GNUnet with the GTK+ user interface
|Initial release||November 5, 2001|
|Stable release||0.9.5 (December 21, 2012) [±]|
|Type||Anonymous P2P, Friend-to-friend|
|License||GNU General Public License|
GNUnet is a free software framework for decentralized, peer-to-peer networking and an official GNU package. The framework offers link encryption, peer discovery, resource allocation, communication over many transports (such as tcp, udp, http, https and wlan) and various basic peer-to-peer algorithms for routing, multicast and network size estimation.
GNUnet's basic network topology is that of a mesh network. GNUnet includes a distributed hash table which is a randomized variant of Kademlia that can still efficiently route in small world networks. GNUnet offers a "F2F topology" option for restricting connections to only the users' trusted friends. The users' friends' own friends (and so on) can then indirectly exchange files with the users' computer, never using its IP address directly.
GNUnet uses Uniform Resource Identifiers (not approved by IANA). GNUnet URIs consist of two major parts: the module and the module specific identifier. A GNUnet URI is of form gnunet://module/identifier where module is the module name and identifier is a module specific string.
The primary codebase is written in C, but with gnunet-java there is an effort to produce an API for developing extensions in Java. GNUnet currently runs on GNU/Linux, BSD, Mac OS X, Solaris and Windows.
GNUnet includes various P2P applications in the main distribution of the framework; additionally, a few external projects (such as SecuShare) are also extending the GNUnet infrastructure.
File sharing 
The primary application at this point is anonymous, censorship-resistant file-sharing, allowing users to anonymously publish or retrieve information of all kinds. GNUnet uses GNU libextractor to automatically annotate shared files with meta data.
The file sharing service uses GNUnet's anonymity protocol for routing queries and replies. Forwarded query messages are used to search for content and blocks of data. Depending on load of the forwarding node, messages are forwarded to zero or more nodes. When a node is under stress it drops requests from its neighbor nodes having lower internal trust value. A special feature of GNUnet's anonymity protocol is that the user can select an individual anonymity level. The anonymity level determines how much cover traffic a peer must have to hide the user's own traffic. Users can specify an anonymity level for each publish, search and download operation. An anonymity level of zero can be used to select non-anonymous file-sharing. GNUnet's DHT infrastructure is only used if non-anonymous file-sharing is specified.
File sharing URIs 
Files shared with GNUnet are ECRS (An Encoding for Censorship-Resistant Sharing) coded. The fs module identifier consists of either chk, sks, ksk or loc followed by a slash and a category specific value.
- chk identifies files, typically: gnunet://fs/chk/[file hash, using 0-9A-V].[query hash, using 0-9A-V].[file size in bytes]
- sks identifies files within namespaces, typically: gnunet://fs/sks/NAMESPACE/IDENTIFIER
- ksk identifies search queries, typically: gnunet://fs/ksk/KEYWORD[+KEYWORD]*
- loc identifies a datum on a specific machine, typically: gnunet://fs/loc/PEER/QUERY.TYPE.KEY.SIZE
A type of GNUnet filesharing URI pointing to a specific copy of GNU GPL license text:
gnunet://fs/chk/9E4MDN4VULE8KJG6U1C8FKH5HA8C5CHSJTILRTTPGK8MJ6VH\ ORERHE68JU8Q0FDTOH1DGLUJ3NLE99N0ML0N9PIBAGKG7MNPBTT6UKG.1I823C58O3L\ KS24LLI9KB384LH82LGF9GUQRJHACCUINSCQH36SI4NF88CMAET3T3BHI93D4S0M5CC\ 6MVDL1K8GFKVBN69Q6T307U6O.17992
Another type of GNUnet filesharing URI, pointing to the search results of a search with keyword "gpl":
GNU Alternative Domain System 
GNUnet includes an implementation of the GNU Alternative Domain System (GADS), a decentralized and censorship-resistant replacement for DNS. In GADS, each user manages his own master zone which is mapped into the DNS namespace under the .gads top level domain. Users can delegate subdomains to zones managed by other users. Lookups of records defined by other users are performed using GNUnet's DHT. A major problem of this approach is that names are no longer globally unique, requiring the use of proxies and other workarounds to address common requirements of legacy applications.
Protocol Translation 
GNUnet can tunnel IP traffic over the peer-to-peer network. If necessary, GNUnet can perform IPv4-IPv6 protocol translation in the process. GNUnet provides a DNS Application-level gateway to proxy DNS requests and map addresses to the desired address family as necessary. This way, GNUnet offers a possible technology to facilitate IPv6 transition. Furthermore, in combination with GADS, GNUnet's protocol translation system can be used to access hidden services --- IP-based services that run locally at some peer in the network and which can only be accessed by resolving a GADS name.
A trivial chat module has been implemented more as a test than as a serious application, but it is usable.
See also 
- Anonymous P2P
- Comparison of file sharing applications
- Anonymous network software : Freenet, I2P, Tor (anonymity network)
- File sharing software : Share, Winny
- Grothoff, Christian (2012-12-21). "GNUnet 0.9.5 released". info-gnunet. http://lists.gnu.org/archive/html/info-gnunet/2012-12/msg00000.html. Retrieved 2012-12-26.
- Official website
- Paper describing ECRS (pdf file)
- A comparison of GNUnet with other peer-to-peer networking
- GNUnet adds VPN, direct wireless peering, and more, LWN.net, December 21, 2011
- Master's thesis about the GNU Alternative Domain System