Watermarking in the Encrypted Domain

Multimedia content protection is with no doubt one of the most important application scenarios for watermarking technology, within those mentioned in Section 1.3. In a content protection scenario, information about the creator, the distributor, the customer, or the licensing terms between these players is embedded into the content itself by means of watermarking. The hidden information can be used later to demonstrate content ownership, content misappropriation or as a proof of purchase [15, 4]. The adoption of digital watermarking for multimedia content protection in realistic scenarios raises a set of important problems, including the possible collusion of malicious customers, the fact that the distribution mechanism may leak sensible information about the customers, the scalability to large scale scenarios. The collusion problem has already been addressed in Chapter 7. In this chapter, we will illustrate possible solutions to the remaining problems. All of the described solutions are based on the possibility of processing encrypted data [28], which permits to efficiently combine watermarking and cryptographic techniques.