it there's yet another layer of Apple employees to review the photo metadata before it ever makes its way to law enforcement.

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#56

Post by kfprt »

It won't be long until these type of systems are mandated. Combined with a hardware root of trust it's not inconceivable that modifying your hardware not to report home will also be made a crime. It never stops with CSAM either, pretty soon it's terrorism and whatever vague new definition they use.

The focus on CSAM seems extremely hypocritical when authorities make such little effort to stop ongoing CSA. I would encourage everyone to research the Sophie Long case. Unless there is image or video evidence the police make little effort to investigate CSA because it's resource intensive.

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#57

Post by nicce »

selsta wrote: post #53
joe_the_user wrote: post #26

Regardless of whether this attack works or not, you'd assume this scheme produces a wider attack surface against pictures in iCloud and against iCloud users. One attack I could imagine is a hacker uploading child porn to a hacked device to trigger immediate enforcement against a user (and sure, maybe there are more controls involved but would you carry around a very well-protected, well-designed hand grenade in your…

How is this iCloud specific? You could do the same with Google Photos or OneDrive.

Literally for almost every other big cloud provider. (Facebook, Instagram, Discord, Reddit, Twitter and so on.) Granting that you have access by phone.

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#58

Post by RHSeeger »

macintux wrote: post #55
amelius wrote: post #49

Earlier quoted context omitted.

There may be another attack. Given some CP image, an attacker could perhaps morph it into an innocent looking image while maintaining the hash. Then spread this image on the web, and incriminate everybody.

> Then spread this image on the web, and incriminate everybody. You'd still have to generate several images and persuade people to download multiple of them into their photo roll. And as I understand it there's yet another layer of Apple employees to review the photo metadata before it ever makes its way to law enforcement.

That does seem like an interesting protest vector, though. Generate a bunch of images that match CSAM images but are mundane. Then have everyone download them and send them to their cloud. Someone then needs to spend resources determining that the images are _not_ actual matches. Basically, a DDOS attack on the functionality.

Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable

#60

Post by macintux »

RHSeeger wrote: post #58
macintux wrote: post #55

Earlier quoted context omitted.

> Then spread this image on the web, and incriminate everybody. You'd still have to generate several images and persuade people to download multiple of them into their photo roll. And as I understand it there's yet another layer of Apple employees to review the photo metadata before it ever makes its way to law enforcement.

That does seem like an interesting protest vector, though. Generate a bunch of images that match CSAM images but are mundane. Then have everyone download them and send them to their cloud. Someone then needs to spend resources determining that the images are _not_ actual matches. Basically, a DDOS attack on the functionality.

Indeed, that thought occurred to me as well.

It's a risky bet, though: if somehow that intermediate layer fails and you find yourself locked up and accused of storing/disseminating CSAM material, it's not like the civil rights era when your friends and neighbors (and hopefully employers) will understand you've been arrested for a peaceful protest.

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