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Why blurring sensitive information is a bad idea (2007)

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Re: Why blurring sensitive information is a bad idea (2007)

#21

Post by currysausage »

nnnnni wrote: post #10

Their answer is to "color over it", but BE CAREFUL if you do that. I'm sure that some of us remember the US government document(s) in the late 90s/early 2000s that were released in redacted form, but the person didn't realize/understand that people with the Acrobat editor program could remove the black bars.

Also great: HTML pages with sensitive passages using #000 for background and foreground. You just need to select and copy to Notepad - voila.

I think I once saw that on the site of a home security company, citing an email from customers who thanked them for burglarproofing their home in XX XXXXXXXX Street. Quite ironic.

Re: Why blurring sensitive information is a bad idea (2007)

#23

Post by bithush »

erikb wrote: post #6

In some cases even blurring faces might be a bad idea. Just because we are unable to unblur a face today doesn't mean we are unable in 10 years or 100 years. In many cases this might not be a problem but in some cases this might lead to trouble later on which can be avoided just as easily.

Indeed. See http://en.wikipedia.org/wiki/Christopher_Paul_Neil

Re: Why blurring sensitive information is a bad idea (2007)

#24

Post by asgard1024 »

goldenkey wrote: post #9
erikb wrote: post #6

In some cases even blurring faces might be a bad idea. Just because we are unable to unblur a face today doesn't mean we are unable in 10 years or 100 years. In many cases this might not be a problem but in some cases this might lead to trouble later on which can be avoided just as easily.

You cannot unblur mosaic blurring. It's the equivalent of a hash. The best you can do is brute force possible input vectors. There will be many collisions. This technique only works because digits/numbers limit the input space for a credit card or bank number. For faces, the best you can do is validate if someone you already suspect or someone you have in a database, is the origin of the mosaic. If you had a picture…

I can imagine you can computationally unblur mosaic on video, if the object (e.g. face) is not changing, just the camera is moving around a little.

Re: Why blurring sensitive information is a bad idea (2007)

#25

Post by kostasjust »

goldenkey wrote: post #9
erikb wrote: post #6

In some cases even blurring faces might be a bad idea. Just because we are unable to unblur a face today doesn't mean we are unable in 10 years or 100 years. In many cases this might not be a problem but in some cases this might lead to trouble later on which can be avoided just as easily.

You cannot unblur mosaic blurring. It's the equivalent of a hash. The best you can do is brute force possible input vectors. There will be many collisions. This technique only works because digits/numbers limit the input space for a credit card or bank number. For faces, the best you can do is validate if someone you already suspect or someone you have in a database, is the origin of the mosaic. If you had a picture…

i agree with erikb.. In theory at least, it seems possible to me that unbluring mosaic could happen if you have in multiple mosaic images from different angles (like mosaic in a video) even without a database with the possible faces).

Re: Why blurring sensitive information is a bad idea (2007)

#26

Post by goldenkey »

kostasjust wrote: post #25
goldenkey wrote: post #9

Earlier quoted context omitted.

You cannot unblur mosaic blurring. It's the equivalent of a hash. The best you can do is brute force possible input vectors. There will be many collisions. This technique only works because digits/numbers limit the input space for a credit card or bank number. For faces, the best you can do is validate if someone you already suspect or someone you have in a database, is the origin of the mosaic. If you had a picture…

i agree with erikb.. In theory at least, it seems possible to me that unbluring mosaic could happen if you have in multiple mosaic images from different angles (like mosaic in a video) even without a database with the possible faces).

Even with that, the amount of information is reduced from 1000s of pixels to less than 100. It's possible to extract some information but not enough to do a reversal

Re: Why blurring sensitive information is a bad idea (2007)

#27

Post by danepowell »

bithush wrote: post #22

I feel this is also very relevant http://en.wikipedia.org/wiki/Christopher_Paul_Neil Police took a photo with a "swirl" effect of a paedophiles face and reversed it to reveal a very usable picture. So good in fact he was found and arrested.

He wasn't just a pedophile, he was a child molester.

Re: Why blurring sensitive information is a bad idea (2007)

#28

Post by vog »

mxfh wrote: post #3

So if something is 1337 days old it gets autoreposted? Could live with that. Previous discussion: https://news.ycombinator.com/item?id=1939607 A bit more precise this post is even older, and was first discussed in 2007 prominently in these two places: http://www.reddit.com/comments/xaae/how_to_extract_personal_... https://www.schneier.com/blog/archives/2007/01/how_to_recove... (please refrain from responding with XKC…

My favourite comment from the old discussion came from andrewreds:

> WHAT... why would you completely black out the number, where you could instead use random coloured squares, that look like it is a blurring, so someone can go through all the effort, decoding your white noise, and thinking in the end they have your number... when they don't ;)

https://news.ycombinator.com/item?id=1939807

Re: Why blurring sensitive information is a bad idea (2007)

#29

Post by [deleted] »

danepowell wrote: post #27
bithush wrote: post #22

I feel this is also very relevant http://en.wikipedia.org/wiki/Christopher_Paul_Neil Police took a photo with a "swirl" effect of a paedophiles face and reversed it to reveal a very usable picture. So good in fact he was found and arrested.

He wasn't just a pedophile, he was a child molester.

[deleted]

Re: Why blurring sensitive information is a bad idea (2007)

#30

Post by nathell »

In some cases, coloring over parts of the image might still not be enough. Specifically, when all of the following are true: (i) the domain of possible entries is reasonably small (e.g., a number or a name and surname), (ii) the text is printed in a proportional (not fixed-width) typeface, and (iii) enough of the rest of the line is visible to infer the font size and kerning settings.
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