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Subject: Re: hacksdmi?
From: aliver vilereal (willeyBLUE.NET)
Date: Thu Oct 12 2000 - 09:50:33 CDT

From: "Ralph Moonen" <ralphTINK.ORG>

-------------------------
> This is not true per se. Might be true for *this* algo, but the guys 'n
> galls at the Fraunhofer institute have figured a way to put in digital
> watermarks that:
> -survives heavy compression
> -survives many sequences of D/A - A/D conversion
> -survives all kinds of effects(!!)
> -survives even in short samples of the music
>
--------------------------

But the fact remains that these watermarks are nothing more than a
representation of bytes, which can be manipulated. The only dependecy from
a strong algorithm is the amount of time and processing power that is used
to crack it. And with distributed computing in the style of SETIHOME the
processing power it takes can easily be spread out. (Which brings up an
interesting point, why doesn't the EFF support a distributed cracking
routine if some form of watermarked music comes out?) But eventully the
watermark will be broken, and when it is, it is only a matter of piecing it
back together to find the key to cracking it. This is true no matter what
algroithm is used to mark it, even the very complex one listed below (from
Ralph's post).

And here is a question for the list:
If the watermark is hidden in the least significant bits, a program could
set all these bits to zero and this should effectively disable the
watermark, because I am guessing that to compute the watermark an _exact_
match must be made with the output of some decoding algorithm. If the
watermark is all NIL, there is no way that this could possibly match the
watermark. Would this have been an effective method to win the HACKSDMI
challenge, are were they looking for an exact replica of the original, even
though the new one with NIL bits has no audible difference?

aliver vilereal

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>It is done by analysing the spectrum and adding or subtracting
>from the lesser (i.e. odd) harmonics. Since these harmonics will
> retain their relative strengths through most processing (compression,
> effects, d/a- a/d etc) the watermark stays intact. By tweaking the
> exact algo dynamically depending on the actual music, it can be
> made inaudible, and even when analysed, practically undetectable.
>
> Scary uh?
>
> > BB:
> > Yes, this is copy protection, and we know
> >that can't be made to work.
>
> Well, all they really want to do is make it cumbersome, so as to
> deter the script kiddies of piracy, so to say.
>
> --Ralph
>
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