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verifying-signatures.wml

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#include "head.wmi" TITLE="Tor Project: Verifying Signatures" CHARSET="UTF-8"
<div id="content" class="clearfix">
  <div id="breadcrumbs">
    <a href="<page index>">Home &raquo; </a>
    <a href="<page docs/verifying-signatures>">Verifying Signatures</a>
  </div>
  <div id="maincol">

<section class="accordion">

 <div>
   <input id="ac-0" name="accordion-0" type="checkbox" checked />
   <label for="ac-0">
    <h1><a name="TOC">How to verify signatures of packages</a></h1>
    <hr>
   </label>
   <article class="ac-small">

    <div class="nav img-shadow">
    <div class="sidenav-sub">
    <ul>
      <li><a href="#Why-verify-signature">Always verify downloads</a></li>
      <li><a href="#ImportKey">Import Tor's signing key</a></li>
      <li><a href="#VerifySignature">Verify OpenPGP signatures</a></li>
      <li><a href="#ChecksumVerification">Verify checksums</a></li>
      <li><a href="#MARVerification">MAR verification</a></li>
      <li><a href="#Troubleshooting">Troubleshooting</a></li>
      <li><a href="#Scripts">Scripts</a></li>
    </ul>
    </div>
    </div>

<p>Digital signature is a process ensuring that a certain package was
    generated by its developers and has not been tampered with. Below we explain
    why it is important and how to verify that the Tor program you download is
    the one we have created and has not been modified by some attacker.</p>

<p>If you want to learn more about how it works see<br/>
    <a href="https://en.wikipedia.org/wiki/Digital_signature">
    https://en.wikipedia.org/wiki/Digital_signature</a>.</p>

<p class="hint">(Click on each headline to show or hide the section.)</p>
  </article>
 </div>

<div>
   <input id="ac-1" name="accordion-1" type="checkbox" />
   <label for="ac-1">
    <a class="nav" title="link here" href="#Why-verify-signature">&#9668;</a>
    <h3><a name="Why-verify-signature">Always verify the signature of
        downloaded files</a></h3>
    <hr>
    <p>
    How do you know that the Tor program you have is really the one we made?
    Digital signatures ensure that the package you are downloading was created
    by our <a href="<>page about/corepeople>">developers</a>. It uses a
    cryptographic mechanism to ensure that the software package that you have
    just downloaded is authentic.
    <span class="hint">(click to toggle)</span></p>
   </label>
   <article class="ac-small">

<p>
    For many Tor users it is important to verify that the Tor software is
    authentic as they have very real adversaries who might try to give them a
    fake version of Tor.
    </p>

<p>
    If the Tor package has been modified by some attacker it is not safe to use
    it. It doesn't matter how secure and anonymous Tor is if you're not running
    the real Tor.
    </p>

<p>
    Before you go ahead and download something, there are a few extra steps you
    should take to make sure you have downloaded an authentic version of Tor.
    </p>

<h4>Always download Tor from torproject.org</h4>

<p>
    There are a variety of attacks that can be used to make you download a fake
    version of Tor. For example, an attacker could trick you into thinking some
    other website is a great place to download Tor. You should always download
    Tor from
    <a href="https://www.torproject.org"><b>https</b>://www.torproject.org/</a>.
    </p>

<h4>Always make sure you are browsing over https</h4>

<p>
    <a href="https://www.torproject.org">https://www.torproject.org/</a> uses
    https. Https is the secure version of the http protocol which uses
    encryption and authentication between your browser and the website.
    This makes it much harder for the attacker to modify your download. But
    it's not perfect. Some places in the world block the Tor website, making
    users to download Tor <a href="<page docs/faq>#GetTor">somewhere else</a>.
    </p>

<p>
    Large companies sometimes force employees to use a modified browser,
    so the company can listen in on all their browsing. We've even
    <a href="https://blog.torproject.org/blog/diginotar-debacle-and-what-you-should-do-about-it">seen</a>
    attackers who have the ability to trick your browser into thinking
    you're talking to the Tor website with https when you're not.
    </p>

<h4>Always verify signatures of packages you have downloaded</h4>

<p>
    Some software sites list
    <a href="https://en.wikipedia.org/wiki/Cryptographic_hash_function">sha1
    hashes</a> alongside the software on their website, so users can
    verify that they downloaded the file without any errors. These
    "checksums" help you answer the question "Did I download this file
    correctly from whoever sent it to me?" They do a good job at making
    sure you didn't have any random errors in your download, but they
    don't help you figure out whether you were downloading it from the
    attacker. The better question to answer is: "Is this file that I
    just downloaded the file that Tor intended me to get?"
    </p>
    <a class="nav" href="#TOC" title="go up">&uarr;</a>
  </article>
 </div>

