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>#inception">Inception</a></li>

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

19)         <li><a href="<page about/overview>#whyweneedtor">Why we need Tor</a></li>
20)         <li><a href="<page about/overview>#thesolution">The Solution</a></li>
21)         <li><a href="<page about/overview>#hiddenservices">Hidden services</a></li>
22)         <li><a href="<page about/overview>#stayinganonymous">Staying anonymous</a></li>
23)         <li><a href="<page about/overview>#thefutureoftor">The future of Tor</a></li>
24)       </ul>
25)     </div>
26)     <!-- END SIDEBAR -->
27)     

28)     <hr>

29) 
30)     <a name="inception"></a>
31)     <h3><a class="anchor" href="#inception">Inception</a></h3>
32) 
33)     <p>
34)     Tor was originally designed, implemented, and deployed as a
35)     third-generation <a href="http://www.onion-router.net/">onion routing
36)     project of the U.S. Naval Research Laboratory</a>.  It was originally
37)     developed with the U.S. Navy in mind, for the primary purpose of
38)     protecting government communications.  Today, it is used every day
39)     for a wide variety of purposes by normal people, the military,
40)     journalists, law enforcement officers, activists, and many
41)     others. </p>

42)     

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

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

45) 

46)     <p>
47)     Tor is a network of virtual tunnels that allows people and groups to
48)     improve their privacy and security on the Internet.  It also enables
49)     software developers to create new communication tools
50)     with built-in privacy features.  Tor provides the foundation for
51)     a range of applications that allow organizations and individuals
52)     to share information over public networks without compromising their
53)     privacy.
54)     </p>
55)     
56)     <p>
57)     Individuals use Tor to keep websites from tracking them and their family
58)     members, or to connect to news sites, instant messaging services, or the
59)     like when these are blocked by their local Internet providers.  Tor's <a
60)     href="<page docs/hidden-services>">hidden services</a>
61)     let users publish web sites and other services without needing to reveal
62)     the location of the site. Individuals also use Tor for socially sensitive
63)     communication: chat rooms and web forums for rape and abuse survivors,
64)     or people with illnesses.
65)     </p>
66)     
67)     <p>
68)     Journalists use Tor to communicate more safely with whistleblowers and
69)     dissidents. Non-governmental organizations (NGOs) use Tor to allow their
70)     workers to connect to their home website while they're in a foreign
71)     country, without notifying everybody nearby that they're working with
72)     that organization.
73)     </p>
74)     
75)     <p>
76)     Groups such as Indymedia recommend Tor for safeguarding their members'
77)     online privacy and security. Activist groups like the Electronic Frontier
78)     Foundation (EFF) recommend Tor as a mechanism for
79)     maintaining civil liberties online. Corporations use Tor as a safe way
80)     to conduct competitive analysis, and to protect sensitive procurement
81)     patterns from eavesdroppers. They also use it to replace traditional
82)     VPNs, which reveal the exact amount and timing of communication. Which
83)     locations have employees working late? Which locations have employees
84)     consulting job-hunting websites? Which research divisions are communicating
85)     with the company's patent lawyers?
86)     </p>
87)     
88)     <p>
89)     A branch of the U.S. Navy uses Tor for open source intelligence
90)     gathering, and one of its teams used Tor while deployed in the Middle
91)     East recently. Law enforcement uses Tor for visiting or surveilling
92)     web sites without leaving government IP addresses in their web logs,
93)     and for security during sting operations.
94)     </p>
95)     
96)     <p>
97)     The variety of people who use Tor is actually <a
98)     href="http://freehaven.net/doc/fc03/econymics.pdf">part of what makes
99)     it so secure</a>.  Tor hides you among <a href="<page about/torusers>">the
100)     other users on the network</a>,
101)     so the more populous and diverse the user base for Tor is, the more your
102)     anonymity will be protected.
103)     </p>
104)     
105)     <a name="whyweneedtor"></a>
106)     <h3><a class="anchor" href="#whyweneedtor">Why we need Tor</a></h3>
107)     
108)     <p>
109)     Using Tor protects you against a common form of Internet surveillance
110)     known as "traffic analysis."  Traffic analysis can be used to infer
111)     who is talking to whom over a public network.  Knowing the source
112)     and destination of your Internet traffic allows others to track your
113)     behavior and interests.  This can impact your checkbook if, for example,
114)     an e-commerce site uses price discrimination based on your country or
115)     institution of origin.  It can even threaten your job and physical safety
116)     by revealing who and where you are. For example, if you're travelling
117)     abroad and you connect to your employer's computers to check or send mail,
118)     you can inadvertently reveal your national origin and professional
119)     affiliation to anyone observing the network, even if the connection
120)     is encrypted.
121)     </p>
122)     
123)     <p>
124)     How does traffic analysis work?  Internet data packets have two parts:
125)     a data payload and a header used for routing.  The data payload is
126)     whatever is being sent, whether that's an email message, a web page, or an
127)     audio file.  Even if you encrypt the data payload of your communications,
128)     traffic analysis still reveals a great deal about what you're doing and,
129)     possibly, what you're saying.  That's because it focuses on the header,
130)     which discloses source, destination, size, timing, and so on.
131)     </p>
132)     
133)     <p>
134)     A basic problem for the privacy minded is that the recipient of your
135)     communications can see that you sent it by looking at headers.  So can
136)     authorized intermediaries like Internet service providers, and sometimes
137)     unauthorized intermediaries as well.  A very simple form of traffic
138)     analysis might involve sitting somewhere between sender and recipient on
139)     the network, looking at headers.
140)     </p>
141)     
142)     <p>
143)     But there are also more powerful kinds of traffic analysis.  Some
144)     attackers spy on multiple parts of the Internet and use sophisticated
145)     statistical techniques to track the communications patterns of many
146)     different organizations and individuals.  Encryption does not help against
147)     these attackers, since it only hides the content of Internet traffic, not
148)     the headers.
149)     </p>
150)     
151)     <a name="thesolution"></a>
152)     <h3><a class="anchor" href="#thesolution">The solution: a distributed, anonymous network</a></h3>

