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5) #include "head.wmi" TITLE="Tor Project: Pluggable Transports" CHARSET="UTF-8"
6) <div id="content" class="clearfix">
7)   <div id="breadcrumbs">
8)     <a href="<page index>">Home &raquo; </a>
9)     <a href="<page docs/documentation>">Documentation &raquo; </a>
10)     <a href="<page docs/pluggable-transports>">Pluggable Transports</a>
11)   </div>
12)   <div id="maincol">
13)     <h2>Tor: Pluggable Transports</h2>
14)     <hr>
15) 
16)     <p>
17)     An increasing number of censoring countries are using Deep Packet
18)     Inspection (DPI) to classify Internet traffic flows by protocol.
19)     While Tor uses <a href="<page docs/bridges>">bridge relays</a> to
20)     get around a censor that blocks by IP address, the censor can use
21)     DPI to recognize and filter Tor traffic flows even when they connect
22)     to unexpected IP addresses.
23)     </p>
24) 
25)     <p>
26)     Pluggable transports transform the Tor traffic flow between the client
27)     and the bridge. This way, censors who monitor traffic between the
28)     client and the bridge will see innocent-looking transformed traffic
29)     instead of the actual Tor traffic.
30)     External programs can talk to Tor clients and Tor bridges using the <a

31) href="https://gitweb.torproject.org/torspec.git/tree/pt-spec.txt">pluggable

32) transport API</a>, to make it easier to build interoperable programs.
33)     </p>
34) 
35)     <hr>
36) 
37)     <ul>

38) 

39)     <li><a href="<page projects/obfsproxy>"><b>Obfsproxy</b></a> is a Python framework for implementing new

40)     pluggable transports. It uses Twisted for its networking needs, and

41)     <a href="https://gitweb.torproject.org/pluggable-transports/pyptlib.git/tree/README.rst">pyptlib</a>

42)     for some pluggable transport-related features. It supports the

43)     <a href="https://gitweb.torproject.org/pluggable-transports/obfsproxy.git/tree/doc/obfs2/obfs2-protocol-spec.txt">obfs2</a>

44)     and

45)     <a href="https://gitweb.torproject.org/pluggable-transports/obfsproxy.git/tree/doc/obfs3/obfs3-protocol-spec.txt">obfs3</a>

46)     pluggable transports. Maintained by asn. <br>

47)     Status: <a href="#download">Deployed</a>

48)     </li>
49) 

50)     <li><a href="https://crypto.stanford.edu/flashproxy/"><b>Flashproxy</b></a> turns ordinary web browsers into bridges using

51)     websockets, and has a little python stub to hook Tor clients to the
52)     websocket connection. See its
53)     <a href="https://gitweb.torproject.org/flashproxy.git">git repository</a>,
54)     and

55)     <a href="https://crypto.stanford.edu/flashproxy/flashproxy.pdf">design paper</a>.

56)     Maintained by David Fifield.

57)     # <iframe src="//crypto.stanford.edu/flashproxy/embed.html" width="80" height="15" frameborder="0" scrolling="no"></iframe>

58)     <br>

59)     Status: <a href="#download">Deployed</a>

60)     </li>
61) 

62)     <li><a href="https://fteproxy.org/"><b>Format-Transforming
63)     Encryption</b></a> (FTE) transforms Tor traffic to arbitrary
64)     formats using their language descriptions. See the <a
65)     href="https://kpdyer.com/publications/ccs2013-fte.pdf">research
66)     paper</a>. <br> Status: <a href="#download">Deployed</a> </li>
67) 
68)     <li><a href="http://www.cs.kau.se/philwint/scramblesuit/"><b>ScrambleSuit</b></a>
69)     is a pluggable transport that protects

70)     against follow-up probing attacks and is also capable of changing
71)     its network fingerprint (packet length distribution,

72)     inter-arrival times, etc.). It's part of the Obfsproxy framework.

