These PDFs apparently used the “incremental update” feature of PDF, where edits to the document are merely appended to the original file.
It’s easy to extract the earlier versions, for example with a plain text editor. Just search for lines starting with “%%EOF”, and truncate the file after that line. Voila, the resulting file is the respective earlier PDF version.
(One exception is the first %%EOF in a so-called linearized PDF, which marks a pseudo-revision that is only there for technical reasons and isn’t a valid PDF file by itself.)
It's hilarious the extent to which Adobe Systems's ridiculously futile attempt to chase MS Word features ended up being the single most productive espionage tool of the last quarter century.
I don’t think this was particularly modeled on MS Word. The incremental update feature was introduced with PDF 1.2 in 1996. It allows to quickly save changes without having to rewrite the whole file, for example when annotating a PDF.
Incremental updates are also essential for PDF signatures, since when you add a subsequent signature to a PDF, you couldn’t rewrite the file without breaking previous signatures. Hence signatures are appended as incremental updates.
I see an interesting parallel to how people think about captured encrypted data, and how long that encryption needs to be effective for until technology catches up and can decrypt (by which point, hopefully the decrypted data is worthless). If all of these documents are stored in durable archives, future methodologies may arrive to extract value or intelligence not originally available at the time of capture and disclosure.
The "print and scan physical papers back to a PDF of images" technique for final release is looking better and better from an information protection perspective.
> The "print and scan physical papers back to a PDF of images" technique for final release is looking better and better from an information protection perspective.
Note that all (edit: color-/ink-) printers have "invisible to the human eye" yellow dotcodes, which contain their serial number, and in some cases even the public IP address when they've already connected to the internet (looking at you, HP and Canon).
So I'd be careful to use a printer of any kind if you're not in control of the printer's firmware.
There's lots of tools that started to decode the information hidden in dotcodes, in case you're interested [1] [2] [3]
It's mindboggling how much open-source 3d printing stuff is out there (and I'm grateful for it) but this is completely lacking in the 2d printing world
Thanks for the links but can you share evidence for the "public IP address" claim? Each time I've read this concept (intriguing! possible!), I search for evidence and I can't find any.
The MIC and yellow dots have been studied and decoded by many and all I've ever seen, including at your links, are essentially date + time + serial#.
Don't get me wrong ... stamping our documents with a fingerprint back to our printers and adding date and time is nasty enough. I don't see a need to overstate the scope of what is shared though.
>Note that all printers have "invisible to the human eye" yellow dotcodes, which contain their serial number, and in some cases even the public IP address when they've already connected to the internet (looking at you, HP and Canon).
I've got a black and white brother printer which uses toner. Is there something similar for this printer?
a better approach is to convert them to jpeg/png. Then convert that to raw BMP, and then share or print that.
A more modern approach for text documents would be to have an LLM read and rephrase, and restructure everything without preserving punctuation and spacing, using a simple encoding like utf-8, and then use the technique above or just take analog pictures of the monitor. The analog (film) part protects against deepfakes and serves as proof if you need it (for the source and final product alike).
There various solutions out there after the leaks that keep happening where documents and confidential information is served/staged in a way that will reveal the person with who it is shared. Even if you copy paste the text into notepad and save it in ascii format, it will reveal you. Off-the-shelf printers are of course a big no-no.
If all else fails, that analog picture technique works best for exfil, but the final thing you share will still track back to you. I bet spies are back to using microfilms these days.
I only say all of that purely out of a fascination into the subject and for the sake of discussion (think like a thief if you want to catch one and all). Ultimately, you shouldn't share private information with unauthorized parties, period. Personal or otherwise. If you, like snowden, feel that all lawful means are exhausted and that is your only option to address some grievance, then don't assume any technique or planning will protect you, if it isn't worth the risk of imprisonment, then you shouldn't be doing it anyways. Assume you will be imprisoned or worse.
It could still be identifiable, for example if the document has been prepared such that the intended recipient's identity is encoded into subtle modulation of the widths of spaces.
There needs to be better tooling for inspecting PDF documents. Right now, my needs are met by using `qpdf` to export QDF [1], but it is just begging for a GUI to wrap around it...
Take a look at the REMNux reverse engineering page for PDF documents (https://docs.remnux.org/discover-the-tools/analyze+documents...). Lots of tools here for looking at malicious PDFs that can be used to inspect/understand even non-malicious documents.
Thank you. The most recent completely new information from the Snowden files is found in Jacob Appelbaum's 2022 thesis[1], in which he revealed information that had not been previously public (not found on any previously published documents and so on). And AFAIK, the most recent new information from the published documents (along with this post) might actually be in our other posts[2], but there might be some others we aren't aware of.
> We contacted Ryan Gallagher, the journalist who led both investigations, to ask about the editorial decision to remove these sections. After more than a week, we have not received a response.
Hopefully we'll hear something now that the Christmas holidays are over.
Traditionally an editor would be obligated to review the material and redact info that could be harmful to others. The publisher has distinct liability independent of govt opinion.
Can someone spell out how this is possible? Do pdfs store a complete document version history? Do they store diffs in the metadata? Does this happen each time the document is edited?
You can replace objects in PDF documents. A PDF is mostly just a bunch of objects of different types so the readers know what to do with them. Each object has a numbered ID. I recommend mutool for decompressing the PDF so you can read it in a text editor:
mutool clean -d in.pdf out.pdf
If you look below you can see a Pages list (1 0 obj) that references (2 0 R) a Page (2 0 obj).
