Governed Content Distribution on DHT Based Networks Walter Allasia, Francesco Gallo Marco Milanesio, Rossano Schifanella EURIX Group Dipartimento di Informatica Torino UniversitadiTorino` {allasia, gallo}@eurixgroup.com {milane, schifane}@di.unito.it Abstract—Peer-to-Peer (P2P) systems are widely used for sha- Our aim is therefore to present a totally distributed system ring digital items without structured metadata and in absence of capable of indexing digital rights metadata, structured in a any kind of digital rights management applied to the distributed complex way on a flat identifier space, thus enhancing the contents. In this paper we propose the implementation of a prototype application that makes use of a structured P2P system expressiveness of the key-based query mechanism on the enabling the indexing of complex metadata, used to express DHTs. To the best of our knowledge, this is the first attempt digital rights. In this way the media contents are exchanged and to index the structure of rights metadata on a structured P2P played according to the expressed grants. The creation and the network, where media contents can be exchanged and shared consumption of the shared contents can be performed through according to the expressed grants. any MPEG-21 REL compliant software and the application allows indexing and search for both governed and ungoverned In Section II we introduce the state-of-the-art of the MPEG- contents. The information about the license can be included in 7 and MPEG-21 standards and of the DHTs, then Section III the queries and the P2P network can be used to share governed describes the system, while in Section IV more details of our contents (both free and with fee) in a legitimate way. In particular implementation are pointed out. Section V presents a possible the proposed approach represents a suitable solution for indexing usage of the application and finally, while in Section VI and querying rights complex structures on DHT based networks. conclusions and on going activities are presented. I. INTRODUCTION II. RELATED WORKS Nowadays, providers and broadcasters are facing the prob- The proposed application makes use of MPEG-7 and lem of managing a huge number of digital items on the MPEG-21 for metadata representation and Distributed Hash Web, coming from heterogeneous archives (e.g., 8mm, tapes, Tables for network topology. In the following we provide a films, digital contents). Each content can be associated with brief description of the used standards and we present the a specific license, so it is necessary to manage the expressed reference software we adopted to implement our system. rights to avoid violating (for example) copyright laws. A solution has been set up with the introduction of the A. MPEG-7 and MPEG-21 MPEG-7 [1] and MPEG-21 [2] standards, which associate MPEG-7 standard [1], formally named Multimedia Content each content with a set of metadata describing the content itself Description Interface, provides a rich set of standardized tools and the related license. In this paper we present the implemen- to describe multimedia contents. It mainly focuses on the tation of a software solution for managing metadata expressing description of the digital items, without considering how and digital rights on a structured overlay network, allowing users where this information is used. MPEG-7 standard has been to perform complex queries on (un)governed contents. Since included in several metadata languages such as ODRL (from the underlying network is a Distributed Hash Table [3], the W3C) and has also been coupled with other important TV proposed application can easily handle the growth in system ontologies (e.g., TVAnytime [5]). Concerning digital rights, size and is suitable for dealing with multimedia contents MPEG-7 provides a standard XML schema and the meta- distributed on an Internet environment. data to define conditions for accessing the content (including With respect to the commonly used P2P systems, where dig- links to a registry with intellectual property rights data and ital items are shared without structured metadata and without price) and additional information about the content (copyright controls, the proposed application makes use of a structured pointers, usage history, broadcast schedule). An MPEG-7 P2P system to index complex metadata and to exchange digital Query Format has recently reached the Final Committee Draft, contents in a controlled environment. In our prototype im- in October 2007 MPEG meeting. Moreover several query plementation, the creation and the consumption of the digital frameworks based on MPEG-7 are still under investigation [6]. media is performed with the Chillout [4] reference software, MPEG-21 [2] differs from MPEG-7 because its aim is which has been extended in the implemented application in the definition of a normative open framework to be used order to fulfill the content government. Moreover, our system by all the players in the delivery and consumption chain. is unbound from a specific MPEG-21 compliant solution. This open framework will provide content creators, producers, distributors and service providers with equal opportunities in B. Distributed Hash Tables the MPEG-21 enabled open market . The goal of MPEG-21 is the definition of a standard technology needed to support users Distributed Hash Tables (DHT) [3] are a class of decen- to exchange, access, consume, trade and otherwise manipulate tralized distributed systems that partition the ownership of a digital items in an efficient, transparent and interoperable way. set of keys among participating nodes. They efficiently route In particular part 5 of MPEG-21 defines a Rights Expression messages to the unique owner of any given key. The nodes in Language (REL) to be used in the description of customized a DHT based system are organized in a well-defined topology rights applied to any digital item, since it is seen as a machine- (e.g., a ring topology in Pastry [12]). Each node is analogous readable language that can declare rights and permissions to an array slot in a hash table. DHTs are conceived to scale to using the terms as defined in the Rights Data Dictionary (also large numbers of nodes and to handle continual node arrivals standardized by MPEG-21). Rights metadata are expressed and failures. by means of MPEG-21 REL [7], which describes the license A DHT provides functions (primitives) to build a mapping associated to a specific resource, as along with several avai- between the resources (e.g., files and nodes) and the keys, <key,value> lable grants (play, copy, modify, print, etc.). According to the using a list of pairs. The core of all primitives schema shown in Figure 1, we can imagine the license as is based on the insert(key,value) and lookup(key) functions. made up of an issuer (with 0 or 1 multiplicity), an undefined Random unambiguous identifiers are assigned to both nodes number of grants (0 or more multiplicity), and a principal (node IDs) and objects (keys). Keys are computed from a large (0 or 1 multiplicity) [8]. In widely used CreativeCommons ID space (e.g, 128 bits) and usually hashing algorithms are licenses the principal is missing because this kind of licenses applied for representing them. Given a message and a key, the is intended for everyone, therefore the grant is not addressed DHT routes the message to the node with the node ID that to a specific logical actor. is numerically closest to the key (usually known as the key’s root in Pastry, or the key’s successor in Chord). In order to route a message each node maintains a local routing table organized in some way. The message routing has a cost that is logarithmic in the size of the network: each node maintains a routing table that contains information on a logarithmic subset of the entire system, and each message is forwarded through a logarithmic number of hops to its destination, granting high scalability to the system. DHTs have grown in popularity and a lot of effort has been devoted to investigate different domains of application (e.g., Fig. 1. Simplified class diagram of a REL license distributed cooperative storage [13], application level multicast [14], and streaming [15]). Several levels of abstraction have Chillout [4] is the reference software of the Digital Media been proposed in literature, simply forwarding the DHT layer Project (DMP) [9]. DMP is a no profit organization that has to a routing infrastructure to deploy more complex systems. recently approved a version 3.0 of its specification, called In- Examples are the self organized metadata overlay network teroperable DRM Platform (IDP-3.0). Chillout is also the ref- described in [16], and the abstraction for resource discovery erence implementation of ISO/IEC 23000-5 Media Streaming (i.e., finding any resource above a given size) of CONE [17]. Application Format [10], targeting the distribution of governed In a structured P2P network, nodes and resources are as- content over streaming channels. The most important technolo- signed with unique identifiers, while messages are exchanged gies adopted by Chillout are: (a) a data structure capable of through keys. This key based routing is an issue because it hosting different data types accompanying a resource (e.g., is simple when keys are known in advance, but this can- audio, video, image, text, etc.), (b) a content identification not be always assumed at the application level. Therefore system, (c) a set of technologies for content protection, (d) distributed applications based on structured overlay networks the Rights Expression Language, (e) a file format for storing have to set up an interface to communicate with the P2P digital items and resources and (f) a technology to transmit network providing the keys used for both routing messages digital items in streaming mode.