Is there really that much space for marking? Any substantial number of marked bits will become obvious in the output stream, no?
Is the watermarking system robust? Is it public? And how long ago has it been published?
If they are only modifying some bits (in the standard representation), then one might probably
be able to alter them. Also notice, that this may harm the quality of the image. Intuitively, one
is expected to have a low quality of image if lots of bits are used for watermarking, and a low
security if a few bits are used for watermarking.
Regarding blacklists, where are they stored? If they are included in every new DVD, then one
doesn't need to buy a new DVD but simply simulate an ID (which is not in the blacklist)
for the DVD. So this opens another place where designers may screw up. Another attack
is to attempt to delete this blacklist from the DVD.
In another respect, closed p2p communities that exchange movies through secure channels
would never get into this revocations lists. So here is another inconvenience for this DRM
scheme.
Regards and (almost) merry christmas, Ariel
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