What is Content Protection for Recordable Media (CPRM)?

CPRM is a mechanism tied to recording media. Only some DVD recorders support it, but not many DVD players. Each blank recordable DVD has a unique 64-bit media ID etched in the BCA. When the protected content is recorded onto the disc, it can be encrypted with a 56-bit C2 (Cryptomeria) cipher derived from the media ID. In the play process, the ID is read from the BCA and used to generate the decryption key content in the disc. If the content on the disc is to be copied to other media, the ID will be absent or wrong, and the data cannot be decrypted.