Peer to Peer Freedom of Speech
The basic framework for each of these networks is a decentralized, peer-to-peer communications model where a node in the network talks to some number of other nodes, sending requests to these peer nodes and handling requests that come from them. The messages sent between nodes are encrypted using a session key that has been negotiated between the nodes using public key encryption. This encryption should be sufficient to deny a 'man in the middle' from determining anything useful about the traffic (other than its existence).
When a node sends a request to one of its peers, there is no reason to assume that the request actually originated on that node as nodes will forward requests that they receive, but cannot satisfy. Any response that is generated to a node is likewise not necessarily ultimately bound for that node and could be the response to a request that was forwarded by the node. With a sufficient number of nodes and amount of traffic, no analysis of the traffic to or from nodes will reveal the true source and destinations of the requests. This stands in stark contrast to the more common peer-to-peer networks where, once the content is found, a direct connection is made from the destination to the source to retrieve the content.
Each node that fully participates in the network provides some local storage for information in the network and can immediately satisfy requests for any data that it has stored locally. In order to provide deniability for the operators of these nodes, this data is encrypted and the operators are unable to determine what content actually resides on their node at any given time. Cryptographic hash functions on the file contents are typically used to identify particular files that have been inserted into the network. These identifiers are not particularly user friendly - for instance a copy of Kevin Mitnick's book The Art of Deception can be found in the Entropy network using the identifier:
SSK@zpxOK~ounTzoDwJKguoUHib8G7sBCMA/ArtOfDeception//
To make the system easier to use, various
network users have put together directories of content to help navigation.
The popularity of a file governs how long it stays in the network and how often it is replicated. Each of the networks has limits on the amount of storage available to it (based on the number of active nodes and the amount of storage allocated to the nodes by each operator) and must sometimes prune content when new content is added. GNUnet tries to overcome the problem of 'freeloaders' (nodes that request content but do not serve any) by adding an 'economic' layer to its network. Each node keeps track of its 'opinion' of the other nodes that it has talked to; nodes that satisfy requests have a better reputation and will be treated preferentially under higher network loads.
Both Freenet and Entropy provide an HTTP proxy that allows the use of standard web browsers as clients to view some of the content on the network. Entropy also adopted the Freenet Client Protocol so that all of the client applications originally written for Freenet will work with Entropy as well. Frost is one of the most widely used clients and provides file sharing and message board functionality. GNUnet appears to mainly use command line tools, though gnunet-gtk provides a graphical front-end.
Security is clearly taking precedence over performance, as it should, but this causes the user experience browsing Freenet or Entropy (at least) to be fairly frustrating. Sites can take tens of minutes to load or fail to load altogether, presumably because the information has either dropped out of the network or any sites that contain the information are currently offline or too far away (in network, not geographic, terms).
Critics of these projects complain that they could be used by criminals
for nefarious purposes and, obviously, that is true. There is no way to
provide for anonymous communication that cannot be abused and these projects
have decided that freedom of communication is more important than stopping
illegal uses. In the end, these networks are tools like computers or
phones and they can be used for good or for ill. It would be impossible
and a serious affront to liberty to outlaw all tools that could be
used to commit a crime.
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