tor-webwml.git

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5) #include "head.wmi" TITLE="Tor Project: Overview" 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 about/overview>">About &raquo; </a>

10)   </div>
11)   <div id="maincol">

12)     <h2>Tor: Overview</h2>

13)     <!-- BEGIN SIDEBAR -->
14)     <div class="sidebar-left">
15)       <h3>Topics</h3>
16)       <ul>

17)         <li><a href="<page about/overview>#overview">Overview</a></li>

18)         <li><a href="<page about/overview>#whyweneedtor">Why we need Tor</a></li>
19)         <li><a href="<page about/overview>#thesolution">The Solution</a></li>
20)         <li><a href="<page about/overview>#stayinganonymous">Staying anonymous</a></li>
21)         <li><a href="<page about/overview>#thefutureoftor">The future of Tor</a></li>
22)       </ul>
23)     </div>
24)     <!-- END SIDEBAR -->

25) 

26)     <hr>

27) 

28)     <a name="overview"></a>

29)     <h3><a class="anchor" href="#overview">Overview</a></h3>

30) 

31)     <p>
32)     Tor is a network of virtual tunnels that allows people and groups to
33)     improve their privacy and security on the Internet.  It also enables
34)     software developers to create new communication tools
35)     with built-in privacy features.  Tor provides the foundation for
36)     a range of applications that allow organizations and individuals
37)     to share information over public networks without compromising their
38)     privacy.
39)     </p>

40) 

41)     <p>
42)     Individuals use Tor to keep websites from tracking them and their family
43)     members, or to connect to news sites, instant messaging services, or the
44)     like when these are blocked by their local Internet providers.  Tor's <a
45)     href="<page docs/hidden-services>">hidden services</a>
46)     let users publish web sites and other services without needing to reveal
47)     the location of the site. Individuals also use Tor for socially sensitive
48)     communication: chat rooms and web forums for rape and abuse survivors,
49)     or people with illnesses.
50)     </p>

51) 

52)     <p>
53)     Journalists use Tor to communicate more safely with whistleblowers and
54)     dissidents. Non-governmental organizations (NGOs) use Tor to allow their
55)     workers to connect to their home website while they're in a foreign
56)     country, without notifying everybody nearby that they're working with
57)     that organization.
58)     </p>

59) 

60)     <p>
61)     Groups such as Indymedia recommend Tor for safeguarding their members'
62)     online privacy and security. Activist groups like the Electronic Frontier
63)     Foundation (EFF) recommend Tor as a mechanism for
64)     maintaining civil liberties online. Corporations use Tor as a safe way
65)     to conduct competitive analysis, and to protect sensitive procurement
66)     patterns from eavesdroppers. They also use it to replace traditional
67)     VPNs, which reveal the exact amount and timing of communication. Which
68)     locations have employees working late? Which locations have employees
69)     consulting job-hunting websites? Which research divisions are communicating
70)     with the company's patent lawyers?
71)     </p>

72) 

73)     <p>
74)     A branch of the U.S. Navy uses Tor for open source intelligence
75)     gathering, and one of its teams used Tor while deployed in the Middle
76)     East recently. Law enforcement uses Tor for visiting or surveilling
77)     web sites without leaving government IP addresses in their web logs,
78)     and for security during sting operations.
79)     </p>

80) 

81)     <p>
82)     The variety of people who use Tor is actually <a
83)     href="http://freehaven.net/doc/fc03/econymics.pdf">part of what makes
84)     it so secure</a>.  Tor hides you among <a href="<page about/torusers>">the
85)     other users on the network</a>,
86)     so the more populous and diverse the user base for Tor is, the more your
87)     anonymity will be protected.
88)     </p>

89) 

90)     <a name="whyweneedtor"></a>
91)     <h3><a class="anchor" href="#whyweneedtor">Why we need Tor</a></h3>

92) 

93)     <p>
94)     Using Tor protects you against a common form of Internet surveillance
95)     known as "traffic analysis."  Traffic analysis can be used to infer
96)     who is talking to whom over a public network.  Knowing the source
97)     and destination of your Internet traffic allows others to track your
98)     behavior and interests.  This can impact your checkbook if, for example,
99)     an e-commerce site uses price discrimination based on your country or
100)     institution of origin.  It can even threaten your job and physical safety
101)     by revealing who and where you are. For example, if you're travelling
102)     abroad and you connect to your employer's computers to check or send mail,
103)     you can inadvertently reveal your national origin and professional
104)     affiliation to anyone observing the network, even if the connection
105)     is encrypted.
106)     </p>

107) 

108)     <p>
109)     How does traffic analysis work?  Internet data packets have two parts:
110)     a data payload and a header used for routing.  The data payload is
111)     whatever is being sent, whether that's an email message, a web page, or an
112)     audio file.  Even if you encrypt the data payload of your communications,
113)     traffic analysis still reveals a great deal about what you're doing and,
114)     possibly, what you're saying.  That's because it focuses on the header,
115)     which discloses source, destination, size, timing, and so on.
116)     </p>

117) 

118)     <p>
119)     A basic problem for the privacy minded is that the recipient of your
120)     communications can see that you sent it by looking at headers.  So can
121)     authorized intermediaries like Internet service providers, and sometimes
122)     unauthorized intermediaries as well.  A very simple form of traffic
123)     analysis might involve sitting somewhere between sender and recipient on
124)     the network, looking at headers.
125)     </p>

