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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/blob/HEAD:/proposals/180-pluggable-transport.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><b>Obfsproxy</b> 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/blob/HEAD:/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/blob/HEAD:/doc/obfs2/obfs2-protocol-spec.txt">obfs2</a>

44)     and

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

46)     pluggable transports. Maintained by George Kadianakis. <br>
47) 

48)     Status: <a href="https://www.torproject.org/projects/obfsproxy.html.en#download">Deployed</a>

49)     </li>
50) 
51)     <li><b>Flashproxy</b> turns ordinary web browsers into bridges using
52)     websockets, and has a little python stub to hook Tor clients to the
53)     websocket connection. See its
54)     <a href="http://crypto.stanford.edu/flashproxy/">web page</a>,
55)     <a href="https://gitweb.torproject.org/flashproxy.git">git repository</a>,
56)     and
57)     <a href="http://crypto.stanford.edu/flashproxy/flashproxy.pdf">design paper</a>.

58)     Maintained by David Fifield.

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

60)     <br>

61)     Status: <a href="https://crypto.stanford.edu/flashproxy/#how-to">Deployed</a>

62)     </li>
63) 

64)     <li><b>ScrambleSuit</b> is a pluggable transport that protects
65)     against follow-up probing attacks and is also capable of changing
66)     its network fingerprint (packet length distribution,
67)     inter-arrival times, etc.). It's part of the Obfsproxy framework. See its
68)     <a href="http://www.cs.kau.se/philwint/scramblesuit/">official page</a>.
69)     Maintained by Philipp Winter. <br>
70)     Status: <em>Undeployed</em>
71)     </li>
72) 

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

78)     Maintained by Zack Weinberg. <br>
79)     Status: <em>Undeployed</em>

80)     </li>
81) 
82)     <li><b>SkypeMorph</b> transforms Tor traffic flows so they look like
83)     Skype Video. See its
84)     <a href="http://crysp.uwaterloo.ca/software/SkypeMorph-0.5.1.tar.gz">source code</a>
85)     and
86)     <a href="http://cacr.uwaterloo.ca/techreports/2012/cacr2012-08.pdf">design paper</a>.

87)     Maintained by Ian Goldberg. <br>
88)     Status: <em>Undeployed</em>

89)     </li>
90) 
91)     <li><b>Dust</b> aims to provide a packet-based (rather than
92)     connection-based) DPI-resistant protocol. See its
93)     <a href="https://github.com/blanu/Dust">git repository</a>.

94)     Maintained by Brandon Wiley. <br>
95)     Status: <em>Undeployed</em>

96)     </li>
97) 

98)     <li><b>Format-Transforming Encryption</b> transforms Tor traffic
99)     to arbitrary formats using their language descriptions. See

100)     the <a href="https://eprint.iacr.org/2012/494">research

101)     paper</a>. <br>
102)     Status: <em>Undeployed</em>

103)     </li>
104) 

105)     </ul>

106)     <hr>
107) 
108)     <p>
109)     Our goal is to have a wide variety of pluggable transport designs.
110)     Many are at the research phase now, so it's a perfect time to play
111)     with them or suggest new designs. Please let us know if you find or
112)     start other projects that could be useful for making Tor's traffic
113)     flows more DPI-resistant!
114)     </p>