Hi everyone, my name is Salix and I'm an astronaut engineer at the Freedom of the Press Foundation.
Today I'm going to discuss about the subject of removing traces from documents real quick
what we're going to see today, I want to discuss mostly about what are the known DNA
and organization vectors we are aware of that may be in documents, we will show you
our service on tools that can help you anonymize those documents and remove traces from them.
And of course we're going to see limitations because the subject of making removing traces
from your activity from documents is actually really hard, if I can speak up, I'll try.
And then finally due to the limitations, we will try to see how we can dump them,
how we can cross this gap between the technical and the practical in order to overcome
let's say these limitations and help people who want to stay anonymous with some practical
devices. Unfortunately, I'm not going to provide some sort of a novel way of removing sophisticated
metadata and traitor tracing schemes that may exist in documents, it's not going to be also
like a deep course in metadata removal, it's mostly going to be like what's out there, what
tools exist to help there and some extra devices. So let's jump writing to the DNAization
vectors. What I'm going to show you today is I'll try to do this to categorize some of the
vectors that are in the literature, hopefully it will be a good categorization and extensive
one. We will focus on this show solely on what is inside the document because the subject of
anonymously obtaining a sensitive document and sharing it with someone else is a whole different subject
that leaves traces outside of the document and we're not going to talk about that. Quick terminology
in case you are not aware of, we're going to talk about OCR at some point, OCR is optical
character recognition and it's the process of retrieving text from images and we're going to talk
about flattening which is making a document, a page let's say a document, but has complex components
making it like a flat image. We're going to talk about metadata but metadata are just the tip of the
iceberg. There are a lot of many more DNAization vectors and if you if you're doing this
presentation you find an example that doesn't fall under one of those categories I will provide
please pick up, would like to know by it. I'm going to start with a very simple example, a very
no one, a vice reporter at some point to the picture of my coffee he was hidden somewhere in the
South America and for go to scrub the metadata of the location while he uploaded and that way
my coffee was traced. So lesson number one okay sure scrub them with the data from simple documents
like files and audio. Now scrubbing them with the data is not that simple when you encounter
complex document types. In this particular case Google at some point tried to anonymously
do some sort of litigation against the eBay in the Australia and the Australian justice
department of justice or whatever wanted to keep the identity anonymous but they forgot that
the title of the world document that they received was also within the PDF as some sort of
metadata and this was probably hard to find the figure out. So a bit of a full proof solution there
is to just flatten the document in order to remove those kind of embedded metadata.
And when we talk about removing traces via some way,
I come away to do it with reductions and reductions are surprisingly or not surprisingly,
very easy to get wrong. This is a famous case where Sony did a filing and they wanted to
deduct how many millions of spend on their games etc and they used a black sharpie to do that
but whenever you try to do reductions with something that is not opaque and that applies
that of course applies to the sharpie but it also applies to other digital tools you're using
your brush in your photo editor, some sort of spray or some a mosaic effect. All those things
if they're not opaque they're bound to be forensically retrieved the text underneath and also
that's like one of the types of bad reduction. There is also the very common bad reduction
where you just take a PDF you add a opaque black bar on top of it and you forgot that it's just
like an layer or top of the text and therefore that text can be retrieved again. So the mitigation here
is to make sure you always use of course opaque black bars to remove sensitive information
and make sure to flatten it afterwards. So as you can see I keep the word flattening gets an
important defense against those types of things. Now there is another way to leave traces in a
document and that's with physical watermarks. In this particular case I'm showing the watermarks
that were in reality winners documents, reality winners, reality winner was a US whistleblower
where she gave some documents to the intercept that journalist from the intercept gave them
showed them to the FBI and then reality winner was called. Some people theorize that that reality
winner was the anonymous due to those printer tracking codes that you see in blue there. In practice
though and that's why I will not talk about the opposite failure here. Reality winner was one of the
six people who had access to this particular document and the only person who contacted the
intercept journalist through her work device. So even if we manage to remove those types of traces
and my suggestion is to use OCR in order to just get the text and put it to another document
you can never trust printed media. Even if you do that though there's bound to be
some traces outside of the document itself but unfortunately we will not talk about that.
And now there's another category that is also like pretty known. It's the subject of digital
watermarks. Besides physical watermarking there's there are certain ways where and that's on the
left you see what a company advertises to certain customers that you can embed somehow in a
steganographic manner and certain tracking codes in pictures in various types of documents.
For images it's like pixels. For the common text it can be zero width unicorn characters. Small
small differences in the care link of the phone. It can be lots of very discrete stuff.
