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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.
Even if you do black box -> separate screenshot? Is that because the OCR is encoded in white pixels you didn't redact?
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.
This reminds of the Markup tool[1] on iPhone. People use it to redact from screenshots, but it was (is?) actually slightly transparent by default. [1] https://9to5mac.com/2018/03/13/ios-markup-reveal-redact-sens...
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.
Because pixelation doesn't attract attention as much as black box and is therefore a better placeholder. A black box with sharp edges has much more contrast than all the legit elements in the image and becomes visually dominant whereas typically you want to attract attention to something else on the page. For a similar reason, designers use "lorem ipsum" placeholder text rather than all-white or all-black placeholder…
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A similar method was used to uncover the name of a game mode in a teaser video from nintendo. Since it was a video the pixels would change as things moved and you could reverse the pixelation fairly well.
What about that bitcoin wallet that was blurred on TV and they managed to reverse engineer it? Cannot find source.
> Two French hackers used their computer skills to reconstruct a blurred-out code on TV and claim bitcoins worth $1,000 (£760).
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Even big black boxes require some amount of skill. https://twitter.com/Phthalaldehyde/status/133471474074092748...
Can't facepalm enough. Just, amazing incompetence.
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This reminds of the Markup tool[1] on iPhone. People use it to redact from screenshots, but it was (is?) actually slightly transparent by default. [1] https://9to5mac.com/2018/03/13/ios-markup-reveal-redact-sens...
one of the "underhanded c" contest winners many years ago was an entry for a redaction tool, which drew black boxes on an image in such a way that the software developer could later effectively recover the redacted information easily, while still being able to claim plausible deniability. The trick was that it worked by producing a ppm file where pixels with single digits would become zeros, but double digits would b…
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.
This way the redacted PDF won't have any metadata from the original (e.g. bookmarks) nor risk any weired PDF redaction bugs.
The downside is that your redacted PDF is (probably) larger than the original and isn't accessible. You can mitigate this by using OCR but it still isn't perfect and has a high chance of messing up tables or any special text placement.
Some fancy combination of encodings (e.g. using JBIG2 except for images) can probably help with the filesize.
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The best way to handle sensitive information is probably to use codenames (for people, places, etc) so you can share the original documents without worrying so much.
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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…
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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…
> Second, if you don't use monospace text, the width of the text you are redacting will reveal information about it. If you do use monospace text, width reveals the exact redacted character count. If you don't use monospace text, it constrains the possible contents in a more complicated way, but it leaks information either way.