# Cryptography/DRM

Digital Rights Management (DRM)or Multimedia Content Security or Digital Watermarking
1. Digital Rights Management (DRM) can be viewed as an attempt to provide "remote control" of digital content. The required level of protection goes beyond simply delivering the digital contents—restriction on the use of the content must be maintained after it has been delivered. In other words, DRM requires "persistent protection", i.e., protection that stays with the contents.
2. Recent advances in multimedia document production, delivery and processing, including the wide availability of increasingly powerful devices for the production, communication, copying and processing of electronic documents, have made available a large number of new opportunities for the dissemination and consumption of multimedia content (audio, video, images, 3D models, …).. At the same time, these rapid developments have raised several important problems regarding intellectual property, digital rights management, authenticity, privacy, conditional access and security, which risk impeding the diffusion of new services. Multimedia data can undergo, during their 'life', a wide variety of (possibly lossy) data manipulations that does not modify their substance (e.g. a change in file format, some processing for quality enhancement, the extractions of subparts,..) and that are not even perceived by the human perception system. This particular characteristic makes sometimes ineffective the classical solutions for security based on cryptography, but on the other hand offer the opportunity to design new solutions exploiting the fact that different documents bearing the same semantic information can be judged as equivalent by the human perceptual system. Driven by the necessities outlined above, the last few years have seen the development of new tools to tackle the problems encountered in media security applications leading to the concept of Secure Media Technologies. Secure Media encompasses a wide range of diverse technological areas working together to cope with the complex problems characterizing this rapidly evolving field. Enabling technologies include watermarking, data hiding, steganography and steganalysis, cryptography, biometrics, fingerprinting, network security and digital forensics. In particular, there are presently research activities concerning the following areas:
a. Robust digital watermarking techniques for images and video sequences: they allow to robustly hide some data useful for proving the content ownership and then to track the copyright violations, identify the content, monitor its usage, etc. They are often designed to be used in the framework of a Digital Rights Management System for the protection of the Intellectual Property Rights. The robustness here means that the embedded information remains intact even after that the content has been altered.
b. Digital watermarking techniques for 3D models: it is a more recent research area with respect to image and video watermarking. Since a mesh (geometrical representation of 3D objects) can't be easily represented in a frequency domain, it is not possible to directly apply to them transformations and filters in the frequency; processing methods for this kind of data then turn to ad hoc mathematical representations, that are different to the methods operating on other multimedia content.
c. Fragile or semi-fragile digital watermarking techniques for the authentication of images: these techniques allow to hide into an image some information useful to prove subsequently its authenticity. In this case, the embedded information is removed when the content is modified. It is possible to assure that an image has not been tampered, and in some cases also to locate the manipulations occurred that altered the original content of the image.
d. Fingerprinting: these techniques allow to unambiguously identify each copy of a multimedia content. In this way, it is possible to identify who, in a group of users in possession of a copy of a same document, illicitly distributed his/her own copy of the content, failing to meet possible limitations of use and distribution.
e. Digital forensic: they are processing techniques supporting detective activities to use multimedia content as an evidence of possible criminal acts. In our case, we are interested in proving if a image or a video sequence we have at disposal has been acquired with a given digital camera.
f. Signal processing in the encrypted domain: it is a new research field studying new technologies to allow the processing of encrypted multimedia content without removing the encryption. Most of technological solutions proposed so far to cope with multimedia security simply tried to apply some cryptographic primitives on top of the signal processing modules. These solutions are based on the assumption that the two communicating parties trust each other, so that the encryption is used only to protect the data against third parties. In many cases, though, this is not the case. A possible solution to the above problems could consist in the application of the signal processing modules in the encrypted domain.
g. Steganography: it is the science of hiding sensitive messages into an apparently innocuous document in such a way that no one apart from the intended recipient knows of the existence of the message. In case of a multimedia document, the information is hidden by means of the application of not perceivable modifications.
h. Steganalysis: it is the science of detecting the presence into a document of messages hidden using steganography techniques, exploiting perceptual or statistical analysis.