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Comment by thih9 | Hacker News Reader

No, we should use pixelation when redacting text, like this:

1. Fill the selected area with a solid color (perhaps an average color of the pixels right outside of the selected area).

2. Write "lorem ipsum dolor sit amet" over that and pixelate the area.

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Yep, this is how I typically do it. I wonder how much concern over pixelation is actually mistaken due to the inability to observe this technique.

I doubt many people are doing this. Many times the pixelation is visibly obviously terrible. In fact if you look at the pixelation challenge in this post, you can almost simply read off the answer with just a bit of concentration. I see a lot of things like that, sadly.

The cryptographers like to say that just because you've created a cryptography scheme strong enough to defeat yourself doesn't mean you've created a strong cryptography scheme. I feel like redaction is much the same. You really need to go with solid, proved techniques, and avoid the proved-weak ones.

That leaks the length of the text

Any in-place redaction leaks the length of the text.

Fortunately, most text is proportionally spaced, rather than monospaced, so you cannot really determine the number of characters, only the length in pixels/points of the redacted phrase.

You're right. In some cases that's plenty, such as with the sentence "Mr. Jones was found XXXXXXXXXXXXXX of the crime."

If you know it's likely either "guilty" or "not guilty," then the length (regardless of font) will automatically give away which of these two options it is since you can just 'bruteforce' the whole solution set of two options. No in-place redaction will work for a case like that, except possibly a longer one where the whole sentence is redacted and hopefully no one can guess what kind of sentence it was.

Not necessarily. You can white/black out the text and replace it with something that's longer or shorter than the original. It's really just a matter of how much effort the person wants to put into the redaction.

Exactly, the stupid bit is using the original text to drive the pixelization. Another approach would be to just generate random gray pixel values over the redacted text. Simple. Simpler even than the weird assumption that you would use the original text.

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