Researchers Calculate Capacity of a Steganographic Channel

KentuckyFC writes "Steganography is the art of hiding a message in such a way that only the sender and receiver realize it is there. (By contrast, cryptography disguises the content of a message but makes no attempt to hide it.) The central problem for steganographers is how much data can be hidden without being detected. But the complexity of this problem has meant it has been largely ignored. Now two computer scientists (one working for Google) have made a major theoretical breakthrough by tackling the problem in the same way that the electrical engineer Claude Shannon calculated the capacity of an ordinary communications channel in the 1940s. In Shannon's theory, a transmission is considered successful if the decoder properly determines which message the encoder has sent. In the stego-channel, a transmission is successful if the decoder properly determines the sent message without anybody else detecting its presence (abstract). Studying a stego-channel in this way leads to some counter-intuitive results: for example, in certain circumstances, doubling the number of algorithms looking for hidden data can increase the capacity of the steganographic channel"

Were's Waldo's message?

[Ostracus]

"Steganography is the art of hiding a message in such a way that only the sender and receiver realize it is there. (By contrast, cryptography disguises the content of a message but makes no attempt to hide it.) "

There's a secret message in this post. Can anyone find it?

Re:Stenography FTW

[zindorsky]

I've always had a warm spot for stenography

...

But how did we communicate our plans and schemes to actually be present at "hotspots" when the shit really went down? Stenography.

...

Of course it's possible to break that kind of thing, but the point of stenography

So you hid your messages with stenography? The action of process of writing in shorthand or taking dictation? This word you keep using ... I do not think it means what you think it means.

Sorry try again

[shadow_slicer]

That's not steganography. That's encryption, and a crappy one at that. If you take your PGP file (and remove any unnecessary header stuff), it will also look like a corrupt file, just like your UUencoded image. Steganography is hiding some data inside something else, like hiding a message in an image. For example, the police see an image of kittens, but you hid your child porn in the LSBs of the image, they can't see it.

Re:Need for steganography

[DingerX]

Don't disrespect it. In fact, steganography has had many many uses over the years. Naming just one case, steganography is the ultima ratio of intellectual property protection. Gulliver's Travels, for example, was published pseudonymously and "signed" steganographically. Even better, it was signed at least two ways, one using a "Soft" method, the other a "Hard" one. Right on the first page, Gulliver states: "Soon after my return from Leyden, I was recommended by my good master, Mr. Bates, to be surgeon to the Swallow." Evidently, Swallow is a synonym for "Swift", and the onanistic gag is thrown in for good measure. That's the one you're supposed to catch. Really fun, however, is the incipit: "My father had a small estate in Nottinghamshire: I was the third of five sons."

I was the third of five sons: Cross out the third and fifth words, and the first letters of the remaining words form an anagram for "swift".

Numerous other cases abound. I'm sure many of us have little coding tricks in which we "sign" our names. A watermark on a jpeg is nice, but it's even nicer if the guy who's going to swipe your images doesn't even know they're signed.

Sometimes it helps to publish something anonymously; at other times, you might have a legitimate worry about your work being appropriated. In those cases, steganography has always been a savior.