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Came here to suggest as much :-) While you can apparently just strip it from the metadata properly like suggested on twitter, maybe a "low level" approach like
by iforgotpassword 5y ago
Came here to suggest as much :-)
While you can apparently just strip it from the metadata properly like suggested on twitter, maybe a "low level" approach like comparing the files on a binary level and setting any bytes that differ to 0 would be more robust. It would still work if they move the hash out of the meta data into the document itself. Only downside is that this requires the hash to be fixed size.
- jrib 5y agoI think this is a clever solution. I'm not seeing why it requires the hash to be a fixed size though. Why can't the algorithm just keep whatever is common between the two files? Or just take the shorter side of the diff and zero it out?
- roblabla 5y agoIf the PDF contains encrypted blocks, this won't work, as simply zeroing out the bits will break the file. Even worse, if the PDF contains compressed chunks (which happens often enough), such a naive approach won't work either - the chunks would have to be uncompressed before comparison. Such a tool would need a lot of smarts to work reliably enough. At this point, I feel like a metadata stripper that understands the various watermarking methods may be easier to write.
- iforgotpassword 5y agoHm, makes sense. But if I were in their shoes, moving the fingerprint out of the metadata would be the first thing to do then, so no easy solution then I guess.