BitTorrent protocol encryption: Difference between revisions

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Revision as of 10:01, 5 February 2006

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'''Protocol header encryptionencrypt''' ('''PHE'''), '''Message stream encryption''' ('''MSE'''), or '''Protocol encryption''' ('''PE''') are features of some [[BitTorrent]] clients that attempt to make BitTorrent hard to throttle. Some [[Internet service provider|ISP]]s throttle BitTorrent traffic because it makes up a large porportion of total traffic and the ISPs don't want to spend money buying extra capacity. Instead, the ISPs spend money on hardware that look for BitTorrent traffic and slow them down.

==History==

Protocol header encryptionencrypt was conceived by [[RnySmile]] and first implemented in the [[BitComet]] client version 0.60 on [[8 September]] [[2005]]. Some software like IPP2P claims BitComet is detectable even with PHE[http://www.ipp2p.org/news_en.html]. Since there are no open specifications to this protocol implementation the only possiblity to support it would have been via [[reverse engineering]].

In late January 2006 the [[Azureus]] developers decided to design and simultanously implement a new, open protocol obfuscation method. It was included in Azureus CVS snapshot 2307-B29 on [[19 January]] [[2006]].

[http://sourceforge.net/mailarchive/forum.php?thread_id=9517694&forum_id=40629]

In the late January of 2006 the Azureus developers decided to design and simultanously implement a new protocol obfuscation method that was openly specified. This first draft was heavily critizied since it lacked several key features the later version should include. After negotations between different BitTorrent developers a new proposal was written and then implemented into the respective [[µTorrent]] and [[Azureus]] betas within days.

Azureus supports the final spec since [[25 January]] [[2006]] (versionCVS 2.3.0.7snapshot 2307-B33) [http://sourceforge.net/mailarchive/message.php?msg_id=14596518] and µTorrent followed 4 days later with Betabeta 1.4.1 build 407. The new protocol is called MSE in Azureus and PE in µTorrent.

[[Bram Cohen]], the inventor of [[BitTorrent]], recently commented disfavouring on the ongoing development to obfuscate the BitTorrent protocol. [http://bramcohen.livejournal.com/29886.html]

==Operation==

The BitComet PHE method is not published. andIt is incompatible with MSE/PE.

MSE/PE uses a [[D-H]] exchange to establish the key, then it uses [[RC4]] to encrypt the data. The specification allows the users to choose between encrypting the headers only or the full connection to perform a CPU time/obfuscation tradeoff. However, PE only supports full encryption.

MSE/PE uses a [[D-H]] exchange to establish the key, then it uses [[RC4]] to encrypt the data. The specification allows the users to choose between header-only and a fullblown stream encryption to perform a CPU time/obfuscation tradeoff. To ensure compatibility with other clients that don't support this specification a userusers may also choose whether unencrypted incoming or outgoing connections are still allowed.

The estimated strength of the encryption lies around 60-80bit (see [http://www.faqs.org/rfcs/rfc3526.html RFC3526] chapter 8) of common symmetric encryption algorithms, which is quite low for todays cryptographic standards but one has to keep in mind that this protocol wasn't designed as a secure transport protocol like SSL or SSH but as fast and efficient mean to obfuscated the transported content.

The estimated strength of the encryption liesis around 60-80bit80 bits symmetrical (see [http://www.faqs.org/rfcs/rfc3526.html RFC3526] chapter 8). of common symmetric encryption algorithms, whichThis is quite low for todays cryptographictoday's standards but one has to keep in mind that this protocol wasn't designed as a secure transport protocol like SSL or SSH but as fast and efficient mean to obfuscated the transportedobfuscation contentmethod.

==External link==

*[http://azureus.aelitis.com/wiki/index.php/Message_Stream_Encryption Description on the official Azureus wiki]

*[http://azureus.aelitis.com/wiki/index.php/Bad_ISPs AnISPs evergrowingthat list ofshape BitTorrent trafficon shapingthe ISPsofficial Azureus wiki]

[[Category:BitTorrent]]

[[Category:Cryptographic protocols]]