<div>
  <input id="ac-2" name="accordion-2" type="checkbox" checked />
  <label for="ac-2">
    <a class="nav" title="link here" href="#ImportKey">&#9668;</a>
    <h3><a name="ImportKey">Step 1: Import Tor's signing key</a></h3>
    <hr>
    <p>
    Each file on <a href="<page download/download>">our download
    page</a> is accompanied by a file with the same name as the
    package and the extension ".asc". These .asc files are GPG
    signatures. They allow you to verify the file you've downloaded
    is exactly the one that we intended you to get. For example,
    torbrowser-install-<version-torbrowserbundle>_en-US.exe is accompanied by
    torbrowser-install-<version-torbrowserbundle>_en-US.exe.asc. For a list
    of which developer signs which package, see our
    <a href="<page docs/signing-keys>">signing keys</a> page.
    </p>
  </label>
  <article class="ac-box">

<p><span class="hint">Choose your operating system:</span>
   <label for="ac-2-1"><a name="KeyWindows">&#9658; Windows</a></label>
   <label for="ac-2-2"><a name="KeyMacOS">&#9658; Mac OS X</a></label>
   <label for="ac-2-3"><a name="KeyLinux">&#9658; Linux</a></label>
   </p>

  <div>
   <input id="ac-2-1" name="accordion-2" type="radio" checked />
   <article class="ac-os">
    <h3>Import OpenPGP key on Windows</h3>
    <p>
    First of all you need to have GnuPG installed before you can verify
    signatures.
    <br/>
    Download it from
    <a href="https://gpg4win.org/download.html">https://gpg4win.org/download.html</a>.
    </p>
    <p>
    Once it's installed, use GnuPG to import the key that signed your
    package. In order to verify the signature you will need to type a few commands
    in windows command-line, <i>cmd.exe</i>.
    </p>
    <p>
    The Tor Browser team signs Tor Browser releases. Import its key
    (0x4E2C6E8793298290) by starting <i>cmd.exe</i> and typing:
    </p>
    <pre>
    > gpg.exe --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290
    </pre>
    <p>
   </article>
  </div>

  <div>
   <input id="ac-2-2" name="accordion-2" type="radio" />
   <article class="ac-os">
    <h3>Import OpenPGP key on Mac OS</h3>
    <p>
    You need to have GnuPG installed before you can verify
    signatures. Install it from
    <a href="https://www.gpgtools.org/">https://www.gpgtools.org/</a>.
    </p>

<p>
    The next step is to use GnuPG to import the key that signed
    your package. The Tor Browser team signs Tor Browser releases. Import its
    key (0x4E2C6E8793298290) by starting the terminal and typing:</p>
    <pre>
    $ gpg --keyserver pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290
    </pre>
    <p>
   </article>
  </div>
  <div>
    <p>
    After importing the key, you can verify that the fingerprint
    is correct:
    </p>
    <pre>
    gpg --fingerprint 0x4E2C6E8793298290
    </pre>
    <p>You should see:</p>
    <pre>
pub   rsa4096/0x4E2C6E8793298290 2014-12-15 [C] [expires: 2020-08-24]
      Key fingerprint = EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
uid                   [ unknown] Tor Browser Developers (signing key) &lt;torbrowser@torproject.org&gt;
sub   rsa4096/0xD1483FA6C3C07136 2016-08-24 [S] [expires: 2018-08-24]
      Key fingerprint = A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
sub   rsa4096/0xEB774491D9FF06E2 2018-05-26 [S] [expires: 2020-09-12]
      Key fingerprint = 1107 75B5 D101 FB36 BC6C  911B EB77 4491 D9FF 06E2
    </pre>
    <a class="nav" href="#TOC" title="go up">&uarr;</a>
  </div>
 </article>
</div>

<div>
 <input id="ac-3" name="accordion-3" type="checkbox" />
 <label for="ac-3">
    <a class="nav" title="link here" href="#VerifySignature">&#9668;</a>
    <h3><a name="VerifySignature">Step 2: Verification with OpenGPG signature</a></h3>
    <hr>
    <p>This section explains how to verify the downloaded file's digital
    signature on different operating systems. Please notice that a signature is
    dated the moment the package has been signed. Therefore every time a new
    file is uploaded a new signature is generated with a different date. As
    long as you have verified the signature you should not worry that the
    reported date may vary.
    </p>
  </label>
  <article class="ac-box">
   <p><span class="hint">Choose your operating system:</span>
   <label for="ac-3-1"><a name="VerifyWindows">&#9658; Windows</a></label>
   <label for="ac-3-2"><a name="VerifyMacOS">&#9658; Mac OS X</a></label>
   <label for="ac-3-3"><a name="VerifyLinux">&#9658; Linux</a></label>
   </p>
   <p>
   If you haven't already, <a href="<page download/download>">download</a>
   the files you are interested in.
   </p>

