There is an interesting constitutional quirk which arises from the scanning being done client side, specifically for US citizens. If the US Government forced Apple to add other entries to the hash table, this would constitute a warrantless Government search of the private physical property of US citizens. This is a clear-cut, unambiguous breach of the 4th Amendment.

Whereas if the CSAM scanning was performed exclusively in the cloud, protection under the 4th Amendment does not exist as it would likely fall under the third party doctrine.

Now I'm not saying the US Government would let mere unconstitutionality get in the way of any surveillance program. But Apple would. You don't think Apple wouldn't be itching for another opportunity to flex in public? Especially now, with their reputation on the line? Apple would love nothing more than to have more opportunities like they got with the San Bernardino iPhone.

Apple could also encrypt every upload to iCloud, and not have any scanning on the client, and still be able to say to the government "sure, you can have the files; we can't read them and neither can you". Apple wants to reduce your privacy from the government above and beyond what the law requires. The questions is: why?

The answer may be related to Pegasus software.

Timeline:

1. Leaked documents show Pegasus software exploits all iphones using an exploit in iMessage 2. Apple releases security update (doesn’t patch imessage. exploit) 3. Apple announces CSAM client scanning coming soon 4. Apple releases another security update (still leaves iMessage exploit unpatched and used by Pegasus)

….

Perhaps Apple is under pressure to provide a back door prior to patching a tool that may be widely used by governments around the world.

The simple answer is: password resets. I’m sure majority of people would be very upset if they lost everything by forgetting a password.

Doesn't the apple backup stuff work that way? The data is gone forever if you lose your password?

Some, but not all. And if you still have access to a Mac or iOS device which remains associated to this iCloud account, the amount that is lost can be even less.

Because Apple doesn't want to be a child porn storage service. This is not a secret.

That's not technically possible, though. Most tech companies don't take on impossible tasks, because it will take an infinite amount of money to realize it, and the shareholders will be bankrupt before the product is delivered.

Every piece of data is CSAM encrypted with a one-time pad. It's just that nobody knows the one-time pad.

I think you're implying that scanning of private personal property by a corporation without a warrant protects users from searches of their content in the cloud that is authorized by a warrant or national security letter. I don't understand the mechanism if there isn't end to end encryption, and I don't understand the mechanism if there is end to end encryption.

Scanning makes phones a greater threat, and also erodes the expectation of privacy that is a legal barrier to surveillance.

I did not intentionally imply anything here, so if anything I wrote appears to include an implied component, that was not intended and may not represent my opinion.

All I'm saying is that the implementation Apple has described would be constitutionally blocked from being co-opted by US law enforcement. Obviously if there's no end-to-end encryption, any cloud operator could still be coerced into searching for material server side, as that falls under the so-called third party doctrine.

What kind of non-CSAM crime could be detected with just a couple of hashes? Wouldn’t Apple need to reduce the similarity score in order to even get something close?

Also Fifth Amendment. People are being compelled to testify against themselves by running this CSAM scanner. Apple's end-to-end encryption was sold to users as exactly that.

To all of a sudden introduce this scanner doesn't negate the expectation of privacy as that is how it was sold and marketed. There is an implied warranty of merchantability of how this service functions.

Are you a lawyer or legal scholar, or just guessing?

The government can't compel warrantless searches of Apple. 3rd party doctrine means Apple can search your iCloud, and can give it away if they choose. Same as how Apple can search your phone if you run their software, and can give away whatever they find if they choose.

> If the US Government forced Apple to add other entries to the hash table, this would constitute a warrantless Government search of the private physical property of US citizens. This is a clear-cut, unambiguous breach of the 4th Amendment.

There's no reason not to assume this isn't already happening, being closed source and proprietary. The question to ask is, what are we going to do about it?

If you take that line of argument, you must also accept that you have no reason not to assume that binary distributions of Android and Windows haven't been doing similar things for the past decade.

