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.

Seti@Home and genome@home

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. http://en.wikipedia.org/wiki/Peer-to-peer