摘要：I..Introduction Consumers and consumer electronics are increasingly using the Internet for distribution of multimedia content, including digital versions of books, articles, music, video, games, software and images. The ease with which multimedia contents can be copied and redistributed makes the Internet well suited for unauthorized copying, modification and redistribution. The rapid adoption of new technologies such as high-bandwidth connections, wireless networks, and peer-to-peer networks is accelerating this process. Digital Rights Management (DRM) techniques and systems are intended to protect the rights of content owners in scenarios in which the participants often have conflicting goals and interests. This adversarial situation introduces interesting new twists on classical problems studied in cryptology and security research, such as key management and access control. Multimedia content's properties, such as large volumes, real-time transmission and interactive consuming, brings new requirements to DRM techniques. Furthermore, novel security mechanisms and innovative designs can enable new business models and applications. Till now, several workshops related to these topics have been held. However, few special issues on journals have been organized. This special issue aims to expose the readership to the latest research results on Digital Rights Management. It is composed of 8 papers selected from best papers recommended by international workshops, covering the research topics of security policies in DRM, security scheme for art protection, digital watermarking for ownership protection, steganography and steganalysis, video encryption, and secure media content distribution. II. The papers in this special issue The first paper, "Security in Collaborative Multimedia Web-based Art Projects" by D. Koukopoulos and G. Styliaras, proposes a three-level approach for handling security issues in web-based collaboration among artists, audience, curators and publishers. The three approaches include authorization, digital certification and watermarking. Among them, authorization mechanism controls users operations in multimedia files based on a set of actions imposed on real-life scenarios. Digital certification mechanism ensures the secure content transfers among users and multimedia content server through Web. Digital watermarking mechanism handles copyright-protection and authentication issues that appear in multimedia systems applying a semantically secure watermark. It is a typical example for digital rights management, and will provide valuable information to researchers or engineers working in this field. In the second paper, "Utility-Analytic Approach and Swarm Simulations of Security Policies in Digital Rights Management" by Z. Zhang et al., the multiparticipant trust in DRM ecosystem is investigated. Firstly, a utility-analytic and non-cooperative game approach is proposed to adopt cost-effective security policies for stakeholders. Then, a series of swarm-based simulation experiments were done in different scenarios, i.e., content acquisition and content sharing, in order to analyze the effect of typical security policies. The simulation results inform that the enhanced security policies combination is not necessarily rational under any circumstance. This work is interesting to drive some potential works on security policies in DRM. The third paper, "Image Watermarking Scheme with Unequal Protection Capability Based on Error Correcting Codes" by C. Qin et al., proposes an image watermarking scheme capable of providing unequal protection levels to different regions in an image. Firstly, the unequal error protection (UEP) code is constructed by designing an unequal coding space using algebra means. Then, the image is divided into high protection region, low protection region and non-protection region. And, the UEP code is used to encode the bits generated by high and low protection regions simultaneously and form the watermark bits to embed in the non-protection region. The unequal protection means that, on the receiver side, the extracted bits with UEP capability can restore the high protection region more correctly than the low protection region after the efficient decoding algorithm is applied. It is an interesting work on watermarking based image authentication and communication. In the fourth paper, "Geometric Invariant Digital Image Watermarking Scheme Based on Histogram in DWT Domain" by C. Pun and X. Yuan, a geometric invariant digital watermarking scheme for gray-level images is proposed. In watermark embedding, the image is decomposed into approximation and details, of which, the approximation's block histogram is used for watermark embedding. In watermark extraction, the pixels in the approximation sub-band are grouped into blocks in the similar manner, and according to the histogram distribution in each block, the watermark is extracted. Some experimental results are given to show that the proposed scheme is robust against some operations, e.g., JPEG compression, geometric attacks and some common signal processing, and it outperforms some of existing methods. It is interesting work on robust watermarking for copyright protection. The fifth paper, "Watermarking for Multimedia Security Using Complex Wavelets" by A. Thompson et al., complex wavelet transforms to applied to digital data hiding. Two methods of deriving visual models for the watermarking system are adapted to the complex wavelet transforms and their performances are compared. To produce improved capacity, a spread transform based embedding algorithm is devised. Comparative results show its performance improvement offered by complex wavelet transforms. It benefit from that complex wavelets offer improved directional selectivity and shift invariance over their discretely sampled counterparts allowing for better adaptation of watermark distortions to the host media. This works provide valuable information for designing watermarking algorithms based on complex wavelet transforms. In the sixth paper, "Improved LSB-matching steganography for preserving statistics" by G. Liu et al., two improved LSB-matching methods are proposed to enhancing the security of the traditional LSB matching. In the embedding process, the second-order statistics, i.e., the Markov Chain distance is chosen as the important metric to control the modification directions in LSB-matching embedding. The first method is LSB matching based on stochastic modification, and the second one is LSB matching based on genetic algorithm. Experimental results show that the proposed algorithms are more secure than the traditional LSB matching. The seventh paper, "An Improved Selective Encryption for H.264 Video Based on Intra Prediction Mode Scrambling" by J. Jiang et al., improves an existing video encryption scheme. Firstly, the existing encryption algorithms are first analyzed with respect to the perception performance, plaintext scrambling space and key security. Then, an encryption algorithm is proposed by taking into account key distribution and synchronization, which obtains the improved encryption effect. Comparative experiments are done, which show that the proposed algorithm gets higher security while less impact on the code length and frame rate. In addition, the computational complexity is reduced and makes it more suitable for real-time video applications. In the eighth paper, "On the DCT Based Joint Fingerprint Embedding and Decryption Scheme" by X. Chen and S. Lian, the secure media distribution scheme based on Joint Fingerprinting and Decryption (JFD) is analyzed and improved. The considered performance includes the compliance with general compression codecs, the security against cryptographic attacks, the security in perception, the relationship between security and robustness, and the relationship between security and imperceptibility. Based on the analysis, some means are proposed to improve the scheme, i.e., the encryption in block based DCT, the multi-key encryption, the DC encryption, etc. These analysis methods can also be used to evaluate some other JFD schemes, and are expected to provide valuable information to design JFD schemes. Acknowledgments The guest editors wish to thank Dr. Jiebo Luo for providing the opportunity to edit this special issue on Digital Rights Management for Multimedia Content, and Dr. George Sun for providing latest publishing information and making this issue published. We would also like to thank the authors for submitting their works as well as the referees who have critically evaluated the papers within the short stipulated time. Finally, we hope the reader will share our joy and find this special issue very useful.
关键词：Special Issue;Digital Rights Management;Multimedia Content