I agree with you in that I don't think the problem is the closed-source aspect. Closed source software can still be audited (with difficulty). The problem is that the source material for the hashes can't be audited, even when we know exactly how the system works.

The audience here should know that where there is capability, there is abuse. Android and Windows are no exception.

This is already a warrantless search that’s effectively controlled by the government. Obviously there’s enough chaff in the air to prevent that from being legally useful in any way.

So far the courts have determined that since providers invade their customer privacy of their own free will with no incentive or coersion by any government agency, that it is not a search by the goverment.

It's just your friendly trillion dollar tech company putting on a mask and cape and engaging in a bit of vigilante fun. You know? Like batman! ( https://www.youtube.com/watch?v=Kr7AONv3FSg )

Nope. It’s not controlled by the government, and it’s not warrantless, since it is opt-in.

Since the govt. supplies the hashes in an unauditable way, it absolutely is controlled by the government. What's to stop them from using hashes of non CSAM material?

The government doesn’t supply the hashes in an unauditable way, that is a totally false statement.

The hashes are supplied by NCMEC, a non-profit which is auditable, not a secret government agency.

In any case, even if a non-CSAM hash were somehow in the database, Apple reviews the images before making reports, and those reports are used in normal criminal prosecutions.

Courts have determined that for this purpose the NCMEC is an agent of the government. NEMEC is 99% funded by the government and its ability to handle child porn is directly deprived from a explicit legislative carveout for them by name. What they do would be a felony for you or I to do. The fact that they are technically non-profit rather than an agency makes them significantly less accountable to the public. We cannot FOIA their communications, their composition isn't subject to public review, we cannot vote them out. And we have no way to tell what their database contains, nor is there any avenue for redress should we somehow learn of an inappropriate listing.

To the extent that you can say that they're not exactly a government agency, they absolutely have been deputized by the government.

> And we have no way to tell what their database contains, nor is there any avenue for redress should we somehow learn of an inappropriate listing.

Yes there is. It’s called legal liability. They are not immune to being held accountable for their actions just like any other non-profit. They may be immune from prosecution for possessing CSAM, but they don’t have any kind of immunity for damages they cause through their own actions.

So you would agree that Apple's use of private set intersection serves the purpose of shielding themselves and their data sources for the purposes of mitigating their legal liability from the harms created by false listings by concealing the content of the databases?

The database of hashes is controlled by the government. They can put whatever they want in there.

False. See my other reply.

https://news.ycombinator.com/item?id=28303966

I don't think it's entirely false. NCMEC is not a regular non-profit. They have special clearance to do things that regular citizens and non-profits are not allowed to do.

A government-funded “NGO” with special legal powers is the government.

Presumably, it’s done this way so they can say computers other than your personal device do not scan photos and “look” at decrypted and potentially innocent photos. And technically the original image is never decrypted in iCloud by Apple - if 30 images are flagged they are then able to decrypt the CSAM scan meta data which contains resized thumbnails, for confirmation.

In summary, I’m guessing they tried to invent a way where their server software never has to decrypt and analyze original photos, so they stay encrypted at rest.

Apple frequently decrypts icloud data including photos based on a valid warrant. This new local scanning method does not stop apple from complying and decrypting images like they have for years.

https://www.apple.com/legal/privacy/law-enforcement-guidelin...

(Note: I have worked with law enforcement in the past specifically on a case involving Apple and two iCloud accounts. You submit a PDF of the valid warrant to Apple. Apple sends two emails one with the iCloud data encrypted. A second email with the decryption key.)

Of course, but it's a kind of last resort thing to support a valid legal process they cannot (and probably don't want to) skirt around. They also publish data on warrant requests.

To me it's pretty clear they are doing the absolute minimum possible to keep congress from regulating them into a corner, where they lose decision making control around their own privacy standards. The system they came up with is their answer for doing it in the most privacy conscious way (e.g. not decrypting user data in icloud) while balancing a lot of other threat model details, like what if CSAM-hash-providing organizations provide img hashes for a burning American flag, and lots of other scenarios outlined in the white paper.

calling resized thumbnails metadata is a bit of a stretch imo.

