webwml/docs/en/bridges.wml

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#include "head.wmi" TITLE="Tor Project: Bridges" CHARSET="UTF-8"

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<div id="content" class="clearfix">
  <div id="breadcrumbs">
    <a href="<page index>">Home &raquo; </a>
    <a href="<page docs/documentation>">Documentation &raquo; </a>
    <a href="<page docs/bridges>">Bridges</a>
  </div>
  <div id="maincol">
    <a id="BridgeIntroduction"></a>
    <h2><a class="anchor" href="#BridgeIntroduction">Tor: Bridges</a></h2>
    <hr>

    <p>
    <img width="7%" height="7%" style="float: left;" src="$(IMGROOT)/icon-Obfsproxy.jpg">
    <b>Tip:</b>
    Having trouble connecting to Tor? You may need to use a different <b>pluggable
    transport</b>. <a class="anchor" href="#PluggableTransports">Click here for
    more information</a>.
    </p>

    <p>
    Bridge relays (or "bridges" for short) are Tor relays that aren't listed in
    the main Tor directory. Since there is no complete public list of them, even if
    your ISP is filtering connections to all the known Tor relays, they probably
    won't be able to block all the bridges. If you suspect your access to the
    Tor network is being blocked, you may want to use bridges.
    </p>

    <p>
    The addition of bridges to Tor is a step forward in the blocking
    resistance race. It is perfectly possible that even if your ISP filters
    the Internet, you do not require a bridge to use Tor. So you should try
    to use Tor without bridges first, since it might work.
    </p>

    <p>
    Note that it's also possible that Tor is non-functional for other
    reasons. The latest version of <a href="<page projects/torbrowser>">
    Tor Browser</a> tries to give you better hints about why Tor is having
    problems connecting. You should also read <a href="<page docs/faq>#DoesntWork">the
    FAQ about problems with running Tor properly</a> when you have issues.
    If you feel that the issue is clearly related to Tor being blocked, or
    you'd simply like to try because you're unsure or feeling adventurous,
    please read on. Ensure that you're using the <a href="<page download/download>#Dev">latest
    Tor Browser for your platform</a>.
    </p>

    <p>
    To use a bridge, you have two options. Tor Browser now provides some
    bridges by default. You can enable these easily. Unfortunately, because
    these bridges are publically distributed, it is easy for censors to block
    some of them, so some of them may not work. In this case, you'll need to
    locate different bridges. Furthermore, you'll need to configure Tor Browser
    with whichever bridge address you intend to use. If your Internet connection
    requires the use of a proxy, you'll probably need to configure Tor Browser
    to use it first. If you don't think you need to configure a proxy for your
    Internet connection, you probably don't. Give it a try and if you have
    issues, <a href="<page about/contact>#support">ask us for help</a>.
    </p>

    <p>
    <ul>
    <li><a href="#PluggableTransports">Obfuscated Bridges and Pluggable Transports</a></li>
    <li><a href="#Understanding">Understanding Bridge Configuration Lines</a></li>
    <li><a href="#AddTorNotWorks">Adding bridges in Tor Browser when Tor doesn't work</a></li>
    <li><a href="#AddTorWorks">Adding bridges in Tor Browser when Tor does work</a></li>
    <li><a href="#FindingMore">Finding more bridges for Tor</a></li>
    </ul>
    </p>

    <a id="PluggableTransports"></a>
    <h2><a class="anchor" href="#PluggableTransports">Pluggable Transports</a></h2>
    <hr>

    <p>Over the last few years, censors have found ways to block Tor even when
    clients are using bridges. They usually do this by installing special
    boxes at ISPs that peek into network traffic and detect Tor; when Tor
    is detected they block the traffic flow.
    </p>

    <p>To circumvent such sophisticated censorship Tor introduced
    <a href="<page docs/pluggable-transports>"><i>pluggable transports</i></a>.
    These transports manipulate all Tor traffic between the client and its
    first hop such that it is not identifiable as a Tor connection. If the
    censor can't decide if the connection is a Tor connection, then they are
    less likely to block it.</p>

    <p>Sadly, pluggable transports are not immune to detection, if a censor
    is given enough time. In the past, we promoted obfs and obfs2 as safe
    transports. These are now deprecated and were replaced by obfs3,
    scramblesuit, fte, and obfs4.</p>

    <p>Bridges which support pluggable transports can be used with Tor Browser
    easily. Tor Browser includes some pre-configured bridges and you can get
    more from <a href="#FindingMore">BridgeDB</a>, if those don't work.</p>

    <a id="Understanding"></a>
    <h2><a class="anchor" href="#Understanding">Understanding A Bridge Configuration Line</a></h2>
    <hr>
    <p>
    As an example, when you obtain a bridge from https://bridges.torproject.org,
    you'll get a bridge entry that looks like the following:
    </p>
    <pre><samp>
    141.201.27.48:443 4352e58420e68f5e40bf7c74faddccd9d1349413
    </samp>
    </pre>

