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I don't think this is a good metaphor. You still get the privacy same privacy aspect as you did before. Only your iCloud images are now being scanned for visual

I don't think this is a good metaphor. You still get the privacy same privacy aspect as you did before. Only your iCloud images are now being scanned for visual matches. If you are already trusting Apple with rest of your private life this hardly is complete 180 degree turn. I don't quite understand why people are so against this. What if some algorithm scans your images? If you are using any cloud service to share your images then your images are already being scanned and far more invasively. Is the the storing of hashes that concerns you? Your password(s) is already being stored as a hash and we trust that it can not be reversed back to plain text, why wouldn't we trust that these image hashes can't be reversed back into images? I've seen some notion that this is a backdoor and governments and other Lovecraftian entities could use it to suppress freedom of speech by censoring certain images, but that would require them to first have the image in question, then creating hash of the image, and then inserting it into the Apple's database and after that it would only be flagged for human verification and again assuming you trust Apple to handle rest of your digital life (such as iMessages) why wouldn't you trust Apple to share your images? If some entity has it's hooks so deep in apple that they start to censor images why wouldn't they just stop all of your messages being sent? Please correct me if I'm missing something obvious.

goldenkey 5y ago
> why wouldn't we trust that these image hashes can't be reversed back into images? You should avoid making political or moral arguments when your technical knowledge is 10 feet below your ego. An image is orders of magnitude larger than a password, meaning that many more collisions. Also, because it's a perceptual hash, even more collisions. One does not simply reverse a perceptual hash. Keep your hat on ;-)
- nextlevelwizard 5y ago
  >You should avoid making political or moral arguments I am not being political or moral. Why would you think that? Is this one of those "since you don't immediately agree with me it means you are the enemy and disagree on everything" type things? >An image is orders of magnitude larger than a password, meaning that many more collisions. Whole point of hashing algorithms is that they produce unique hashes for different inputs. Wouldn't a larger input value (bits of the image) make it harder to have collisions? >One does not simply reverse a perceptual hash So what actually is the privacy concern here? There is no way to get the original image from the hash at best you can get an approximation of it. >Keep your hat on ;-) I guess this is suppose to be some kind of dig at me. No need to be an asshole even if you don't agree with someone.
  - goldenkey 5y ago
    > Whole point of hashing algorithms is that they produce unique hashes for different inputs. Wouldn't a larger input value (bits of the image) make it harder to have collisions? Standard cryptographic hashes should have certain properties like https://en.wikipedia.org/wiki/Avalanche_effect https://en.wikipedia.org/wiki/Avalanche_effect However, a perceptual hash desires the opposite. Due to the pigeonhole principle, a larger space mapping to a smaller space, involves more collisions. In fact, all hashes have infinite collisions, one just tries to design hashes that don't have many collisions on smaller length inputs. Ultimately though, there will be at least 2^n collisions for all inputs n bits long if the hash is n bit output. You can easily calculate this by looking at the excess in size between input space size and output space size. https://en.wikipedia.org/wiki/Pigeonhole_principle https://en.wikipedia.org/wiki/Pigeonhole_principle Perceptual hashes are essentially designed to collide on similar data. The fine details are lost. An ideal perceptual hash algorithm would quantize as many alterable properties of an image as possible. Contrast, brightness, edges, hue, fine details, etc. In the end, you have a bunch of splotches in a certain composition that form the low dimensional eigenbasis of the hash.
    - nextlevelwizard 5y ago
      Thanks for that, I still dont get why this is such a big privacy concern for everyone.
      - goldenkey 5y ago
        You're welcome. I think the crux is that people are worried about the police knocking at their door and/or inspecting their photos due to mismatching on this purportedly unreliable hash method.
        nextlevelwizard 5y ago
        That feels like purposefully misundertanding the situation. The hash match only escalates the matter to a human inspection. In no sane world is that inspection done physically. It means that if your picture approximitely matches a known abuse picture someone gets to view it to verify if it contains abuse or not and then potential legal actions can be taken. Police knocking down your door will only happen if you are found to posses multiple abuse pictures and they suspect you might be endagering people.

goldenkey 5y ago

> why wouldn't we trust that these image hashes can't be reversed back into images? You should avoid making political or moral arguments when your technical knowledge is 10 feet below your ego. An image is orders of magnitude larger than a password, meaning that many more collisions. Also, because it's a perceptual hash, even more collisions. One does not simply reverse a perceptual hash. Keep your hat on ;-)

nextlevelwizard 5y ago
>You should avoid making political or moral arguments I am not being political or moral. Why would you think that? Is this one of those "since you don't immediately agree with me it means you are the enemy and disagree on everything" type things? >An image is orders of magnitude larger than a password, meaning that many more collisions. Whole point of hashing algorithms is that they produce unique hashes for different inputs. Wouldn't a larger input value (bits of the image) make it harder to have collisions? >One does not simply reverse a perceptual hash So what actually is the privacy concern here? There is no way to get the original image from the hash at best you can get an approximation of it. >Keep your hat on ;-) I guess this is suppose to be some kind of dig at me. No need to be an asshole even if you don't agree with someone.
- goldenkey 5y ago
  > Whole point of hashing algorithms is that they produce unique hashes for different inputs. Wouldn't a larger input value (bits of the image) make it harder to have collisions? Standard cryptographic hashes should have certain properties like https://en.wikipedia.org/wiki/Avalanche_effect https://en.wikipedia.org/wiki/Avalanche_effect However, a perceptual hash desires the opposite. Due to the pigeonhole principle, a larger space mapping to a smaller space, involves more collisions. In fact, all hashes have infinite collisions, one just tries to design hashes that don't have many collisions on smaller length inputs. Ultimately though, there will be at least 2^n collisions for all inputs n bits long if the hash is n bit output. You can easily calculate this by looking at the excess in size between input space size and output space size. https://en.wikipedia.org/wiki/Pigeonhole_principle https://en.wikipedia.org/wiki/Pigeonhole_principle Perceptual hashes are essentially designed to collide on similar data. The fine details are lost. An ideal perceptual hash algorithm would quantize as many alterable properties of an image as possible. Contrast, brightness, edges, hue, fine details, etc. In the end, you have a bunch of splotches in a certain composition that form the low dimensional eigenbasis of the hash.
  - nextlevelwizard 5y ago
    Thanks for that, I still dont get why this is such a big privacy concern for everyone.
    - goldenkey 5y ago
      You're welcome. I think the crux is that people are worried about the police knocking at their door and/or inspecting their photos due to mismatching on this purportedly unreliable hash method.
      - nextlevelwizard 5y ago
        That feels like purposefully misundertanding the situation. The hash match only escalates the matter to a human inspection. In no sane world is that inspection done physically. It means that if your picture approximitely matches a known abuse picture someone gets to view it to verify if it contains abuse or not and then potential legal actions can be taken. Police knocking down your door will only happen if you are found to posses multiple abuse pictures and they suspect you might be endagering people.