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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)     <li><b>Obfsproxy</b> is a framework for implementing new transport
39)     protocols in C using libevent. See its
40)     <a href="<page projects/obfsproxy>">web page</a>,
41)     <a href="https://gitweb.torproject.org/obfsproxy.git">git repository</a>,
42)     <a href="https://gitweb.torproject.org/obfsproxy.git/blob/HEAD:/doc/obfs2/protocol-spec.txt">obfs2 protocol description</a>,
43)     and
44)     <a href="https://blog.torproject.org/blog/obfsproxy-next-step-censorship-arms-race">blog post</a>.
45)     Maintained by George Kadianakis.
46)     </li>
47) 
48)     <li><b>Flashproxy</b> turns ordinary web browsers into bridges using
49)     websockets, and has a little python stub to hook Tor clients to the
50)     websocket connection. See its
51)     <a href="http://crypto.stanford.edu/flashproxy/">web page</a>,
52)     <a href="https://gitweb.torproject.org/flashproxy.git">git repository</a>,
53)     and
54)     <a href="http://crypto.stanford.edu/flashproxy/flashproxy.pdf">design paper</a>.
55)     Maintained by David Fifield.
56)     </li>
57) 
58)     <li><b>StegoTorus</b> is an Obfsproxy fork that extends it to a)
59)     split Tor streams across multiple connections to avoid packet size
60)     signatures, and b) embed the traffic flows in traces that look like
61)     html, javascript, or pdf. See its
62)     <a href="https://gitweb.torproject.org/stegotorus.git">git repository</a>.
63)     Maintained by Zack Weinberg.
64)     </li>
65) 
66)     <li><b>SkypeMorph</b> transforms Tor traffic flows so they look like
67)     Skype Video. See its
68)     <a href="http://crysp.uwaterloo.ca/software/SkypeMorph-0.5.1.tar.gz">source code</a>
69)     and
70)     <a href="http://cacr.uwaterloo.ca/techreports/2012/cacr2012-08.pdf">design paper</a>.

71)     Maintained by Ian Goldberg.

72)     </li>
73) 
74)     <li><b>Dust</b> aims to provide a packet-based (rather than
75)     connection-based) DPI-resistant protocol. See its
76)     <a href="https://github.com/blanu/Dust">git repository</a>.
77)     Maintained by Brandon Wiley.
78)     </li>
79) 

80)     <li><b>Format-Transforming Encryption</b> transforms Tor traffic
81)     to arbitrary formats using their language descriptions. See
82)     the <a href="http://eprint.iacr.org/2012/494">research
83)     paper</a>. The scheme is not deployed yet.
84)     </li>
85) 

86)     </ul>

87)     <hr>
88) 
89)     <p>
90)     Our goal is to have a wide variety of pluggable transport designs.
91)     Many are at the research phase now, so it's a perfect time to play
92)     with them or suggest new designs. Please let us know if you find or
93)     start other projects that could be useful for making Tor's traffic
94)     flows more DPI-resistant!
95)     </p>