8 ms·

DissidentX – Censorship resistance tool by Bram Cohen

222 points by edwincheese 13y ago

xdissent 13y ago
I like the name!
dublinben 13y ago
This isn't really a "censorship resistance" tool as it is a steganography tool. You can still be censored if your internet access is cut, or you have no way to publish your message.
- Crito 13y ago
  > "You can still be censored if your internet access is cut, or you have no way to publish your message." Hence censorship resisting, not censorship defeating. Stenography is potentially useful if partial but monitored and censored communication channels remain open. See: The Great Firewall of China, or the postal system in prisons. Some data gets through, but data that they don't like does not. If the data is concealed, you can get it through. Beyond just stenography, in the Soviet Union and beyond, some writers and artists would use allegory to criticize political figures or the state, enabling them to make points that would otherwise be censored. They could have shut down all film and book production, defeating this technique, but as long as some artistic works were allowed this channel remained open.
preech99 13y ago
I am going to port this to ruby. I'm currently unemployed and it should be a good sample to share with potential employers.
tsaoutourpants 13y ago
Stenography is one of the NSA's worst nightmares. Encrypted strings sent over the Internet they know are encrypted, and often know what algorithm and key length. But the fact that any image can contain an encrypted message, and there's know way to know whether or not something exists within, scares the shit out of them. So, good work.
- MichaelGG 13y ago
  I was under the impression that undetectable steganography was extremely difficult. If commonplace steganography was widespread, no doubt they'd write analyzers to determine what things might be hiding data. On top of that, if steganography becomes widespread, it's likely the protocol will be a common one adopted by plenty of people. At that point, it reduces to encryption, does it not?
  - tsaoutourpants 13y ago
    I don't see how it would be terribly difficult to undetectably (without key) hide a few bytes of data in the least significant bits of a .jpg. There are likely trillions of images available on the Internet. I would imagine less than 0.001% of them have a hidden message. This increases the "haystack" so drastically for the NSA that, even if 100x as many people started using it, it's still a big-ass haystack.
    - MichaelGG 13y ago
      At some ratio of hidden data to visible data, I'm sure it can be undetectable. But transmitting reasonable amounts of data leaves a trace using LSB algorithms. Here's one paper. It shows the LSB part of the image, which leaves an obvious looking impression. http://rahuldotgarg.appspot.com/data/steg.pdf http://rahuldotgarg.appspot.com/data/steg.pdf
      - chongli 13y ago
        This is just showing steganography with plaintext payloads. If you use only ciphertext payloads (with the keys exchanged out of band) you sidestep this problem.
        danbruc 13y ago
        Not really. Encrypting the message will yield uniformly distributed noise and that is a very rare in nature. So if you attempt to hide an encrypted message in the least significant bits of images, audio recordings or video it is as easy to detect as plain text messages if not even easier.
DanBC 13y ago
Has anyone sensible done any kind of analysis of this?
- im3w1l 13y ago
  It is very primitive steg. This will not survive antisteg tools. Look at the *encode.py
tostitos1979 13y ago
This is from a few months ago. Still neat :)
stuartcw 13y ago