Rather than editing the PDFs in place, it's possible to update these objects to overwrite them by appending a new "generation" of an object. Notice the 0 has been incremented to a 1 here. This allows leaving the original PDF intact while making edits.
1 1 obj
<<
/Type /Pages
/Count 2
/Kids [ 2 0 R 200 0 R ]
>>
endobj
You can have anything inside a PDF that you want really and it could be orphaned so a PDF reader never picks up on it. There's nothing to say an object needs to be referenced (oh, there's a "trailer" at the end of the PDF that says where the Root node is, so they know where to start).
Thanks for the technical explanation! This is pretty fascinating.
So it works kind of like a soft delete — dereference instead of scrubbing the bits.
Is this behavior generally explicitly defined in PDF editors (i.e. an intended feature)? Is it defined in some standard or set of best practices? Or is it a hack (or half baked feature) someone implemented years ago that has just kind of stuck around and propagated?
At the bottom of the page there's a link to the pdfresurrect package, whose description says
"The PDF format allows for previous changes to be retained in a revised version of the document, thereby keeping a running history of revisions to the document.
This tool extracts all previous revisions while also producing a summary of changes between revisions."
PDFs are just a table of objects and tree of references to those objects; probably, prior versions of the document were expressed in objects with no references or something like that.
Readit News
It’s easy to extract the earlier versions, for example with a plain text editor. Just search for lines starting with “%%EOF”, and truncate the file after that line. Voila, the resulting file is the respective earlier PDF version.
(One exception is the first %%EOF in a so-called linearized PDF, which marks a pseudo-revision that is only there for technical reasons and isn’t a valid PDF file by itself.)
Incremental updates are also essential for PDF signatures, since when you add a subsequent signature to a PDF, you couldn’t rewrite the file without breaking previous signatures. Hence signatures are appended as incremental updates.
Note that all (edit: color-/ink-) printers have "invisible to the human eye" yellow dotcodes, which contain their serial number, and in some cases even the public IP address when they've already connected to the internet (looking at you, HP and Canon).
So I'd be careful to use a printer of any kind if you're not in control of the printer's firmware.
There's lots of tools that started to decode the information hidden in dotcodes, in case you're interested [1] [2] [3]
[1] https://github.com/Natounet/YellowDotDecode
[2] https://github.com/mcandre/dotsecrets
[3] (when I first found out about it in 2007) https://fahrplan.events.ccc.de/camp/2007/Fahrplan/events/197...
It's mindboggling how much open-source 3d printing stuff is out there (and I'm grateful for it) but this is completely lacking in the 2d printing world
The MIC and yellow dots have been studied and decoded by many and all I've ever seen, including at your links, are essentially date + time + serial#.
Don't get me wrong ... stamping our documents with a fingerprint back to our printers and adding date and time is nasty enough. I don't see a need to overstate the scope of what is shared though.
I've got a black and white brother printer which uses toner. Is there something similar for this printer?
And of course we have to include the Wikipedia entry:
https://en.wikipedia.org/wiki/Printer_tracking_dots
A more modern approach for text documents would be to have an LLM read and rephrase, and restructure everything without preserving punctuation and spacing, using a simple encoding like utf-8, and then use the technique above or just take analog pictures of the monitor. The analog (film) part protects against deepfakes and serves as proof if you need it (for the source and final product alike).
There various solutions out there after the leaks that keep happening where documents and confidential information is served/staged in a way that will reveal the person with who it is shared. Even if you copy paste the text into notepad and save it in ascii format, it will reveal you. Off-the-shelf printers are of course a big no-no.
If all else fails, that analog picture technique works best for exfil, but the final thing you share will still track back to you. I bet spies are back to using microfilms these days.
I only say all of that purely out of a fascination into the subject and for the sake of discussion (think like a thief if you want to catch one and all). Ultimately, you shouldn't share private information with unauthorized parties, period. Personal or otherwise. If you, like snowden, feel that all lawful means are exhausted and that is your only option to address some grievance, then don't assume any technique or planning will protect you, if it isn't worth the risk of imprisonment, then you shouldn't be doing it anyways. Assume you will be imprisoned or worse.
if really paranoid, I suppose one could run a filter on the image files to make them a bit fuzzy/noisy
Deleted Comment
[1] https://qpdf.readthedocs.io/en/stable/qdf.html
Very tempting to fool around with the ideas especially after the Epstein pdf debacle.
Deleted Comment
Recently someone else revisited the Snowden documents and also found more info, but I can't recall the exact details.
Snowden and the archives were absolute gifts to us all. It's a shame he didn't release everything in full though.
[1]: https://www.electrospaces.net/2023/09/some-new-snippets-from...
[2]: Part 2: https://libroot.org/posts/going-through-snowden-documents-pa...
and part 3: https://libroot.org/posts/going-through-snowden-documents-pa...
Dead Comment
Hopefully we'll hear something now that the Christmas holidays are over.
Is there something in here so damaging that they refuse to publish it?
Did the government tell them they'd be in trouble if they published it?
Are the journalists the only ones with access to the raw files?
So it works kind of like a soft delete — dereference instead of scrubbing the bits.
Is this behavior generally explicitly defined in PDF editors (i.e. an intended feature)? Is it defined in some standard or set of best practices? Or is it a hack (or half baked feature) someone implemented years ago that has just kind of stuck around and propagated?
"The PDF format allows for previous changes to be retained in a revised version of the document, thereby keeping a running history of revisions to the document.
This tool extracts all previous revisions while also producing a summary of changes between revisions."
https://github.com/enferex/pdfresurrect