The Problem with Perceptual Hashes • Hacker News Board

Re: The Problem with Perceptual Hashes

#231

Post by visarga » Sat, Aug 07, 2021, 6:15 AM UTC

dogma1138 wrote: post #106

starkd wrote: post #59

The method Apple is using looks more like a cryptographic hash. That's entirely different (and more secure) than a perceptual hash. From https://www.apple.com/child-safety/ "Before an image is stored in iCloud Photos, an on-device matching process is performed for that image against the known CSAM hashes. This matching process is powered by a cryptographic technology called private set intersection, which determines…

The cryptography is most likely done at a higher level than the perception comparison and is quite likely done to protect the CSAM hashes than your privacy. My interpretation of this is that they still use some sort of a perception based matching algorithm they just encrypt the hashes and then use some “zero knowledge proof” when comparing the locally generated hashes against the list, the result of which would be ju…

> the result of which would be just that X hashes marched but not which X

That means you can't prove an incriminating file was not deleted even if you're the victim of a false positive. So they will suspect you and put you through the whole police investigation routine.

Re: The Problem with Perceptual Hashes

#232

Post by esyir » Sat, Aug 07, 2021, 6:16 AM UTC

bigyikes wrote: post #183

esyir wrote: post #167

Earlier quoted context omitted.

>but there is still a very strong culture of free speech In my opinion, that culture has been rapidly dying, chipped away by a very sizable and growing chunk that doesn't value it at all, seeing it only as a legal technicality to be sidestepped.

I find this varies greatly depending on location. Living in California, I was convinced of the same. Living in Texas now, I’m more optimistic.

I'm not nearly as happy to hear that as you might think. California is currently the heart of power of the US tech industry, which means they hold outsized power over the rest of the US and the world. That means illiberal values growing there are going to have similarly outsized effects

Re: The Problem with Perceptual Hashes

#233

Post by p2t2p » Sat, Aug 07, 2021, 6:16 AM UTC

Blammar wrote: post #132

zionic wrote: post #78

Earlier quoted context omitted.

So what are we going to do about it? I have a large user base on iOS. Considering a blackout protest.

Write an iCloud photo frontend that uploads only encrypted images to iCloud and decrypts on your phone only?

Won't help, the detection of on your phone now. I wonder if one can have a local VPN with a profile installed which could MITM iCloud upload process and take those matching envelops out.

But in the end of the day the only robust way to communicate privately is good old Linux with good old mutt with good old PGP

Re: The Problem with Perceptual Hashes

#234

Post by mrtksn » Sat, Aug 07, 2021, 6:32 AM UTC

HWR_14 wrote: post #123

mrtksn wrote: post #80

Earlier quoted context omitted.

IMHO, Unless everything being E2E encrypted becomes the law we can’t do anything about it because that’s not Apple’s initiative but comes from people whose job is to know things and they cannot resist keeping their hands out of these data collecting devices. They promise politicians that all the troubles will go away if we do that. Child pornography, Terrorism? Solve it the old way. I don’t know why citizens are obli…

> Solve it the old way. In fairness, in the "old way" it was impossible for two random people to communicate in real-time between continents without the ability of authorities to observe/break it. Privacy and security is quite important, but let's not lose track of the fact that there are many tools authorities have lost in the past few decades. In WWII major powers weren't able to have the same security of military…

The difference is that previously you had to be targeted and intercepted. Thinking that someone is listening was something that paranoid people would do.

Now your device is actually watching you and reporting you. Today only for child porn but there’s no technical reason of it not being extended to anything.

Re: The Problem with Perceptual Hashes

#235

Post by SavantIdiot » Sat, Aug 07, 2021, 6:37 AM UTC

chipotle_coyote wrote: post #145

SavantIdiot wrote: post #66

This article covers three methods, all of which just look for alterations of a source image to find a fast match (in fact, that's the paper referenced). It is still a "squint to see if it is similar" test. I was under the impression there were more sophisticated methods that looked for types of images, not just altered known images. Am I misunderstanding?

Apple's proposed system compares against a database of known images. I can't think of a way to "look for types of images" other than trying to do it with machine learning, which strikes me as fraught with incredible fiasco potential. (The compare-to-a-known-database approach has its own issues, including the ones the article talks about, of course.)

Ok, that's what it is seeming like. Since a crypto hash by definition has to generate a huge hamming distance for a small change, everything i've read about perceptual hashes is just the opposite: they should be tolerant enough of a certain amount of difference.

Re: The Problem with Perceptual Hashes

#236

Post by [deleted] » Sat, Aug 07, 2021, 6:39 AM UTC

emodendroket wrote: post #95

josephcsible wrote: post #58

Earlier quoted context omitted.

They look at content that people actively and explicitly chose to share with wider audiences.

While that's a snappy response, it doesn't seem to have much to do with the concern about perverts getting jobs specifically to view child abuse footage, which is what I thought this thread was about.

[deleted]

Re: The Problem with Perceptual Hashes

#237

Post by bcrosby95 » Sat, Aug 07, 2021, 6:53 AM UTC

jiggawatts wrote: post #213

The world in the 1900s: Librarians: "It is unthinkable that we would ever share a patron's borrowing history!" Post office employees: "Letters are private, only those commie countries open the mail their citizens send!" Police officers: "A search warrant from a Judge or probable cause is required before we can search a premises or tap a single, specific phone line!" The census: "Do you agree to share the full details…

Your view of the 1900s is very idyllic.

Re: The Problem with Perceptual Hashes

#238

Post by legulere » Sat, Aug 07, 2021, 6:53 AM UTC

Which photos does Apple scan? Also of emails and messages? Could you swat somebody by sending them benign images that have the same hash?

Re: The Problem with Perceptual Hashes

#239

Post by goldenkey » Sat, Aug 07, 2021, 6:58 AM UTC

esyir wrote: post #232

bigyikes wrote: post #183

Earlier quoted context omitted.

I find this varies greatly depending on location. Living in California, I was convinced of the same. Living in Texas now, I’m more optimistic.

I'm not nearly as happy to hear that as you might think. California is currently the heart of power of the US tech industry, which means they hold outsized power over the rest of the US and the world. That means illiberal values growing there are going to have similarly outsized effects

I think you mean liberal values. The paradox of the left includes censorship, gun control, etc..

Re: The Problem with Perceptual Hashes

#240

Post by colordrops » Sat, Aug 07, 2021, 7:12 AM UTC

goldenkey wrote: post #239

esyir wrote: post #232

Earlier quoted context omitted.

I'm not nearly as happy to hear that as you might think. California is currently the heart of power of the US tech industry, which means they hold outsized power over the rest of the US and the world. That means illiberal values growing there are going to have similarly outsized effects

I think you mean liberal values. The paradox of the left includes censorship, gun control, etc..

I think your mean liberal as in tribe, and gp means liberal as in values.