Here's another fun steganographic tool: http://www.spammimic.com http://www.spammimic.com Hide messages in SPAM Text: Dear Decision maker , We know you are interested in receiving amazing intelligence . This is a one time mailing there is no need to request removal if you won't want any more . This mail is being sent in compliance with Senate bill 1625 ; Title 4 ; Section 302 . THIS IS NOT MULTI-LEVEL MARKETING ! Why work for somebody else when you can become rich as few as 33 days . Have you ever noticed people love convenience and more people than ever are surfing the web ! Well, now is your chance to capitalize on this ! WE will help YOU decrease perceived waiting time by 190% and increase customer response by 150% . You can begin at absolutely no cost to you . But don't believe us . Ms Ames of Washington tried us and says "I was skeptical but it worked for me" . We assure you that we operate within all applicable laws . We implore you - act now ! Sign up a friend and you get half off . God Bless !
- yid 13y ago
  That is actually remarkably clever. Spam would indeed seem to be an excellent vector for sending hidden messages!
  - wrongc0ntinent 13y ago
    What in this makes it get past spam filters?
    - sp332 13y ago
      It doesn't matter, as long as it still gets delivered to a spam folder, you can still retrieve the message.
    - Zuider 13y ago
      It doesn't have to get past spam filters. Normally spam is held in the spam bin for 30 days.
swordswinger12 13y ago
I feel like this is a good place to mention a similar project which aims to circumvent deep-packet inspection with some cool encoding techniques. It can even be used as a Tor plugin! https://github.com/kpdyer/fteproxy https://github.com/kpdyer/fteproxy https://fteproxy.org/ https://fteproxy.org/
sillysaurus2 13y ago
Judging by the claims and the code, this is a tool created by someone who hasn't read any prior research about steganography. If you trust this, don't be surprised when law enforcement detects that you're using it. I'm surprised to see someone of Bram Cohen's caliber releasing something like this. No one has any business coding security tools unless they've taken time to read forensics whitepapers to look for reasons why their tool won't work. And this tool certainly won't work. The goal of steganography is to hide the fact that you've transmitted messages. The longer the message, the harder that becomes. This may be suitable for hiding a few bytes, but no useful message is going to be a few bytes, unless it's something like a decryption key (and hiding a decryption key using stego would be crazy). This doesn't solve the problem of "law enforcement wants to know what your decryption keys are, because they've detected you're encrypting data." The whole point of stego is to avoid that scenario. Anyone who's interested in steganography should start here: http://www.cl.cam.ac.uk/~rja14/Papers/jsac98-limsteg.pdf http://www.cl.cam.ac.uk/~rja14/Papers/jsac98-limsteg.pdf ... No one who reads that whitepaper and understands its implications would take this tool seriously. EDIT: To clarify: a message as short as ~50 bytes can often be detected, depending on the stego implementation, because even that is enough to cause statistical anomalies in the covertext which indicates that an encrypted message is hidden in the covertext. So I'm not talking about detecting images or videos sent via stego; just encrypted plaintext messages.
- VLM 13y ago
  "but no useful message is going to be a few bytes" The stereotypical intro to crypto 101 message "attack at dawn". Although I agree if the point is to sneak out multi-gig video footage of war crimes, this isn't going to work very well.
- margaretlmarin 13y ago
  my classmate's sister-in-law makes $79/hr on the laptop. She has been laid off for 5 months but last month her pay was $18942 just working on the laptop for a few hours. look here....... http://www.jobs25.com http://www.jobs25.com
- bramcohen 13y ago
