Digital Video Disk (DVD) Protection “Watermarks allow embedded signals to be extracted from audio and video content for a variety of purposes. One application is copyright control…” Ingemar J Cox, Jean-Paul M.G. Linnartz

Summary Introduction Introduction Restricted/Unrestricted Watermarking Restricted/Unrestricted Watermarking Usage of Unrestricted key watermarks for DVD copy protection Usage of Unrestricted key watermarks for DVD copy protection Intentional Attacks Intentional Attacks –Exploiting the presence of a Watermark Detector Device –Attacks based on the presence of a Watermark Inserter –Attacks by Statistical Averaging –Attacks on the Copy Control Mechanism Conclusion Conclusion

Introduction A combination of encryption and watermarking is unlikely to stop professional piracy A combination of encryption and watermarking is unlikely to stop professional piracy Video content for a DVD is scambled before being placed on a disk, but after descrambling the content is unprotected Video content for a DVD is scambled before being placed on a disk, but after descrambling the content is unprotected A DVD player checks for watermarks and prevents playback if a ‘never copy’ watermark is detected on a recordable disk A DVD player checks for watermarks and prevents playback if a ‘never copy’ watermark is detected on a recordable disk The watermark must be able to survive signal transformations and survive trivial attacks by normal users The watermark must be able to survive signal transformations and survive trivial attacks by normal users

Restricted/Unrestricted Watermarking The Key The Key –“The key itself may simply be a pseudo-random number sequence embedded in all images or might be some parameter of the original unwatermarked image, such that a different key is used for each different image” Ingemar J Cox, Jean-Paul M.G. Linnartz Unrestricted-key Unrestricted-key –The watermark key is availible to a large number of detectors Restricted-key Restricted-key –The watermark is only readable from a limited number of trusteded recievers which know the key

Usuage of Unrestricted-key watermarks for DVD copy protection The image quality of DVD’s provides a significant improvement over existing home video equipment but is a greater risk to content providers as each DVD is an exact digital reproduction The image quality of DVD’s provides a significant improvement over existing home video equipment but is a greater risk to content providers as each DVD is an exact digital reproduction The aim of copy protection is to prevent illegal copies being made, or if this fails to reduce the value of illegal copies The aim of copy protection is to prevent illegal copies being made, or if this fails to reduce the value of illegal copies Copy protection is supported in three ways Copy protection is supported in three ways –Video Content is encrypted –DVD players are equiped with an Analog Protection System (APS) –A watermark prevents copying by telling compliant devices not to copy it, it also reduces the value of illegal copies by preventing them being played on compliant devices

Exploiting the presence of a Watermark Detector Device The attacker has access to a watermark detector The attacker has access to a watermark detector The watermark detector provides information about whether an image contains a watermark The watermark detector provides information about whether an image contains a watermark The attacker can use this information to remove the watermark, or change the image so the detector doesn’t recognise the watermark The attacker can use this information to remove the watermark, or change the image so the detector doesn’t recognise the watermark

Attacks based on a Watermark Inserter The attacker has access to a watermark inserter The attacker has access to a watermark inserter The DVD copy control management information is modified The DVD copy control management information is modified The attacker has access to the material both before and after the changing of the watermark, and can use this to calculate the original The attacker has access to the material both before and after the changing of the watermark, and can use this to calculate the original

Attacks by Statisical Averaging If the watermark doesn’t depend significantly on the image an attacker may estimate the watermark, and refine his estimate over many frames If the watermark doesn’t depend significantly on the image an attacker may estimate the watermark, and refine his estimate over many frames This would enable the attacker to remove the watermark from all remaining frames with very little extra effort This would enable the attacker to remove the watermark from all remaining frames with very little extra effort

Attacks on the copy control Mechanism An attacker, rather then modifing the watermarked image, may just tamper with the copy control mechanism and modify the output of the watermark detector so it always sees a ‘no- watermark’ detection, even if the watermark is present An attacker, rather then modifing the watermarked image, may just tamper with the copy control mechanism and modify the output of the watermark detector so it always sees a ‘no- watermark’ detection, even if the watermark is present The watermark detection process of the player is only designed to detect the watermark when the image is perceptually meaningful, so distort/scramble the content, copy it, then undistort/unscramble it, and a perfect digital copy is produced The watermark detection process of the player is only designed to detect the watermark when the image is perceptually meaningful, so distort/scramble the content, copy it, then undistort/unscramble it, and a perfect digital copy is produced

Conclusion Legal, economic and technological efforts are all needed to prevent and/or deter DVD piracy. Legal, economic and technological efforts are all needed to prevent and/or deter DVD piracy. Unrestricted key watermarking is a promising technology, especially when combined with encryption, but unfortuantly one that cannot be absolutly secure. Unrestricted key watermarking is a promising technology, especially when combined with encryption, but unfortuantly one that cannot be absolutly secure.

Questions Why can Unrestricted-key watermarking never be fully secure? Why can Unrestricted-key watermarking never be fully secure? Does Watermarking for DVD’s need to be totally secure? Does Watermarking for DVD’s need to be totally secure?