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Convert potentially dangerous PDFs to safe PDFs

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Re: Convert potentially dangerous PDFs to safe PDFs

#11

Post by alphazard »

coppsilgold wrote: post #9

While useful it needs a big red warning to potential leakers. If they were personally served documents (such as via email, while logged in, etc) there really isn't much that can be done to ascertain the safety of leaking it. It's not even safe if there are two or more leakers and they "compare notes" to try and "clean" something for release. https://en.wikipedia.org/wiki/Traitor_tracing#Watermarking https://arxiv.org…

I seem to remember Yahoo finance (I think it was them, maybe someone else) introducing benign errors into their market data feeds, to prevent scraping. This lead to people doing 3 requests instead of just 1, to correct the errors, which was very expensive for them, so they turned it off.

I don't think watermarking is a winning game for the watermarker, with enough copies any errors can be cancelled.

Re: Convert potentially dangerous PDFs to safe PDFs

#12

Post by chaps »

Heh, I've seen this a bunch of times and it's of interest to me, but honestly? It's sooooo limiting by being an interface without a complementary command line tool. Like, I'd like to put this into some workflows but it doesn't really make sense to without using something like pyautogui. But maybe I'm missing something hidden in the documentation.

Re: Convert potentially dangerous PDFs to safe PDFs

#14

Post by crazygringo »

chaps wrote: post #12

Heh, I've seen this a bunch of times and it's of interest to me, but honestly? It's sooooo limiting by being an interface without a complementary command line tool. Like, I'd like to put this into some workflows but it doesn't really make sense to without using something like pyautogui. But maybe I'm missing something hidden in the documentation.

It seems to meant for end-users like journalists processing files individually like e-mail attachments.

It doesn't seem to be meant for usage at scale -- it's not for general-purpose conversion, as the resulting files are huge, will have OCR errors, etc.

Re: Convert potentially dangerous PDFs to safe PDFs

#15

Post by chaps »

crazygringo wrote: post #14
chaps wrote: post #12

Heh, I've seen this a bunch of times and it's of interest to me, but honestly? It's sooooo limiting by being an interface without a complementary command line tool. Like, I'd like to put this into some workflows but it doesn't really make sense to without using something like pyautogui. But maybe I'm missing something hidden in the documentation.

It seems to meant for end-users like journalists processing files individually like e-mail attachments. It doesn't seem to be meant for usage at scale -- it's not for general-purpose conversion, as the resulting files are huge, will have OCR errors, etc.

I'm the target audience for this sort of tool. :)

Re: Convert potentially dangerous PDFs to safe PDFs

#16

Post by crazygringo »

coppsilgold wrote: post #9

While useful it needs a big red warning to potential leakers. If they were personally served documents (such as via email, while logged in, etc) there really isn't much that can be done to ascertain the safety of leaking it. It's not even safe if there are two or more leakers and they "compare notes" to try and "clean" something for release. https://en.wikipedia.org/wiki/Traitor_tracing#Watermarking https://arxiv.org…

This doesn't seem to be designed for leakers, i.e. people sending PDF's -- it's specifically for people receiving untrusted files, i.e. journalists.

And specifically about them not being hacked by malicious code. I'm not seeing anything that suggests it's about trying to remove traces of a file's origin.

I don't see why it would need a warning for something it's not designed for at all.

Re: Convert potentially dangerous PDFs to safe PDFs

#17

Post by coppsilgold »

alphazard wrote: post #11
coppsilgold wrote: post #9

While useful it needs a big red warning to potential leakers. If they were personally served documents (such as via email, while logged in, etc) there really isn't much that can be done to ascertain the safety of leaking it. It's not even safe if there are two or more leakers and they "compare notes" to try and "clean" something for release. https://en.wikipedia.org/wiki/Traitor_tracing#Watermarking https://arxiv.org…

I seem to remember Yahoo finance (I think it was them, maybe someone else) introducing benign errors into their market data feeds, to prevent scraping. This lead to people doing 3 requests instead of just 1, to correct the errors, which was very expensive for them, so they turned it off. I don't think watermarking is a winning game for the watermarker, with enough copies any errors can be cancelled.

> I don't think watermarking is a winning game for the watermarker, with enough copies any errors can be cancelled.

This is a very common assumption that turns out to be false.

There are Tardos probabilistic codes (see the paper I linked) which have the watermark scale as the square of the traitor count.

For example, with a watermark of just 400 bits, 4 traitors (who try their best to corrupt the watermark) will stand out enough to merit investigation and with 800 bits be accused without any doubt. This is for a binary alphabet, with text you can generate a bigger alphabet and have shorter watermarks.

These are typically intended for tracing pirated content, so they carry the so-called Marking Assumption (if given two or more versions of a piece of content, you must choose one. A pirate isn't going to corrupt or remove a piece of video, that would be unsuitable for leaking). So it would likely be possible to get better results with documents, may require larger watermarks to get such traitors reliably.

Re: Convert potentially dangerous PDFs to safe PDFs

#18

Post by coppsilgold »

crazygringo wrote: post #16
coppsilgold wrote: post #9

While useful it needs a big red warning to potential leakers. If they were personally served documents (such as via email, while logged in, etc) there really isn't much that can be done to ascertain the safety of leaking it. It's not even safe if there are two or more leakers and they "compare notes" to try and "clean" something for release. https://en.wikipedia.org/wiki/Traitor_tracing#Watermarking https://arxiv.org…

This doesn't seem to be designed for leakers, i.e. people sending PDF's -- it's specifically for people receiving untrusted files, i.e. journalists. And specifically about them not being hacked by malicious code . I'm not seeing anything that suggests it's about trying to remove traces of a file's origin. I don't see why it would need a warning for something it's not designed for at all.

It would be natural for a leaker to assume that the PDF contains something "extra" and to try and and remove it with this method. It may not occur to them that this something extra could be part of the content they are going to get back.
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