While the researchers' solutions seem to require only a lightweight PC, there is no way for them to judge the quality of the music as well as the SDMI can, said Talal Shamoon, chairman of the Perimeter Technologies Working Group of the SDMI.
"[Audio quality] needs to be evaluated empirically," he said. "If it sounds good to them, that does not form a robust hearing test." Instead, specific listeners who are pros at detecting audio degradation -- known in the industry as "golden ears" -- will judge the submissions.
Even so, the researchers did their own tests on the music and found that the quality had not degraded significantly, said Felten. "The primary test is obviously to listen to the tracks and see whether the sound quality is high enough," said Felten. "This was a bit tricky in the case of the SDMI challenge, because the original tracks SDMI provided already had a significant amount of noise on them." Each technology only appeared in one of six songs specifically made for the experiment. For reasons yet unknown, several of those songs had quite a bit of noise and "popping" as well.
"We are confident that our attacks on the four watermarking schemes can be carried out while maintaining the required level of sound quality," said Felten. "We don't know who the SDMI has hired to judge the sound quality, so we cannot comment on their qualifications. "In any case, I think 'golden-ear' tests are beside the point, because pirates would be satisfied to distribute music that sounds -- to everybody but a few highly trained experts -- just like the original."
But with just one song for each technology, there is no way to prove without a doubt that researchers actually broke the watermark technology. Instead, it is possible -- though unlikely -- that they only broke the watermark on a single song.
Further complicating matters: one of the oracles for the two non-watermark technologies apparently did not work, said Drew Dean, a computer science researcher for Xerox PARC and one of the team members.
"We were never able to get the oracle to function in a way which provided any useful information," said Dean. Rather than a reject or an accept, the oracle marked all of the music files -- even the original ones -- as invalid. SDMI's Shamoon waved off the controversy and stressed that, even if all the watermarks are broken, the technologies can still be a useful part of the secure-music future.
"Will you be able to create a watermarking-only wall that will be able to hold back the tide of piracy? No," said Shamoon. "Can you build a watermarking-enhanced technology that can interact with digital-rights management solutions and other technologies to make a robust e-commerce? Yes, I think we can do that."
Go back to Part I: SDMI copyright technology easily hacked
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