And also besides those very cool paper worthy stuff on the left there is also like
the play note techniques that have been used since the in called water or whatever where you just
craft a document and you create different permutations with different maybe facts in order to
and you give them to various people. And when something is leaked you can trace it back to the
passion who elected. And although we can do some stuff for removing like the the left category
for instance in order to make sure that you don't deal with with zero width characters and
small changes in the document you can probably ocean our document and do a double translation
translate your document to a separate language and then back to your own because some people used
mispellings in order to do that or a different type of phrasing. You can never be able to
remove like just plain old fabricated facts that may be in the document. So we're starting to see
some categories where there is lack of limitation that the tool can never give protection.
There is also another interesting category, a more active type of tracing which is kind of
it tokens. Those are some sort of code that is embedded in the document and this code will be
able to let's say form home whenever the document is opened. Now most same viewers will silently
ignore those types of code in the NPDFs etc. But Microsoft Office will happily ask to enable
macros and Adobe Acrobat as you see in the left screen. We will ask you if you want to connect
to some random URL. In this case it's kind of a tokens.com but if it was a legit URL it's a
high percent possibility that some person would just click on it and their IP and operating system etc
will be revealed and the fact that the access to the document will be revealed to the source of
the document. So a good defense here is to immediately flatten the document before once once you obtain it.
And then there is a subject of fingerprinting which is different from watermarking. The
this category has to do with not just the document itself but also the equipment you had in order to
create that document and it turns out that your phone camera, your microphone has some unique
characteristics that make it easier to associate different copies of different pictures let's say you
take. So we call it fingerprinting because unlike watermarking where you just need one thing in order
to trace it back to you with fingerprinting you need like a match for like if you leave a fingerprint
on the scene you also need some somehow to match it with the person. So in that particular case
if you take for instance a photo of some sort of document and then with the same phone you upload
your family photo. In theory there's the same characteristic in there that can trace it back to you.
So the advisor and we are again moving somewhere that shows are limited is to use disposable
equipment and because you're writing style as well it can be fingerprinted and some people you
have been found due to this way it's best to use common chords or do this double translation
trick. And again in this particular case there's no way to be one hundred percent safe that
the document you create will not have something from you. And finally besides the equipment besides
the thing you capturing there's also something that can sip into the picture of the video the
audio is the environment factor. And in this particular case you're seeing the iris of Japanese
Pope Ido who was taking some selfies and posting them in social media and attacker a stalker
managed to zoom into her iris and find out her surroundings and trace her route to a particular
train and therefore keep made an attack in this particular case. So in order to be safer in this regard
the suggestion is to avoid any types of selfies that may reflect the environment or avoid
locations especially in case of audio where you cannot just do sound proofing something where it
can be associated with you. But again there's no way to be one hundred percent safe.
Now we saw some categories if you have anything that doesn't apply to those categories
and mention of being happy to learn after the talk or as a question. Now we're going to show
some tooling. Exitive tool probably most of you know it's a tool that can view
metadata about file types. It can also remove metadata data as well and it can work with lots of files
besides images which is a de facto thing. Here's how it does it with PDFs you can see some
we can see that we can remove the metadata and then the end result is something that doesn't
have any metadata in it. But there is a warning although the tool succeeded and although it
seems that there are no metadata and that warning is actually xif2 does not remove any metadata in
some file types. If you see here this PDF from the PDF from the left is the redacted one
in this particular case xif2 just added its own section where it basically says there are
no metadata on this file and this is not good. Exitive tool to their credit of course it's a
very bad attitude so of course there are written limitations in the website but if you are doing
something automatically or if you're not like superware of every limitation that is in there
you may just miss it. Now for something more professional there is a map to alter it's an
open source library it supports lots of documents it has a very thoughtful thought model about the
things that can anonymize what not. There is a GUI option as well but unfortunately it's a
make not maintained right now. What it does is that it takes it removes the data from some
file types but it needs to flatten other file types known to be 100% safe. The end result is that you
get back the exact same file that you provided in most cases where it's not flattened so that's
very useful if you want to work with the end result and this is how much you does it you can see
it detects the metadata it download it can remove them and then it shows that there's nothing
else left however because the other side has a very thoughtful thought model the author of
metadata of Matju claims that it's not 100% safe to remove complex metadata and then keep the original
file because there may be some things that you don't anticipate the structure some files so there may
be some update and then you miss some other type of metadata that's in there so you need to exercise
some caution with tools that are not flattening the documents and now the tool but this presentation
was like mostly about it's danger zone it supports lots of documents but unfortunately it does not
support audio and video. The main idea is to sanitize malware but the but removing the metadata
because of the fact that the weight works is that you pass the document in a container it breaks it
