Peer-to-Peer Network Tzu-Wei Kuo

Outline What is Peer-to-Peer(P2P)? P2P Architecture Applications Advantages and Weaknesses Security Controversy

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.

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

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

What is Peer-to-Peer? P2P is a computer network architecture where computers use resources of network participants rather than conventional centralized resources

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

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

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

Applications Communication and Collaboration  Direct, real-time, communication  Internet Relay Chat (IRC), Skype, Instant Messaging (AOL, Yahoo, Msn) and Jabber

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.  and

Applications Internet Service Support  Peer-to-peer multicast systems  Internet indirection infrastructures  Security applications

Applications Content Distribution  Sharing of digital media and other data between users  Most P2P applications fall within this category  Gnutella, FastTrack

Advantages and Weaknesses All clients provide resources Increases robustness Unsecure and unsigned codes

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

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.

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

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

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.

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

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

References Stephanos Androutsellis-Theotokis and Diomidis Spinellis. “A Survey of Peer-to-Peer Content Distribution Technologies” Wikipedia: Peer-to-peer.