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128 lines
5.4 KiB
HTML
128 lines
5.4 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
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<head>
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<title>Tor: Overview</title>
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<meta name="Author" content="Roger Dingledine">
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<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1" />
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<link rel="stylesheet" type="text/css" href="default.css" />
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</head>
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<body>
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<div class="menu" id="side">
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<!-- <img id="logo" src="tor.jpg" alt="cute tor gate" /> -->
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<a href="index.html">Home</a> <br>
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<a class="current">Overview</a> <br>
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<a href="download.html">Download</a> <br>
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<a href="documentation.html">Documentation</a><br>
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<a href="contribute.html">Contribute</a> <br>
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<a href="design.html">Design</a> <br>
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<a href="developers.html">Developers</a> <br>
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<a href="research.html">Research</a> <br>
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<a href="people.html">People</a> <br>
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</div><!-- #side -->
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<div class="main" id="main">
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<h2>Tor: an anonymizing overlay network for TCP</h2>
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<p>
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Traffic analysis can be used to infer who is talking to whom over a
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public network. For example, Internet packets have a header used for
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routing, and a payload that carries the data. The header, which must be
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visible to the network (and to observers of the network), reveals the
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source and destination of the packet. Even if the header were obscured
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in some way, the packet could still be tracked as it moves through the
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network. Encrypting the payload is similarly ineffective, because the
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routing information is all an observer needs.
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</p>
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<p>
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Knowing the source and destination of your Internet traffic allows
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somebody to track your behavior and interests, impacting your checkbook or
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even threatening your job or physical safety.
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</p>
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<p>
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Individuals, corporations, and governments all have an interest in
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traffic analysis protection. Individuals want to protect themselves and
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their family members from remote websites, or connect to resources such
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as news sites or instant messaging services that are blocked locally.
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User groups such as the German "Diabetes People" organization recommend
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Tor for their members' online privacy and security. Activist groups such
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as the Electronic Frontier Foundation are publicizing Tor as a mechanism
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for maintaining civil liberties online. Corporations such as Google and
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Wal-Mart are investigating Tor as a safe avenue for competitive analysis
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or to try out new experimental projects without associating their name
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with the project. A branch of the U.S. Navy uses Tor for open source
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intelligence gathering at its headquarters, and one of their teams used
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Tor while deployed in the Middle East recently.
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</p>
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<p>
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Tor helps to reduce the traffic analysis risk by distributing your
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transactions over several places on the Internet, so no single point can
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link you to your destination. To make private connections in Tor, users
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incrementally build a path or <em>circuit</em> of encrypted connections
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through servers on the network, extending it one step at a time so that
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each server in the circuit only learns which server extended to it and
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which server it has been asked to extend to. The client negotiates a
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separate set of encryption keys for each step along the circuit.
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</p>
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<p>
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[Insert snazzy onion diagram here.]
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</p>
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<p>
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Once a circuit has been established, the client software waits for
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applications to request TCP connections, and directs these application
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streams along the circuit. Many streams can be multiplexed along a single
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circuit, so applications don't need to wait for keys to be negotiated
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every time they open a connection. Because each server sees no
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more than one end of the connection, a local eavesdropper or a compromised
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server cannot use traffic analysis to link the connection's source and
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destination. The Tor client software rotates circuits periodically
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to prevent long-term linkability between different actions by a
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single user.
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</p>
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<!--
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<p>
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Many protocols, not just web.
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</p>
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-->
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<p>
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Tor also makes it possible for the clients to be hidden. Using Tor
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"rendezvous points," other Tor clients can connect to these hidden
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services, each without knowing the other's network identity. These hidden
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websites let users publish material without worrying about censorship.
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</p>
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<p>
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Of course, Tor can't solve all privacy problems itself. Tor focuses on
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protecting the <em>transport</em>. You need to use other protocol-specific
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software, such as Privoxy for web browsing, to clean identifying
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information such as browser type and characteristics, and you need
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to use other common sense such as not providing your name or other
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revealing information in web forms. Also, like all anonymizing networks
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that are fast enough for web browsing, Tor does not provide protection
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against end-to-end timing attacks: if your attacker can watch the traffic
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coming out of your computer, and also the traffic arriving at your chosen
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destination, he can use simple statistics to discover that they are part
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of the same circuit.
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</p>
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<p>
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Providing a usable anonymizing network on the Internet today is hard,
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both in terms of providing usable software that meets users' needs,
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and also in terms of solving the research challenges. But we're making
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progress at finding a good balance to provide both usability and security.
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Our goal is to supplement laws by giving people the power to make their
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own decisions about their privacy.
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</p>
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</div><!-- #main -->
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</body>
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</html>
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