tor-webwml.git

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2) # Revision: $Revision$

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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)     <p>
31) 	A two-minute video explaining what Tor is and how it works.
32) 	This video is available for <a href="https://media.torproject
33) 	.org/video/2015-03-animation/">download</a> and streaming
34) 	both on Tor Project <a href="https://blog.torproject.org/blog/
35) 	releasing-tor-animation">website</a> and via <a href="https://www
36) 	.youtube.com/playlist?list=PLwyU2dZ3LJErtu3GGElIa7VyORE2B6H1H">
37) 	YouTube</a> in many different languages.
38)     </p>
39)     <div style="text-align:center;">
40)     <video width="500" height="281" controls preload="none" poster="../images/tor-animation.jpg">
41) 	<source src="https://www.torproject.org/videos/Tor_Animation_en.mp4" type="video/mp4">
42) 	<track label="English" kind="captions" src="https://www.torproject.org/videos/en.vtt" srclang="en" default>
43)     </video>
44)     </div>

45)     <p>

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

57)     </p>

58) 

59)     <p>
60)     Individuals use Tor to keep websites from tracking them and their family
61)     members, or to connect to news sites, instant messaging services, or the
62)     like when these are blocked by their local Internet providers.  Tor's <a

63)     href="<page docs/onion-services>">onion services</a>

64)     let users publish web sites and other services without needing to reveal
65)     the location of the site. Individuals also use Tor for socially sensitive
66)     communication: chat rooms and web forums for rape and abuse survivors,
67)     or people with illnesses.
68)     </p>

69) 

70)     <p>
71)     Journalists use Tor to communicate more safely with whistleblowers and
72)     dissidents. Non-governmental organizations (NGOs) use Tor to allow their
73)     workers to connect to their home website while they're in a foreign
74)     country, without notifying everybody nearby that they're working with
75)     that organization.
76)     </p>

77) 

78)     <p>
79)     Groups such as Indymedia recommend Tor for safeguarding their members'
80)     online privacy and security. Activist groups like the Electronic Frontier
81)     Foundation (EFF) recommend Tor as a mechanism for
82)     maintaining civil liberties online. Corporations use Tor as a safe way
83)     to conduct competitive analysis, and to protect sensitive procurement
84)     patterns from eavesdroppers. They also use it to replace traditional
85)     VPNs, which reveal the exact amount and timing of communication. Which
86)     locations have employees working late? Which locations have employees
87)     consulting job-hunting websites? Which research divisions are communicating
88)     with the company's patent lawyers?
89)     </p>

90) 

91)     <p>
92)     A branch of the U.S. Navy uses Tor for open source intelligence
93)     gathering, and one of its teams used Tor while deployed in the Middle
94)     East recently. Law enforcement uses Tor for visiting or surveilling
95)     web sites without leaving government IP addresses in their web logs,
96)     and for security during sting operations.
97)     </p>

98) 

99)     <p>
100)     The variety of people who use Tor is actually <a
101)     href="http://freehaven.net/doc/fc03/econymics.pdf">part of what makes
102)     it so secure</a>.  Tor hides you among <a href="<page about/torusers>">the
103)     other users on the network</a>,
104)     so the more populous and diverse the user base for Tor is, the more your
105)     anonymity will be protected.
106)     </p>

107) 

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

110) 

111)     <p>
112)     Using Tor protects you against a common form of Internet surveillance
113)     known as "traffic analysis."  Traffic analysis can be used to infer
114)     who is talking to whom over a public network.  Knowing the source
115)     and destination of your Internet traffic allows others to track your
116)     behavior and interests.  This can impact your checkbook if, for example,
117)     an e-commerce site uses price discrimination based on your country or
118)     institution of origin.  It can even threaten your job and physical safety
119)     by revealing who and where you are. For example, if you're travelling
120)     abroad and you connect to your employer's computers to check or send mail,
121)     you can inadvertently reveal your national origin and professional
122)     affiliation to anyone observing the network, even if the connection
123)     is encrypted.
124)     </p>

125) 

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

135) 

136)     <p>
137)     A basic problem for the privacy minded is that the recipient of your
138)     communications can see that you sent it by looking at headers.  So can
139)     authorized intermediaries like Internet service providers, and sometimes
140)     unauthorized intermediaries as well.  A very simple form of traffic
141)     analysis might involve sitting somewhere between sender and recipient on
142)     the network, looking at headers.
143)     </p>

144) 

145)     <p>
146)     But there are also more powerful kinds of traffic analysis.  Some
147)     attackers spy on multiple parts of the Internet and use sophisticated
148)     statistical techniques to track the communications patterns of many
149)     different organizations and individuals.  Encryption does not help against
150)     these attackers, since it only hides the content of Internet traffic, not
151)     the headers.
152)     </p>

153) 

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

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

157) 

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

169) 

170)     <p>
171)     To create a private network pathway with Tor, the user's software or
172)     client incrementally builds a circuit of encrypted connections through
173)     relays on the network.  The circuit is extended one hop at a time, and
174)     each relay along the way knows only which relay gave it data and which
175)     relay it is giving data to.  No individual relay ever knows the
176)     complete path that a data packet has taken.  The client negotiates a
177)     separate set of encryption keys for each hop along the circuit to ensure
178)     that each hop can't trace these connections as they pass through.
179)     </p>

180) 

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

182) 

183)     <p>
184)     Once a circuit has been established, many kinds of data can be exchanged
185)     and several different sorts of software applications can be deployed
186)     over the Tor network.  Because each relay sees no more than one hop in
187)     the circuit, neither an eavesdropper nor a compromised relay can use
188)     traffic analysis to link the connection's source and destination.  Tor
189)     only works for TCP streams and can be used by any application with SOCKS
190)     support.
191)     </p>

192) 

193)     <p>
194)     For efficiency, the Tor software uses the same circuit for connections
195)     that happen within the same ten minutes or so.  Later requests are given a
196)     new circuit, to keep people from linking your earlier actions to the new
197)     ones.
198)     </p>

199) 

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

201) 

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

204) 

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

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

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

213)     </p>

214) 

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

224) 

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

227) 

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

241) 

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

251) 

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