Gregory's ServerMore fun publisher surveillance:
Elsevier embeds a hash in the PDF metadata that is *unique for each time a PDF is downloaded*, this is a diff between metadata from two of the same paper. Combined with access timestamps, they can uniquely identify the source of any shared PDFs.
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You can see for yourself using exiftool. exiftool -all:all= <path.pdf> -o <output1.pdf> To remove *all* metadata, you can use dangerzone or mat2 Also present in the metadata are NISO tags for document status indicating the "final published version" (VoR), and limits on what domains it should be present on. Elsevier scans for PDFs with this metadata, so good idea to strip it any time you're sharing a copy. Links: here's a shell script that recursively removes metadata from pdfs in a provided (or current) directory as described above. For mac/*nix-like computers, and you need to have qpdf and exiftool installed: The metadata appears to be preserved on papers from sci-hub. since it works by using harvested academic credentials to download papers, this would allow publishers to identify which accounts need to be closed/secured for any security researchers out there, here are a few more "hashes" that a few have noted do not appear to be random and might be decodable. exiftool apparently squashed the whitespace so there is a bit more structure to them than in the OP: this is the way to get the correct tags: of course there's smarter watermarking, the metadata is notable because you could scan billions of pdfs fast. this comment on HN got me thinking about this PDF /OpenAction I couldn't make sense of earlier, on open, access metadata, so something with sizes and layout... updated the above gist with correctly extracted tags, and included python code to extract your own, feel free to add them in the comments. since we don't know what they contain yet not adding other metadata. definitely patterned, not a hash, but idk yet. follow-up: there does not appear to be any further watermarking: taking two files with different identifying tags, stripping metadata, and relinearizing with qpdf's --deterministic-id flag yields PDFs identical with a diff, ie. no differentiating watermark (but plz check my work) It's a couple things: a) Elsevier's vendor's tool only has to be good enough to impress Elsevier b) Deterrence being more efficient than prevention   @jonny hmmm, alternatively start inserting copies of that metadata into blank or template PDFs. Send 'em chasing wild geese and make them look at Lorem Ipsum 50 times a day 😈 @http_error_418 @jonny Very well.  @jonny word of caution is that while removing exif is good, knowing publishers there's a bunch of other ways they'd directly include such trackers into the file, in a less human/machine readable spot than EXIF. so be careful  @jonny they're almost getting to the level of ISO standards for metadata f'wittery. For a while, many ISO standards that you bought (for $$$$) looked like a bad photocopy. If you zoomed in really close to the marks on the page, they were made up of a pattern of punctuation characters. Totally screwed up any screen reading, though  @jonny@social.coop seems like some countermeasures against scihub, libgen and other shadow libraries that provide those PDFs for free 🤨  @jonny this is the same technique that was being used in the OS designed in North Korea called Red Star OS. It was in the Chaos Congress talk about it.  @jonny this makes me think some horrible things are going to happen to students because of this but I can’t quickly think of an example @jonny But what meaningful data can they attach to that unique ID? The IP adress? Assume a user is not logged in, has cleared tracking cookies and is using a VPN. @cmkobel This is for sure embedded watermarking but I'm not seeing active surveillance in this (unlike, say Kindle or the myraiad of phone-home technologies). While I would strongly prefer Free Culture media where there is permission granted for distribution, modification, attribution mandates, and redistribution, if the media is DRM-free but does not permit widespread distribution, what mechanisms do you see as appropriate for the copyright holder to use to identify unauthorized distributed copies? I agree with you that for-profit publishing and academia are not good bedfellows, and I generally think copyright is broken in more ways than one. The issue for me is given the current legal environment, this seemed a simple way to address unauthorized duplication that doesn't involve DRM or other surveillance tech. @jonny this is the same tracking technique used in the operating system from North Korea called Red Star OS. @jonny If this "hash" is the only difference, then it can easily be removed or replaced, as it seems to be related to a user id. The question is if there are further differences, but looking at your later posts it seems that no.  @jonny Aaah yes, DMCA against random citizens, enforced by the same govs who original funded the majority of the papers in the first place. So, the tax payer gets to pay for the education, the research, the access fee AND the cops and legal system who have to go after the right minded citizens who publish the stuff they already payed for at least twice. This is fine. 🔥 The market will regualte itself. |
@jonny they look kind of meaningful. Not base64. Any ideas what could be in there?