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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)

#71

Post by gknoy »

izzydata wrote: post #64
frogpelt wrote: post #54

Earlier quoted context omitted.

"just a pedophile" A phrase I never thought I'd see.

Someone who is homosexual isn't any more inclined to molest or rape someone of their own sex than a pedophile is to molest or rape a child. More on topic about censoring important information. I'm not entirely sure about this, but I feel like I've seen images where the thumbnail was retained from a previous version. Even at 32x32 there might be some way to expand it and gather some kind of information from its pixela…

Given that most thumbnails are done with resampling to scale, I imagine this attack would work similarly there as well.

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

#72

Post by dalke »

bryondowd wrote: post #52
userbinator wrote: post #38

Earlier quoted context omitted.

Actually, using fixed-width would be even easier since it reveals the length.

I'd be curious to see some numbers backing one or the other, but I suspect proportional would be better. Fixed width narrows to a number of characters. So it depends how many possible values have x characters. Proportional narrows to a particular width, which could be more granular than character count. So it depends how many possible values turn out to be exactly x pixels across given the type settings.

Proportional is easier to try to decode. See http://cryptome.org/cia-decrypt.htm for an example from 2004 about inferring words from a redacted US document.

From the Le Monde article: The space occupied by an "I" differs from that taken by "W," which can give additional clues, compared to the text-spacing known as "monospace," like that of often used in e-mailwhere all the letters have the same spacing.

From the NYT article: In January, the State Department required that its documents use a more modern font, Times New Roman, instead of Courier, Mr. Naccache said. Because Courier is a monospace font, in which all letters are of the same width, it is harder to decipher with the computer technique. There is no indication that the State Department knew that.

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

#73

Post by DigitalJack »

izzydata wrote: post #64
frogpelt wrote: post #54

Earlier quoted context omitted.

"just a pedophile" A phrase I never thought I'd see.

Someone who is homosexual isn't any more inclined to molest or rape someone of their own sex than a pedophile is to molest or rape a child. More on topic about censoring important information. I'm not entirely sure about this, but I feel like I've seen images where the thumbnail was retained from a previous version. Even at 32x32 there might be some way to expand it and gather some kind of information from its pixela…

"Someone who is homosexual isn't any more inclined to molest or rape someone of their own sex than a pedophile is to molest or rape a child."

I'm sure you meant something about the proclivity to commit rape or molestation, but all this statement does is say there is a positive correlation between the two groups (and no citation or explanation of reasoning either).

Your statement would still be true if both groups had a large increase in probability of rape or molestation, vs the non-homosexual and/or non-pedophile.

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

#74

Post by Pxtl »

gus_massa wrote: post #46
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…

You can't use the brute force method to find any "person" you have in the database. You can only find any "photograph" that you have in the database. If you have a photograph of me, and I just let my hair and beard grow for a month, then you won't match the mosaic version of my hairy version with the old photograph. Perhaps you can add some filters to adapt the contrast, luminosity, hue, illumination, rotation, pixel…

Imagine a future where 3D depth-sensitive cameras are prevalent - this means that a 3D model of a person's head can be easily obtained.

Then futuristic analysis software that, from a picture, can determine all the light-sources in that image and 3D positions thereof.

So take a photo, analyze it for light-sources, then brute-force it by applying 3D models of every face in your database with the known light-sources and run it through the mosaic filter.

Futuristic technology could help here. Probably wouldn't work since I'm sure one person's mosaic would match too closely somebody with similar features and a similarly-shaped head.

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

#76

Post by robin_reala »

akadruid1 wrote: post #42
robin_reala wrote: post #40

Earlier quoted context omitted.

Do they? First I’ve heard of that…

The thumbnail is part of the EXIF metadata. It's reasonably well-known now, but it was not always the case... http://graphicssoft.about.com/b/2003/07/26/techtvs-cat-schwa...

Huh, interesting. Thanks!

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

#77

Post by sliverstorm »

frogpelt wrote: post #54
danepowell wrote: post #27

Earlier quoted context omitted.

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

"just a pedophile" A phrase I never thought I'd see.

Pedophilia in itself isn't a crime.

Well, unless we've started prosecuting thought-crime. I could have missed that update.

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

#78

Post by cbhl »

bjourne wrote: post #34

Has this attack actually been proved possible? He writes that he thinks it should work but doesn't have the time or inclination to prove it. If anyone wants to take a stab at it, I'll gladly submit a mosaiced photo of my credit card because I don't think the attack is practical. If you crack it, you're free to keep whatever you can get. :)

In North America, all the checks (cheques) use the same fonts. See http://en.wikipedia.org/wiki/Magnetic_ink_character_recognit...

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

#79

Post by matchu »

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.

For a fun variant of this problem, see the 2008 Underhanded C Contest: http://underhanded.xcott.com/?page_id=17

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

#80

Post by CreakyKnuckle »

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…

To be fair, that's a pretty numerically apropos age for HN.
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