  <div>
   <input id="ac-3-1" name="accordion-3" type="radio" checked />
   <article class="ac-os">
    <h3>Verify with OpenPGP signature on Windows</h3>
    <p>
    To verify the signature of the package you downloaded, you will need
    to download the ".asc" file as well. Assuming you downloaded the
    package and its signature to your Desktop, run:
    </p>
    <pre>
    > gpg.exe --verify C:\Users\Alice\Desktop\torbrowser-install-<version-torbrowserbundle>_en-US.exe.asc
    </pre>

<p>Please substitute "Alice" with your own username.</p>
    <p>The output should say "Good signature":</p>
    <pre>
gpg: assuming signed data in 'torbrowser-install-<version-torbrowserbundle>_en-US.exe'
gpg: Signature made Wed 15 Nov 2017 05:52:38 PM CET
gpg:                using RSA key 0xD1483FA6C3C07136
gpg: Good signature from "Tor Browser Developers (signing key) &lt;torbrowser@torproject.org&gt;" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
     Subkey fingerprint: A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
    </pre>
   </article>
  </div>

  <div>
   <input id="ac-3-2" name="accordion-3" type="radio" />
   <article class="ac-os">
    <h3>Verify with OpenPGP signature on Mac OS</h3>
    <p>
    To verify the signature of the package you downloaded, you will need
    to download the ".asc" file as well. Assuming you downloaded the
    package and its signature to your Downloads folder, run:
    </p>

<pre>
    $ gpg --verify ~/Downloads/TorBrowser-<version-torbrowserbundleosx64>_en-US.dmg{.asc*,}
    </pre>

<p>The output should say "Good signature":</p>

<pre>
gpg: assuming signed data in 'tor-browser-osx64-<version-torbrowserbundleosx64>_en-US.tar.xz'
gpg: Signature made Wed 15 Nov 2017 05:52:38 PM CET
gpg:                using RSA key 0xD1483FA6C3C07136
gpg: Good signature from "Tor Browser Developers (signing key) &lt;torbrowser@torproject.org&gt;" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
     Subkey fingerprint: A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
    </pre>
   </article>
  </div>

  <div>
   <input id="ac-3-3" name="accordion-3" type="radio" />
   <article class="ac-os">
    <h3>Verify with OpenPGP signature on Linux</h3>
    <p>
    To verify the signature of the package you downloaded, you will need
    to download the ".asc" file as well. Assuming you downloaded the
    package and its signature to your Downloads folder, run:
    </p>

<p>Change 64 to 32 if you have the 32-bit package:</p>

<pre>
    $ gpg --verify tor-browser-linux64-<version-torbrowserbundlelinux64>_en-US.tar.xz.asc
    </pre>

<p>The output should say "Good signature":</p>

<pre>
gpg: assuming signed data in 'tor-browser-linux64-<version-torbrowserbundlelinux64>_en-US.tar.xz'
gpg: Signature made Wed 15 Nov 2017 05:52:38 PM CET
gpg:                using RSA key 0xD1483FA6C3C07136
gpg: Good signature from "Tor Browser Developers (signing key) &lt;torbrowser@torproject.org&gt;" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7  DE68 4E2C 6E87 9329 8290
     Subkey fingerprint: A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
    </pre>

<p>
    On <b>Debian</b> for Tor (not Tor Browser) packages, you should read the
    instructions on
    <a href="<page docs/debian>#packages">importing these keys to apt</a>.
    If you're using the <b>RPMs</b> (for Tor, not Tor Browser), you can
    manually verify the signatures on the RPM packages by
    <pre>rpm -K filename.rpm</pre>
    </p>

</article>
 </div>

    <p>
    Currently valid subkey fingerprints are:
    </p>
    <pre>
    5242 013F 02AF C851 B1C7  36B8 7017 ADCE F65C 2036
    BA1E E421 BBB4 5263 180E  1FC7 2E1A C68E D408 14E0
    A430 0A6B C93C 0877 A445  1486 D148 3FA6 C3C0 7136
    </pre>
    <p>
    Notice that there is a warning because you haven't assigned a trust
    index to this person. This means that GnuPG verified that the key made
    that signature, but it's up to you to decide if that key really belongs
    to the developer. The best method is to meet the developer in person and
    exchange key fingerprints.
    </p>

