DVD-Audio - Copy Protection

Copy Protection

DVD-Audio discs may optionally employ a copy protection mechanism called Content Protection for Prerecorded Media (CPPM). CPPM, managed by the 4C Entity, was designed to prevent users from extracting audio to computers and portable media players.

Because DVD-Video's content-scrambling system (CSS) was quickly broken, DVD-Audio's developers sought a better method of blocking unauthorized duplications. They developed CPPM, which uses a media key block (MKB) to authenticate DVD-Audio players. In order to decrypt the audio, players must obtain a media key from the MKB, which also is encrypted. The player must use its own unique key to decrypt the MKB. If a DVD-Audio player's decryption key is compromised, that key can be rendered useless for decrypting future DVD-Audio discs. DVD-Audio discs can also utilize digital watermarking technology developed by the Verance Corporation, typically embedded into the audio once every thirty seconds. If a DVD-Audio player encounters a watermark on a disc without a valid MKB, it will halt playback. The 4C Entity also developed a similar specification, Content Protection for Recordable Media (CPRM), which is used on Secure Digital cards.

DVD-Audio's copy protection was overcome in 2005 by tools which allow data to be decrypted or converted to 6 channel .WAV files without going through lossy digital-to-analog conversion. Previously that conversion had required expensive equipment to retain all six channels of audio rather than having it downmixed to stereo. In the digital method, the decryption is done by a commercial software player which has been patched to allow access to the unprotected audio.

In 2007 the encryption scheme was overcome with a tool called dvdcpxm. In 12 February 2008 a program called DVD-Audio Explorer was released, containing aforementioned libdvdcpxm coupled with an open source MLP decoder.

Like DVD-Video decryption, such tools may be illegal to use in the United States under the controversial Digital Millennium Copyright Act. While the Recording Industry Association of America has been successful in keeping these tools off websites, they are still distributed on P2P file sharing networks and newsgroups, Additionally, in 2007 the widely-used commercial software DVDFab Platinum added DVD-Audio decryption, allowing users to back up a full DVD-A image to ISO.