News for hackers. Stuff that matters.

A comment on Unredacter: Never ever use pixelation as a redaction technique. Parent comment

Re:Unredacter: Never ever use pixelation as a redaction tech... by laudecum on Saturday December 17, 2022 @10:14PM (#34034735)
I don’t think what you’re saying makes sense. If you covered all information, no information is left. The blocks are irrelevant since 100% of the information is gone. There’s no “history leak” in JPEG, which is basically what’s being asked.

The only issue I see is meta tags and embedded thumbnails, which some cameras do. Stripping EXIF is always required.

[ Parent | on HN ]
Re:Unredacter: Never ever use pixelation as a redaction tech... by wtallis on Saturday December 17, 2022 @10:46PM (#34034861)
> If you covered all information, no information is left.

JPEG compression causes ringing artifacts that can extend out past the pixels you're trying to redact, up to the next block boundary. This is a problem if what you're trying to redact is already a JPEG, rather than a pristine uncompressed image.

[ Parent | on HN ]
Re:Unredacter: Never ever use pixelation as a redaction tech... by addaon on Sunday December 18, 2022 @01:27AM (#34035504)
> JPEG compression causes ringing artifacts that can extend out past the pixels you're trying to redact, up to the next block boundary.

This.

I made a response to the parent question that goes into the practical side of this in a bit more detail, but this is a much better one-sentence summary of /how/ the information leaks.

[ Parent | on HN ]