Secure and traceable multimedia distribution for convergent Mobile TV services
Introduction
With the development of multimedia technology and communication technology, multimedia data (image, audio, video, text, etc.) are used more and more widely in human being’s daily life. The wide application makes multimedia content protection more and more urgent and necessary. Till now, some multimedia protection means have been reported, among which, multimedia encryption and digital watermarking are two typical ones. Multimedia encryption [1], [2], [25] often transforms the original data into an unintelligible form, which protects the confidentiality. Only the authorized customer who has the correct key can recover the data successfully. Generally, multimedia encryption algorithms should be not only secure against cryptographic attacks but also secure in human perception. Digital watermarking [3], [4] is the technique that embeds some information (e.g., copyright, ownership, integrity, etc.) into the original data by slightly modifying the data, which protects the data’s copyright, ownership, integrity, etc. The embedded information can be extracted from the marked data and used to authenticate the originality. Generally, a good watermarking algorithm has such properties as imperceptibility, robustness and so on. The imperceptibility means that the watermarked media is perceptually different from the original media. The robustness denotes to the ability to survive such common signal processing as recompression, adding noise, filtering, resizing, etc.
Existing Digital Rights Management (DRM) [37], [38] and Conditional Access (CA) [39] systems aim to protect the digital multimedia content and the related access rights, but ignore the traceability of contents or users. For example, during media transmission, the media data are often encrypted to resist attackers. However, the decrypted media content may be redistributed to unauthorized users (e.g., free sharing over Internet), which often leads to great benefit–losses to content/service providers. Due to this case, secure multimedia distribution [5], [6], [26], [27] becomes more and more popular in practical applications, which transmits multimedia content from the sender to different receivers in a secure manner. Generally, two properties of multimedia contents need to be protected, i.e., confidentiality and traitor tracing. Among them, the confidentiality can be protected by multimedia encryption, while the traitor tracing is often protected by digital fingerprinting. Digital fingerprinting [7], [8] is the technique that embeds the unique customer information (e.g., customer ID) into media content with watermarking technology. If an illegal media copy is found, the unique information can be extracted from the media copy and used to trace the traitor who distributes the media copy to other unauthorized customers. As a fingerprinting algorithm, it should be secure against collusion attack [8] that combines several copies together to produce a new copy without customer information.
According to the aims of secure multimedia distribution, such techniques as watermarking, encryption and fingerprinting need to be used for the design, thus, various properties belonging to different techniques should be considered, which are list as follows.
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Secure against cryptographic attacks. The encryption algorithm should be secure against typical attacks, such as brute-force attacks, statistical attacks, differential attacks, etc. Additionally, the watermarking algorithm can resist some attackers who aim to forge the watermark or remove the watermark in an unauthorized manner.
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Robust against common processing. The processing operations include typical signal processing (e.g., compression, adding noise, filtering, etc.) and intentional operations (e.g., camera capture, rotation, shifting, translation, etc.).
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Robust against collusion attacks. The embedded fingerprint code can survive such operations that combine several media copies together to produce a new copy. The combination operation [8] includes pixel averaging, min–max pixel selection, linear combination, etc.
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Imperceptibility. The embedded fingerprint information should be invisible. That is, there is no perceptual difference between the original copy and the watermarked copy.
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Distribution efficiency. For the media sender, its loading should not be too large to support large number of concurrent users who request multimedia services. For the user, the media receiving operation should be efficient in order to confirm the real-time services.
There exist some secure multimedia distribution schemes [5], [9], [10], [11], [12], [13], [14], [15]. However, they have some typical disadvantages and are not targeted on mobile applications, e.g., such mobile services as Mobile TV and mobile image/video/music sharing. Generally, in Mobile TV, the content is encoded into low bit rate streams by such codec as MPEG-4, and the service has the property of real time interaction. The existing secure distribution schemes do not consider the Mobile TV compression process, and are not lightweight enough to reduce the delay and meet real time interactions. More details about their performances will be presented in the next section.
Now, there exist some schemes for securing mobile video communication, e.g., Mobile TV services. Taking the ubiquitous Mobile TV [36] based on the convergence of DVB-H (Digital Video Broadcasting – Handheld) [28] and GPRS/GSM [29], [30] for example, the TV content is broadcasted through the DVB-H channel, while the user interaction information is unicasted to each user through GPRS/GSM network’s channel, as shown in Fig. 1. In [31], we proposed the scheme to provide secure Mobile TV services, which encrypts the TV program’s video content partially during the video compression process, transmits the encrypted content through DVB-H broadcasting and distributes the encrypted access licenses to users through the GPRS/GSM channel. Additionally, the scheme is extended to convergent TV services (between Mobile TV and Home TV) by encrypting the video content in a scalable manner [32], [33]. Although these schemes show good performances for secure Mobile TV services, they do not consider the illegal redistribution issues.
This paper aims to propose a secure multimedia distribution scheme for the converged Mobile TV services. This scheme will adopt both multimedia encryption and digital fingerprinting techniques to trace illegal redistributions. Among them, the encryption operation will be combined with compression operation in order to get high efficiency, while the fingerprinting operation will be combined with the decryption operation in order to get high security. To show the proposed scheme’s superior properties, we analyze the existing secure distribution schemes’ performances, and compare our scheme with the most similar existing one.
The rest of the paper is arranged as follows. In Section 2, the existing secure multimedia services and distribution schemes are reviewed, and the typical traceable scheme is introduced briefly. The architecture of the proposed secure distribution scheme is presented in Section 3. In Section 4, the performance of the proposed scheme is evaluated, and the comparison with an existing scheme is presented. Finally, some conclusions are drawn, and the future work is given.
Section snippets
Secure multimedia services
Digital Rights Management (DRM) and Conditional Access (CA) systems provide multimedia content protection and secure user interactions during multimedia services. Generally, different systems are designed for different application scenarios. For example, Open Mobile Alliance (OMA) DRM [37] provides the principles for managing digital rights in mobile environment. It defines the format and the protection mechanism for content and the rights objects, and also the security model for management of
The proposed secure distribution scheme for Mobile TV
Taking Mobile TV for example, the proposed secure distribution scheme is shown in Fig. 3. At the server side, the TV program is compressed and encrypted by the Joint Compression and Encryption method, and the Content Key is encrypted before being sent to a mobile terminal. At the terminal side, the media content is decrypted by the Joint Decryption and Fingerprinting method after the Content Key is decrypted. If the mobile user redistributes his decrypted TV program to public networks, such as
Performance evaluation
In the following content, some performance issues of the proposed scheme are evaluated and compared with Lemma et al.’s scheme, including the security of the encryption algorithm, the imperceptibility of the fingerprint and the robustness of the fingerprint.
Discussions and future work
In this paper, a secure multimedia distribution scheme is presented for the converged Mobile TV service. The TV content is encrypted during MPEG-4 Advanced Simple Profile encoding at the server side. At the mobile terminal side, the TV content is decrypted and fingerprinted simultaneously. In the encryption process, the signs of ACs and MVDs are encrypted with a stream cipher during encoding, while the DCs are firstly preprocessed with the proposed preprocessing, and then encrypted with the
Acknowledgements
This work was partially supported by the EU Project “MOBISERVE” through the Grant code of FP6-2005-IST-61-045410, National Natural Science Foundation of China under Grant No. 70901039, National Postdoctoral Science Foundation of China under Grant No. 20090450144, France Telecom Project “Crypto” through the Grant No. PEK08-ILAB-006 and Jiangsu Postdoctoral Science Foundation under Grant No. 0901104C.
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