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Security quote of the weekSecurity quote of the weekPosted Apr 18, 2012 21:44 UTC (Wed) by khim (subscriber, #9252)In reply to: Security quote of the week by nybble41 Parent article: Security quote of the week
> I think you don't get the full implications of the fact that we are talking about lossy compression here, not about lossless one. Ah, finally got your idea. Ok, if you'll invent some compression scheme which compresses sound just enough to make sure not a single human can distinguish it from the original in minimum possible set of bits then it can be used to strip the watermark. This is great plan. The only problem: it's impossible to implement it if you don't have a detailed information about all future listeners and about all states of all these future listeners. You can as well invent something more realistic. perpetual motion machine (2nd kind if you know what I'm talking about), for example. Any realistic compression scheme leaves tons of information which can be perceived by some theoretically possible human, but is not perceived by any real human on real planet Earth (because there are insane number of possible combinations of receptors and less then seven billions of human beings). This is where you theory falls apart. I was under impression that we are talking about real music, real watermarks and real compression. If you want to discuss how many angels you'll need to remove the watermarks then it's separate issue - and I'm not sure I want to participate in such theological discussions.
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Security quote of the week Posted Apr 18, 2012 22:18 UTC (Wed) by nybble41 (subscriber, #55106) [Link]
> ... it's impossible to implement it if you don't have a detailed information about all future listeners and about all states of all these future listeners.
> Any realistic compression scheme leaves tons of information which can be perceived by some theoretically possible human, but is not perceived by any real human on real planet Earth...
The watermark scheme is under the same constraints. Sure, for any given listener and state there is quite a bit of redundant information left over. However, that information is needed for other listeners and other states, so it can't be used for watermarking.
A perfect compression scheme would make watermarking impossible. However, short of that, a _good_ compression scheme will still make watermarking _very difficult_. Moreover, knowing how to make a watermark which survives compression immediately tells us how to make a better compression codec which would remove the watermark. After all, any bits which can be changed to watermark the file without diminishing quality can just as easily be removed during compression without diminishing quality.
Security quote of the week Posted Apr 18, 2012 22:48 UTC (Wed) by khim (subscriber, #9252) [Link] Moreover, knowing how to make a watermark which survives compression immediately tells us how to make a better compression codec which would remove the watermark. In theory, but not in practice. In practice you can only have sample of some files with watermerks, you don't have a machine which applies these watermarks. Thus now we are very-very firmly in “how many angels can dance on the head of a pin” territory. Watermarks add negligible overhead thus practical advantage in using this information for compression purposes is minuscule. We are talking not about compression at this point but about “watermarking removal” procedure. And like with real watermarks and real banknotes it becomes cat and mouse game. As history shows this game can only be won for a short periods of time: sure you may counterfeit old banknotes (and you'll probably be able to remove old watermarks from sound records), but people on the other side will introduce newer and newer schemes.
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