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276 lines
13 KiB
Plaintext
## translation metadata
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# Revision: $Revision$
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# Translation-Priority: 2-medium
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#include "head.wmi" TITLE="Tor Project: Overview" CHARSET="UTF-8"
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<div id="content" class="clearfix">
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<div id="breadcrumbs">
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<a href="<page index>">Home » </a>
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<a href="<page about/overview>">About » </a>
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</div>
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<div id="maincol">
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<h2>Tor: Overview</h2>
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<!-- BEGIN SIDEBAR -->
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<div class="sidebar-left">
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<h3>Topics</h3>
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<ul>
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<li><a href="<page about/overview>#inception">Inception</a></li>
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<li><a href="<page about/overview>#overview">Overview</a></li>
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<li><a href="<page about/overview>#whyweneedtor">Why we need Tor</a></li>
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<li><a href="<page about/overview>#thesolution">The Solution</a></li>
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<li><a href="<page about/overview>#hiddenservices">Hidden services</a></li>
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<li><a href="<page about/overview>#stayinganonymous">Staying anonymous</a></li>
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<li><a href="<page about/overview>#thefutureoftor">The future of Tor</a></li>
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</ul>
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</div>
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<!-- END SIDEBAR -->
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<hr>
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<a name="inception"></a>
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<h3><a class="anchor" href="#inception">Inception</a></h3>
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<p>
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Tor was originally designed, implemented, and deployed as a
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third-generation <a href="http://www.onion-router.net/">onion routing
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project of the U.S. Naval Research Laboratory</a>. It was originally
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developed with the U.S. Navy in mind, for the primary purpose of
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protecting government communications. Today, it is used every day
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for a wide variety of purposes by normal people, the military,
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journalists, law enforcement officers, activists, and many
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others. </p>
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<a name="overview"></a>
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<h3><a class="anchor" href="#overview">Overview</a></h3>
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<p>
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Tor is a network of virtual tunnels that allows people and groups to
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improve their privacy and security on the Internet. It also enables
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software developers to create new communication tools
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with built-in privacy features. Tor provides the foundation for
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a range of applications that allow organizations and individuals
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to share information over public networks without compromising their
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privacy.
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</p>
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<p>
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Individuals use Tor to keep websites from tracking them and their family
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members, or to connect to news sites, instant messaging services, or the
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like when these are blocked by their local Internet providers. Tor's <a
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href="<page docs/hidden-services>">hidden services</a>
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let users publish web sites and other services without needing to reveal
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the location of the site. Individuals also use Tor for socially sensitive
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communication: chat rooms and web forums for rape and abuse survivors,
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or people with illnesses.
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</p>
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<p>
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Journalists use Tor to communicate more safely with whistleblowers and
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dissidents. Non-governmental organizations (NGOs) use Tor to allow their
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workers to connect to their home website while they're in a foreign
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country, without notifying everybody nearby that they're working with
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that organization.
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</p>
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<p>
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Groups such as Indymedia recommend Tor for safeguarding their members'
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online privacy and security. Activist groups like the Electronic Frontier
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Foundation (EFF) recommend Tor as a mechanism for
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maintaining civil liberties online. Corporations use Tor as a safe way
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to conduct competitive analysis, and to protect sensitive procurement
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patterns from eavesdroppers. They also use it to replace traditional
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VPNs, which reveal the exact amount and timing of communication. Which
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locations have employees working late? Which locations have employees
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consulting job-hunting websites? Which research divisions are communicating
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with the company's patent lawyers?
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</p>
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<p>
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A branch of the U.S. Navy uses Tor for open source intelligence
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gathering, and one of its teams used Tor while deployed in the Middle
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East recently. Law enforcement uses Tor for visiting or surveilling
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web sites without leaving government IP addresses in their web logs,
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and for security during sting operations.
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</p>
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<p>
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The variety of people who use Tor is actually <a
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href="http://freehaven.net/doc/fc03/econymics.pdf">part of what makes
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it so secure</a>. Tor hides you among <a href="<page about/torusers>">the
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other users on the network</a>,
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so the more populous and diverse the user base for Tor is, the more your
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anonymity will be protected.
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</p>
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<a name="whyweneedtor"></a>
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<h3><a class="anchor" href="#whyweneedtor">Why we need Tor</a></h3>
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<p>
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Using Tor protects you against a common form of Internet surveillance
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known as "traffic analysis." Traffic analysis can be used to infer
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who is talking to whom over a public network. Knowing the source
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and destination of your Internet traffic allows others to track your
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behavior and interests. This can impact your checkbook if, for example,
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an e-commerce site uses price discrimination based on your country or
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institution of origin. It can even threaten your job and physical safety
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by revealing who and where you are. For example, if you're travelling
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abroad and you connect to your employer's computers to check or send mail,
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you can inadvertently reveal your national origin and professional
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affiliation to anyone observing the network, even if the connection
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is encrypted.
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</p>
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<p>
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How does traffic analysis work? Internet data packets have two parts:
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a data payload and a header used for routing. The data payload is
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whatever is being sent, whether that's an email message, a web page, or an
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audio file. Even if you encrypt the data payload of your communications,
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traffic analysis still reveals a great deal about what you're doing and,
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possibly, what you're saying. That's because it focuses on the header,
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which discloses source, destination, size, timing, and so on.
