Cracked the case? Computer scientist Ed Felten and his team took up SDMI's challenge.

Digital Music Safeguard May Need Retuning

A hacker-professor says he and his graduate students have cracked the four leading methods proposed for thwarting audio pirates. The achievement shows that so-called digital watermarks--identifying signals hidden inside streams of data--cannot protect music from illegal copying, they claim. Music industry representatives disagree.

A consortium of music, technology, and electronics companies called the Secure Digital Music Initiative (SDMI) has been searching for the best scheme for protecting audio files. A digital watermark might be used to prevent a file from being copied more than once, or at all--a strategy that would only work if audio players are constructed to obey the hidden message. But such instructions would be moot if hackers could wash off the watermark at will.

In September, SDMI posted four proposed watermarking schemes on one of its Web sites. An accompanying letter offered $10,000 to anyone who could hack any of the security schemes within 3 weeks. Last week, computer scientist Ed Felten and grad students at Princeton University announced that they had. "Basically, for each of the technologies, we figured out where in the signal each watermark was put and then washed it out," Felten says. "For instance, if it's all stored in a narrow frequency band, you can add a bit of noise in that frequency band."

SDMI isn't convinced that the team cracked the watermarking schemes. SDMI officials say that the Princeton team did not submit technical information showing that it had devised a general strategy for defeating watermarks. But other experts see Felten's attack as a confirmation that copy-protection schemes can be cracked. "Digital bits can be copied; it's the natural way, and any procedure that tries to go against the tide will fail," says Bruce Schneier, chief technology officer of Counterpane Internet Security in San Jose, California. "Accept the inevitable, and figure out how to make money anyway."

Related sites

SDMI's challenge to crack its watermark schemes

The Felten team announcement