126) 

127)     <p>
128)     But there are also more powerful kinds of traffic analysis.  Some
129)     attackers spy on multiple parts of the Internet and use sophisticated
130)     statistical techniques to track the communications patterns of many
131)     different organizations and individuals.  Encryption does not help against
132)     these attackers, since it only hides the content of Internet traffic, not
133)     the headers.
134)     </p>

135) 

136)     <a name="thesolution"></a>
137)     <h3><a class="anchor" href="#thesolution">The solution: a distributed, anonymous network</a></h3>

138)     <img src="$(IMGROOT)/htw1.png" alt="How Tor works">

139) 

140)     <p>
141)     Tor helps to reduce the risks of both simple and sophisticated traffic
142)     analysis by distributing your transactions over several places on the
143)     Internet, so no single point can link you to your destination.  The idea
144)     is similar to using a twisty, hard-to-follow route in order to throw off
145)     somebody who is tailing you &mdash; and then periodically erasing your
146)     footprints.  Instead of taking a direct route from source to
147)     destination, data packets on the Tor network take a random pathway
148)     through several relays that cover your tracks so no observer at any
149)     single point can tell where the data came from or where it's going.
150)     </p>

151) 

152)     <p>
153)     To create a private network pathway with Tor, the user's software or
154)     client incrementally builds a circuit of encrypted connections through
155)     relays on the network.  The circuit is extended one hop at a time, and
156)     each relay along the way knows only which relay gave it data and which
157)     relay it is giving data to.  No individual relay ever knows the
158)     complete path that a data packet has taken.  The client negotiates a
159)     separate set of encryption keys for each hop along the circuit to ensure
160)     that each hop can't trace these connections as they pass through.
161)     </p>

162) 

163)     <p><img alt="Tor circuit step two"  src="$(IMGROOT)/htw2.png"></p>

164) 

165)     <p>
166)     Once a circuit has been established, many kinds of data can be exchanged
167)     and several different sorts of software applications can be deployed
168)     over the Tor network.  Because each relay sees no more than one hop in
169)     the circuit, neither an eavesdropper nor a compromised relay can use
170)     traffic analysis to link the connection's source and destination.  Tor
171)     only works for TCP streams and can be used by any application with SOCKS
172)     support.
173)     </p>

174) 

175)     <p>
176)     For efficiency, the Tor software uses the same circuit for connections
177)     that happen within the same ten minutes or so.  Later requests are given a
178)     new circuit, to keep people from linking your earlier actions to the new
179)     ones.
180)     </p>

181) 

182)     <p><img alt="Tor circuit step three" src="$(IMGROOT)/htw3.png"></p>

183) 

184)     <a name="stayinganonymous"></a>
185)     <h3><a class="anchor" href="#stayinganonymous">Staying anonymous</a></h3>

186) 

187)     <p>
188)     Tor can't solve all anonymity problems.  It focuses only on
189)     protecting the transport of data.  You need to use protocol-specific
190)     support software if you don't want the sites you visit to see your

191)     identifying information. For example, you can use <a href="<page
192)     projects/torbrowser>">Tor Browser</a>

193)     while browsing the web to withhold some information about your computer's
194)     configuration.

195)     </p>

196) 

197)     <p>
198)     Also, to protect your anonymity, be smart.  Don't provide your name
199)     or other revealing information in web forms.  Be aware that, like all
200)     anonymizing networks that are fast enough for web browsing, Tor does not
201)     provide protection against end-to-end timing attacks: If your attacker
202)     can watch the traffic coming out of your computer, and also the traffic
203)     arriving at your chosen destination, he can use statistical analysis to
204)     discover that they are part of the same circuit.
205)     </p>

206) 

207)     <a name="thefutureoftor"></a>
208)     <h3><a class="anchor" href="#thefutureoftor">The future of Tor</a></h3>

209) 

210)     <p>
211)     Providing a usable anonymizing network on the Internet today is an
212)     ongoing challenge. We want software that meets users' needs. We also
213)     want to keep the network up and running in a way that handles as many
214)     users as possible. Security and usability don't have to be at odds:
215)     As Tor's usability increases, it will attract more users, which will
216)     increase the possible sources and destinations of each communication,
217)     thus increasing security for everyone.
218)     We're making progress, but we need your help.  Please consider
219)     <a href="<page docs/tor-doc-relay>">running a relay</a>
220)     or <a href="<page getinvolved/volunteer>">volunteering</a> as a
221)     <a href="<page docs/documentation>#Developers">developer</a>.
222)     </p>

223) 

224)     <p>
225)     Ongoing trends in law, policy, and technology threaten anonymity as never
226)     before, undermining our ability to speak and read freely online. These
227)     trends also undermine national security and critical infrastructure by
228)     making communication among individuals, organizations, corporations,
229)     and governments more vulnerable to analysis. Each new user and relay
230)     provides additional diversity, enhancing Tor's ability to put control
231)     over your security and privacy back into your hands.
232)     </p>

233) 

234)   </div>
235)   <!-- END MAINCOL -->
236)   <div id = "sidecol">
237) #include "side.wmi"
238) #include "info.wmi"
239)   </div>
240)   <!-- END SIDECOL -->
241) </div>
242) <!-- END CONTENT -->