73)     Maintained by Philipp Winter. <br>

74)     Status: <em>To be deployed</em>
75)     </li>
76) 

77)     <li><a href="https://trac.torproject.org/projects/tor/wiki/doc/meek"><b>Meek</b></a>
78)     is a transport that uses HTTP for carrying bytes and TLS for
79)     obfuscation. Traffic is relayed through a third-party server
80)     (​Google App Engine). It uses a trick to talk to the third party so
81)     that it looks like it is talking to an unblocked server.

82)     Maintained by David Fifield. <br>
83)     Status: <e>Coming soon</em>

84)     </li>
85) 

86)     <li><a href="https://github.com/Yawning/obfs4/blob/master/doc/obfs4-spec.txt"><b>obfs4</b></a>
87)     is a transport with the same features as <a href="http://www.cs.kau.se/philwint/scramblesuit/"><b>ScrambleSuit</b></a>

88)     but utilizing Dan Bernstein's <a href="http://elligator.cr.yp.to/elligator-20130828.pdf">elligator2</b></a>

89)     technique for public key obfuscation, and the

90)     <a href="https://gitweb.torproject.org/torspec.git/tree/proposals/216-ntor-handshake.txt">ntor protocol</a>

91)     for one-way authentication. This results in a faster protocol. Written in Go.
92)     Maintained by Yawning Angel. <br>
93)     Status: <e>Coming soon</em>
94)     </li>
95) 
96)     <li><a href="https://github.com/yawning/obfsclient"><b>obfsclient</b></a>
97)     is a multi-transport pluggable transport proxy (like obfsproxy),
98)     written in C++ that implements the client-side of <em>obfs2</em>,
99)     <em>obfs3</em> and <em>scramblesuit</em>. It's used by
100)     <a href="https://guardianproject.info/apps/orbot/">Orbot</a> on
101)     Android because of the difficulties of using Python applications.
102)     Maintained by Yawning Angel. <br>
103)     Status: <a href="https://guardianproject.info/apps/orbot/">Deployed</a>
104)     </li>
105) 

106)     <li><b>StegoTorus</b> is an Obfsproxy fork that extends it to a)
107)     split Tor streams across multiple connections to avoid packet size
108)     signatures, and b) embed the traffic flows in traces that look like
109)     html, javascript, or pdf. See its
110)     <a href="https://gitweb.torproject.org/stegotorus.git">git repository</a>.

111)     Maintained by Zack Weinberg. <br>
112)     Status: <em>Undeployed</em>

113)     </li>
114) 
115)     <li><b>SkypeMorph</b> transforms Tor traffic flows so they look like
116)     Skype Video. See its
117)     <a href="http://crysp.uwaterloo.ca/software/SkypeMorph-0.5.1.tar.gz">source code</a>
118)     and
119)     <a href="http://cacr.uwaterloo.ca/techreports/2012/cacr2012-08.pdf">design paper</a>.

120)     Maintained by Ian Goldberg. <br>
121)     Status: <em>Undeployed</em>

122)     </li>
123) 
124)     <li><b>Dust</b> aims to provide a packet-based (rather than
125)     connection-based) DPI-resistant protocol. See its
126)     <a href="https://github.com/blanu/Dust">git repository</a>.

127)     Maintained by Brandon Wiley. <br>
128)     Status: <em>Undeployed</em>

129)     </li>
130) 
131)     </ul>

132) 
133)     <p> Also see the <emph>unofficial</emph> pluggable transports <a
134)     href="https://trac.torproject.org/projects/tor/wiki/doc/PluggableTransports">wiki
135)     page</a> for more pluggable transport information.</p>
136) 

137)     <hr>
138) 
139)     <p>
140)     Our goal is to have a wide variety of pluggable transport designs.
141)     Many are at the research phase now, so it's a perfect time to play
142)     with them or suggest new designs. Please let us know if you find or
143)     start other projects that could be useful for making Tor's traffic
144)     flows more DPI-resistant!
145)     </p>

146) 

147)     <hr>

148)     <a id="download"></a>

149)     <h2><a href="<page download/download-easy>">Download the Pluggable Transports Tor Browser</a></h2>

150)     <p>

151)     As of Tor Browser 3.6-beta-1, pluggable transports are now included in the

152) <a href="<page download/download-easy>">official

153) Tor Browser packages</a>.

154)     </p>
155)