Secure Multimedia Content Distribution Based on Watermarking Technology

Introduction

With the development of multimedia technology and network technology, multimedia content becomes more and more popular in human's life. To keep security and privacy, multimedia content protection attracts more and more researchers. Generally, for multimedia data, the confidentiality and copyright are important properties that should be protected (Lin, et al., 2005). Among them, confidentiality protection means to make only authorized users access multimedia content, and copyright protection means to verify the ownership of multimedia content. To realize these functionalities, two means have been proposed, i.e., digital watermarking and multimedia encryption.

Digital watermarking (Moulin & Koetter, 2005; Bloom, et al., 1999; Hauer & Thiemert, 2004) embeds information (also named watermark) into multimedia data by modifying multimedia content slightly, which can also be detected or extracted from multimedia data. According to the visibility of the watermark, digital watermarking can be classified into two types, i.e., visible watermarking and invisible watermarking. In visible watermarking, the embedded watermark is visible in multimedia data. In invisible watermarking, the watermark is imperceptible. Digital watermarking can be used for various applications (Cox, et al., 2002), such as copyright protection, copy protection, transaction tracking, and so on. In copyright protection, the copyright information (e.g., ownership information) is embedded into multimedia content, which can be extracted and used to tell the ownership of the content. In copy protection, the permission information (e.g., copy times) is embedded into multimedia content, which can be modified according to copy operations. For example, if the original embedded copy time is 3, then after once copy operation, the embedded copy time is changed into 2. When the copy time becomes 0, copy operation is forbidden. As an important application, to trace illegal distributors, customer information, e.g., customer ID, can be embedded into media data. Thus, each customer receives a slightly different copy, and the contained customer ID can be used to identify the customer. In this chapter, only the traitor tracing property is emphasized, and only the invisible watermarking is used here. In traitor tracing, some properties (Cox, et al., 2002) should be satisfied, e.g., robustness, imperceptibility and security. Robustness denotes that the watermark can survive some intentional or unintentional operations, such as general signal processing (e.g., compression, adding noise, filtering, etc.) or intentional operations (e.g., camera capture, rotation, shifting, translation, etc.). Imperceptibility means that there is no perceptual difference between the watermarked multimedia content and the original content. Security denotes the ability to resist some attackers who forge the watermark or remove the watermark in an unauthorized manner.

Multimedia encryption (Lin, et al., 2005; Maniccam & Nikolaos, 2004; Wu & Kuo, 2001) transforms multimedia content into an unintelligible form that can only be recovered by the correct key. Thus, for the authorized customer who has the key, the content can be recovered, while for the unauthorized customer who has no key, he can only watch the unintelligible content. As multimedia encryption algorithms, security is the most important requirement. Generally, as an encryption algorithm, it should be secure against such cryptographic attacks (Mollin, 2006) as brute-force attacks, statistical attacks, differential attacks, etc. Some detailed information about multimedia encryption will be presented in Section 2.

Secure multimedia distribution is a practical application in multimedia communication, which transmits multimedia content from the sender to customers in a secure manner. Generally, both confidentiality protection and copyright protection should be confirmed. Thus, it is reasonable to adopt both multimedia encryption and digital watermarking techniques. For it implements both watermarking and encryption operations, the properties belonging to both watermarking and encryption should be satisfied, which are list as follows.