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 Developer(s) GNUnet with the GTK+ user interface GNUnet e.V. [1] November 5, 2001 ; 20 years ago 0.17.1 (June 13, 2022 ; 3 months ago [2] ) C [3] official: Free software operating systems ( Linux , FreeBSD , NetBSD , OpenBSD ); unofficial: Other operating systems ( OS X , Windows ) Spanish, English, Russian, German, French Anonymous P2P , Friend-to-friend 2018: AGPL-3.0-or-later [a] [4] 2007: GPL-3.0-or-later [b] 2001: GPL-2.0-or-later [c]
Christian Grothoff , maintainer of GNUnet, in Berlin on August 1, 2013 at the " #youbroketheinternet. We'll make ourselves a GNU one. " event.

GNUnet is a 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 , WLAN and Bluetooth ) and various basic peer-to-peer algorithms for routing , multicast and network size estimation . [5] [6]

GNUnet's basic network topology is that of a mesh network . GNUnet includes a distributed hash table (DHT) 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 , although an application has been made). [ when? ] 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 there are bindings in other languages to produce an API for developing extensions in those languages. GNUnet is part of the GNU Project . It has gained interest in the hacker community after the PRISM revelations. [7]

GNUnet consists of several subsystems, of which essential ones are Transport and Core subsystems. [8] Transport subsystem provides insecure link-layer communications, while Core provides peer discovery and encryption. [9] On top of the core subsystem various applications are built.

GNUnet includes various P2P applications in the main distribution of the framework, including filesharing, chat and VPN; additionally, a few external projects (such as secushare ) are also extending the GNUnet infrastructure.

GNUnet is unrelated to the older Gnutella P2P protocol. Gnutella is not an official GNU project, while GNUnet is. [10]

## Transport

Originally, GNUnet used UDP for underlying transport. [11] Now GNUnet transport subsystem provides multiple options, such as TCP and SMTP. [12]

The communication port, officially registered at IANA , is 2086 ( tcp + udp ). [13]

## Trust system

GNUnet provides trust system based on excess-based economic model. [14] The idea of employing economic system is taken from MojoNation network. [15]

GNUnet network has no trusted entities so it is impossible to maintain global reputation . Instead, each peer maintains its own trust for each of its local links.

When resources, such as bandwidth and CPU time, are in excess, peer provides them to all requesting neighbors without reducing trust or otherwise charging them. When a node is under stress it drops requests from its neighbor nodes having lower internal trust value. However, when peer has less resources than enough to fulfill everyone's requests, it denies requests of those neighbors that it trusts less and charges others by reducing their trust.

## 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. The GNUnet protocol which provides anonymity is called GAP (GNUnet anonymity protocol). [16] GNUnet FS can additionally make use of GNU libextractor to automatically annotate shared files with metadata .

### File encoding

Files shared with GNUnet are ECRS (An Encoding for Censorship-Resistant Sharing) coded. [17]

All content is represented as GBlocks. Each GBlock contains 1024 bytes. There are several types of GBlocks, each of them serves a particular purpose. Any GBlock ${\displaystyle B}$ is uniquely identified by its RIPEMD-160 hash ${\displaystyle H(B)}$ .

DBlocks store actual file contents and nothing else. File is split at 1024 byte boundaries and resulting chunks are stored in DBlocks. DBlocks are linked together into Merkle tree by means of IBlocks that store DBlock identifiers.

Blocks are encrypted with a symmetric key derived from ${\displaystyle H(B)}$ when they are stored in the network.

### Queries and replies

GNUnet Anonymity Protocol consists of queries and replies. Depending on load of the forwarding node, messages are forwarded to zero or more nodes.

Queries are used to search for content and request data blocks.

Query contains resource identifier, reply address, priority and TTL (Time-to-Live).

Resource identifier of datum ${\displaystyle Q}$ is a triple-hash ${\displaystyle H(H(H(Q)))}$ . [18] Peer that replies to query provides ${\displaystyle H(H(Q))}$ to prove that it indeed has the requested resource without providing ${\displaystyle H(Q)}$ to intermediate nodes, so intermediate nodes can't decrypt ${\displaystyle Q}$ .

Priority specifies how much of its trust user wants to spend in case of resource shortage.

TTL is used to prevent queries from staying in the network for too long.

