BitTorrent
BitTorrent, also referred to as simply torrent, is a communication protocol for peer-to-peer file sharing (P2P), which enables users to distribute data and electronic files over the Internet in a decentralized manner. The protocol is developed and maintained by Rainberry, Inc., and was first released in 2001.[2]
This article is about the file sharing protocol. For other uses, see BitTorrent (disambiguation).Original author(s)
2001
The BitTorrent Protocol Specification[1]
To send or receive files, users use a BitTorrent client on their Internet-connected computer, which are available for a variety of computing platforms and operating systems, including an official client. BitTorrent trackers provide a list of files available for transfer and allow the client to find peer users, known as "seeds", who may transfer the files. BitTorrent downloading is considered to be faster than HTTP ("direct downloading") and FTP due to the lack of a central server that could limit bandwidth.[3][4]
BitTorrent is one of the most common protocols for transferring large files, such as digital video files containing TV shows and video clips, or digital audio files containing songs. BitTorrent accounted for a third of all internet traffic in 2004, according to a study by Cachelogic.[5] As recently as 2019 BitTorrent remained a significant file sharing protocol according to Sandvine, generating a substantial amount of Internet traffic, with 2.46% of downstream, and 27.58% of upstream traffic,[6] although this share has declined significantly since then.[7]
Associated technologies[edit]
Distributed trackers[edit]
On 2 May 2005, Azureus 2.3.0.0 (now known as Vuze) was released,[40] utilizing a distributed database system. This system is a distributed hash table implementation which allows the client to use torrents that do not have a working BitTorrent tracker. A bootstrap server is instead utilized.. The following month, BitTorrent, Inc. released version 4.2.0 of the Mainline BitTorrent client, which supported an alternative DHT implementation (popularly known as "Mainline DHT", outlined in a draft on their website) that is incompatible with that of Azureus. In 2014, measurement showed concurrent users of Mainline DHT to be from 10 million to 25 million, with a daily churn of at least 10 million.[41]
Current versions of the official BitTorrent client, μTorrent, BitComet, Transmission and BitSpirit all share compatibility with Mainline DHT. Both DHT implementations are based on Kademlia.[42] As of version 3.0.5.0, Azureus also supports Mainline DHT in addition to its own distributed database through use of an optional application plugin.[43] This potentially allows the Azureus/Vuze client to reach a bigger swarm.
Another idea that has surfaced in Vuze is that of virtual torrents. This idea is based on the distributed tracker approach and is used to describe some web resource. Currently, it is used for instant messaging. It is implemented using a special messaging protocol and requires an appropriate plugin. Anatomic P2P is another approach, which uses a decentralized network of nodes that route traffic to dynamic trackers. Most BitTorrent clients also use peer exchange (PEX) to gather peers in addition to trackers and DHT. Peer exchange checks with known peers to see if they know of any other peers. With the 3.0.5.0 release of Vuze, all major BitTorrent clients now have compatible peer exchange.
Security[edit]
One concern is the UDP flood attack. BitTorrent implementations often use μTP for their communication. To achieve high bandwidths, the underlying protocol used is UDP, which allows spoofing of source addresses of internet traffic. It has been possible to carry out denial-of-service attacks in a P2P lab environment, where users running BitTorrent clients act as amplifiers for an attack at another service.[115] However this is not always an effective attack because ISPs can check if the source address is correct.
Several studies on BitTorrent found files available for download containing malware. In particular, one small sample indicated that 18% of all executable programs available for download contained malware.[116] Another study claims that as much as 14.5% of BitTorrent downloads contain zero-day malware, and that BitTorrent was used as the distribution mechanism for 47% of all zero-day malware they have found.[117]