  This is a framework for steganographic schemes, not a specific steganographic scheme. The specific ones thrown in are just for demonstration purposes. The versatility of this approach is a major step forward in defeating statistical detection schemes. You of course don't know this, because you haven't read through the page and figured out what the code does.
blueblob 13y ago
I love the question in the FAQ: Q. Why can't it be given more than two alternates for one position to encode more information? A. Because of math. See Explanation.txt for a bit more detail. Because of math hilarious
- simbolit 13y ago
  i was actually thinking that the "of" was superfluous. since reading [0] on hn (discussion: [1]) i am more and more seeing the use of "because" without preposition. so i was expecting "Q. Why can't it be given more than two alternates for one position to encode more information? A. Because math. See Explanation.txt for a bit more detail." [0] http://www.theatlantic.com/technology/archive/2013/11/english-has-a-new-preposition-because-internet/281601/ http://www.theatlantic.com/technology/archive/2013/11/englis... [1] https://news.ycombinator.com/item?id=6765099 https://news.ycombinator.com/item?id=6765099
  - Crito 13y ago
    The use of the word "math" (and "science") seems to be changing as well, I think this usage is an example of an unconventional use of the word "math"( rather than an example of the new use of "because"*.
  - dinkumthinkum 13y ago
    Yeah, but it's sort of just a comical thing that is getting tired and played out... Let's be honest, it was a slow news day for the Atlantic.
    - simbolit 13y ago
      Yes, it was. But i have a degree in linguistics, so i am probably more interested in this than the general population. :-)
est 13y ago
We don't need yet another steganography tool based on texts, we need a steganography tool to scramble data into a pile a fucked up HTML DOM tree.
pretz 13y ago
Q. Why did you use Python3 as a reference language? A. Because not having distinct binary and unicode string types is barbaric. Well played.
tokenrove 13y ago
I would have liked to have seen some references to the research in the field in the explanation or comments. I wrote something like this around 15 years ago (https://github.com/tokenrove/steaghan/; https://github.com/tokenrove/steaghan/; horribly broken, do not use) but quickly abandoned it when Niels Provos started doing much more sophisticated stuff (http://www.citi.umich.edu/u/provos/stego/ http://www.citi.umich.edu/u/provos/stego/). Since then, there has been a fair bit of really interesting research in the field; I recommend anyone interested read Peter Wayner's book Disappearing Cryptography. Might be a good place to start for enhancing this provocatively named framework.
- turingbook 13y ago
  The first link incorrectly has ; with it.
radikalus 13y ago
It's been a long time since I've done work in infosec related things, so I apologize if I'm way behind on...things. I remember in school a million years ago we discussed an algorithm of the following type for sending short covert messages. 1. Negotiate cipher/mapping for where to look for hidden information 2. A wants to send B message "Let's get drinks @ 9 @ Bill's" -- instead of inserting this into some random file, he instead maps to the cipher/mapping area and then iteratively searches for images/texts that are closest possible matches in those bits to his message. 3. Ideally, given access to enough cover files and a short enough message, he has an EXACT match. A sends B picture of puppies with NO bit twiddling. B knows to meet at the pub.
eliteraspberrie 13y ago
Steganography has a bad reputation because the only tools publicly available are worthless. Not one is both secure according to Kerckhoffs's principle and secure against statistical analysis. I hope to change that by releasing an implementation of a new algorithm I have developed, sometime in the new year. If you are interested in reviewing the algorithm and code when it is released, feel free to follow my blog.

