A darknet (or dark net) is an overlay network that can only be accessed with specific software, configurations, or authorization, often using non-standard communications protocols and ports. Two typical darknet types are friend-to-friend networks (usually used for file sharing with a peer-to-peer connection) and anonymity networks such as Tor via an anonymized series of connections.
The reciprocal term for an encrypted darknet is clearnet or surface web when referring to search engine indexable content.
All darknets require specific software installed or network configurations made to access them, such as Tor which can be accessed via a customised browser from Vidalia, aka the Tor browser bundle or alternatively via a proxy server configured to perform the same function.
- Tor (The onion router) is an anonymity network that also features a darknet - its "hidden services". It is the most popular instance of a darknet.
- I2P (Invisible Internet Project) is another overlay network that features a darknet whose sites are called "Eepsites".
- Freenet is a popular darknet (friend-to-friend) by default; since version 0.7 it can run as a "opennet" (peer nodes are discovered automatically).
- RetroShare can be run as a darknet (friend-to-friend) by default to perform anonymous file transfers if DHT and Discovery features are disabled.
- GNUnet is a darknet if the "F2F (network) topology" option is enabled.
- Zeronet is open source software aimed to build an internet-like computer network of peer-to-peer users of Tor.
- Syndie is software used to publish distributed forums over the anonymous networks of I2P, Tor and Freenet.
- OneSwarm can be run as a darknet for friend-to-friend file-sharing.
- Tribler can be run as a darknet for file-sharing.
- Decentralized network 42 (not for anonymity but research purposes)