In order to protect the copy right, CPTWG of DVD forum offers a kind of CSS to protect the content of DVD.It is possible to prevent copying by setting a key.But copy may happen on the point of signal transmission. So, , Hitachi, Intel, Panasonic, Sony, Toshiba and other companies to five digital transmission copy protection (DTCP); IBM, NEC, Hitachi, Pioneer, Sony Group and the Milky Way consisting of Macrovision, Digimarc, Philips formed the Millennium Group of video watermarking technology; IBM, Intel, Matsushita, Toshiba and other four companies to copy protection system, its content: CPSA (content protection system Association), CPRM (for the recordable media content protection), CPPM ( for the pre-recorded media content protection).
Content Scramble System (CSS) is a kind of security solution that is used to prevent copying files directly from DVD disc data with encryption and authentication program. CSS certificate has a key for each certificate, which is stored in each CSS encrypted disc which is drew from the master concentration with 400 key components. After the key is removed, the certificate shall be invalid. CSS decryption algorithm exchanges keys with the drive unit to generate the set encryption key. The generated key is used to disrupt the disc with the movie key exchange key. Video key is used to decrypt the data on the disc. The DVD player shall decrypt the data with the CSS circuit. If it is the computer, the DVD decoder hardware and software must include a CSS decryption module. All DVD-ROM drive has an extra device can exchange authentication and decryption keys with computer CSS systems. In order to use CSS, producers that made DVD video devices (drives, decoder chips, decoder software, display adapters, etc.) must certify the CSS. Verification of CSS shall be of no cost. To ensure the confidentiality of CSS algorithms and keys, the certificate is extremely stringent. Of course, so many people around the world players and drives, nothing can ever be secret. In October 1999, CSS algorithm was cracked Norwegians, and was spread on the Internet, after stop.