<p>To learn more about GnuPG see
    <a href="https://www.gnupg.org/documentation/">https://www.gnupg.org/documentation/</a>
    </p>

<div>
  <input id="ac-4" name="accordion-4" type="checkbox" />
   <label for="ac-4">
    <a class="nav" title="link here" href="#ChecksumVerification">&#9668;</a>
    <h3><a id="ChecksumVerification">Step 3: Verify the file integrity by sha256 checksum</a></h3>
    <hr>
    <p>
    Build reproducibility is a
    <a href="https://blog.torproject.org/blog/deterministic-builds-part-one-cyberwar-and-global-compromise">
    security property</a> of Tor Browser 3.0 and later. Anyone can build
    Tor Browser on their own machine and produce a binary that is bit-for-bit
    identical to the binary we offer on the download page.
    Fortunately, it is not necessary for everyone to build Tor Browser locally
    to get this security. Verifying and comparing the signed list of
    <a href="https://en.wikipedia.org/wiki/Cryptographic_hash">hashes</a>
    will confirm that multiple people have built Tor Browsers identical to the
    download.
    </p>
   </label>
  <article>
    <p>
    Note: This process does not work on OS X yet due to Apple's codesigning requirement.
    See <a href="#MARVerification">MAR verification</a> below.
    </p>
     <ul>
      <li>
      <a href="<page download/download>">Download</a> the Tor Browser package,
      the <tt>sha256sums-unsigned-build.txt</tt> file, and the
      <tt>sha256sums-unsigned-build.txt.asc</tt> signature file.
      They can all be found in the same directory under
      <a href="https://www.torproject.org/dist/torbrowser/">
      https://www.torproject.org/dist/torbrowser/</a>, for example in '<version-torbrowserbundlelinux64>'
      for Tor Browser <version-torbrowserbundlelinux64>.
      </li>
      <li>
      Retrieve the signers' GPG key with following ID with the method <a href="#ImportKey">described above</a>:<br/>
      (Other developers' key IDs can be found
      <a href="<page docs/signing-keys>">here)</a>
      </li>
     </ul>
     <pre>
     0x4E2C6E8793298290
     </pre>
  </article>
  <article class="ac-box">
  
   <p><span class="hint">Choose your operating system:</span>
   <span>

<label for="ac-4-1"><a name="ChecksumsWindows">&#9658; Windows</a></label>
   </span>
   
   <span>
    <label for="ac-4-3"><a name="ChecksumsLinux">&#9658; Linux</a></label>
   </span>
   </p>

<div>
    <input id="ac-4-1" name="accordion-4" type="radio" checked />
   <article class="ac-os">
    
    <h3>Verififcation with a checksum on Windows</h3>
    <h4>Verify the signature of the checksum file</h4>
    <p>
    Verify the sha256sums-unsigned-build.txt file by executing this command:
    </p>
    <pre>
    > gpg.exe --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt
    </pre>

<p>
    You should see a message like
    <pre>"Good signature from &lt;DEVELOPER NAME&gt;"</pre>.
    If you don't, there is a problem. Try these steps again.
    </p>

<h4>Verify the file integrity of Tor Browser</h4>
    <p>
    If you want to verify a Windows Tor Browser package you need to first
    strip off the authenticode signature of it.<br/>
    Tools that can be used for this purpose are
    <a href="http://osslsigncode.sourceforge.net">osslsigncode</a> and
    <a href="http://forum.xda-developers.com/showthread.php?t=416175">delcert.exe</a>.
    Assuming you have built e.g. <tt>osslsigncode</tt> on a Linux computer you can enter
    </p>
    <pre>
    > C:\path\to\osslsigncode remove-signature &#92;
        where\you\saved\\&lt;TOR BROWSER FILE NAME&gt;.exe &lt;TOR BROWSER FILE NAME&gt;.exe
    </pre>

<p>Now use the sha256sum of the Tor Browser package with the
    <a href="http://md5deep.sourceforge.net/">hashdeep utility</a> and run
    </p>
    <pre>
    C:\location\of\hashdeep -c sha256sum &lt;TOR BROWSER FILE NAME&gt;.exe
    </pre>
   </article>
  </div>

<div>
   <input id="ac-4-3" name="accordion-4" type="radio" />
   <article class="ac-os ac-4-3">
    
    <h3>Verififcation with a checksum on Linux</h3>
    <h4>Verify the signature of the checksum file</h4>
    <ul>
     <li>Verify the sha256sums-unsigned-build.txt with this command:</li>
     <pre>$ gpg --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt</pre>

