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Computer Scientist Says CD Copy-protection “Worthless”

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Princeton’s John Halderman is quoted by Barry Fox in New Scientist:

    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.

    ….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.”

Halderman’s recommendation for the industry? Reduce the cost of CDs to a few dollars and people won’t bother with copying.

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