Editing BitTorrent (section)

=== Throttling and encryption ===
{{Main|BitTorrent protocol encryption}}

Since BitTorrent makes up a large proportion of total traffic, some [[ISP]]s have chosen to "throttle" (slow down) BitTorrent transfers. For this reason, methods have been developed to disguise BitTorrent traffic in an attempt to thwart these efforts.<ref>{{cite web|url=https://torrentfreak.com/encrypting-bittorrent-to-take-out-traffic-shapers/|title=Encrypting Bittorrent to take out traffic shapers|date=5 February 2006|publisher=Torrentfreak.com|url-status=live|archive-url=https://web.archive.org/web/20140326092903/http://torrentfreak.com/encrypting-bittorrent-to-take-out-traffic-shapers/|archive-date=26 March 2014|access-date=9 May 2006}}</ref> Protocol header encrypt (PHE) and [[BitTorrent protocol encryption|Message stream encryption/Protocol encryption (MSE/PE)]] are features of some BitTorrent clients that attempt to make BitTorrent hard to detect and throttle. As of November 2015, [[Vuze]], [[BitComet]], [[KTorrent]], [[Transmission (BitTorrent client)|Transmission]], [[Deluge (BitTorrent client)|Deluge]], [[μTorrent]], MooPolice, Halite, [[qBittorrent]], [[rTorrent]], and the latest official BitTorrent client (v6) support MSE/PE encryption.

In August 2007, [[Comcast]] was preventing BitTorrent seeding by monitoring and interfering with the communication between peers. Protection against these efforts is provided by [[proxy server|proxying]] the client-tracker traffic via an [[tunneling protocol|encrypted tunnel]] to a point outside of the Comcast network.<ref>{{cite web|url=https://torrentfreak.com/comcast-throttles-bittorrent-traffic-seeding-impossible/|title=Comcast Throttles BitTorrent Traffic, Seeding Impossible|url-status=live|archive-url=https://web.archive.org/web/20131011044156/http://torrentfreak.com/comcast-throttles-bittorrent-traffic-seeding-impossible/|archive-date=11 October 2013}}, ''TorrentFreak'', 17 August 2007.</ref> In 2008, Comcast called a "truce" with BitTorrent, Inc. with the intention of shaping traffic in a protocol-agnostic manner.<ref>{{cite web|url=https://www.cnet.com/news/comcast-and-bittorrent-agree-to-collaborate/|title=Comcast and BitTorrent Agree to Collaborate|last=Broache|first=Anne|date=27 March 2008|publisher=News.com|url-status=live|archive-url=https://web.archive.org/web/20080509150131/http://www.news.com/8301-10784_3-9904494-7.html|archive-date=9 May 2008|access-date=9 July 2012}}</ref> Questions about the ethics and legality of Comcast's behavior have led to renewed debate about [[net neutrality in the United States]].<ref>{{cite web|url=https://www.cnet.com/news/is-comcasts-bittorrent-filtering-violating-the-law/|title=Is Comcast's BitTorrent filtering violating the law?|last=Soghoian|first=Chris|date=4 September 2007|website=Cnet.com|url-status=live|archive-url=https://web.archive.org/web/20100715153001/http://www.cnet.com/8301-13739_1-9769645-46.html|archive-date=15 July 2010|access-date=9 July 2012}}</ref> In general, although encryption can make it difficult to determine ''what'' is being shared, BitTorrent is vulnerable to [[traffic analysis]]. Thus, even with MSE/PE, it may be possible for an ISP to recognize BitTorrent and also to determine that a system is no longer downloading but only uploading data, and terminate its connection by injecting [[Transmission Control Protocol|TCP]] RST (reset flag) packets.