    <p>
    Understanding the components of a bridge line isn't strictly required
    but may prove useful. You can skip this section if you'd like.<br>
    The first element is the IP address of the bridge: <tt>'141.201.27.48'</tt><br>
    The second element is the port number: <tt>'443'</tt><br>
    The third element, the fingerprint (unique identifier of the
    bridge), is optional:
    <tt>'4352e58420e68f5e40bf7c74faddccd9d1349413'</tt><br>

    <p>
    <img width="7%" height="7%" style="vertical-align:middle" src="$(IMGROOT)/icon-Obfsproxy.jpg">
         <span><b>Pluggable transports tip:</b></span>
    </p>
    <p>
    If your bridge line looks like this:
    <pre><samp>
    obfs3 141.201.27.48:420 4352e58420e68f5e40bf7c74faddccd9d1349413
    </samp>
    </pre>

    The first element is the name of the pluggable transport
    technology used by the bridge. For example, in the case above, the
    bridge is using the <i>obfs3</i> pluggable transport.
    </p>

    <a id="UsingBridges"></a>
    <h2><a class="anchor" href="#UsingBridges">Using bridges with Tor
    Browser</a></h2>
    <hr>

    <ul>
    <li><a href="#AddTorNotWorks">Adding bridges in Tor Browser when Tor doesn't work</a></li>
    <li><a href="#AddTorWorks">Adding bridges in Tor Browser when Tor does work</a></li>
    </ul>

    <a id="AddTorNotWorks"></a>
    <h3><a href="#AddTorNotWorks">Adding bridges in Tor Browser when Tor <em>does not</em> work:</a></h3>
    <hr>

    <p>First, you should read <a href="<page docs/faq>#DoesntWork">the
    FAQ about problems with running Tor properly</a> when you have issues.
    Sometimes Tor does not work due to a silly mistake rather than your
    ISP interfering with your Internet connection.</p>

    <br><br>
    <h3>1) To add a bridge, follow the instructions on screen. Click the
        "Configure" button.
    </h3>
    <br/>
    <img src="$(IMGROOT)/tb-tor-launcher-startup.png" alt="Tor Browser's Initial Configuration page">
    <br><br><br>
    <h3>2) If you must configure a proxy then select "Yes" and enter the
        details on the following page.
        <br/>If you do not use a proxy then select "No" and click "Next".
        <br/>If you do not know if you must configure a proxy then you likely
        do not need to do it.
    </h3>
    <br/>
    <img src="$(IMGROOT)/tb-tor-launcher-no-proxy.png" alt="Tor Browser's Proxy page">
    <br><br><br>
    <h3>3) After you configure a proxy or skip over that configuration page,
        the following page asks "Does your Internet Service Provider (ISP)
        block or otherwise censor connections to the Tor Network?". Select
        "Yes" and then click "Next".</h3>
    <br/>
    <img src="$(IMGROOT)/tb-tor-launcher-isp-interference.png" alt="Tor Browser's Bridge page">
    <br><br><br>
    <h3>4) Now you have two configuration options. You can use bridges which are
        preconfigured and provided with Tor Browser, or you can specify your
        own bridge(s).</h3>
    <br/>
    <img src="$(IMGROOT)/tb-tor-launcher-bridges-options.png" alt="Tor Browser's Bridge Configuration page">
    <br><br><br>
    <h3>5a) If you want to use one of the provided bridges, then choose the
    transport type you want to use. obfs3 is currently the recommend
    type, but depending on where you are located another type may work better
    for you. If you have any questions, please <a href="<page about/contact>#support">contact
    us.</a></h3>
    <br/>
    <img src="$(IMGROOT)/tb-tor-launcher-bridges-provided.png" alt="Tor Browser's Bridge Configuration page - provided bridges">
    <br><br><br>
    <h3>5b) Alternatively, if you want to use a <a href="#FindingMore">custom
    bridge</a>, then select "Enter custom bridges" and copy-and-paste the
    bridge information into the textbox.
    </h3>
    <br/>
    <img src="$(IMGROOT)/tb-tor-launcher-bridges-custom.png" alt="Tor Browser's Bridge Configuration page - provided bridges">
    <br><br><br>
    <h3>6) After you decide which bridges you want to use, click "Connect".
    Tor should now be able to load successfully and the browser window
    should appear.</h3>
    <br/>
    <img src="$(IMGROOT)/tb-frontpage.png" alt="Tor Browser's Front Page">
    <br><br><br><br>

    <a id="AddTorWorks"></a>
    <h3><a href="#AddTorWorks">Adding bridges in Tor Browser when Tor <em>does</em> work:</a></h3>
    <hr>

    <p>The following instructions assume Tor Browser successfully loads and
    you are able to surf the web. If you do not see the web browser when you
    run Tor Browser (like in step (1) below), you may need to follow the
    <a href="#AddTorNotWorks">instructions above</a>.