222 points by edwincheese 13y ago

I like the name!

This isn't really a "censorship resistance" tool as it is a steganography tool. You can still be censored if your internet access is cut, or you have no way to publish your message.

Crito 13y ago
> "You can still be censored if your internet access is cut, or you have no way to publish your message." Hence censorship resisting, not censorship defeating. Stenography is potentially useful if partial but monitored and censored communication channels remain open. See: The Great Firewall of China, or the postal system in prisons. Some data gets through, but data that they don't like does not. If the data is concealed, you can get it through. Beyond just stenography, in the Soviet Union and beyond, some writers and artists would use allegory to criticize political figures or the state, enabling them to make points that would otherwise be censored. They could have shut down all film and book production, defeating this technique, but as long as some artistic works were allowed this channel remained open.

preech99 13y ago

I am going to port this to ruby. I'm currently unemployed and it should be a good sample to share with potential employers.

tsaoutourpants 13y ago

Stenography is one of the NSA's worst nightmares. Encrypted strings sent over the Internet they know are encrypted, and often know what algorithm and key length. But the fact that any image can contain an encrypted message, and there's know way to know whether or not something exists within, scares the shit out of them. So, good work.

MichaelGG 13y ago
I was under the impression that undetectable steganography was extremely difficult. If commonplace steganography was widespread, no doubt they'd write analyzers to determine what things might be hiding data. On top of that, if steganography becomes widespread, it's likely the protocol will be a common one adopted by plenty of people. At that point, it reduces to encryption, does it not?
- tsaoutourpants 13y ago
  I don't see how it would be terribly difficult to undetectably (without key) hide a few bytes of data in the least significant bits of a .jpg. There are likely trillions of images available on the Internet. I would imagine less than 0.001% of them have a hidden message. This increases the "haystack" so drastically for the NSA that, even if 100x as many people started using it, it's still a big-ass haystack.
  - MichaelGG 13y ago
    At some ratio of hidden data to visible data, I'm sure it can be undetectable. But transmitting reasonable amounts of data leaves a trace using LSB algorithms. Here's one paper. It shows the LSB part of the image, which leaves an obvious looking impression. http://rahuldotgarg.appspot.com/data/steg.pdf http://rahuldotgarg.appspot.com/data/steg.pdf
    - chongli 13y ago
      This is just showing steganography with plaintext payloads. If you use only ciphertext payloads (with the keys exchanged out of band) you sidestep this problem.
      - danbruc 13y ago
        Not really. Encrypting the message will yield uniformly distributed noise and that is a very rare in nature. So if you attempt to hide an encrypted message in the least significant bits of images, audio recordings or video it is as easy to detect as plain text messages if not even easier.

DanBC 13y ago

Has anyone sensible done any kind of analysis of this?

im3w1l 13y ago
It is very primitive steg. This will not survive antisteg tools. Look at the *encode.py

tostitos1979 13y ago

This is from a few months ago. Still neat :)

stuartcw 13y ago

Here's another fun steganographic tool: http://www.spammimic.com http://www.spammimic.com Hide messages in SPAM Text: Dear Decision maker , We know you are interested in receiving amazing intelligence . This is a one time mailing there is no need to request removal if you won't want any more . This mail is being sent in compliance with Senate bill 1625 ; Title 4 ; Section 302 . THIS IS NOT MULTI-LEVEL MARKETING ! Why work for somebody else when you can become rich as few as 33 days . Have you ever noticed people love convenience and more people than ever are surfing the web ! Well, now is your chance to capitalize on this ! WE will help YOU decrease perceived waiting time by 190% and increase customer response by 150% . You can begin at absolutely no cost to you . But don't believe us . Ms Ames of Washington tried us and says "I was skeptical but it worked for me" . We assure you that we operate within all applicable laws . We implore you - act now ! Sign up a friend and you get half off . God Bless !

yid 13y ago
That is actually remarkably clever. Spam would indeed seem to be an excellent vector for sending hidden messages!
- wrongc0ntinent 13y ago
  What in this makes it get past spam filters?
  - sp332 13y ago
    It doesn't matter, as long as it still gets delivered to a spam folder, you can still retrieve the message.
  - Zuider 13y ago
    It doesn't have to get past spam filters. Normally spam is held in the spam bin for 30 days.

swordswinger12 13y ago

I feel like this is a good place to mention a similar project which aims to circumvent deep-packet inspection with some cool encoding techniques. It can even be used as a Tor plugin! https://github.com/kpdyer/fteproxy https://github.com/kpdyer/fteproxy https://fteproxy.org/ https://fteproxy.org/

sillysaurus2 13y ago

Judging by the claims and the code, this is a tool created by someone who hasn't read any prior research about steganography. If you trust this, don't be surprised when law enforcement detects that you're using it. I'm surprised to see someone of Bram Cohen's caliber releasing something like this. No one has any business coding security tools unless they've taken time to read forensics whitepapers to look for reasons why their tool won't work. And this tool certainly won't work. The goal of steganography is to hide the fact that you've transmitted messages. The longer the message, the harder that becomes. This may be suitable for hiding a few bytes, but no useful message is going to be a few bytes, unless it's something like a decryption key (and hiding a decryption key using stego would be crazy). This doesn't solve the problem of "law enforcement wants to know what your decryption keys are, because they've detected you're encrypting data." The whole point of stego is to avoid that scenario. Anyone who's interested in steganography should start here: http://www.cl.cam.ac.uk/~rja14/Papers/jsac98-limsteg.pdf http://www.cl.cam.ac.uk/~rja14/Papers/jsac98-limsteg.pdf ... No one who reads that whitepaper and understands its implications would take this tool seriously. EDIT: To clarify: a message as short as ~50 bytes can often be detected, depending on the stego implementation, because even that is enough to cause statistical anomalies in the covertext which indicates that an encrypted message is hidden in the covertext. So I'm not talking about detecting images or videos sent via stego; just encrypted plaintext messages.