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</p>
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<p>
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A basic problem for the privacy minded is that the recipient of your
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communications can see that you sent it by looking at headers. So can
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authorized intermediaries like Internet service providers, and sometimes
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unauthorized intermediaries as well. A very simple form of traffic
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analysis might involve sitting somewhere between sender and recipient on
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the network, looking at headers.
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</p>
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<p>
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But there are also more powerful kinds of traffic analysis. Some
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attackers spy on multiple parts of the Internet and use sophisticated
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statistical techniques to track the communications patterns of many
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different organizations and individuals. Encryption does not help against
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these attackers, since it only hides the content of Internet traffic, not
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the headers.
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</p>
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<a name="thesolution"></a>
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<h3><a class="anchor" href="#thesolution">The solution: a distributed, anonymous network</a></h3>
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<img src="$(IMGROOT)/htw1.png" alt="How Tor works">
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<p>
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Tor helps to reduce the risks of both simple and sophisticated traffic
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analysis by distributing your transactions over several places on the
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Internet, so no single point can link you to your destination. The idea
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is similar to using a twisty, hard-to-follow route in order to throw off
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somebody who is tailing you — and then periodically erasing your
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footprints. Instead of taking a direct route from source to
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destination, data packets on the Tor network take a random pathway
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through several relays that cover your tracks so no observer at any
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single point can tell where the data came from or where it's going.
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</p>
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<p>
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To create a private network pathway with Tor, the user's software or
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client incrementally builds a circuit of encrypted connections through
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relays on the network. The circuit is extended one hop at a time, and
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each relay along the way knows only which relay gave it data and which
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relay it is giving data to. No individual relay ever knows the
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complete path that a data packet has taken. The client negotiates a
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separate set of encryption keys for each hop along the circuit to ensure
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that each hop can't trace these connections as they pass through.
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</p>
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<p><img alt="Tor circuit step two" src="$(IMGROOT)/htw2.png"></p>
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<p>
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Once a circuit has been established, many kinds of data can be exchanged
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and several different sorts of software applications can be deployed
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over the Tor network. Because each relay sees no more than one hop in
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the circuit, neither an eavesdropper nor a compromised relay can use
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traffic analysis to link the connection's source and destination. Tor
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only works for TCP streams and can be used by any application with SOCKS
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support.
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</p>
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<p>
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For efficiency, the Tor software uses the same circuit for connections
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that happen within the same ten minutes or so. Later requests are given a
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new circuit, to keep people from linking your earlier actions to the new
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ones.
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</p>
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<p><img alt="Tor circuit step three" src="$(IMGROOT)/htw3.png"></p>
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<a name="hiddenservices"></a>
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<h3><a class="anchor" href="#hiddenservices">Hidden services</a></h3>
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<p>
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Tor also makes it possible for users to hide their locations while
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offering various kinds of services, such as web publishing or an instant
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messaging server. Using Tor "rendezvous points," other Tor users can
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connect to these hidden services, each without knowing the other's
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network identity. This hidden service functionality could allow Tor
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users to set up a website where people publish material without worrying
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about censorship. Nobody would be able to determine who was offering
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the site, and nobody who offered the site would know who was posting to it.
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Learn more about <a href="<page docs/tor-hidden-service>">configuring
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hidden services</a> and how the <a href="<page docs/hidden-services>">hidden
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service protocol</a> works.
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</p>
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<a name="stayinganonymous"></a>
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<h3><a class="anchor" href="#stayinganonymous">Staying anonymous</a></h3>
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<p>
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Tor can't solve all anonymity problems. It focuses only on
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protecting the transport of data. You need to use protocol-specific
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support software if you don't want the sites you visit to see your
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identifying information. For example, you can use Torbutton
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while browsing the web to withhold some information about your computer's
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configuration.
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</p>
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<p>
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Also, to protect your anonymity, be smart. Don't provide your name
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or other revealing information in web forms. Be aware that, like all
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anonymizing networks that are fast enough for web browsing, Tor does not
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provide protection against end-to-end timing attacks: If your attacker
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can watch the traffic coming out of your computer, and also the traffic
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arriving at your chosen destination, he can use statistical analysis to
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discover that they are part of the same circuit.
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</p>
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<a name="thefutureoftor"></a>
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<h3><a class="anchor" href="#thefutureoftor">The future of Tor</a></h3>
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<p>
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Providing a usable anonymizing network on the Internet today is an
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ongoing challenge. We want software that meets users' needs. We also
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want to keep the network up and running in a way that handles as many
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users as possible. Security and usability don't have to be at odds:
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As Tor's usability increases, it will attract more users, which will
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increase the possible sources and destinations of each communication,
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thus increasing security for everyone.
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We're making progress, but we need your help. Please consider
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<a href="<page docs/tor-doc-relay>">running a relay</a>
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or <a href="<page getinvolved/volunteer>">volunteering</a> as a
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<a href="<page docs/documentation>#Developers">developer</a>.
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</p>
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<p>
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Ongoing trends in law, policy, and technology threaten anonymity as never
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before, undermining our ability to speak and read freely online. These
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trends also undermine national security and critical infrastructure by
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making communication among individuals, organizations, corporations,
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and governments more vulnerable to analysis. Each new user and relay
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provides additional diversity, enhancing Tor's ability to put control
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over your security and privacy back into your hands.
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</p>
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</div>
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<!-- END MAINCOL -->
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<div id = "sidecol">
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#include "side.wmi"
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#include "info.wmi"
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</div>
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<!-- END SIDECOL -->
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</div>
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<!-- END CONTENT -->
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#include <foot.wmi>
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