A peer-to-peer (P2P) system is a popular means of file distribution. Existing P2P systems do not adequately address a variety of common problems including (1) limited search scope, (2) dynamic nature of peers and (3) lack of collaboration among peers. In this paper, we propose a server-mediated peer-to-peer system to address these problems and to improve the performance of existing decentralized P2P systems by incorporating a central server into the decentralized P2P system to facilitate collaboration among peers. Two main features of our proposed system are Assisted-search and Assisted-download. Experimental results show that the search coverage was increased by 289.91% by using Assisted-search, while the overall download speed was improved by 33% by using Assisted-download.
Abstract-In order to offer backward and forward secrecy for multicast applications (i.e., a new member cannot decrypt the multicast data sent before its joining and a former member cannot decrypt the data sent after its leaving), the data encryption key has to be changed whenever a user joins or leaves the system. Such a change has to be made known to all the current users. The bandwidth used for such re-key messaging can be high when the user pool is large. In this paper, we propose a distributed servers approach to minimize the overall system bandwidth (and complexity) by splitting the user pool into multiple groups each served by a (logical) server. After presenting an analytic model for the system based on a hierarchical key tree, we show that there is an optimal number of servers to achieve minimum system bandwidth. As the underlying user traffic fluctuates, we propose a simple dynamic scheme with low overhead where a physical server adaptively splits and merges its traffic into multiple groups each served by a logical server so as to minimize its total bandwidth. Our results show that a distributed servers approach is able to substantially reduce the total bandwidth required as compared with the traditional singleserver approach, especially for those applications with a large user pool, short holding time, and relatively low bandwidth of a data stream, as in the Internet stock quote applications.Index Terms-Distributed servers approach, key tree, multicast security, re-key messaging, split-and-merge scheme.
Multicasting is an efficient way to deliver data to a large group of users in applications such as Internet stock quotes, audio and music delivery, file and video distribution, etc. Many of these applications require the security feature of data confidentiality, which is not readily offered by the "open" nature of multicast. In order to offer such confidentiality, the encryption and decryption keys must be constantly changed upon a membership change. In this article, after discussing some performance criteria to offer secure multicast, we present a number of the proposed key management schemes for data confidentiality. We categorize these schemes into four groups: key tree-based approaches, contributory key agreement schemes supported by the Diffie-Hellman algorithm, computational number theoretic approaches, and secure multicast framework approaches. Through examples, we describe the operation of the schemes and compare their performances.
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