<li>
     In case your operating system is adding the .txt extension automatically
     to the SHA256 sums signature file strip it again by running
     </li>
     <pre>$ mv sha256sums-unsigned-build.txt.asc.txt sha256sums-unsigned-build.txt.asc</pre>

<li>
     Verify the sha256sums-unsigned-build.txt file by executing this command:
     </li>
     <pre>$ gpg --verify sha256sums-unsigned-build.txt.asc sha256sums-unsigned-build.txt</pre>

<li>
     If you don't see a message like this, there is a problem
     and you should try these steps again:
     </li>
     <pre>"Good signature from &lt;DEVELOPER NAME&gt;"</pre>.
    </ul>

<h4>Verify the file integrity of Tor Browser</h4>
    <ul>
     <li>Calculate the SHA-256 checksum of Tor Browser:</li>
     <pre>$ sha256sum &lt;TOR BROWSER FILE NAME&gt;.tar.gz</pre>

<li>You will see a string of letters and numbers.</li>

<li>Open <tt>sha256sums-unsigned-build.txt</tt> in a text editor.</li>

<li>Locate the name of the Tor Browser file you downloaded.</li>

<li>
     Compare the string of letters and numbers to the left of your filename with
     the string of letters and numbers that appeared on your command line.
     If they match, you've successfully verified the build.
     </li>
    </ul>
    </article>
   </div>
   <a class="nav" href="#TOC" title="go up">&uarr;</a>
  </article>
 </div>

<div>
  <input id="ac-5" name="accordion-5" type="checkbox" />
   <label for="ac-5">
    <a class="nav" title="link here" href="#MARVerification">&#9668;</a>
    <h3><a name="MARVerification">MAR verification</a></h3>
    <hr>
    <p>
    Starting with Tor Browser 4.5a4 we sign our MAR files which helps
    securing our update process. The downside of this is the need for additional
    instructions to verify that the MAR files we ship are indeed the ones we
    produced with our rbm setup.
    </p>
   </label>
   <article class="ac-small">
    <p>
    Assuming the verification happens on a Linux computer one first needs the
    <tt>mar-tools-linux*.zip</tt> out of the <tt>gitian-builder/inputs</tt>
    directory to remove the embedded signature(s). The steps to get the unsigned
    MAR file on a 64 bit Linux are</p>
    <pre>
    $ cd /path/to/MAR/file
    $ unzip /path/to/gitian-builder/inputs/mar-tools-linux64.zip
    $ export LD_LIBRARY_PATH=/path/to/MAR/file/mar-tools
    $ mar-tools/signmar -r your-signed-mar-file.mar your-unsigned-mar-file.mar</pre>
    <p>Now you can compare the SHA256 sum of <tt>your-unsigned-mar-file.mar</tt>
    with the one provided in the <tt>sha265sums-unsigned-build.txt</tt> or
    <tt>sha256sums-unsigned-build.incremental.txt</tt> as outlined in
    <a href="#ChekcksumVerification">Checksum verification</a> above.
    </p>
   </article>
 </div>

<div>
  <input id="ac-6" name="accordion-6" type="checkbox" />
   <label for="ac-6">
    <a class="nav" title="link here" href="#Troubleshooting">&#9668;</a>
    <h3><a id="Troubleshooting">Troubleshooting</a></h3>
    <hr>
    <p>Does this guide work for you? Is a question missing?
    <a href="<page about/contact>#support">Reach out to us</a>!</p>
   </label>
   <article class="ac-small">
    <p>Send us your question!</p>
    <a class="nav" href="#TOC" title="go up">&uarr;</a>
  </article>
 </div>

<div>
  <input id="ac-7" name="accordion-7" type="checkbox" checked />
   <label for="ac-7">
    <a class="nav" title="link here" href="#Scripts">&#9668;</a>
    <h3><a id="Scripts">Automate the process with a script</a></h3>
    <hr>
    <p><a href="https://github.com/isislovecruft/scripts/blob/master/verify-gitian-builder-signatures">Scripts</a>
    to <a href="https://tor.stackexchange.com/questions/648/how-to-verify-tor-browser-bundle-tbb-3-x">automate</a>
    these steps have been written, but to use them you will need to modify
    them yourself with the latest Tor Browser filename.</p>
   </label>
   <article class="ac-small">
    <p>
    This needs to be explained. <a href="<page getinvolved/volunteer>">Help!</a>
    </p>
    <a class="nav" href="#TOC" title="go up">&uarr;</a>
  </article>
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