A Study on Watermark Content Protection System in Information Storage Devices

• Main Authors: Guo-Zua Wu, 吳國瑞
• Other Authors: Wen-Hsing Hsu
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/39028637345583251315

博士 === 國立清華大學 === 電機工程學系 === 92 === More recently, the application of digital data storage devices and medias expands from the computer platforms to the CE (consumer electronics) platforms. A lot of audio/video titles were transmitted via the digital storage medias. Digital medias become the main vehicles to transmit multi-media information for studio industry. However, the advantages of digital multimedia come at the prices of increased risk of illegal copying. Because of illegal reproduction, the piracy issues strongly damage the content industry. Developing a secure content protection system for next generation digital multimedia devices is a very important issue of Hollywood studio industries today. Currently, some digital storage devices, such as DVD and SD memory card, use a variety of encryption/decryption methods compounded with the physical format of storage media to record the key data to prevent illegal digital to digital copy. However, encryption alone could not provide an overall solutions. Once the content is decrypted, it is no longer protected, because the content should be transmitted to users via analog input/output interface, e.g. NTSC, PAL and RGB ports. The pirates can copy the content by capturing the data in the interfaces. Besides, it is possible that the key management system for handling the secure media key may be broken. Once the secure disc key is not secure, the content protection system could not work. There are two ways to enhance the robustness of the conventional content protection system. The first method is to build a watermark playback/recording control system in the playback/recording devices, the playback devices should recognize the legal watermark of the content before sending out the content via the display interfaces and embed suitable CCI (Copy Control Information) information into the displayed contents. The recording devices should recognize the CCI information before recording the content into the storage media and embed suitable watermarks for the playback control function to be executed in the legal player. The second method is to provide a flexible key management mechanism for the digital content protection system to reduce the danger of being broken. In order to provide the solution for the aforementioned methods, this study investigates three important issues to fit the requirements. They include developing a robust image watermarking system to resist JPEG compression, designing a video watermarking system to resist the compression attacks of high compression ratio in H.264 video and proposing a new optical disk format to support the function of limited playback times. The achievements are summarized as follows: a) This study designs a new image watermark embedding/detection system based on sub-band image shift in spatial domain. Since sub-band image shift in space domain can induce large amounts of DCT coefficient changes without artifacts, the proposed method can modulate watermark information into low frequency DCT coefficients with strong embedding strength. The embedded information can survive JPEG compression attacks with more than 13:1 compression ratio. Also, the watermarked images can resist filter attacks with serious quality degradation. b) A public video watermarking system designed based on the coding unit of H.264 compression standard is implemented. Proposed method comprises a picture quality control mechanism to control the embedding location of frequency components. The PSNR values of watermarked pictures can reserve more than 40 dB by the embedding strength 36. The embedded watermark can survive H.264 compression attack with more than 40:1 compression ratio in I pictures and 120:1 compression ratio in video sequence. Also, they can resist various attacks , such as noise attacks and cropping attacks. c) A new optical disk format comprising both read-only and recordable medias in single disc was proposed. The read-only media was used to record scrambled audio/video data. The scrambled audio/video data recorded on read-only media can be de-scrambled by using the key data recorded on the recordable media. However, the life of the recordable media is limited by the light exposure to reading laser. Controlling the power of reading laser can limit the life the disks. Furthermore, the new format provides the flexibility to get the key data from the data sources outside the discs, such as card reader or inter-net. This new format provides the possibility to create new business models for the studio industries. With the aforementioned studies, we already build up the basic technology to constitute a secure content protection system for next generation digital storage devices.