Copy protection(CP) is used to protect information from unauthorized use and disclosure. This can be text, graphic, audio and video files or software. Copy protection can be applied to the information file, but also to the storage medium. To make illegal copying of audio and video files as well as storage media impossible, there are various protection mechanisms for analog and digital information.
The copy protection also regulates the possibility of copying. Depending on the technique, no copies are possible, only a single copy or multiple copies can be made. Completely different techniques are used for copy protection: mechanical techniques, scrambling techniques, hardware components as dongles, the watermark technique, the container technique and some more.
- When it comes to copy protection of audio files, there is the Electronic Media Management System( EMMS), a method that works with watermarks. Another, the Audiosoft File Structure( ASFS), packages MP3 files in a container.
- Copy protection for video files uses, among other things, the scrambling technique, which causes changes in the video image. When transferring video files to other media, this causes interference that makes viewing impossible. Another technique relies on watermarks that are inserted in the blanking interval of the video signal.
- There are several copy protection methods for DVDs: Analog Protection System( APS), Analog Copy Protection System( ACPS), Content Protection for Prerecorded Media ( CPPM), Content Protection for Recordable Media ( CPRM), Content Scrambling System ( CSS), Digital Copy Protection System( DCPS), Copy Generation Management System ( CGMS), Advanced Access Content System ( AACS) and the watermarked technique. In addition, there are techniques such as High-Bandwidth Digital Content Protection( HDCP) with which the data transmission between a graphics card or a Blu-Ray player and a display are encrypted and thus copy-protected. HD-DVD uses copy protection called Interactive High Definition( iHD), which allows the user to make a protected copy.
- With floppy disks and video cassettes, there is mechanical copy protection. For 3.5" floppy disks, it is a small slider that provides write protection when in the open position; for 5" disks, it is the notch on the side that must be closed; and for video cassettes, it is the plastic notch on the back side of the cassette.
- For copy protection on the interface level, there is Digital Transmission Copy Protection( DTCP), a copy protection for Firewire resp. for the IEEE 1394 interface. And for the DVI interface, Intel and Silicon Image have developed High-Bandwidth Digital Content Protection (HDCP), which can also be used with VHS recorders, set-top boxes and DVD players.
- Documents and ID cards with barcodes that must not be duplicated without permission often include copy protection to prevent unauthorized copying of the data. As copy protection, a foil is glued to the barcode that is transparent to infrared light. The foil has a filter function with a wavelength of 900 nm. The bar code readers used for these applications work with a wavelength of >900 nm.