Ask Ubuntu General Room

9:01 PM

Ah, that makes sense:)

P.S. After many "what the heck?" moments I got my steganography program working today... turns out I forgot to change a bitwse OR to a bitwise AND

Nathan Osman

@RobotHumans I agree.

Android Dev

Now I just need to port it to Android :)

Byte Commander

Don't forget to obfuscate the steganography

Depending on how you do it, it's pretty easy to analyze whether there is something hidden (and then to extract it).

Android Dev

@ByteCommander I was thinking that I'd just encrypt the payload

Byte Commander

Not sure, but that would probably still be visible as "something is there"

It works by analyzing the noise in the image and comparing it to what one would expect in a natural photo

I've read a few articles a year ago or so

Nathan Osman

9:05 PM

If the data is encoded with an OTP, it really doesn't matter.

Nobody will be able to retrieve the data.

Android Dev

@ByteCommander Hmmm... well I'm only manipulating the LSB... would that be enough to trigger the detection?

Byte Commander

Yep

Android Dev

@NathanOsman That's what I was thinking. They can know it's there, but they can't get at it

Nathan Osman

Exactly.

RobotHumans

I stopped aiming at the security field. Met some cool people there, but it's all so tedious. I'ld rather just write solutions to math problems or something.

Android Dev

9:07 PM

@ByteCommander How would one obfuscate it? Use a pseudo-rand generator to embed the data in random pixels instead of just iterating through the columns and rows?

Byte Commander

It has been a while...

Nathan Osman

That would still be obvious.

Byte Commander

Steganalysis

Steganalysis is the study of detecting messages hidden using steganography; this is analogous to cryptanalysis applied to cryptography. == Overview == The goal of steganalysis is to identify suspected packages, determine whether or not they have a payload encoded into them, and, if possible, recover that payload. Unlike cryptanalysis, where it is obvious that intercepted data contains a message (though that message is encrypted), steganalysis generally starts with a pile of suspect data files, but little information about which of the files, if any, contain a payload. The steganalyst is usually...

^ probably a good start

Nathan Osman

The problem is that images often have saturated white or black.

So if you're randomly changing the LSB of saturated pixels, it's going to be obvious.

RobotHumans

fractal seeds would probably be an interesting place to start. if you wanted to have an a or b answer to something.

also, undetectable. >.>

Byte Commander

9:10 PM

E.g. if the host image is a JPEG, you can find inconsistencies in the compression artifacts

Android Dev

@NathanOsman True. And it would also probably be suspicious that the image was PNG or Bitmap. The problem is it's incredibly difficult to do the LSB method on a JPEG because the compression is lossy... I think the only way to do it is to manipulate the FFT coefficients..

Byte Commander

Or if the original image is publicly available, one can simply compare.

> In particular, many simple steganographic systems simply modify the least-significant bit (LSB) of a sample;
this causes the modified samples to have not only different noise profiles than unmodified samples, but also for their LSBs to have different noise profiles than could be expected from analysis of their higher-order bits, which will still show some amount of noise. Such LSB-only modification can be detected with appropriate algorithms, in some cases detecting encoding densities as low as 1% with reasonable reliability.

Android Dev

@ByteCommander But, remember that there's a 50% chance that the target bit is already what you need it to be.

Byte Commander

Why does it say "message too long" if it is one line, but sends fine if I add a single line break somewhere? Stupid chat.

@AndroidDev Noise is not nose.

The LSBs are not equally distributed

RobotHumans

that's called javascript - destroyallsoftware.com/talks/wat

Android Dev

9:14 PM

If I really want it to be as undetectable as possible, I could just use Steghide: github.com/StefanoDeVuono/steghide

But I wanted to write my own :D