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Peer-to-Peer Network Tzu-Wei Kuo
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Outline What is Peer-to-Peer(P2P)? P2P Architecture Applications Advantages and Weaknesses Security Controversy
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What is Peer-to-Peer? History Peer-to-Peer (P2P) architecture described in the first Internet Request for Comments, RFC 1, "Host Software" dated April 7, 1969.
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What is Peer-to-Peer? Peers An entity with capabilities similar to other entities in the system Equally privileged Equipotent participants in the application Form a peer-to-peer network of nodes
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What is Peer-to-Peer? The strictest definition of “pure” P2P Totally distributed system All nodes are completely equivalent in terms of functionality and tasks they perform
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What is Peer-to-Peer? P2P is a computer network architecture where computers use resources of network participants rather than conventional centralized resources
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P2P Architecture Two defining characteristics of P2P architectures The sharing of computer resources by direct exchange, rather than requiring the intermediation of a centralized server Their ability to treat instability and variable connectivity as the norm, automatically adapting to failures in both network connections and computers, as well as to a transient population of nodes
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P2P Architecture Classified by Centralized Model Pure P2P (decentralized) Peers are both client and server at the same time No central server and central router e.g. Gnutella, Freenet Hybrid P2P (centralized ) Have a central server (supernodes) e.g. Napster, Kazaa
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P2P Architecture Classified by Network Topology Structured P2P Employ a globally consistent protocol Efficiently route a search Distributed hash tables (DHTs) e.g. Chord, CAN Unstructured P2P Overlay links are established arbitrarily Disadvantage: the queries may not always be resolved e.g. Gnutella
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Applications Communication and Collaboration Direct, real-time, communication Internet Relay Chat (IRC), Skype, Instant Messaging (AOL, Yahoo, Msn) and Jabber
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Applications Distributed Computation Breaking down a computer intensive task into small work units and distributing them to different peer computers which execute their corresponding work unit and return results. Seti@Home and genome@home
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Applications Internet Service Support Peer-to-peer multicast systems Internet indirection infrastructures Security applications
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Applications Content Distribution Sharing of digital media and other data between users Most P2P applications fall within this category Gnutella, FastTrack
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Advantages and Weaknesses All clients provide resources Increases robustness Unsecure and unsigned codes
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Security Self-Certifying Data Integrity can be verified Hashing function Information Dispersal Files are encoded into m blocks Any n is sufficient to reassemble the original data (m < n) This gives resilience “proportional” to a redundancy factor equal to m/n
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Security Shamir’s Secret Sharing Scheme Encrypts a file with a key K Splits K into L shares So any k of them can reproduce K but k − 1 give no hints about K. Each server then encrypts one of the key shares, along with the file block. In order for the file to become inaccessible, at least (l − k − 1) servers containing the key must be shut down.
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Security Smartcards Tracking each node’s use of remote resources Issuing digitally signed tickets This would allow nodes to prove to other nodes that they are operating within their quota
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Security Distributed Steganographic File Systems Encrypted blocks are indistinguishable from a random substrate Their presence cannot be detected. First writing random data to all blocks, and then files are stored by encrypting their blocks and placing them at pseudo-randomly chosen locations To avoid collisions, a considerable amount of replication is required
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Security Erasure Coding Data is broken in to blocks and spread over many servers Giving them globally unique identifiers. This provides data integrity, by ensuring that a recovered file has not been corrupted, since a corrupted file would produce a different identifier.
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Controversy Core issues: share illegal content In October 2007, Comcast started blocking P2P applications such as BitTorrent Critics point out that P2P networking has legitimate uses Solution: Control use and content on the Internet
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Summary Peer-to-peer systems are distributed systems consisting of interconnected nodes, able to self-organize into network topologies with the purpose of sharing resources Peer-to-peer technologies are still evolving How to make it more efficient security How to prevent people use P2P share illegal content
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References Stephanos Androutsellis-Theotokis and Diomidis Spinellis. “A Survey of Peer-to-Peer Content Distribution Technologies” Wikipedia: Peer-to-peer. http://en.wikipedia.org/wiki/Peer-to-peer http://en.wikipedia.org/wiki/Peer-to-peer
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