A tool for recovering passwords from pixelized screenshots • Hacker News Board

Re: A tool for recovering passwords from pixelized screenshots

#21

Post by davchana » Sun, Dec 06, 2020, 10:53 PM UTC

est31 wrote: post #12

rriepe wrote: post #3

Earlier quoted context omitted.

It's not. There's never going to be a tool that does this with black bars. The only benefit I can think of is legitimacy. Having something blurred there suggests that there was actually something there.

Black bars alone may still leak info. First, if you add black bars on your own and don't use professional redaction features of software, you might miss the OCR text layer of the PDF, or the bar might be added as a separate object entirely which means it can also be removed later on. Second, if you don't use monospace text, the width of the text you are redacting will reveal information about it. That's why monospace…

Yes, in pdf, add bars, & then print it again as pdf, but as image.

Re: A tool for recovering passwords from pixelized screenshots

#22

Post by tobr » Sun, Dec 06, 2020, 10:56 PM UTC

So as I understand it this technique rests on a number of assumptions:

- You know the exact parameters used to render the text

- You can render new text with the exact same parameters

- The pixelated image hasn’t been ruined by color quantization or other destructive compression

Re: A tool for recovering passwords from pixelized screenshots

#23

Post by dawnerd » Sun, Dec 06, 2020, 10:59 PM UTC

sly010 wrote: post #13

Relatedly (and this is probably not surprising to anyone here) if you draw a black box on a PDF file to cover sensitive information, chances are a simple screen reader will still able to extract the information just fine.

Found this out the other day on that story from the port explosion. They had a pdf with blacked out names, but you could just copy the text and paste it and it wasn't blacked out.

Re: A tool for recovering passwords from pixelized screenshots

#24

Post by seltzered_ » Sun, Dec 06, 2020, 11:04 PM UTC

riidom wrote: post #6

MattGaiser wrote: post #2

Why is pixelation preferable to a big black obliterating box? To me, it seems like a lot of wasted time and effort and potential arms race between encoders and decoders and the risk of being exposed when you could just put a big black box over whatever you wish to obscure.

Only reason I can think of: Pixelation has a more elegant touch than covering everything with a box (be it black, or some better suited color). Took a while to convince people to not use a bit of gaussian blur, because it's insecure. Well, ready for round 2...

What stops one from making a more secure pixelation algorithm?

One that will shuffle around or maybe just randomly derive the pixelated blocks if they're within a certain color threshold of similarity?

I still generally like pixelation over drawing a box for aesthetic purposes.

Re: A tool for recovering passwords from pixelized screenshots

#25

Post by trhway » Sun, Dec 06, 2020, 11:08 PM UTC

That basically how I did OCR 20 years ago :) One can also notice that kernels inside a text trained NN would have somewhat similar blocks and as a result what the net would be doing is a similar matching.

Re: A tool for recovering passwords from pixelized screenshots

#26

Post by lrossi » Sun, Dec 06, 2020, 11:11 PM UTC

This kind of techniques have been discussed here many times. See for example: https://news.ycombinator.com/item?id=8078747

I think one of the reasons people use blurring/pixelation is that it looks nicer than black boxes.

Wondering if it would make sense to build a tool that renders a pixelated version of lorem ipsum or something like that. It would be secure while also looking good.

Re: A tool for recovering passwords from pixelized screenshots

#27

Post by scalablenotions » Sun, Dec 06, 2020, 11:11 PM UTC

I've always thought that people's confidence is pixelation filters was unjustified, and that reversal algorithms are eminently achievable. This goes for pixelation of faces for hiding identities, too. Deep learning or even just genetic algorithms testing lots of possibilities and re-pixelating should be able to infer the original image.

Re: A tool for recovering passwords from pixelized screenshots

#28

Post by roelschroeven » Sun, Dec 06, 2020, 11:11 PM UTC

jbn wrote: post #11

rriepe wrote: post #4

Is "pixelized" the norm somewhere? I'm used to "pixelated."

could it be that the author's first language is not English? "pixelized" sounds like a literal translation of the French word for "pixelated".

Judging from the author's username, he/she is almost certainly Dutch, and in Dutch we tend to use English terminology in most technical matters. But we don't always use it 100% correctly, so that could be a reason.

Re: A tool for recovering passwords from pixelized screenshots

#29

Post by Jakobeha » Sun, Dec 06, 2020, 11:12 PM UTC

would a neural network be able to do something like this?

Re: A tool for recovering passwords from pixelized screenshots

#30

Post by jamiek88 » Sun, Dec 06, 2020, 11:21 PM UTC

seltzered_ wrote: post #24

riidom wrote: post #6

Earlier quoted context omitted.

Only reason I can think of: Pixelation has a more elegant touch than covering everything with a box (be it black, or some better suited color). Took a while to convince people to not use a bit of gaussian blur, because it's insecure. Well, ready for round 2...

What stops one from making a more secure pixelation algorithm? One that will shuffle around or maybe just randomly derive the pixelated blocks if they're within a certain color threshold of similarity? I still generally like pixelation over drawing a box for aesthetic purposes.

Why bother? Just have the tool put random text to fit then pixelize that.