Pixelating Text Not A Good Idea

People have gotten much savvier about computer security in the last decade or so. Most people know that sending a document with sensitive information in it is a no-no, so many people try to redact documents with varying levels of success. A common strategy is to replace text with a black box, but you sometimes see sophisticated users pixelate part of an image or document they want to keep private. If you do this for text, be careful. It is possible to unredact pixelated images through software.

It appears that the algorithm is pretty straightforward. It simply guesses letters, pixelates them, and matches the result. You do have to estimate the size of the pixelation, but that’s usually not very hard to do. The code is built using TypeScript and while the process does require a little manual preparation, there’s nothing that seems very difficult or that couldn’t be automated if you were sufficiently motivated.

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PDF Redaction Still Not Working


Facebook’s internal valuation was revealed this week thanks to shoddy PDF redaction. Court documents from a settlement between Facebook and ConnectU showed that Facebook values itself at $3.7 billion, much less than the $15 billion that was speculated during the Microsoft investment. The AP uncovered this by cutting and pasting from the redacted court document. It’s the same thing we showed in our PDF redaction screencast last summer… and it will never cease to be funny.

[photo: Bryan Veloso]