22-09-2008, 09:54 AM
Definition
Networked computer systems are rapidly growing in importance as the medium of choice for the storage and exchange of information. However, current systems afford little privacy to their users, and typically store any given data item in only one or a few fixed places, creating a central point of failure. Because of a continued desire among individuals to protect the privacy of their authorship or readership of various types of sensitive information, and the undesirability of central points of failure which can be attacked by opponents wishing to remove data from the system or simply overloaded by too much interest, systems offering greater security and reliability are needed.
Freenet is being developed as a distributed information storage and retrieval system designed to address these concerns of privacy and availability. The system operates as a location-independent distributed file system across many individual computers that allow files to be inserted, stored, and requested anonymously. There are five main design goals:
1.Anonymity for both producers and consumers of information
2.Deniability for storers of information
3.Resistance to attempts by third parties to deny access to information
4.Efficient dynamic storage and routing of information
5.Decentralization of all network functions
The system is designed to respond adaptively to usage patterns, transparently moving, replicating, and deleting files as necessary to provide efficient service without resorting to broadcast searches or centralized location indexes. It is not intended to guarantee permanent file storage, although it is hoped that a sufficient number of nodes will join with enough storage capacity that most files will be able to remain indefinitely. In addition, the system operates at the application layer and assumes the existence of a secure transport layer, although it is transport-independent. It does not seek to provide anonymity for general network usage, only for Freenet file transactions.
Freenet Architecture
Freenet is implemented as an adaptive peer-to-peer network of nodes that query one another to store and retrieve
data files, which are named by location-independent keys. Each node maintains its own local datastore which it makes available to the network for reading and writing, as well as a dynamic routing table containing addresses of other nodes and the keys that they are thought to hold. It is intended that most users of the system will run nodes, both to provide security guarantees against inadvertently using a hostile foreign node and to increase the storage capacity available to the network as a whole.
The system can be regarded as a cooperative distributed filesystem incorporating location independence and transparent lazy replication. Freenet enables users to share unused disk space being directly useful to users themselves, acting as an extension to there own hard drives.
The basic model is that requests for keys are passed along from node to node through a chain of proxy requests in which each node makes a local decision about where to send the request next, in the style of IP (Internet Protocol) routing. Depending on the key requested, routes will vary. The routing algorithms for storing and retrieving data described in the following sections are designed to adaptively adjust routes over time to provide efficient performance while using only local, rather than global, knowledge. This is necessary since nodes only have knowledge of their immediate upstream and downstream neighbors in the proxy chain, to maintain privacy.
Each request is given a hops-to-live limit, analogous to IP's time-to-live, which is decremented at each node to prevent infinite chains. Each request is also assigned a pseudo-unique random identifier, so that nodes can prevent loops by rejecting requests they have seen before. When this happens, the immediately preceding node simply chooses a different node to forward to. This process continues until the request is either satisfied or exceeds its hops-to-live limit. Then the success or failure result is passed back up the chain to the sending node.
No node is privileged over any other node, so no hierarchy or central point of failure exists. Joining the network is simply a matter of first discovering the address of one or more existing nodes through out-of-band means, then starting to send messages.
