Secret Data: Steganography v Steganalysis

gManZboy writes "Two researchers in China has taken a look at the steganography vs. steganalysis arms race. Steganography (hiding data) has drawn more attention recently, as those concerned about information security have recognized that illicit use of the technique might become a threat (to companies or even states). Researchers have thus increased study of steganalysis, the detection of embedded information."

Comments

Re:Hiding data ...pfft

[Darth_brooks]

There's some truth to the idea of a hidden message in comic strips.

During the 50's and 60's the air force used a particular comic strip ("smokey stover" i think. http://www.toonopedia.com/smokey.htm, also the origin of "foo" and "foo fighter") to train recon. photo interpreters. The artist would hide his wife's name somewhere in every strip, and the new recruits would have to find it.

Re:Problem with statistical analysis

[Kjella]

There's a good story on something vaugely related that has to do with the frequency of digits in measured numbers. (That is, it isn't equally probable to see every digit -- earlier digits in a number favor lower digits, like "1".) People who were falsifying accounting records were caught because the numbers they used were "too random".

Actually, here the fault is that they didn't understood the target. Expenses have no "natural" size, they're likely to be scale invariant. Basicly, you're looking for a distribution where C*f(x) = f(x). If you took 1..9, try C=2: 2,4,6,8,10,12,14,16,18... suddenly you have 5 leading 1s.

Turns out the right distribution is following Benford's law:

30.1% 17.6% 12.5% 9.7% 7.9% 6.7% 5.8% 5.1% 4.6%

The second example you have is that the human "RNG" is flawed.

A computer doesn't really suffer from this problem. The stenagography problem is really this.

1. Find randomness in source data
2. Replace random data with pseudorandom data

Of course, if you overwrite non-random data, you're doing it wrong. If you're going to use the LSB, you need to verfiy that it is random, or find the portion of it that is random (which is kinda what you're doing when you pick the LSB from a pixel anyway).

The biggest problem is really to hide it in a "reasonable" way.

Perfect steganography should replace all randomness with noise.

Perfect compression should eliminate all randomness.

In other words, steganography operates on the thin slice between good compression (jpg, mp3, divx) and perfect compression. It's much easier to hide information in bmp, wav, uncompressed avi, but it also looks damn obvious.

Kjella