Surely that's just the data, but resized?

Yes I agree, bit of a stretch. Based on their whitepaper, it's a smaller version of the original image, I guess just large enough to support the human verification step.

But I'm unsure that the thumbnail is included with every CSAM "voucher" -- it's likely only included when you pass the 30 image limit. Need to read that section more clearly.

A thumbnail is included with every safety voucher. However, it is encrypted with a key that resides on your hardware and is unknown to Apple. So Apple doesn't have enough information to decrypt your thumbnails at will.

A secret sharing scheme is used to drip-feed Apple the key: each time a positive match occurs, Apple learns a bit more about your key. Once the threshold is reached, Apple will have learned enough to recover your encryption key, and will be able to use it to decrypt all your matching thumbnails at once.

Fascinating, thanks for clarifying.

> Based on their whitepaper, it's a smaller version of the original image,

I seem to recall that the white paper speaks of a "visual derivative" without specifying it further.

The Technical Summary uses "visual derivative" without clarification, but their Threat Model PDF clarifies it further as thumbnails:

>The decrypted vouchers allow Apple servers to access a visual derivative – such as a low-resolution version – of each matching image.

https://www.apple.com/child-safety/pdf/Security_Threat_Model...

Resized thumbnails aren't a stretch... they're a scale. Bum dum tiss.... I'll let myself out

Interesting technical problem/solution. Another benefit is saving on millions of server computations when modern iOS devices have neural chips etc.

I suppose folks who don’t like privacy implications can downgrade to an iPhone 4 and maybe it will not support the feature.

Or turn off iCloud syncing of photos.

Most people feel that things that happen on your device are safer than things in the cloud, you have probably noticed how Apple constantly stress that this or that happens "on device".

And for the suspicious, it's of course much easier to notice if Apple would change their algorithms if they happen on device.

Also they will be doing scanning in their server anyways as there are other ways to upload it in iCloud than using latest iOS.

Apple basically never announces things before they are ready to be released, so them not announcing this means very little. They may be working on it, and their usual secrecy is biting them in the ass very hard.

One reason for client side could be to save on datacenter compute resources. That would seem like a perfectly valid reason, if that’s their reasoning.

If it’s going to really save a significant amount of data center resources, then it’s also probably going to reduce the battery lifespan of all these devices significantly. That may probably be good for Apple’s bottom line temporarily, but it will hurt in the long run. I’d imagine it’d be a lot easier to optimize the data center compute resources than optimizing the scanning on individual devices and not trashing battery lifespan.

> I’d imagine it’d be a lot easier to optimize the data center compute resources than optimizing the scanning on individual devices and not trashing battery lifespan.

No amount of data center optimization will beat running computations on hundreds of millions of devices other people have to pay for.

If that’s a valid reason to steal electricity and compute resources from your customers, then why not go the whole way and use all the Mac’s as storage and compute for iCloud?

> If this is the case there is zero reason to scan locally and you can just scan the uploaded image once it is on the server.

You’re having a house party. Because of the pandemic, you’d rather people who have COVID not attend. You can’t trust everyone to get vaccinated or get tested beforehand. So, you decided to set up a rapid-test system, just to be sure.

Would you rather test in your kitchen or your driveway?

Why the contagion analogy?

If contagion wasn't a factor, I'd rather test in the kitchen, it's cozier.

Are you suggesting CSAM will infect more unwilling victims if it gets into a private iCloud account?

CSAM on the server means the server is tainted and likely to be searched by governments. Good plan to keep it off eliminates that excuse.

I don't see how this scanning reduces the likelihood of a government searching their servers. Seems to me like this can only result in more court orders than they had before scanning.

If you’re Apple, and you’re throwing your weight around in the US bread and butter market to convince the FBI to not scan your servers for CSAM, which is more compelling: we check for it when it gets here, or we keep it off our servers using crypto hash magic?