On 2002-10-01, Ben Laurie uttered to Peter Gutmann:
Yeah, right - and green felt-tip around the edges of your CD improves the sound, too.
I'm not sure about HDCD as a technology, but the principle is sound. If we can compress sound transparently, we can also transparently embed quite a lot of data into the part which is perceptually irrelevant. We might also depart with perceptual equivalence and go with perceptual similarity instead -- e.g. multiband compress the audio, and embed data which allows us to expand to a higher perceptual resolution. Whatever the implementation, putting data in the gap between statistical (i.e. computed against a Markov model) and perceptual (against a perceptual similarity model) entropy which compensates for some of the perceptual shortcomings (like total dynamic range) of a particular recording technology seems like an excellent idea. However, applications like these have very little to do with steganography proper. In this case, we can (and want) to fill up the entire gap between statistical and perceptual entropy estimates with useful data, leaving us with signals which have statistical entropies consistently higher than we'd expect of a typical recording with similar perceptual characteristics. That is, the encoded signal will appear manifestly random compared to typical unencoded material from a similar source, and we can easily see there is hidden communication going on. Such encodings will be of little value in the context of industrial strength steganography used for hidden communication. Steganography used in the latter sense will also have to be imperceptible, true, but but here the entropic gap we're filling is the one between the entropy estimates of our best model of the source material vs. that of the adversary's. Be the models Markov ones, perceptual, something else, or composites of the above. Consequently the margin is much thinner (bandwidths are probably at least a decade or two lower), and the aims remain completely separate. Consequently, I don't believe encodings developed for the first purpose could ever be the best ones for the latter, or that HDCD-like endeavors really have that much to do with the subject matter of this list. -- Sampo Syreeni, aka decoy - mailto:decoy@iki.fi, tel:+358-50-5756111 student/math+cs/helsinki university, http://www.iki.fi/~decoy/front openpgp: 050985C2/025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to majordomo@wasabisystems.com