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DissidentX – Censorship resistance tool by Bram Cohen

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Re: DissidentX – Censorship resistance tool by Bram Cohen

#61

Post by tokenrove »

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/; 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/).

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.

Re: DissidentX – Censorship resistance tool by Bram Cohen

#62

Post by sillysaurus2 »

infinity0 wrote: post #58
sillysaurus2 wrote: post #57

Earlier quoted context omitted.

Every time someone iterates and releases the code on github, law enforcement will then be capable of writing a DissidentX encoding detector for that encoder. Every time you publicly release stego code, that stego code becomes ineffective. At best, this framework provides a way for people to write stego encoders that they don't plan on releasing publicly. But you should say that! Warn people how dangerous it is to be…

Can you elaborate? I don't see why this must be true. Just as good encryption is indistinguishable from random data, good steganography should be indistinguishable from whatever universe of target plaintexts you've chosen. In both cases, the code is public, but the secret key is needed to see that the message is non-random, or non-plaintext. I am interested in how this scheme is different from https://fteproxy.org/ t…

Here's one way it might go down in practice. After law enforcement seizes your computer, they'll scan your computer for any encrypted containers, along with any code that looks like it's used for steganography. They'll find DissidentX, since its README mentions "steganography," which is a keyword that their forensics tools will search for. Then they'll use each encoder in your DissidentX folder to scan your computer for any encoded messages. Unless the message is trivially short (Check out http://www.cl.cam.ac.uk/~rja14/Papers/jsac98-limsteg.pdf and related literature. In particular this quote:

Shannon provided us with a proof that such systems are secure regardless of the computational power of the opponent [43]. [...] Yet we still have no comparable theory of steganography.

The problem is that there's no such thing as perfectly secure stego (undetectable covert messages), even though there is perfectly secure encryption (unbreakable encrypted messages, regardless of the computational power of the adversary, when implemented correctly, and when not defeated via side channel attacks, and when not compelled to cooperate by a judge).

Re: DissidentX – Censorship resistance tool by Bram Cohen

#63

Post by chongli »

rosser wrote: post #56
chongli wrote: post #53

Earlier quoted context omitted.

The question is: would it be feasible to search for them? Scan every single video on youtube looking for noise with some elevated probability of containing hidden text? What happens when you find a candidate? Pick random pixels out of every frame and then try and brute force it with every known symmetric cipher and every single key? You could flip a single, random, least-significant bit on each frame of a 1 hour movi…

Depends on your use case and threat model. If I'm the Secret Police in some oppressive state, then I just need to find out whether you seem to be using stego — which is naturally against the law, itself, and hence grounds for arrest. Then, I can use rubber hoses, bamboo splinters, the threat of violence against your loved ones, and what-not to "brute force" your passphrase. If I'm the NSA, I just detect the presence…

If I'm the Secret Police in some oppressive state, then I just need to find out whether you seem to be using stego — which is naturally against the law, itself, and hence grounds for arrest. Then, I can use rubber hoses, bamboo splinters, the threat of violence against your loved ones, and what-not to "brute force" your passphrase.

Me? I'm the entire population of the country. Which one of us is using stego?

To my reckoning, the search space would put the number of atoms in the universe to shame.

Re: DissidentX – Censorship resistance tool by Bram Cohen

#64

Post by nate_meurer »

sillysaurus2 wrote: post #62
infinity0 wrote: post #58

Earlier quoted context omitted.

Can you elaborate? I don't see why this must be true. Just as good encryption is indistinguishable from random data, good steganography should be indistinguishable from whatever universe of target plaintexts you've chosen. In both cases, the code is public, but the secret key is needed to see that the message is non-random, or non-plaintext. I am interested in how this scheme is different from https://fteproxy.org/ t…

Here's one way it might go down in practice. After law enforcement seizes your computer, they'll scan your computer for any encrypted containers, along with any code that looks like it's used for steganography. They'll find DissidentX, since its README mentions "steganography," which is a keyword that their forensics tools will search for. Then they'll use each encoder in your DissidentX folder to scan your computer…

I'm terribly confused by your argument. Who's talking about equipment seizure here? What does that have to do with the on-the-wire security of the encoded messages?

Your argument appears to concern only the risk in openly publishing encoders. Are you also arguing that Bram's framework encourages such publishing? If not, then what exactly is your beef with it (the framework)?

Re: DissidentX – Censorship resistance tool by Bram Cohen

#65

Post by infinity0 »

sillysaurus2 wrote: post #62
infinity0 wrote: post #58

Earlier quoted context omitted.