### File sharing URIs

The fs module identifier consists of either chk , sks , ksk or loc followed by a slash and a category specific value. Most URIs contain hashes, which are encoded in base32hex . [19]

• chk identifies files, typically: ``` gnunet://fs/chk/[file hash].[query hash].[file size in bytes] ```
File hash is the hash of the plaintext file, which allows decrypting it once it is downloaded. Query hash is the hash of topmost GBlock which allows downloading the whole tree of GBlocks that contain encrypted file. File size is required to determine the shape of the tree.
• 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 ```

#### Examples

A type of GNUnet filesharing URI pointing to a specific copy of GNU GPL license text: ``` gnunet://fs/chk/9E4MDN4VULE8KJG6U1C8FKH5HA8C5CHSJTILRTTPGK8MJ6VHORERHE68JU8Q0FDTOH1DGLUJ3NLE99N0ML0N9PIBAGKG7MNPBTT6UKG.1I823C58O3LKS24LLI9KB384LH82LGF9GUQRJHACCUINSCQH36SI4NF88CMAET3T3BHI93D4S0M5CC6MVDL1K8GFKVBN69Q6T307U6O.17992 ```

Another type of GNUnet filesharing URI, pointing to the search results of a search with keyword "gpl": ``` gnunet://fs/ksk/gpl ```

## GNU Name System

GNUnet includes an implementation of the GNU Name System (GNS), a decentralized and censorship-resistant replacement for DNS . In GNS, each user manages their own zones and can delegate subdomains to zones managed by other users. Lookups of records defined by other users are performed using GNUnet's DHT. [20]

## 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 GNS, 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 GNS name.

## Social API

Gabor X Toth published in early September 2013 a thesis [21] to present the design of a social messaging service for the GNUnet peer-to-peer framework that offers scalability, extensibility, and end-to-end encrypted communication. The scalability property is achieved through multicast message delivery, while extensibility is made possible by using PSYC (Protocol for SYnchronous Conferencing), which provides an extensible RPC (Remote Procedure Call) syntax that can evolve over time without having to upgrade the software on all nodes in the network. Another key feature provided by the PSYC layer are stateful multicast channels, which are used to store e.g. user profiles. End-to-end encrypted communication is provided by the mesh service of GNUnet, upon which the multicast channels are built. Pseudonymous users and social places in the system have cryptographical identities — identified by their public key — these are mapped to human memorable names using GNS ( GNU Name System ), where each pseudonym has a zone pointing to its places.

That is the required building block for turning the GNUnet framework into a fully peer-to-peer social networking platform.

## Chat

A chat has been implemented in the CADET module, [22] for which a GTK interface for GNOME exists, [23] specifically designed for the emerging Linux phones (such as the Librem 5 or the PinePhone ). [24]

## Notes

1. AGPL-3.0-or-later since 2018-06-05.
2. GPL-3.0-or-later from 2007-07-02 until 2018-06-05.
3. GPL-2.0-or-later from 2001 until 2007-07-02.

## References

1. Schanzenbach, Martin (2022-06-13). [hhttps://www.gnunet.org/en/news/2022-06-0.17.1.html "2022-06-13: GNUnet 0.17.1 released"]. gnunet.org . Retrieved 2022-06-17 .
2. "license notice placed at the top in one of the source files of the project's repository, probably in each of its source files" . Retrieved June 8, 2018 . GNUnet is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
3. Grothoff, Christian (2017-10-10). The GNUnet System (habilitation thesis). Université de Rennes 1.
4. FerreiraGrothoffRuth 2003 , Figure 1.
5. FerreiraGrothoffRuth 2003 , II. GNUNET AND THE TRANSPORT LAYER: "The core is responsible for link-to-link encryption, binding of node identities to routable addresses, and peer discovery."
6. "GNU Software" . Software - GNU Project - Free Software Foundation . Free Software Foundation, Inc . Retrieved 25 January 2020 .
7. GrothoffPatrascuBennettStef 2002 , 3.1.1 UDP.
8. GrothoffPatrascuBennettStef 2002 , 2.4 Mojo Nation.
9. GrothoffPatrascuBennettStef 2002 , 5.5 More on queries.
10. Grothoff, Christian. "File-Sharing URIs" . www.gnunet.org . Retrieved 15 July 2016 .
11. Wachs 2014 .
12. Toth, Gabor X (2013-09-05), Design of a Social Messaging System Using Stateful Multicast Archived 2014-02-22 at the Wayback Machine - Retrieved 2013-09-28
13. GNUnet.org documentation (2019-11-14) Chatting with a (simple) client - Retrieved 2019-11-14