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>#hiddenservices">Hidden services</a></li>
21)         <li><a href="<page about/overview>#stayinganonymous">Staying anonymous</a></li>
22)         <li><a href="<page about/overview>#thefutureoftor">The future of Tor</a></li>
23)       </ul>
24)     </div>
25)     <!-- END SIDEBAR -->

26) 

27)     <hr>

28) 

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

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

31) 

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

41) 

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

52) 

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

60) 

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

73) 

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

81) 

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

90) 

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

93) 

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

108) 

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

118) 

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

127) 

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

136) 

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

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

140) 

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

152) 

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

163) 

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

165) 

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

175) 

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

182) 

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

184) 
185) 

186)     <a name="hiddenservices"></a>
187)     <h3><a class="anchor" href="#hiddenservices">Hidden services</a></h3>

188) 

189)     <p>
190)     Tor also makes it possible for users to hide their locations while
191)     offering various kinds of services, such as web publishing or an instant
192)     messaging server.  Using Tor "rendezvous points," other Tor users can
193)     connect to these hidden services, each without knowing the other's
194)     network identity.  This hidden service functionality could allow Tor
195)     users to set up a website where people publish material without worrying
196)     about censorship.  Nobody would be able to determine who was offering
197)     the site, and nobody who offered the site would know who was posting to it.
198)     Learn more about <a href="<page docs/tor-hidden-service>">configuring
199)     hidden services</a> and how the <a href="<page docs/hidden-services>">hidden
200)     service protocol</a> works.
201)     </p>

202) 

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

205) 

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

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

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

214)     </p>

215) 

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

225) 

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

228) 

229)     <p>
230)     Providing a usable anonymizing network on the Internet today is an
231)     ongoing challenge. We want software that meets users' needs. We also
232)     want to keep the network up and running in a way that handles as many
233)     users as possible. Security and usability don't have to be at odds:
234)     As Tor's usability increases, it will attract more users, which will
235)     increase the possible sources and destinations of each communication,
236)     thus increasing security for everyone.
237)     We're making progress, but we need your help.  Please consider
238)     <a href="<page docs/tor-doc-relay>">running a relay</a>
239)     or <a href="<page getinvolved/volunteer>">volunteering</a> as a
240)     <a href="<page docs/documentation>#Developers">developer</a>.
241)     </p>

242) 

243)     <p>
244)     Ongoing trends in law, policy, and technology threaten anonymity as never
245)     before, undermining our ability to speak and read freely online. These
246)     trends also undermine national security and critical infrastructure by
247)     making communication among individuals, organizations, corporations,
248)     and governments more vulnerable to analysis. Each new user and relay
249)     provides additional diversity, enhancing Tor's ability to put control
250)     over your security and privacy back into your hands.
251)     </p>

252) 

253)   </div>
254)   <!-- END MAINCOL -->
255)   <div id = "sidecol">
256) #include "side.wmi"
257) #include "info.wmi"
258)   </div>
259)   <!-- END SIDECOL -->
260) </div>
261) <!-- END CONTENT -->