Recordable DVD discs can include CPRM copy protection to prevent further copying. All the latest versions of DVD recordable discs (except authoring type DVD-R) offer copy protection using CPRM (Content Protection for Recordable Media).
CPRM technology provides the following features:
- Cryptomeria Cipher (C2) for content encryption
- 4 layers of encryption using 56-bit keys
- Unique device key for each recording/playback device
- Media Key Block (MKB) to allow for revoking a hacked device
- Unique Media ID to prevent copying bit-for-bit.
- Mutual identification process for PC based systems, which must be performed before CPRM protected data is transferred from DVD drive to the PC.
CPRM is similar to CPPM in using a MKB. All media used with CPRM must include a BCA (Burst Cutting Area) which can be used to record a unique media ID as part of the manufacturing process. This will then prevent the data from being copied to another disc because it will not have the same unique media ID and therefore the data cannot be decrypted.
CPRM was developed by 4C (comprising IBM, Intel, MEI and Toshiba) and uses 56-bit keys and the for content encryption. It allows for a hacked playback device to be revoked using a Media Key Block (MKB). The MKB is stored as a file on the disc and contains a very large number of keys. Each licensed recorder has assigned to it a set of unique device keys that allow it to obtain the Media Key (used to encrypt the audio content) from the MKB and decrypt the audio content.