down into pixels and then outside the container it reconstructs the original document as a pdf from
these pixels so through this process there is no malware but also there are no metadata from the original
document as the end result though is that it's a completely flattened so you cannot easily
you cannot edit it or anything however you can ocean it's maintained by freedom of the press foundation
and disclaimer I work on this project. That's the CLI option for the addition as you can see
you can pass the document and you can also pass the ocean language in order to create a layer
over the text. Now quick summary we have seen that metadata removal makes file
saytable however it doesn't remove every denanimization vector we have seen two main tools for
removing traces from your data danger zone match you match you provide produces a double files
and it's definitely faster danger zone tries to be safe and flat as everything but does not
provide something that's easy to work with and I have applied the tools and the category is an
dimension before and we can see that there are clear limitations even in the case of the
addition where the the user cannot be fully protected but in order to be protected though
we need to help them a bit more and the x is that you saw before is like the gap the gap
where the tooling cannot actually help you and you need to do something extra yourself so
tools that flat in documents are good for a step but there is like but if they're not you can
not remove everything however we know that we should lower and activists will still try to do
to share documents that are sensitive and try to improve society this way and we need to
help them in this situation we cannot just say that those are limitations and you cannot
do anything else so what we need to offer in this particular case is something that goes beyond tooling
it's something that goes beyond the technical stuff and it's basically playing out harm reduction
it's basically advices that you can give to those people that go besides tooling and
can't help them avoid some common issues that we know from the literature they're bound to be
risks and this is what they're doing is at some point they're bound to be get caught by some
law enforcement because there are lots of mistakes that you can do along the way but at least
we should be able to educate them and so that they can make an informed choice about what they're doing
and I'm going to go very quick from some types of documents and some examples some
clear advice that we can give to whistleblowers and activists so for a video we do not support it
the engine does not support it so prefer using matu if it was a recording if you record yourself
please use disposable equipment and locations that are away from you if it's accessible only to you
please be aware of digital watermarking and prefer not to go public without document and as always
remember it's not my hand percent safe to share for images again disposable equipment if it's
accessible only to you it may be digital watermarked so prefer not to go public if it's a
print or a scan try to use the original files else again prefer not to go public and with reductions
make sure you aid them with black opaque bars before you do anything with any tool and finally for
documents because documents convey less information than pictures we have a bit more of a leeway there
if it's a printed material make sure to wash out or retipe it manually a reductions black bars again
if it's something that's accessible to you you can again it may be watermarked and may be watermarked
in ways where the facts may be completed fabricated and can be traced back to you so that's an issue
however this does not mean you don't need to do anything at least try to or share it to
remove it any zero width factors etc and prefer and maybe do some double translation
and for writing the documents just remember to use common words do the double translation
quick and as always you may be think of it and in that case prefer not going public if it's like
your document and again and this is something everyone needs to remember there's no one
how to save a safe way to do this risky thing but you need to be educated so that's it for me
thanks a lot for watching this sok and here's some links where you can learn more about the
projects and I'm happy to take in questions
your comments about printing was that we're trying to like if you print to a PDF so print for digital
format and then to what what is actually written out is it just some sort of unique identify
or is there a more information event so the question was what do we mean about printed material
I'm referring to printing in a physical material as in a typical printer and the thing that
goes out originally it was some tracking dots in modern times you cannot even say it it may be
much more difficult if you print for a PDF is that not flattening up if you print a mean error
say you just choose print to PDF yeah in the question is if you print a PDF to a physical material
or if you do the print to PDF think yeah if it's creating a flat version if it's creating a
flat version of a web page for instance no in that particular case it's not a flat version because
PDF can contain complex file types in there as well they they may still remain under
so it's not that much of a scale we've been interested to use the project like
documents where you can do it all the art of all the time so you just get the actual thanks to
can you repeat that project name please duckling so you're asking if it's
the structure so it would be very easy because that doesn't happen and you make the data
okay that's fine is it something that runs locally in that case okay then I guess I'll be an
interesting option as well please
yeah so there are some more complex ways to deal with that in order to get back
oh yeah sure if the question was if it if it makes sense to if you have a PDF for instance
to convert to postcript and then convert it back to PDF in that case removing the metadata
sure maybe that's a way to do that I'm not sure if it removes everything I don't know
for instance what happens with images that are in the PDF if those are the metadata of those
images are removed as well what happens with audio recordings videos that may be in some
PDFs you can embed lots of things there but the point is I didn't stress it out that much
the point is that this is this tools should be used by people who are not technical they should be
used by people who use windows macOS in our case it's just a good application and it needs to work
with the office documents so we do the exact same thing everywhere and we do not take any
chances of like what may leak or malatmid not