this post was submitted on 28 Jun 2023
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[–] generalpotato@lemmy.world 4 points 2 years ago (9 children)

Didn’t Apple try to introduce this and got a ton of flak from all sorts of privacy “experts”? They then scrapped their plans, did they not? How is this any better/different? Any sort of “backdoor” into encryption means that the encryption is compromised. They tackled this in 2014 in the US. Feels like deja vu all over again.

[–] AlexKingstonsGigolo@kbin.social 3 points 2 years ago (5 children)

@generalpotato Ish. I read the technical write up and they actually came up with a very clever privacy-focused way of scanning for child porn.

First, only photos were scanned and only if they were stored in iCloud.

Then, only cryptographic hashes of the photos were collected.

Those hashes were grepped for other cryptographic hashes of known child porn images, images which had to be in databases of multiple non-governmental organizations; so, if an image was only in the database of, say, the National Center For Missing And Exploited Children or only in the database of China's equivalent, its cryptographic hash couldn't be used. This requirement would make it harder for a dictator to slip in a hash to look for dissidents by making it substantially more difficult to get an image in enough databases.

Even then, an Apple employee would have to verify actual child porn was being stored in iCloud only after 20 separate images were flagged. (The odds any innocent person even makes it to this stage incorrectly was estimated to be something like one false positive a year, I think, because of all of the safeguards Apple had.)

Only after an Apple employee confirmed the existence of child porn would the iCloud account be frozen and the relevant non-government organizations alerted.

Honestly, I have a better chance of getting a handjob from Natalie Portman in the next 24 hours than an innocent person being incorrectly reported to any government authority.

[–] HelixDab@kbin.social 1 points 2 years ago (1 children)

From a technical perspective, how much would an image need to be changed before the hash no longer matched? I've heard of people including junk .txt files in repacked and zipped pirated games, movies, etc., so that they aren't automatically flagged for removal from file sharing sites.

I am not a technical expert by any means, and I don't even use Apple products, so this is just curiosity.

[–] MisuseCase 1 points 2 years ago

That's a good question. First it's important to understand that hash functions for pirated games or other programs are actually different from hash functions used to detect media like pictures, movies, and sound recordings.

If you alter a piece of code or text from the original version the hashes will no longer match, but typically those hashes should match and some kind of alarm gets tripped if they don't.

With media files like music, movies, or pictures, it works the other way around. Detection tools are looking for something that is not necessarily an exact match, but a very close match, and when such a match is found, alarms get tripped (because it's CSAM, or a copyright violation, or something like that).

As to the techniques you mentioned for concealing a pirated game in a ZIP file with a bunch of junk TXT files, that's not going to work. The reason it doesn't work is that if you ZIP something, all that uses compression algorithms that change the contents of the ZIP file in predictable repeating patterns. It's easy to detect and compensate for. Now, if you use your ZIP/compression tool to actually encrypt the file with a good algorithm and a strong password, that's different, but then you don't need to pack it with junk. (And distributing the password securely will be a problem.)

Please, people who know more about hashing and media detection with hashing, let me know if I got something wrong, I probably did.

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