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Comment by cogman10 | Hacker News Reader

In fact, there was a famous de-censoring that happened because the censoring which happened was a simple "whirlpool" algorithm that was very easy to unwind.

If media companies want to actually censor something, nothing does better than a simple black box.

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> nothing does better than a simple black box

You still need to be aware of the context that you're censoring in. Just adding black boxes over text in a PDF will hide the text on the screen, but might still allow the text to be extracted from the file.

Indeed. And famously, using black boxes as a background on individual words in a non-monospaced font is also susceptible to a dictionary attack on an image of the widths of the black boxes.

And even taking sharpie and drawing a black box doesn't mean the words can be seen at a certain angle or by removing the sharpie ink but not the printed ink.

Really, if you need to censor something create a duplicate without the originals. Preferably literally without the originals as the size of the black box is also an information leak.

No need for the monospaced requirement - it would reduce the search space, but it's solvable even before this reduction.

The additional leakage provided by non-monospace is rather large. With monospace all you know is the character count.

Curious anyone know if the specific censoring tool in the MacOS viewer has this problem? I had assumed not because they warn you when using the draw shapes tool that text below it can be recovered later and they don't warn you about that when using the censoring tool.

Ah yes, Mr. Swirl Face.

This was pretty different though. The decensoring algorithm I'm describing is just a linear search. But pixelation is not an invertible transformation.

Mr. Swirl Face just applied a swirl to his face, which is invertible (-ish, with some data lost), and could naively be reversed. (I am pretty sure someone on 4chan did it before the authorities did, but this might just be an Internet Legend).

A long while ago, taking an image (typically porn), scrambling a portion of it, and having others try to figure out how to undo the scrambling was a game played on various chans.

Christopher Paul Neil is a real person who went to jail.

Shhhhh!!!!!

Yeah but if you read about him it serves as a rallying cry for right wing types since he's an example of the candaian legal systems extreme leniency. This guy should be in prison forever and he's been free since 2017. Look at his record of sentencing. I love being a bleeding heart liberal/progressive and all, but this is too far.

Furthermore, don't look too hard at Isreal and it's policy of being very, very open to pedophiles and similar types.

A completely opaque shape or emoji does it. A simple black box overlay is not recommended unless you that’s the look you’re going for. Also very slightly transparent overlays come in all shapes and colors and are hard to recognize whether it’s a black box or another shape, so either way you need to be careful it’s 100% opaque.

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