Can you elaborate? I don't see why this must be true. Just as good encryption is indistinguishable from random data, good steganography should be indistinguishable from whatever universe of target plaintexts you've chosen. In both cases, the code is public, but the secret key is needed to see that the message is non-random, or non-plaintext. I am interested in how this scheme is different from https://fteproxy.org/ t…

Here's one way it might go down in practice. After law enforcement seizes your computer, they'll scan your computer for any encrypted containers, along with any code that looks like it's used for steganography. They'll find DissidentX, since its README mentions "steganography," which is a keyword that their forensics tools will search for. Then they'll use each encoder in your DissidentX folder to scan your computer…

I just read it, and you are completely extrapolating what that paper says. It does not say steganography is hopeless. It contains no mathematical proofs, and it's also from over 15 years ago.

More generally, "we do not have a proof" does not mean "we disprove". You also completely ignored my point about the secret, without which the encoder will not work when an attacker tries to run it.

Re: DissidentX – Censorship resistance tool by Bram Cohen

#66

Post by rosser »

chongli wrote: post #63
rosser wrote: post #56

Earlier quoted context omitted.

Depends on your use case and threat model. If I'm the Secret Police in some oppressive state, then I just need to find out whether you seem to be using stego — which is naturally against the law, itself, and hence grounds for arrest. Then, I can use rubber hoses, bamboo splinters, the threat of violence against your loved ones, and what-not to "brute force" your passphrase. If I'm the NSA, I just detect the presence…

If I'm the Secret Police in some oppressive state, then I just need to find out whether you seem to be using stego — which is naturally against the law, itself, and hence grounds for arrest. Then, I can use rubber hoses, bamboo splinters, the threat of violence against your loved ones, and what-not to "brute force" your passphrase. Me? I'm the entire population of the country. Which one of us is using stego? To my re…

Maybe start with the guy who uploaded the video to YouTube?

Re: DissidentX – Censorship resistance tool by Bram Cohen

#67

Post by anon4 »

sillysaurus2 wrote: post #62
infinity0 wrote: post #58

Earlier quoted context omitted.

Can you elaborate? I don't see why this must be true. Just as good encryption is indistinguishable from random data, good steganography should be indistinguishable from whatever universe of target plaintexts you've chosen. In both cases, the code is public, but the secret key is needed to see that the message is non-random, or non-plaintext. I am interested in how this scheme is different from https://fteproxy.org/ t…

Here's one way it might go down in practice. After law enforcement seizes your computer, they'll scan your computer for any encrypted containers, along with any code that looks like it's used for steganography. They'll find DissidentX, since its README mentions "steganography," which is a keyword that their forensics tools will search for. Then they'll use each encoder in your DissidentX folder to scan your computer…

So can't you just embed messages in every file you own? Then when asked for the keys, give out fake keys for the really really secret stuff. So law enforcement ends up with a few sensitive documents and a whole bunch of random bytes where you cannot distinguish between "actual random bytes" and "bytes decoded with the wrong key". And there is your plausible deniability.

Obviously it's not perfect. Obviously a totalitarian regime which suspects you of dissident activity will pick any reason out of thin air to lock you up for as long as they like, or just execute you.

But being able to say "here's the keys" with them having no way to know if they are all the right keys, is at least something.

Though of course at best you won't keep those files on your PC in the first place. You'd keep them on a microSD card that you keep in a tiny pouch under your skin. You'd keep them encoded in photos you have printed out and hung as wall pictures. You'd have them embedded in a well-torrented movie and backed up willingly by hundreds of thousands people (though not you). And if you just use them to send encoded messages, neither you nor the recipient will ever store them on an hdd.

I mean, you're not stupid, right?

Re: DissidentX – Censorship resistance tool by Bram Cohen

#68

Post by wrongc0ntinent »

yid wrote: post #48
stuartcw wrote: post #14

Here's another fun steganographic tool: 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 w…

That is actually remarkably clever. Spam would indeed seem to be an excellent vector for sending hidden messages!

What in this makes it get past spam filters?

Re: DissidentX – Censorship resistance tool by Bram Cohen

#69

Post by zzzeek »

sillysaurus2 wrote: post #59
infinity0 wrote: post #55

Earlier quoted context omitted.

From the README: Q. Can someone detect that a file has messages encoded in it? A. That depends on the encoding used and the properties of the file the data is being encoded in. There's a whole field of academic literature on steganography, none of which is invalidated by this code. What this code does is vastly simplify the implementation of new steganographic techniques, and allow a universal decoder and encoding of…

The README should read: Q. Can someone detect that a file has messages encoded in it? A. If the file was generated with an encoder whose code is public (i.e. Github, bitbucket, ...) then yes. Always. And even if the code is private, it may not be secure. Unless you come up with an encoding scheme that's never been thought of before, then law enforcement will likely be able to detect the encoded messages unless they'r…

random peanut gallery thought....mentioning "law enforcement" in the README itself might open up the tool itself to legal attacks, no ?

Re: DissidentX – Censorship resistance tool by Bram Cohen

#70

Post by turingbook »

tokenrove wrote: post #61

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/ ; 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/ ). Since then, there has been a fair bit of really interesti…

The first link incorrectly has ; with it.
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