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Apple to scan iPhones for child sex abuse images

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Ste
Not Work Safe



Joined: 01 Sep 2002
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PostPosted: 18:30 - 08 Aug 2021    Post subject: Reply with quote
Im-a-Ridah wrote:
I'm saying that is what counts as child porn according to the government.

Apple will be scanning for known images of child sexual abuse and that's done base on image hashes rather than AI scanning for anything which might match the definition of child porn.

From a page I previously linked to:

"A Perceptual image hash (PIH) is a short hexadecimal string (e.g. ‘00081c3c3c181818’ ) based on an image’s appearance. Perceptual image hashes, despite being hashes, are not cryptographically secure hashes. This is by design, because PIHs aim to be smoothly invariant to small changes in the image (rotation, crop, gamma correction, noise addition, adding a border). This is in contrast to cryptographic hash functions that are designed for non-smoothness and to change entirely if any single bit changes."
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Polarbear
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Joined: 24 Feb 2007
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PostPosted: 18:37 - 08 Aug 2021    Post subject: Reply with quote
Ste wrote:
Im-a-Ridah wrote:
I'm saying that is what counts as child porn according to the government.

Apple will be scanning for known images of child sexual abuse and that's done base on image hashes rather than AI scanning for anything which might match the definition of child porn.

From a page I previously linked to:

"A Perceptual image hash (PIH) is a short hexadecimal string (e.g. ‘00081c3c3c181818’ ) based on an image’s appearance. Perceptual image hashes, despite being hashes, are not cryptographically secure hashes. This is by design, because PIHs aim to be smoothly invariant to small changes in the image (rotation, crop, gamma correction, noise addition, adding a border). This is in contrast to cryptographic hash functions that are designed for non-smoothness and to change entirely if any single bit changes."


For the IT dunderheads here (me Embarassed ) does that mean the Apple thing only compares the picture's electronic 'title' with the title of known porn images?
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Ste
Not Work Safe



Joined: 01 Sep 2002
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PostPosted: 19:19 - 08 Aug 2021    Post subject: Reply with quote
Roughly yes, it's more of a fingerprint than a title. However due to being roughly, different images can have the same fingerprint.

From the same site:

https://miro.medium.com/max/2400/1*dsnvYmX-5cLRjC6UcgZTSQ.png

Above is a diagram illustrating our network generating an image of a face that has a hash collision with the Coca-Cola logo. These share the same hashes and would allow a user to poison a hash database and prevent a corporate logo from being uploaded to a platform. Here are some more corporate logos with generated faces that are hash collisions.

https://miro.medium.com/max/612/1*Tm4bBLXz0SrW_Ml3JJCdXg.png

That lot is from this site: https://towardsdatascience.com/black-box-attacks-on-perceptual-image-hashes-with-gans-cc1be11f277

Imagine someone sends you a perfectly harmless political media file that you share with a friend. But that file shares a hash with some known child porn file?

There's a good explanation of it all that's not too geeky here: https://archive.is/L9AFj

Those are real concerns about what Apple are starting to do. Not that it's anything new, it's just new to Apple.
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Easy-X
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Joined: 08 Mar 2019
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PostPosted: 19:25 - 08 Aug 2021    Post subject: Reply with quote
<edit> ffs, ste beat me to it, ste for mod!

Polarbear wrote:
For the IT dunderheads here (me Embarassed ) does that mean the Apple thing only compares the picture's electronic 'title' with the title of known porn images?


Sort of. A picture, like any other digital information these days, is just a load of numbers. For example an "X" in a simple B&W image might be:
Code:
10000001
01000010
00100100
00011000
00011000
00100100
01000010
10000001

And this is stored in the memory of a computer as:
Code:
129, 66, 36, 24, 24, 36, 66, 129

Now if I wanted to compare this image to another image I could step through all these numbers in turn to see if they're the same but for very large amounts of data that's not a practical use of processing power. Instead it's usual to compare the Hashes.

A hash function is any attempt to capture the essence of the data. For example a simple hash function might be "add all the numbers together and just use the last two digits"
Quote:
129 + 66 + 36 + 24 + 24 + 36 + 66 + 129 = 510, hash = 10

It should be pretty obvious with this example that various combinations of numbers might give the same hash result. This is called a clash or collision and the probability of a hash function generating collisions is an important quality.

The hash function ste mentions is clever in that changes a human is indifferent too - resizing, rotating, colour balance changes - are ignored and so a true signature of the picture is known.

Even so collisions are possible hence the reason a human would need to check flagged pictures manually.
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Old Thread Alert!

The last post was made 2 years, 259 days ago. Instead of replying here, would creating a new thread be more useful?
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