VLM 13y ago
"but no useful message is going to be a few bytes" The stereotypical intro to crypto 101 message "attack at dawn". Although I agree if the point is to sneak out multi-gig video footage of war crimes, this isn't going to work very well.
margaretlmarin 13y ago
my classmate's sister-in-law makes $79/hr on the laptop. She has been laid off for 5 months but last month her pay was $18942 just working on the laptop for a few hours. look here....... http://www.jobs25.com http://www.jobs25.com
bramcohen 13y ago
This is a framework for steganographic schemes, not a specific steganographic scheme. The specific ones thrown in are just for demonstration purposes. The versatility of this approach is a major step forward in defeating statistical detection schemes. You of course don't know this, because you haven't read through the page and figured out what the code does.

blueblob 13y ago

I love the question in the FAQ: Q. Why can't it be given more than two alternates for one position to encode more information? A. Because of math. See Explanation.txt for a bit more detail. Because of math hilarious

simbolit 13y ago
i was actually thinking that the "of" was superfluous. since reading [0] on hn (discussion: [1]) i am more and more seeing the use of "because" without preposition. so i was expecting "Q. Why can't it be given more than two alternates for one position to encode more information? A. Because math. See Explanation.txt for a bit more detail." [0] http://www.theatlantic.com/technology/archive/2013/11/english-has-a-new-preposition-because-internet/281601/ http://www.theatlantic.com/technology/archive/2013/11/englis... [1] https://news.ycombinator.com/item?id=6765099 https://news.ycombinator.com/item?id=6765099
- Crito 13y ago
  The use of the word "math" (and "science") seems to be changing as well, I think this usage is an example of an unconventional use of the word "math"( rather than an example of the new use of "because"*.
- dinkumthinkum 13y ago
  Yeah, but it's sort of just a comical thing that is getting tired and played out... Let's be honest, it was a slow news day for the Atlantic.
  - simbolit 13y ago
    Yes, it was. But i have a degree in linguistics, so i am probably more interested in this than the general population. :-)

est 13y ago

We don't need yet another steganography tool based on texts, we need a steganography tool to scramble data into a pile a fucked up HTML DOM tree.

pretz 13y ago

Q. Why did you use Python3 as a reference language? A. Because not having distinct binary and unicode string types is barbaric. Well played.

tokenrove 13y ago

I would have liked to have seen some references to the research in the field in the explanation or comments. I wrote something like this around 15 years ago (https://github.com/tokenrove/steaghan/; https://github.com/tokenrove/steaghan/; horribly broken, do not use) but quickly abandoned it when Niels Provos started doing much more sophisticated stuff (http://www.citi.umich.edu/u/provos/stego/ http://www.citi.umich.edu/u/provos/stego/). Since then, there has been a fair bit of really interesting research in the field; I recommend anyone interested read Peter Wayner's book Disappearing Cryptography. Might be a good place to start for enhancing this provocatively named framework.

turingbook 13y ago
The first link incorrectly has ; with it.

radikalus 13y ago

It's been a long time since I've done work in infosec related things, so I apologize if I'm way behind on...things. I remember in school a million years ago we discussed an algorithm of the following type for sending short covert messages. 1. Negotiate cipher/mapping for where to look for hidden information 2. A wants to send B message "Let's get drinks @ 9 @ Bill's" -- instead of inserting this into some random file, he instead maps to the cipher/mapping area and then iteratively searches for images/texts that are closest possible matches in those bits to his message. 3. Ideally, given access to enough cover files and a short enough message, he has an EXACT match. A sends B picture of puppies with NO bit twiddling. B knows to meet at the pub.

eliteraspberrie 13y ago

Steganography has a bad reputation because the only tools publicly available are worthless. Not one is both secure according to Kerckhoffs's principle and secure against statistical analysis. I hope to change that by releasing an implementation of a new algorithm I have developed, sometime in the new year. If you are interested in reviewing the algorithm and code when it is released, feel free to follow my blog.