Remember that psuedorandom or encrypted data has a certain noise spectrum. This noise spectrum is extremely different based on what PRBS one is using...PRBS 2^23-1 looks completely different from other 'noise' (and remember noise is a relative term).
If you spatially fft a random photo, you'll find that the image detail energy largely occupies certain bands. These are not the bands that stego uses (or so I assume...it really can't be otherwise). The stego-able spectrum will indeed be noise, but this noise will have a certain spectrum.
Stego, done well, will I assume try to mimic this noise, but there may be problems. If the message is encrypted, then merely loading that message into the photo will, I assume, NOT result in a noise spectrum that looks like real noise. So you'll need some kind of chopper or spectrum-spreader I guess.
If no chopper's used, however, I'm guessing that stego-ed 'noise' doesn't look like true photo noise. If the photo has been de-stegoed stupidly (ie, by writing a random message in its place), that noise won't look like photo noise. So it seems to me that you'd need a sophisticated agent to make the de-steoed photo look like it never had stego. In other words, if the FBI are your man-in-the-middle, then you'll be able to detect that the photo was de-stegoed. If the NSA is your man-in-the-middle, you might not be able to tell.
Any of you TLA lurkers wanna come in on a remailer and set me straight?
-TD
From: "A.Melon" <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Subject: Re: Has this photo been de-stegoed? Date: Wed, 10 Dec 2003 13:28:31 -0800 (PST)
Tyler Durden ([EMAIL PROTECTED]) wrote on 2003-12-08:
> Is it possible to determine that the photo 'originally' (ie, when it was
> sent to me) contained stegoed information, but that it was intercepted in
> transit and the real message overwritten with noise or whatever?
Hardly, given the simple fact that well-encrypted content is indistinguishable from noise.
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