    <br><br>
    <h3>1) Start Tor Browser:</h3>
    <br>
    <img src="$(IMGROOT)/tb-frontpage.png" alt="Tor Browser's Front Page">
    <br><br><br>
    <h3>2) To begin using bridges, open Tor Browser's Network Settings:</h3>
    <br>
    <img src="$(IMGROOT)/tb-tor-button-menu.png" alt="Tor Browser's TorButton Menu">
    <br><br><br>
    <h3>3) Select "My Internet Service Provider (ISP) blocks connections to the Tor network":</h3>
    <br>
    <img src="$(IMGROOT)/tb-bridge-networksettings.png" alt="Tor Browser's Network Settings page">
    <br><br><br>
    <h3>4) Now you have two configuration options. You can use bridges which are
        preconfigured and provided with Tor Browser, or you can specify your
        own bridge(s).</h3>
    <br>
    <img src="$(IMGROOT)/tb-bridges-options-from-browser.png" alt="Tor Browser's TorButton Menu">
    <br><br><br>
    <h3>5a) If you want to use one of the provided bridges, then choose the
    transport type you want to use. obfs3 is currently the recommend
    type, but depending on where you are located another type may work better
    for you. If you have any questions, please <a href="<page about/contact>#support">contact
    us.</a></h3>
    <br>
    <img src="$(IMGROOT)/tb-bridges-provided-from-browser.png" alt="My Internet Service Provider (ISP) blocks connections to the Tor network">
    <br><br><br>
    <h3>5b) Alternatively, if you want to use a <a href="#FindingMore">custom
    bridge</a>, then select "Enter custom bridges" and copy-and-paste the
    bridge information into the textbox.
    </h3>
    <br>
    <img src="$(IMGROOT)/tb-bridges-custom-from-browser.png" alt="Add bridges in the custom bridges textbox">
    <br><br><br>

    <p>
    Tor will only use one bridge at a time, but it is good to add more than one
    bridge so you can continue using Tor even if your first bridge becomes
    unavailable.
    </p>
    <br><br>


    <a id="FindingMore"></a>
    <h2><a class="anchor" href="#FindingMore">Finding more bridges for Tor</a></h2>
    <hr>

    <p>
    If you need to get bridges, you can get a bridge by visiting
    <a href="https://bridges.torproject.org/">https://bridges.torproject.org/</a>
    with your web browser.
    </p>

    <p>
    You can also get bridges by sending mail to bridges@bridges.torproject.org
    with the line "get bridges" by itself in the body of the mail. You'll need
    to send this request from a Gmail, Riseup!, or Yahoo! account, though
    &mdash; we only accept these providers because otherwise we make it too
    easy for an attacker to make a lot of email addresses and learn about all
    the bridges.  Almost instantly, you'll receive a reply that includes:
    </p>
    <pre>
    Here are your bridges:

     60.16.182.53:9001
     87.237.118.139:444
     60.63.97.221:443

    </pre>
    <p>
    Similarly, if you need bridges with a specific pluggable transport, the
    process is just as easy. First, decide which type you want. Currently we
    provide obfs2, obfs3, scramblesuit, and fte. If you don't know which one
    you should choose, then obfs3 is usually a good choice. Send an email to
    bridges@bridges.torproject.org with "get transport obfs3" by itself in
    the body of the email (replace "obfs3" with whichever pluggable transport
    you want to use). You should receive an email like this:
    </p>
    <pre>
    Here are your bridges:

      obfs3 60.16.182.53:9001 cc8ca10a63aae8176a52ca5129ce816d011523f5
      obfs3 87.237.118.139:444 0ed110497858f784dfd32d448dc8c0b93fee20ca
      obfs3 60.63.97.221:443 daa5e435819275f88d695cb7fce73ed986878cf3
    </pre>
    <p>
    Once you've received the email with bridge information, you can
    continue the configuration steps outlined <a href="#UsingBridges">above</a>.
    </p>

    <a id="RunningABridge"></a>
    <h2><a class="anchor" href="#RunningABridge">Running a Tor Bridge</a></h2>
    <hr>

    <p>
    If you want to help out, you should <a href="<page
    docs/faq>#RelayOrBridge">decide whether you want to run a normal Tor
    relay or a bridge relay</a>. You can configure your bridge either
    manually or graphically:
    <ul>
    <li>manually <a href="<page docs/faq>#torrc">edit
    your torrc file</a> to be just these four lines:<br>
    <pre><code>
    SocksPort 0
    ORPort auto
    BridgeRelay 1
    Exitpolicy reject *:*
    </code></pre></li>
    </ul>
    </p>

    <p>
    When configured as a bridge, your server will <b>not</b> appear in the public
    Tor network.
    </p>

    <p>
    Your bridge relay will automatically publish its address to the bridge
    authority, which will give it out via https or email as above.
    You can construct the bridge address
    using the <a href="#Understanding">format above</a> (you can find the
    fingerprint in your Tor log files or in <tt>/var/lib/tor/fingerprint</tt>
    depending on your platform).
    </p>

    <p>
    If you would like to learn more about our bridge
    design from a technical standpoint, please read the <a
    href="<specblob>attic/bridges-spec.txt">Tor bridges
    specification</a>. If you're interested in running an unpublished bridge
    or other non-standard uses, please do read the specification.
    </p>
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