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)     The Tor network is a group of <a href="<page
33)     getinvolved/volunteer>">volunteer</a>-operated servers that allows people
34)     to improve their privacy and security on the Internet. Tor's users employ
35)     this network by connecting through a series of virtual tunnels rather than
36)     making a direct connection, thus allowing both organizations and
37)     individuals to share information over public networks without compromising
38)     their privacy. Along the same line, Tor is an effective censorship
39)     circumvention tool, allowing its users to reach otherwise blocked
40)     destinations or content.  Tor can also be used as a building block for
41)     software developers to create new communication tools with built-in privacy
42)     features.

43)     </p>

44) 

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

55) 

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

63) 

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

76) 

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

84) 

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

93) 

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

96) 

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

111) 

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

121) 

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

130) 

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

139) 

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

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

143) 

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

155) 

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

166) 

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

168) 

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

178) 

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

185) 

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

187) 

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

190) 

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

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

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

199)     </p>

200) 

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

210) 

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

213) 

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

227) 

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

237) 

238)   </div>
239)   <!-- END MAINCOL -->
240)   <div id = "sidecol">
241) #include "side.wmi"
242) #include "info.wmi"
243)   </div>
244)   <!-- END SIDECOL -->
245) </div>
246) <!-- END CONTENT -->