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

154)     
155)     <p>
156)     Tor helps to reduce the risks of both simple and sophisticated traffic
157)     analysis by distributing your transactions over several places on the
158)     Internet, so no single point can link you to your destination.  The idea
159)     is similar to using a twisty, hard-to-follow route in order to throw off
160)     somebody who is tailing you &mdash; and then periodically erasing your
161)     footprints.  Instead of taking a direct route from source to
162)     destination, data packets on the Tor network take a random pathway
163)     through several relays that cover your tracks so no observer at any
164)     single point can tell where the data came from or where it's going.
165)     </p>
166)     
167)     <p>
168)     To create a private network pathway with Tor, the user's software or
169)     client incrementally builds a circuit of encrypted connections through
170)     relays on the network.  The circuit is extended one hop at a time, and
171)     each relay along the way knows only which relay gave it data and which
172)     relay it is giving data to.  No individual relay ever knows the
173)     complete path that a data packet has taken.  The client negotiates a
174)     separate set of encryption keys for each hop along the circuit to ensure
175)     that each hop can't trace these connections as they pass through.
176)     </p>
177)     

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

179)     
180)     <p>
181)     Once a circuit has been established, many kinds of data can be exchanged
182)     and several different sorts of software applications can be deployed
183)     over the Tor network.  Because each relay sees no more than one hop in
184)     the circuit, neither an eavesdropper nor a compromised relay can use
185)     traffic analysis to link the connection's source and destination.  Tor
186)     only works for TCP streams and can be used by any application with SOCKS
187)     support.
188)     </p>
189)     
190)     <p>
191)     For efficiency, the Tor software uses the same circuit for connections
192)     that happen within the same ten minutes or so.  Later requests are given a
193)     new circuit, to keep people from linking your earlier actions to the new
194)     ones.
195)     </p>
196)     

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

198)     
199)     
200)     <a name="hiddenservices"></a>
201)     <h3><a class="anchor" href="#hiddenservices">Hidden services</a></h3>
202)     
203)     <p>
204)     Tor also makes it possible for users to hide their locations while
205)     offering various kinds of services, such as web publishing or an instant
206)     messaging server.  Using Tor "rendezvous points," other Tor users can
207)     connect to these hidden services, each without knowing the other's
208)     network identity.  This hidden service functionality could allow Tor
209)     users to set up a website where people publish material without worrying
210)     about censorship.  Nobody would be able to determine who was offering
211)     the site, and nobody who offered the site would know who was posting to it.
212)     Learn more about <a href="<page docs/tor-hidden-service>">configuring
213)     hidden services</a> and how the <a href="<page docs/hidden-services>">hidden
214)     service protocol</a> works.
215)     </p>
216)     
217)     <a name="stayinganonymous"></a>
218)     <h3><a class="anchor" href="#stayinganonymous">Staying anonymous</a></h3>
219)     
220)     <p>
221)     Tor can't solve all anonymity problems.  It focuses only on
222)     protecting the transport of data.  You need to use protocol-specific
223)     support software if you don't want the sites you visit to see your

224)     identifying information. For example, you can use Torbutton
225)     while browsing the web to withhold some information about your computer's
226)     configuration.