The technology built into some CDs to stop people copying them is futile, according to a computer scientist who has put today's antipiracy systems under the microscope. He believes the continual software and hardware upgrades issued by the makers of computer CD drives and audio CD players render copy protection systems pointless in the long run.

John Halderman, a computer scientist from Princeton University in New Jersey, plans to show delegates at a digital copyright conference in Washington DC next week that the idea of CD copy-prevention is "fundamentally misguided".

In 2001, Princeton University scientists debunked the technology the music industry planned to use to inaudibly watermark sound. Halderman is now doing a similar job on copy prevention systems.

Halderman looked at three widely available copy-protected CDs. He found that the three different copy protection formats they used all had one thing in common: they all index the contents of music discs using a system meant only for recording CDs on a computer's CD drive.

Table of contents

A conventional music CD has an electronic table of contents at the beginning of each disc. But a PC-recorded CD has several tables, with a new one written every time a new recording session adds something to the disc. Each of these tables points back to the previous one.

Personal computer CD drives read the last, most recent table first and work back through the series of indices - but audio CD players read only the first table.

A CD containing a copy-prevention system indexes the music correctly in the first table but then adds dummy tables containing deliberate errors. So CD players that read only the first table will play the music normally. But PC CD drives - which people use for copying - look at the last table, see garbage, get confused and play or record nothing.

Unfortunately, some audio CD players and in-car players use PC CD drives, and will not legitimately play a protected CD you have paid for. Nor can people play music CDs on their PCs.

"Simple modifications"

But all these measures can be sidestepped, says Halderman, thanks to the computer industry's habit of continual upgrading and bug fixing. Makers of CD players and CD-ROM drives only need to make "relatively simple modifications" to their software and supposedly protected CDs can be played with ease. So playback and recording equipment is becoming resistant to copy-prevention techniques.

"Software upgrades can be delivered easily using the internet," says Halderman, "and this will permanently undermine the usefulness of audio CD copy prevention." To ban upgrades, he argues, would lead to "buggy software and poor hardware."

The record industry could lose a fortune if people stop buying CDs and make their own copies. Halderman reckons he has a solution for them. "Reduce the cost of new CDs; if discs cost only a few dollars each, buying them might be preferable to spending the time and effort to make copies or find them online."