tor-webwml.git

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2) # Revision: $Revision$
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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 (PT) 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)     <h3>How to use PTs to bypass censorship</h3>
36)     <p>

37)       If connections to the Tor network are being blocked by your ISP or
38)       country, follow these instructions:

39)     </p>
40)     <a href="$(IMGROOT)/PT/2016-07-how-to-use-PT.png">
41)     <img src="$(IMGROOT)/PT/2016-07-how-to-use-PT.png" width="830"
42)     alt="How to use PTs: 1-download tor (send email to gettor@torproject.org) 2-select configure 3-check 'my isp blocks tor...'
43)     4-select obfs4 5-press connect" /></a>
44)     <!-- TODO: move alt to instructions in plain text for visually impaird users -->
45) 

46)     <h3>How to run PTs to help censored users</h3>
47)     <p>
48)       obfs4 is currently the most effective transport to bypass censorship.

49)       To learn how to run this transport, please visit the <a href="https://trac.torproject.org/projects/tor/wiki/doc/PluggableTransports/obfs4proxy">obfs4proxy wiki page</a>.

50)     </p>
51) 

52)     <hr>
53) 

54)     <h3>Currently deployed PTs</h3>
55)     <p>
56)       These Pluggable Transports are currently deployed in Tor Browser, and you can start using them by <a href="<page download/download-easy>">downloading and using Tor Browser</a>.
57)     </p>
58) 
59)       <ul>
60) 
61)         <li><a href="https://github.com/Yawning/obfs4/blob/master/doc/obfs4-spec.txt"><b>obfs4</b></a>
62)         is a transport with the same features as <a href="http://www.cs.kau.se/philwint/scramblesuit/"><b>ScrambleSuit</b></a>
63)         but utilizing Dan Bernstein's <a href="http://elligator.cr.yp.to/elligator-20130828.pdf">elligator2</b></a>
64)         technique for public key obfuscation, and the
65)         <a href="https://gitweb.torproject.org/torspec.git/tree/proposals/216-ntor-handshake.txt">ntor protocol</a>
66)         for one-way authentication. This results in a faster protocol. Written in Go.
67)         Maintained by Yawning Angel.
68)         </li>
69)         <!-- TODO: update the link with repo hosted on git.tpo. and make a note that this client supports obfs3 -->
70) 
71)         <li><a href="https://trac.torproject.org/projects/tor/wiki/doc/meek"><b>meek</b></a>
72)         is a transport that uses HTTP for carrying bytes and TLS for
73)         obfuscation. Traffic is relayed through a third-party server
74)         (​Google App Engine). It uses a trick to talk to the third party so
75)         that it looks like it is talking to an unblocked server.
76)         Maintained by David Fifield.
77)         </li>
78)         <!-- TODO: add more info about meek. include amazon and azure and maybe remove google for now -->
79) 
80)         <li><a href="https://fteproxy.org/"><b>Format-Transforming
81)         Encryption</b></a> (FTE) transforms Tor traffic to arbitrary
82)         formats using their language descriptions. See the <a
83)         href="https://kpdyer.com/publications/ccs2013-fte.pdf">research
84)         paper</a>.</li>
85) 
86)         <li><a href="http://www.cs.kau.se/philwint/scramblesuit/"><b>ScrambleSuit</b></a>
87)         is a pluggable transport that protects
88)         against follow-up probing attacks and is also capable of changing
89)         its network fingerprint (packet length distribution,
90)         inter-arrival times, etc.). It's part of the Obfsproxy framework.
91)         Maintained by Philipp Winter.
92)         </li>
93) 
94)         <!-- TODO: it's unclear whether orbot still uses obfsclient or not;
95)                    commenting out untill furthure notice -->
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)         </li> -->
104) 
105)       </ul>
106) 
107)       <hr>
108) 
109)       <h3>Deprecated PTs; Removed from Tor Browser</h3>

110)       <br>

111)       <ul>
112)         <!-- TODO: add deprecation note for each PT -->

113)         <li><b>Obfsproxy</b> is a Python framework for implementing new

114)         pluggable transports. It uses Twisted for its networking needs, and
115)         <a href="https://gitweb.torproject.org/pluggable-transports/pyptlib.git/tree/README.rst">pyptlib</a>
116)         for some pluggable transport-related features. It supports the
117)         <a href="https://gitweb.torproject.org/pluggable-transports/obfsproxy.git/tree/doc/obfs2/obfs2-protocol-spec.txt">obfs2</a>
118)         and
119)         <a href="https://gitweb.torproject.org/pluggable-transports/obfsproxy.git/tree/doc/obfs3/obfs3-protocol-spec.txt">obfs3</a>
120)         pluggable transports. Maintained by asn.
121)         </li>
122) 
123)         <li><a href="https://crypto.stanford.edu/flashproxy/"><b>Flashproxy</b></a> turns ordinary web browsers into bridges using
124)         websockets, and has a little python stub to hook Tor clients to the
125)         websocket connection. See its
126)         <a href="https://gitweb.torproject.org/flashproxy.git">git repository</a>,
127)         and
128)         <a href="https://crypto.stanford.edu/flashproxy/flashproxy.pdf">design paper</a>.
129)         Maintained by David Fifield.
130)         <!-- # <iframe src="//crypto.stanford.edu/flashproxy/embed.html" width="80" height="15" frameborder="0" scrolling="no"></iframe> -->
131)         </li>
132) 
133)       </ul>
134) 
135)       <hr>
136) 
137)       <h3>Undeployed PTs</h3>

138)       <br>

139)       <!-- TODO: move this section to wiki -->
140)       <!-- TODO: add snowflake -->

141)     <ul>

142) 

143)     <li><b>StegoTorus</b> is an Obfsproxy fork that extends it to a)
144)     split Tor streams across multiple connections to avoid packet size
145)     signatures, and b) embed the traffic flows in traces that look like

146)     HTML, JavasCript, or PDF. See its

147)     <a href="https://gitweb.torproject.org/stegotorus.git">git repository</a>.

148)     Maintained by Zack Weinberg. <br>

149)     </li>
150) 
151)     <li><b>SkypeMorph</b> transforms Tor traffic flows so they look like
152)     Skype Video. See its
153)     <a href="http://crysp.uwaterloo.ca/software/SkypeMorph-0.5.1.tar.gz">source code</a>
154)     and
155)     <a href="http://cacr.uwaterloo.ca/techreports/2012/cacr2012-08.pdf">design paper</a>.

156)     Maintained by Ian Goldberg. <br>

157)     </li>
158) 
159)     <li><b>Dust</b> aims to provide a packet-based (rather than
160)     connection-based) DPI-resistant protocol. See its
161)     <a href="https://github.com/blanu/Dust">git repository</a>.

162)     Maintained by Brandon Wiley. <br>

163)     </li>
164) 
165)     </ul>

166) 
167)     <p> Also see the <emph>unofficial</emph> pluggable transports <a
168)     href="https://trac.torproject.org/projects/tor/wiki/doc/PluggableTransports">wiki
169)     page</a> for more pluggable transport information.</p>
170) 

171)     <hr>
172) 
173)     <p>

174)     Our goal is to have a wide variety of Pluggable Transport designs.

175)     Many are at the research phase now, so it's a perfect time to play
176)     with them or suggest new designs. Please let us know if you find or
177)     start other projects that could be useful for making Tor's traffic
178)     flows more DPI-resistant!
179)     </p>