Retroshare

Retroshare is a free and open-source peer-to-peer communication and app based on a friend-to-friend network built by GNU Privacy Guard (GPG). Optionally, peers may exchange certificates and IP addresses to their friends and vice versa. Retroshare was founded in 2004 by Mark Fernie. An unofficial build for the single-board computer Raspberry Pi, named PiShare, since 2012. On 4 November 2014, Retroshare scored 6 out of 7 points on the Electronic Frontier Foundation's secure messaging scorecard, which is now out-of-date. It lost a point because there had not been a recent independent code audit. In August 2015, Retroshare repository was migrated from SourceForge to GitHub. In 2016, Linux Magazine reviewed security gaps in Retroshare and described it as "a brave effort, but, in the end, an ineffective one." Retroshare is an instant messaging and network that uses a distributed hash table for address discovery. Users can communicate indirectly through mutual friends and request direct connections. After initial installation, the user generates a pair of (GPG) cryptographic keys with Retroshare. After authentication and exchanging an asymmetric key, OpenSSL is used to establish a connection, and for end-to-end encryption. Friends of friends cannot connect by default, but they can see each other, if the users allow it. IPv6 support was merged into the master branch and will be released in the next version. It is possible to share folders between friends. File transfer is carried on using a multi-hop swarming system (inspired by the "Turtle Hopping" feature from the Turtle F2F project, but implemented differently). In essence, data is only exchanged between friends, although it is possible that the ultimate source and destination of a given transfer are multiple friends apart. A search function performing anonymous multi-hop search is another source of finding files in the network. Files are represented by their SHA-1 hash value, and HTTP-compliant file and links may be exported, copied, and pasted into/out of Retroshare to publish their virtual location into the Retroshare network.