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Lumifer comments on A pair of free information security tools I wrote - Less Wrong
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That's pretty useless -- what you want is to look at some statistical measures of the empirical distributions of lower-order bits in these images. See e.g. this outdated page.
I don't blame you for not spotting this, since these comments have gone really all over the place. But I did describe how an attacker would use LSB or Chi^2 analysis to determine:
For posterity here is that section: "Incidentally, regarding the specific details of such a detection method:
We (and the attacker) already know that the distribution of base64 characters in an AES-encrypted ciphertext is approximately random and follows no discernible pattern. We also know that the ciphertext is encoded into the last 2 bits of each 8-bit pixel. So, we can, with X amount of confidence, show that an image is not a Decoy if we extract the last 2 bits of each pixel and discover the resulting data is non-randomly distributed.
However, because it is possible for normal, non-Decoy, compressed JPEGs to exhibit a random distribution of the data in the last 2 bits of each pixel, the presence of randomness does not confirm that an image is a Decoy.
The only viable attack here would be to pull images which are "visually similar" (a trivial task by simply using Google image search), reduce them to the same size, compress them heavily, and then examine the last 2 bits of each of their pixels. If there is a significant difference in the randomness of the control images vs. the randomness of the suspected image, you could then suggest with X% confidence that the suspected image has been tampered with.
However, because it is possible for an image to be tampered with and yet NOT be a Decoy image, even then you could still not, with any legitimate amount of confidence, use such a test to state that an image is a Decoy."
The point you're missing is that the purpose of steganography is not to be noticed as opposed to "you can't prove this beyond reasonable doubt". If I run statistical analysis on the images in your phone and enough of them show suspicious randomness in LSBs, your steganography has failed already.
I've already said this like, five times, but I am giving you a pass here because there are a billion comments on this post and I wouldn't expect someone to read all of them.
So, I just don't get it. What is your point here? That steganography has potential weaknesses? Is anyone suggesting otherwise?
Also just for the record, here are the relevant statements I made personally about Decoy:
Which, by request I clarified:
These clarifications were provided very early on in the conversation. It has since devolved into a criticism of steganography in general, which at no point have I ever tried to insinuate that steganography is anything other than security through obscurity.
Protection against what? Your lack of the threat model is tripping you up. If all you want is protection against a Fappening, you don't need steganography, just encrypt images to binary blobs and you're done.
Why steal? Imagine a scenario: you're drove to Canada from the US for a weekend and when you're returning, a polite TSA officer asks for your phone and plugs it into a gizmo. The gizmo displays some blinkenlights, beeps, and the polite officer tells you that your phone is likely to have hidden encrypted information and would you mind stepping inside that office to have a conversation about it?
Encrypting your images has obvious benefits, but what exactly do you gain by keeping them inside other images as opposed to random binary files?
I specifically outlined the three primary attack types: fusking, stolen-phone, targeted attacks.
In that scenario, I would hope the "beyond a reasonable doubt" standard would apply (which this protocol passes). But if we're assuming an evil government that doesn't stick to that standard, the same hypothetical gizmo can be used to detect any encrypted data.
Convenience, a deterrent against attacks, and moderate protection.
No need for hope here. "Beyond a reasonable doubt" is a legal standard that applies to evidence presented in criminal prosecutions. It does not apply to investigations or, for example, things like being put on the no-fly list. Or the "next target for the drone assassination" list.
Moreover, at a border crossing the Fourth Amendment basically does not apply, too. A border control official can search all your belongings including your electronic devices without needing to show any cause, never mind about "reasonable doubt". At the border, TSA can trawl through your laptop or phone at will.
Relevant quote: "[I]f we're assuming an evil government that doesn't stick to that standard, the same hypothetical gizmo can be used to detect any encrypted data."